++
abducens (VI) nerve: cranial nerve; axons innervate the lateral rectus muscle
++
abducens nucleus: contains lateral rectus motor neurons and internuclear neurons; located in pons
++
accessory cuneate nucleus: relays somatic sensory information from upper trunk, arm, and neck to the cerebellum; located in medulla
++
accessory (XI) nerve: cranial nerve that innervates the sternocleidomastoid muscle and the upper part of the trapezius muscle
++
accessory optic system: transmits visual information to brain stem nuclei for eye movement control
++
accommodation-convergence reaction: a complex response that prepares the eyes for near vision by (1) increasing lens curvature, (2) constricting the pupils, and (3) coordinating convergence of the eyes
++
accommodation reflex: increase in lens curvature that occurs during near vision
++
acetylcholine: neurotransmitter used by motor neurons and neurons in several nuclei, including the basal nucleus and the pedunculopontine nucleus
++
acetylcholinesterase: enzyme that inactivates acetylcholine
++
acousticomotor function: motor behavioral response triggered or controlled by sound such as orienting towards a sound
++
adrenergic: neuron that uses adrenalin as a neurotransmitter or neuromodulator
++
afferent: axons that transmit information toward a particular structure; afferent is not synonymous with sensory, which means related to processing information from a receptor sheet (eg, body surface or retina)
++
airway protective reflex: closure of the larynx to prevent fluid and food from entering the trachea
++
akinesia: impairment in initiating voluntary movement
++
alar plate: dorsal portion of the neuroepithelium that gives rise to sensory nuclei of the spinal cord and brain stem
++
allocortex: cortex having a variable number of layers, but always fewer than six
++
alveus: thin sheet of myelinated axons covering hippocampal formation; axons of pyramidal neurons in the hippocampus and subiculum
++
Alzheimer disease: presenile dementia
++
amacrine cells: retinal interneuron
++
amygdala: telencephalic structure that plays an essential role in emotions and their behavioral expression; has three component nuclear divisions: basolateral, central, and corticomedial
++
amygdaloid nuclear complex: another name for the amygdala
++
anastomosis: a network of interconnected arteries
++
aneurysm: an abnormal ballooning of a part of an artery due to weakening of the arterial wall
++
angiogram: radiological image of vasculature
++
anosmia: absence of the sense of smell
++
ansa lenticularis: output pathway of the internal segment of the globus pallidus; axons terminate in the thalamus
++
anterior: toward the abdomen; synonymous with ventral
++
anterior cerebral artery: supplies blood to the medial frontal lobes and underlying deep structures
++
anterior choroidal artery: supplies blood to the choroid plexus in the lateral ventricle and several deep structures
++
anterior cingulate gyrus: portion of the cingulate important for emotions; activated while experiencing painful stimuli; a major target of the limbic loop of the basal ganglia
++
anterior circulation: arterial supply provided by the internal carotid artery
++
anterior commissure: tract that interconnects the anterior temporal lobes and olfactory structures on the two sides of the brain
++
anterior communicating artery: interconnects anterior cerebral arteries on the two sides of the brain; part of the circle of Willis
++
anterior inferior cerebellar artery (AICA): supplies the caudal pons and parts of the cerebellum
++
anterior limb of the internal capsule: subcortical tract between the anterior portions of the caudate nucleus and putamen; rostral to the thalamus
++
anterior lobe of the pituitary gland: contains epithelial cells that release hormones for controlling a variety of target glands in the periphery
++
anterior nuclei of the thalamus: receive input from the mammillary bodies and project to the cingulate gyrus
++
anterior nucleus of the thalamus: receives input from the mammillothalamic tract and projects to the cingulate cortex
++
anterior olfactory nucleus: relays information from the olfactory nucleus to other parts of the central nervous system
++
anterior perforated substance: basal forebrain region where branches of the anterior and middle cerebral arteries (lenticulostriate) penetrate and supply deep structures
++
anterior spinal arteries: branches of the vertebral artery that supply the ventral half of the spinal cord; courses within the ventral sulcus of the spinal cord; also receives arterial blood from radicular arteries
++
anterior temporal lobes: involved in emotions, especially during anxiety states
++
anterior thalamic nuclei: participate in aspects of learning and memory; principal target of the mammillary bodies
++
anterograde: away from a neuron's cell body and toward the axon terminal; typically related to the pattern of degeneration (see Wallerian degeneration) or axonal transport
++
anterograde amnesia: failure to remember new events
++
anterolateral system: spinal pathways for pain, temperature, and itch; includes spinothalamic, spinomesencephalic (spinotectal), and spinoreticular tracts
++
anteroventral cochlear nucleus: portion of the cochlear nucleus important for sound localization in the horizontal plane; located in the rostral medulla
++
antidiuretic hormone: released by the posterior lobe of the pituitary; acts on the kidney to concentrate urine
++
aphasia: impairment in language; characterized by reduced ability of a person to read, write, or speak their intentions
++
apraxia: inability to perform a movement when asked, even though the person has the physical ability to contract the muscles, is willing to perform the movement, and has already learned to make the movement
++
aortic arch: site of arterial blood pressure sensor
++
arachnoid granulations: unidirectional valves for cerebrospinal fluid to flow from the subarachnoid space to the circulatory system
++
arachnoid mater: middle meningeal layer
++
arachnoid villi: see arachnoid granulations
++
arbor vitae: appearance of cerebellar white matter on sagittal section
++
archicortex: primitive three-layered cortex; primarily in hippocampal formation
++
arcuate nucleus: hypothalamic nucleus important for control of neuroendocrine function and feeding
++
area 3a: Brodmann's cytoarchitectonic area; part of the primary somatic sensory cortex that receives information from muscle receptors; involved in balance sense
++
area postrema: portion of caudal medulla where there is no blood-brain barrier; important for sensing blood-borne toxins and in control of vomiting
++
Argyll Robertson pupils: pupil sign characterized by a small diameter and unreactive to light but which gets smaller to accommodation; associated with neurosyphilis
++
ascending pathway: pathway transmitting information from lower levels of the central nervous system to higher levels; typically used to describe somatic sensory pathways of the spinal cord and brain stem
++
association cortex: areas of cortex that serve diverse mental processes but that are not engaged in basic stimulus processing or control of muscle contractions; formally those areas that associate sensory events with motor responses and perform mental processes that intervene between sensory inputs and motor outputs
++
associative loop (of basal ganglia): the basal ganglia circuit that receives input primarily from association cortex of the frontal, parietal, and temporal lobes and projects to prefrontal and premotor cortical areas
++
astrocytes: class of glial cell that serve diverse support functions, including axonal guidance during development and helping to maintain the blood-brain barrier
++
ataxia: uncoordinated and highly inaccurate movements; typically associated with cerebellar damage
++
athetosis: slow, writhing involuntary movements
++
autism spectrum disorder: a condition presenting with deficits in social interactions, impaired verbal and nonverbal communication, and expression of stereotyped patterns of behavior
++
autonomic motor column: formation of sympathetic and parasympathetic preganglionic neurons into rostrocaudal columns in the spinal cord and brain stem
++
autonomic nervous system: part of peripheral nervous system engaged in the control of body organs; consists of separate sympathetic and parasympathetic divisions
++
axial muscles: muscles located close to the body midline; control neck and back
++
axon: portion of neuron specialized for conducting information encoded in the form of action potentials
++
axon terminal: presynaptic component of the synapse; where neurotransmitters are released
++
β-endorphin: an endogenous opiate cleaved from the large peptide proopiomelanocortin; plays a role in opiate analgesia
++
Babinski's sign: extension (also termed dorsiflexion) of the big toe in response to scratching the lateral margin and then the ball of the foot (but not the toes); associated with lesions of the corticospinal system in adults; present normally in children until about two years of age
++
ballistic movement: movement with high initial velocity
++
bare nerve endings: sensitive to noxious and thermal stimuli as well as itch-producing agents
++
baroreceptor: blood pressure receptor
++
basal cells: cells that differentiate to become taste receptor cells; thought to be stem cells
++
basal forebrain: portion of the ventral telencephalon caudal to the frontal lobes; contains the basal nucleus (of Meynert) and structures for emotions and olfaction
++
basal ganglia: telencephalic nuclei with strong interconnections with the cerebral cortex; serve diverse motor, cognitive, and emotional functions
++
basal hair cells: auditory hair cells located near the cochlear base
++
basal nucleus (of Meynert): contains neurons that use acetylcholine as their neurotransmitter and project widely throughout the cerebral cortex; neurons are among the first to degenerate in Alzheimer disease
++
basal plate: portion of the ventral neuroepithelium that gives rise to motor nuclei of the spinal cord and brain stem
++
base (midbrain): the most ventral portion of the midbrain; also termed basis pedunculi
++
base of the pons: ventral portion of the pons; contains primarily pontine nuclei and descending cortical axons
++
basilar artery: supplies pons and parts of the cerebellum and midbrain
++
basilar membrane: component of the organ of Corti that oscillates in response to sounds; mechanical displacement of the membrane stimulates auditory hair cells
++
basis pedunculi: ventral portion of the midbrain; contains descending cortical axons
++
basket neurons: inhibitory interneurons of the cerebellar cortex; make dense and strong synaptic connections on cell body of Purkinje neuron
++
basolateral nuclei (of the amygdala): division of amygdala that receives information from sensory systems and cortical association areas
++
bed nucleus of the stria terminalis: C-shaped component of the amygdala; related in function to the central nucleus
++
benign positional vertigo: most common form of vertigo, or the sudden sensation of spinning; can be evoked for testing purposes by placement of the head in a particular position and then quickly lying down backwards over a table
++
bilateral control: form of somatic or visceromotor control in which a cranial nerve or spinal motor nucleus receives projections from both sides of the cortex; typically provides a measure of redundancy, so that if one projection becomes damaged, the other projection can provide basic control
++
bilateral projection: one structure sends axons to both sides of the central nervous system
++
bilateral temporal visual field defect: see bitemporal heteronymous hemianopia
++
bipolar morphology: neuron shape characterized by a pair of axon-like processes emerging from opposite sides of a neuron's cell body; bipolar neuron
++
bipolar neurons: one of three major morphological types of neuron; characterized by a pair of axon-like processes emerging from opposite sides of the neuron's cell body; most commonly sensory relay neurons
++
bitemporal heteronymous hemianopia: loss of peripheral vision; common with lesions involving the optic chiasm
++
blind spot: blind portion of visual field; corresponds on the retina to the exit point of the optic nerve, where there are no photoreceptors
++
blobs: location of color-sensitive neurons in primary visual cortex; primarily in layers II and III
++
blood-brain barrier: cellular specializations that prevent blood-borne materials from gaining access to the central nervous system
++
blood-cerebrospinal fluid barrier: specializations that prevent blood-borne materials from gaining access to the cerebrospinal fluid
++
border zone infarct: loss of arterial supply at the peripheral borders of the territories supplied by major cerebral vessels
++
border zones: peripheral borders of the territories supplied by major cerebral vessels
++
brachium of inferior colliculus: output pathway from the inferior colliculus to the medial geniculate nucleus
++
brachium of superior colliculus: input pathway to the superior colliculus from the retina
++
bradykinesia: movement disorder in which movements are slowed or absent
++
brain: cerebral hemispheres, diencephalon, cerebellum and brain stem
++
brain stem: medulla, pons, and midbrain
++
branchial arches: also known as gill arches; territory of developing head and neck; many cranial nerves develop in association with the branchial arches
++
branchiomeric: derived from the branchial arches
++
branchiomeric motor column: motor neurons that innervate muscles that develop from the branchial arches
++
branchiomeric skeletal motor fibers: see branchiomeric motor column
++
Broca's area: portion of the inferior frontal lobe important for articulation of speech
++
Brodmann's areas: divisions of the cerebral cortex based on the size and shapes of neurons in the different laminae and their packing densities; named after Korbinian Brodmann, a German neuroanatomist who worked during the late 19th and early 20th centuries
++
Brown-Séquard syndrome: set of signs associated with spinal cord hemisection; include ipsilateral loss of motor functions, ipsilateral loss of mechanical sensations, and contralateral loss of pain, temperature, and itch; all caudal to the lesion
++
bulb: archaic term for medulla and pons; commonly used to describe a cortical projection system (see corticobulbar tract)
++
C-shaped: description of the shape of many telencephalic structures
++
calcarine fissure: located in the primary visual cortex; occipital lobe
++
callosal connections: connections made by callosal neurons
++
callosal neurons: class of cortical projection neuron
++
capillary endothelium: inner layer of a capillary in brain and spinal cord contributes to the blood brain barrier
++
carotid circulation: see anterior circulation
++
carotid sinus: blood-pressure-sensing organ
++
carotid siphon: segment of the internal carotid artery
++
cataplexy: transient loss of muscle tone without loss of consciousness
++
cauda equina: spinal nerves within the vertebral canal caudal to the last spinal segment
++
caudal: toward the tail or coccyx
++
caudal nucleus (of the spinal trigeminal nucleus): important for facial pain, temperature sense, and itch; located in the caudal medulla; rostral extension of the dorsal horn
++
caudal solitary nucleus: important for viscerosensory function; located in the caudal medulla
++
caudate nucleus: input nucleus of the basal ganglia; comprised of the head, body and tail
++
cell body: where the nucleus is located and from which the axon and dendrites emerge
++
cell bridges: see striatal cell bridges
++
cell stains: method of revealing neuronal cell bodies; an example is the Nissl stain
++
central canal: portion of the ventricular system located in the spinal cord and caudal medulla
++
central nervous system: division of the nervous system located within the skull and vertebral column
++
central nucleus (of the amygdala): nuclear division of the amygdala important for the visceral expression of emotions, such as changes in blood pressure and gastrointestinal function during anxiety
++
central sulcus: separates frontal and parietal lobes
++
central tegmental tract: contains the ascending gustatory projection from the solitary nucleus to the thalamus and descending axons from the parvocellular red nucleus to the inferior olivary nucleus
++
centromedian nucleus: thalamic diffuse-projecting nucleus with widespread projections to the frontal lobe and striatum
++
cephalic flexure: bend in neuraxis at the level of the midbrain
++
cerebellar glomerulus: basic processing unit of the cerebellum; comprises one mossy fiber axon terminal (presynaptic), and many granule cell dendrites and several Golgi axons (postsynaptic)
++
cerebellar tentorium: rigid dural flap dorsal to the cerebellum; separates the cerebellum from the cerebral cortex and defines the posterior fossa
++
cerebellopontine angle: where the cerebellum joins the brain stem
++
cerebellothalamic tract: output pathway from the deep cerebellar nuclei to the thalamus
++
cerebellum: portion of the hindbrain; important for automatic control of movements and thought to play a role in automating many complex sensory and cognitive functions
++
cerebral angiography: radiological technique for imaging brain vasculature
++
cerebral aqueduct (of Sylvius): portion of the ventricular system in the midbrain
++
cerebral cortex: portion of the telencephalon; important for diverse sensory, motor, cognitive, emotional, and integrative functions
++
cerebral hemispheres: major brain division
++
cerebral peduncle: ventral portion of midbrain, formally corresponds to the tegmentum and base
++
cerebral segment (of internal carotid artery): immediately proximal to the bifurcation into the middle and anterior cerebral arteries
++
cerebrocerebellum: comprises the lateral cerebellar cortex and dentate nucleus; important for motor planning
++
cerebrospinal fluid: watery fluid contained within the ventricular system and subarachnoid space
++
cervical: spinal cord segment; there are eight in total
++
cervical flexure: bend in the developing nervous system; located in the midbrain; persists into maturity
++
cervical segment (of internal carotid artery): the most proximal portion of the internal carotid; from the carotid bifurcation to the point of entrance to the carotid canal of the skull
++
cholinergic: a neuron that uses acetylcholine as its neurotransmitter
++
chorda tympani nerve: a branch of cranial nerve VII; carries taste afferents
++
chorea: disordered movement characterized by involuntary rapid and random movements of the limbs and trunk
++
choroid epithelium: cells of the choroid plexus specialized to secrete cerebrospinal fluid
++
choroid plexus: intraventricular organ that contains cells that secrete cerebrospinal fluid
++
ciliary ganglion: peripheral ganglion containing parasympathetic postganglionic neurons
++
ciliary muscle: intraocular muscle that increases lens curvature
++
cingulate cortex: comprises anterior, middle and posterior divisions; diverse behavioral functions, including role in emotional valance and movement control
++
cingulate gyrus: C-shaped gyrus on medial brain surface spanning the frontal and parietal lobes; surrounds the corpus callosum
++
cingulate motor areas: premotor cortical area located in the cingulate gyrus
++
cingulum: C-shaped tract located within the white matter of the cortex beneath the cingulate gyrus
++
circle of Willis: anastomotic network of arteries on the ventral surface of the diencephalon
++
circumventricular organs: a set of eight structures lying near the ventricular surface that do not have a blood-brain barrier
++
cisterna magna: the portion of the subarachnoid space, dorsal to the medulla and caudal to the cerebellum, where cerebrospinal fluid pools
++
cisterns: portions of the subarachnoid space where cerebrospinal fluid pools
++
Clarke's nucleus: contains neurons that project to the ipsilateral cerebellum via the dorsal spinocerebellar tract
++
claustrum: telencephalic nucleus located beneath the insular cortex
++
climbing fibers: axons of the inferior olivary nucleus that synapse on Purkinje neurons in the cerebellar cortex; forms one of the strongest excitatory synapses in the central nervous system
++
cochlea: inner ear organ for hearing
++
cochlear apex: portion of the cochlea sensitive to low-frequency tones
++
cochlear division (of the vestibulocochlear nerve): cranial nerve sensitive to sounds
++
cochlear nuclei: first relay site for axons of the cochlear division of the vestibulocochlear nerve; located in the medulla
++
collateral circulation: redundant arterial supply for a given structure
++
collateral sulcus: separates the parahippocampal gyrus from more lateral temporal lobe regions
++
colliculi: set of four structures on the dorsal midbrain; superior colliculi are important for saccadic eye movement control, and inferior colliculi are important for hearing
++
color columns: collections of neurons in the primary visual cortex, predominantly located in layers II and III; also termed color blobs
++
columnar organization (of the cerebral cortex): vertical arrays of neurons that serve similar functions
++
commissural neurons: class of cortical neuron that contains an axon that projects to the contralateral cortex via the corpus callosum
++
commissure: tract through which axons cross the midline
++
computerized tomography: a technique for producing images of a single plane of tissue
++
conditioned taste aversion: rapid and very robust form of learning in which an individual avoids foods that made it ill
++
cone bipolar cells: class of retinal interneuron that transmits control signals from cone cells to ganglion neurons
++
cones: photoreceptor class sensitive to light wavelength (ie, color)
++
constrictor muscles of the iris: produce pupillary constriction
++
contralateral: relative spatial term related to the opposite side of the body
++
contralateral homonymous hemianopia with macular sparing: visual field defect in which there is a loss of vision in the contralateral visual field but preservation of foveal (or macular) vision; can be produced with visual system lesions affecting a portion of the primary visual cortex
++
contralateral homonymous hemianopia: visual field defect characterized by the loss of sight of the contralateral visual field; can be produced with visual system lesions affecting the optic tract, lateral geniculate nucleus, optic radiations, or primary visual cortex
++
cornea: transparent avascular portion of the sclera
++
corona radiata: portion of the subcortical white matter superior (or dorsal) to the internal capsule
++
coronal: plane of section or imaging plane; parallel to the coronal suture; equivalent to transverse plane for cerebral hemispheres and diencephalon
++
corpus callosum: commissure connecting the two cerebral hemispheres; contains four major subdivisions: rostrum, genu, body, and splenium
++
corpus striatum: subcortical telencephalic nuclei comprised of the caudate nucleus, putamen, and nucleus accumbens; generally synonymous with the striatum
++
cortex: thin sheet of neuronal cell bodies and afferent and efferent axons
++
cortical column: collection of radially oriented neurons that have similar functions and anatomical connections; basic functional unit of the cerebral cortex
++
cortical nucleus (of the amygdala): receives input from olfactory structures; projects to the hypothalamus via the stria terminalis
++
corticobulbar fibers: axons that originate in the cerebral cortex and project to the brain stem; primarily terminating in the cranial nerve motor nuclei of the pons and medulla; projections to specific nuclei and to the reticular formation usually have more specific terms (eg, corticoreticular)
++
corticobulbar tract: cortical projections that terminate on cranial nerve motor nuclei in the medulla and pons
++
corticocortical association connections: connections between cortical areas on the same side
++
corticocortical association neurons: cortical neurons that project axons to cortical areas on the same side
++
corticomedial nuclei: nuclei of the amygdala that play a role in visceral motor control
++
corticopontine pathway: descending projection from the cerebral cortex to the pontine nuclei; major input to the cerebrocerebellum
++
corticoreticular fibers: axons that originate from neurons in layer V of the cortex that project to the reticular formation
++
cortico-reticulo-spinal pathway: indirect cortical pathway to the spinal cord via neurons of the reticulospinal tract
++
corticospinal tract: projection from the cerebral cortex to the spinal cord
++
cranial and spinal roots: nerves that enter and exit the spinal cord and brain stem
++
cranial nerve II: optic nerve; contains axons of retinal ganglion cells; major targets are the lateral geniculate nucleus, rostral midbrain, nuclei at the midbrain-diencephalon junction, and hypothalamus
++
cranial nerve motor nuclei: location of motor neurons whose axons are located in the cranial nerves
++
cranial nerves: sensory and motor nerves containing axons that enter and exit the brain stem, diencephalon, and telencephalon; analogous to the spinal nerves
++
cribriform plate: part of the ethmoid bone; contains tiny foramina through which olfactory nerve fibers course from the olfactory epithelium to the olfactory bulb
++
crude touch: a nondiscriminative form of tactile sensation that remains after damage to the dorsal column-medial lemniscal pathway or to large-diameter afferent fibers; may be mediated by unmyelinated C-fiber mechanoreceptors
++
crus (of the fornix): posterior portion of fornix where it has a flattened appearance
++
cuneate fascicle: tract containing ascending axons of dorsal root ganglion neurons that innervate the upper trunk (rostral to T6), arm, neck, and back of the head; mediates mechanosensations
++
cuneate nucleus: termination of axons in the cuneate fascicle; neurons project axons to contralateral ventral posterior nucleus of the thalamus; mediates mechanosensations
++
cuneocerebellar tract: pathway from the lateral cuneate nucleus to the cerebellum; courses through the inferior cerebellar peduncle
++
cytoarchitecture: characterization of the morphology of the cerebral cortex based on the density of neuronal cell bodies
++
cytochrome oxidase: mitochondrial enzyme; marker for neuronal metabolism
++
declarative memory: memory such as the conscious recollection of facts
++
decussate: crossing the midline
++
decussation: a site where axons cross the midline
++
deep brain stimulation (DBS): use of electrodes to electrically stimulate an area of the brain; most commonly used in the basal ganglia to treat movement disorders
++
deep cerebellar nuclei: sets of nuclei located beneath the cerebellar cortex; fastigial, interposed (comprising the globose and emboliform), and dentate nuclei
++
deep cerebral veins: veins that drain the diencephalon and parts of the brain stem
++
Deiters' nucleus: lateral vestibular nucleus; origin of the lateral vestibulospinal tract
++
dendrites: receptive portion of a neuron
++
dentate gyrus: component of the hippocampal formation; receives input from the entorhinal cortex and contains neurons that project to the hippocampus proper
++
dentate nucleus: one of the deep cerebellar nuclei; transmits the output of the lateral cerebellar hemisphere
++
depression: a psychiatric disorder characterized by the persistent feeling of hopelessness and dejection; can be associated with poor concentration, lethargy, and sometimes suicidal tendencies
++
dermatome: area of skin innervated by sensory axons within a single dorsal root
++
descending motor pathways: connections between the cerebral cortex or brain stem to the spinal cord; densest to the intermediate zone and ventral horn
++
descending pain inhibitory system: neural circuit for modulating transmission of information about pain from nociceptors, through the dorsal horn, and to the brain stem; primarily originates from serotonergic neurons in the raphe nuclei and noradrenergic neurons in the reticular formation; projects to the spinal cord dorsal horn
++
descending projection neurons: neurons that give rise to descending pathways
++
detached retina: pathological condition in which portions of the retina separate from the pigment epithelium
++
diabetes insipidus: condition in which the kidneys are unable to concentrate urine because of the absence of vasopressin (or antidiuretic hormone); the individual produces copious amounts of urine
++
diencephalon: one of the secondary brain vesicles; major brain division in maturity, containing primarily the thalamus and hypothalamus; means "between brain"
++
diffuse-projecting neurons: thalamic neurons that project widely to several cortical areas
++
diffuse-projecting nuclei: location of thalamic diffuse-projecting neurons
++
diffusion-weighted magnetic resonance imaging: type of magnetic resonance imaging that can distinguish axonal orientation, especially axons within tracts
++
direct path: pathway through the basal ganglia from the striatum to the internal segment of the globus pallidus; promotes the production of movements
++
disinhibition: removal of inhibition; net effect is similar to excitation
++
distal muscles: muscles that innervate the limbs, especially distal to the elbow; controlled principally by the lateral descending motor pathways
++
dopamine: neurotransmitter
++
dopaminergic: neurons that use dopamine as their neurotransmitter
++
dorsal: close to the back; also termed posterior
++
dorsal cochlear nucleus: auditory relay nucleus located in the pons; receives input from primary auditory receptors and projects to the contralateral inferior colliculus; implicated in vertical localization of sounds
++
dorsal column nuclei: cuneate and gracile nuclei; receive input from mechanoreceptor axons in the dorsal columns
++
dorsal column–medial lemniscal system: tracts, nuclei, and cortical areas collectively involved in mechanosensations (touch, vibration sense, pressure, and limb position sense)
++
dorsal columns: located on the dorsal spinal cord surface; contain ascending axons of mechanoreceptors; gracile fascicle (or tract) carries axons that originate from receptors on the leg and lower back, whereas the cuneate tract carries axons that originate from receptors on the upper back, arm, neck, and back of the head
++
dorsal cortex (of inferior colliculus): portion of the surface of the inferior colliculus
++
dorsal horn: laminae I–VI of the spinal gray matter; processes incoming somatic sensory information, especially about pain, temperature, and itch
++
dorsal intermediate septum: separates the cuneate and gracile fascicles
++
dorsal longitudinal fasciculus: pathway to and from the hypothalamus; located in the periventricular and aqueductal gray matter
++
dorsal median septum: divides the dorsal columns into right and left halves
++
dorsal motor nucleus of the vagus: contains parasympathetic preganglionic neurons whose axons course in the vagus nerve (cranial nerve X); located in the medulla
++
dorsal raphe nucleus: located in the rostral pons and caudal midbrain; most neurons in the nucleus use serotonin as their neurotransmitter; projects widely to telencephalic and diencephalic structures
++
dorsal root: spinal sensory root
++
dorsal root ganglia: contains cell bodies of primary sensory neurons that innervate skin and deep tissues of the back of the head, neck, limbs, and trunk
++
dorsal root ganglion neurons: cell bodies of primary sensory neurons that innervate skin and deep tissues of the back of the head, neck, limbs, and trunk
++
dorsal spinocerebellar tract: an ipsilateral pathway to the cerebellum; originates in Clarke's nucleus
++
dorsolateral prefrontal cortex: cortical region important for organizing behavior, working memory, and a variety of higher mental processes
++
dorsoventral axis: between the back and abdomen
++
dura mater: outermost and toughest meningeal layer; contains an outer periosteal layer and an inner meningeal layer
++
dural sinus: channel for returning venous blood to the systemic circulation; also a path for flow of cerebrospinal fluid into the venous circulation
++
dural sinuses: channels within the meningeal layer of the dura, through which venous blood and cerebrospinal fluids are returned to the systemic circulation
++
dynorphin: neurotransmitter/neuromodulator
++
dysphagia: impairment in ability to swallow
++
ectoderm: outermost layer of the embryo
++
Edinger-Westphal nucleus: contains parasympathetic preganglionic neurons that innervate smooth muscle in the eye to control pupil diameter and lens curvature
++
efferent: axons transmit information away from a particular structure, efferent is not synonymous with motor, which means related to muscle or glandular function
++
eighth cranial nerve (VIII): vestibulocochlear nerve; separate cochlear division for hearing and vestibular division for balance
++
electrical synapses: site of communication between neurons that does not use a neurotransmitter; usually associated with a gap junction, where ions and other small and intermediate-sized molecules can pass
++
emboliform nucleus: one of the deep cerebellar nuclei; together with the globose nucleus is termed the interposed nucleus
++
encapsulated axon terminals: specialized tissue surrounding the terminal of certain mechanoreceptors; helps to determine the sensitivity and duration of the response of the receptor to a mechanical stimulus
++
endocrine hormones: biologically active chemicals released by endocrine cells into the blood; regulate metabolism, growth, and other cellular and bodily functions
++
endoderm: innermost layer of the embryo
++
endolymph: fluid that fills most of the membranous labyrinth; resembles intracellular fluid in its ionic constituents; has a high potassium concentration and low sodium concentration
++
enkephalin: neurotransmitter
++
enteric nervous system: nervous system division that controls the functions of the large intestine
++
enteroendocrine cells: specialized cells located in the gastrointestinal tract; ghrelin, which promotes feeding, is secreted by enteroendoendocrine cells in the stomach
++
entorhinal cortex: portion of the medial temporal lobe; major input to the hippocampal formation
++
ependymal cells: epithelial cell type that lines the ventricles
++
epiglottis: pharyngeal structure that, during swallowing, helps to prevent passage of fluids and food into the trachea
++
episodic memory: memory of events that have a specific spatial and temporal context (such as meeting a friend last week)
++
ethmoid bone: cranial bone; contains the cribriform plate, through which olfactory sensory axons course en route from the olfactory mucosa to the olfactory bulb
++
explicit memory: conscious recollection of facts; also termed declarative memory
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extended amygdala: collection of basal forebrain nuclei that share morphological, histochemical, and connection characteristics; includes central nuclei of the amygdala and the bed nucleus of the stria terminalis; participates in reward and substance abuse along with the ventral striatum
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external capsule: white matter region between the putamen and the claustrum; contains primarily cortical association fibers
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external nucleus: component of the inferior colliculus that participates in ear reflexes in animals, such as when a cat orients its ears to a sound source
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external segment of the globus pallidus: contains neurons that project to the subthalamic nucleus; part of the indirect basal ganglia path
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extrastriate cortex: visual cortical areas excluding the primary (or striate) cortex
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extreme capsule: white matter region between the claustrum and insular cortex; contains primarily cortical association fibers
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facial (VII) nerve: contains axons of motor neurons that innervate muscles of facial expression, as well as the stapedius muscle and part of the digastric muscle; exits from the pontomedullary junction
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facial colliculus: surface landmark on ventricular (dorsal) surface of the pons; overlies the genu of the facial nerve and the abducens nucleus
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facial motor nucleus: located in the pons, it contains motor neurons whose axons course within the facial nerve to innervate muscles of facial expression, the posterior belly of the digastric muscle, and the stapedius muscle
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facial nucleus: contains motor neurons that innervate muscles of facial expression, as well as the stapedius muscle and part of the digastric muscle; located in the pons
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falx cerebri: dural flap between the two cerebral hemi-spheres; extension of the meningeal layer of the dura
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fastigial nucleus: one of the deep cerebellar nuclei; transmits the output of the vermis to the medial descending motor pathways
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fenestrated capillaries: contain pores through which substances can diffuse from within the capillary to surrounding tissue
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fimbria: portion of the fornix that covers part of the hippocampal formation
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first lumbar vertebra: marks the approximate location of the caudal end of the spinal cord within the vertebral canal
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fissure: groove in the cortical surface; more consistent in shape and depth than a sulcus
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flaccid paralysis: inability to contract a muscle, together with a profound loss of muscle tone
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FLAIR: MRI pulse sequence that suppresses signal related to cerebrospinal fluid; abbreviation for fluid attenuated inversion recovery
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flexure: bend in the axis of the central nervous system or axis of the embryo
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flocculonodular lobe: portion of the cerebellar cortex involved in eye movement control and balance
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flocculus: see flocculonodular lobe
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floor plate: ventral surface of the developing central nervous system; key site for organizing the dorsoventral patterning of the spinal cord during development
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folia: thin folds of the cerebellar cortex
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foramen of Magendie: opening in the fourth ventricle where cerebrospinal fluid can pass into the subarachnoid space; located on the midline
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foramina of Luschka: openings in the fourth ventricle where cerebrospinal fluid can pass into the subarachnoid space; located at the lateral recesses of the ventricle
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forebrain: most rostral primary brain vesicle; divides into the telencephalon and diencephalon
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Forel's field H2: another name for the lenticular fasciculus; region of the white matter though which axons from the internal segment of the globus pallidus course en route to the thalamus
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form pathway (for vision): circuit specialized for discriminating features of the shapes of visual stimuli; information in this path is used for object recognition
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fornix: a major output tract from the hippocampal formation
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fourth ventricle: portion of the ventricular system located in the brain stem; separates medulla and pons from the cerebellum
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fovea: portion of the retina with the greatest visual acuity, where only cone receptors are located; located in the center of the macula
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fractionate movements: ability to isolate one movement from another, such as move one finger while keeping the other fingers still
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fractionation (of movement): ability to move one finger or limb segment independent of the other fingers or limb segments; often termed individuation
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fractured somatotopy: characteristic of a central sensory or motor representation in which the somatotopic plan is disorganized and a single body part becomes represented at multiple sites
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Friedreich's ataxia: an autosomal recessive disease that results in progressive spinocerebellar ataxia; chromosome 9 mutation; expansion of a GAA trinucleotide repeat within the gene that codes for the mitochondrial protein frataxin
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frontal: close to the forehead
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frontal association cortex: major association area located rostral to the premotor cortical regions on the lateral and medial brain surfaces and on the orbital surface
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frontal eye fields: portion of the lateral frontal lobe important in the control of eye movements
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frontal lobe: one of the lobes of the cerebral hemisphere
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functional localization: identification of brain regions that participate in particular functions
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functional magnetic resonance imaging (fMRI): a form of magnetic resonance imaging that can monitor blood oxygenation, which correlates with neuronal activity
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functional neuroanatomy: examines those parts of the nervous system that work together to accomplish a particular task
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GABA: γ-aminobutyric acid; principal inhibitory neurotransmitter in the central nervous system
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gag reflex: stereotypic contraction of pharyngeal muscles in response to stimulation of the posterior oral cavity; the afferent limb is the glossopharyngeal nerve, and the efferent limb is the vagus nerve primarily
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ganglion: collections of neuronal cell bodies outside the central nervous system
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ganglion cell layer: innermost retinal cell layer; contains cell bodies of ganglion cells
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ganglion cells: retinal projection neurons; axons course in the optic nerve and terminate in the diencephalon and midbrain
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geniculate ganglion: location of cell bodies of primary sensory neurons that project in the intermediate nerve (cranial nerve VII)
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genu: Latin for knee; used to describe structures with an acute bend, such as the corpus callosum and facial nerve
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genu of the internal capsule: separates the anterior and posterior limbs of the internal capsule
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ghrelin: protein secreted by enteroendocrine cells of the stomach; promotes food intake
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girdle muscles: striated muscles that insert proximally and attach on parts of the shoulder or hip
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glial cells: major cell type in the nervous system; outnumber neurons about 10 to 1; also termed glia
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globose nucleus: deep cerebellar nucleus; together with the emboliform nucleus comprise the interposed nuclei, which transmit information from the intermediate cerebellar hemisphere
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globus pallidus: basal ganglia nucleus; comprises distinct internal and external divisions
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glomerulus: collection of neuronal cell bodies and processes surrounded by glial cells; structures within the glomerulus are physically isolated from surrounding neurons; typically corresponds to a basic functional processing unit
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glossopharyngeal (IX) nerve: cranial nerve; located in the medulla
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glutamate: principal excitatory neurotransmitter of neurons in the central nervous system
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Golgi neurons: inhibitory interneurons of the cerebellar cortex
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Golgi tendon organ (or receptor): stretch receptors in muscle tendon that signals active muscle force; afferent component of the golgi tendon reflex; distal receptive portion of group Ib axons
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gracile fascicle: medial component of the dorsal column; transmits mechanoreceptive information from the legs and lower trunk to the ipsilateral gracile nucleus
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gracile nucleus: target of the axons of the gracile fascicle; transmits information to the contralateral thalamus via the medial lemniscus
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granular layer: innermost cell layer of the cerebellum; primarily contains granule and Golgi neurons and the axon terminals of mossy fibers
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granule cell: cerebellar excitatory interneuron; cell of origin of parallel fibers
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granule neurons: the only excitatory interneuron of the cerebellar cortex
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gray matter: portions of the central nervous system that contain predominantly neuronal cell bodies
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great cerebral vein (of Galen): major vein; carries venous drainage from the diencephalon and deep telencephalic structures
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gyri: grooves in the cerebral cortex
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gyrus rectus: located on the inferior frontal lobe; runs parallel to the olfactory tract
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habenula: portion of the diencephalon; located lateral and ventral to the pineal gland; part of a circuit with the midbrain medial dopaminergic and the serotonergic systems
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hair cells: auditory receptor neurons
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hearing: one of the five major senses
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hemiballism: movement disorder produced by damage to the subthalamic nucleus; characterized by involuntary rapid (ballistic) limb movements
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hemiplegic cerebral palsy: an acquired condition characterized by perinatal damage to brain circuits; commonly affects sensory and motor cortical areas; damage to the corticospinal tract produces motor signs that include spasticity and incoordination
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hemorrhagic stroke: condition following the rupture of an artery; tissue around the hemorrhage can become damaged because blood leaks out of the artery under high pressure
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Heschl's gyri: location of primary auditory cortex
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hierarchical organization: property of neural systems in which individual components comprise distinct functional levels with respect to one another
++
higher-order auditory areas: regions of the temporal lobe that process complex aspects of sounds; major input from lower-order auditory areas (eg, primary and secondary)
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hindbrain: most caudal portion of the brain; includes the medulla, pons, and cerebellum
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hippocampal formation: telencephalic structure located primarily within the temporal lobe; comprises the dentate gyrus, hippocampus, and subiculum; involved in learning and memory
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hippocampal sulcus: separates the dentate gyrus from the subiculum; largely obscured in the mature brain
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hippocampus: component of the hippocampal formation
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histamine: neuroactive compound; generally excitatory; important in hypothalamic circuits for regulating sleep and wakefulness
++
Hoffmann's sign: thumb adduction in response to flexion of the distal phalanx of the third digit; an upper limb equivalent of the Babinski sign
++
horizontal cells: retinal interneuron
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horizontal localization of sound: ability to identify the position of the source of a sound in the horizontal plane
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Horner syndrome: constellation of neurological signs associated with dysfunction of the sympathetic innervation of the head
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Huntington disease: genetic autosomal dominant disorder; produces hyperkinetic motor signs
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hydrocephalus: buildup of cerebrospinal fluid within the brain
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hyperkinetic signs: set of abnormal involuntary motor behaviors characterized by increased rate of occurrence and inability to control; examples include tremor, tics, chorea, and athetosis
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hypoglossal motor neurons: innervate intrinsic tongue muscles
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hypoglossal (XII) nerve: cranial nerve located in the medulla
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hypoglossal nucleus: location of hypoglossal motor neurons
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hypokinetic signs: set of abnormal involuntary motor behaviors characterized by decreased rate of occurrence or slowing; examples include bradykinesia (slowing of movements) and failure to initiate a motor behavior in a timely manner
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hypothalamic sulcus: roughly separates the hypothalamus and thalamus on the medial brain surface
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hypothalamus: major brain division; part of diencephalon
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immunocytochemistry: process in which antibodies to a particular molecule are used to label that molecule in tissue
++
implicit memory: memory of procedures and actions; also termed nondeclarative memory
++
incus: one of the middle ear ossicles (bones); essential for conducting changes in air pressure from the tympanic membrane to the oval window; located between the other two ossicles
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indirect cortical pathways: motor pathway from the cerebral cortex that synapses first in the brain stem before synapsing on spinal neurons
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indirect path: pathway through the basal ganglia from the striatum, to the external segment of the globus pallidus, to the subthalamic nucleus, and then to the internal segment of the globus pallidus; functions to retard the production of movements
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infarction: death of tissue because of cessation of blood flow
++
inferior cerebellar peduncle: predominantly an input pathway to the cerebellum
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inferior colliculus: located in the caudal midbrain, on its dorsal surface; contains neurons that are part of the ascending auditory pathway
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inferior ganglia: location of primary somatic sensory cell bodies of vagus and glossopharyngeal nerves that innervate visceral tissues
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inferior oblique muscle: extraocular muscle that depresses the eye, mostly when the eye is adducted
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inferior olivary nuclear complex: collection of nuclei in the medulla that give rise to the climbing fibers of the cerebellum; forms the olive, a surface landmark on the ventral medullar surface
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inferior parietal lobule: located dorsal to the lateral sulcus; important for a variety of higher brain functions, including language and perception
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inferior petrosal sinus: major dural sinus
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inferior rectus muscle: extraocular muscle that depresses the eye, especially when eye is abducted
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inferior sagittal sinus: major dural sinus
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inferior salivatory nuclei: location of parasympathetic preganglionic neurons that innervate cranial glands
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inferior temporal gyrus: important in visual form perception
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inferior vestibular nucleus: receives direct input from the vestibular organs; projects to various brain stem and spinal targets for eye movement control and balance
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infundibular stalk: interconnects hypothalamus and pituitary gland; also termed the infundibulum
++
initial segment: junction of the neuronal cell body and axon; important site for integration of electrical signals and for initiating action potentials conducted along the axon
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inner hair cells: principal auditory receptor neuron
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inner nuclear layer: retinal layer that contains the cell bodies and proximal processes of the retinal interneurons: bipolar, horizontal, and amacrine cells
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inner synaptic (or plexiform) layer: where synaptic connections between the bipolar cells and the ganglion cells are made
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input nuclei (of basal ganglia): consisting of the striatum; receive input from cerebral cortex
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insular cortex: portion of the cerebral cortex buried beneath the frontal, parietal, and temporal lobes; several sensory representations are located there, including those for taste, balance, and pain
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insulin: hormone secreted by the pancreatic islet cells; can inhibit food intake through hypothalamic circuits
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intention tremor: slow oscillatory movement of the distal limb as it approaches the endpoint of the movement; results from cerebellar dysfunction or damage
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interaural intensity difference: a mechanism for determining the horizontal location of high-frequency sounds
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interaural time difference: a mechanism for determining the horizontal location of low-frequency sounds
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intermediate hemisphere: portion of the cerebellar cortex involved in limb and trunk control
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intermediate horn: the lateral intermediate zone of the spinal cord; location of sympathetic preganglionic neurons
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intermediate nerve: sensory and parasympathetic branch of cranial nerve VII
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intermediate zone: portion of spinal gray matter located between the dorsal and ventral horns
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intermediolateral cell column: see intermediolateral nucleus
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intermediolateral nucleus: location of sympathetic preganglionic neurons; present from about T1 to about L2
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internal arcuate fibers: decussating fibers of the dorsal column nuclei
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internal capsule: location of axons coursing to and from the cerebral cortex; present between the thalamus and parts of the basal ganglia
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internal carotid artery: major cerebral artery; supplies blood to the cerebral cortex and many deep structures excluding the brain stem and cerebellum
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internal medullary laminae: bands of white matter that divide the thalamus into several nuclear divisions
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internal segment of the globus pallidus: one of the principal output nuclei of the basal ganglia
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interneurons: neurons with an axon that remains locally within the nucleus or cortical region where the cell body is located
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internuclear neurons: neurons located in the abducens nucleus that project to the contralateral oculomotor nucleus to transmit control signals for horizontal saccadic eye movements
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internuclear ophthalmoplegia: produced by lesion of the medial longitudinal fasciculus between the levels of the abducens and oculomotor nuclei; interrupts axons of internuclear neurons; inability to adduct the ipsilateral eye when looking to the side opposite the lesion
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interpeduncular cistern: where cerebrospinal fluid collects between the cerebral peduncles
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interpeduncular fossa: space between the cerebral peduncles
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interpolar nucleus: component of the spinal trigeminal nucleus; important for facial pain, especially within the mouth and teeth
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interposed nuclei: deep cerebellar nuclei; comprises the globose and emboliform nuclei
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intersegmental neurons: spinal interneurons that interconnect neurons in different segments; also termed propriospinal neurons
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interstitial nucleus of Cajal: involved in eye and head control; located in rostral midbrain; gives rise to a small descending motor pathway
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interstitial nucleus of the MLF: center for control of vertical eye movements; located in rostral midbrain
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interventricular foramen (of Monro): conduit through which cerebrospinal fluid and choroid plexus passes from the lateral ventricles to the third ventricle
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interventricular foramina: see interventricular foramen
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intracavernous segment: portion of internal carotid artery as it passes through the cavernous sinus
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intralaminar nuclei: set of thalamic nuclei that have diffuse cortical projections and may play a role in regulating the level of cortical activity and arousal
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intrapetrosal segment: portion of the carotid artery as it travels through the petrous bone
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intrasegmental neurons: local spinal interneurons; their axons remain with the segment of the cell body
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intrinsic nuclei (of basal ganglia): include the external part of the globus pallidus, part of the ventral pallidum, subthalamic nucleus, substantia nigra pars compacta, ventral tegmental area
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ipsilateral: on the same side; term used relative to a particular landmark or event
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ischemia: decreased delivery of oxygenated blood to the tissue
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ischemic stroke: occlusion of an artery that results in downstream cessation of blood flow
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isthmus: narrow portion of the developing brain stem between the pons and midbrain; in maturity the isthmus is typically included as part of the rostral pons
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itch: sensory experience produced by histamine
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itch-sensitive receptors: activation leads to the sensation itch; also termed pruritic receptor
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jaw-jerk (or closure) reflex: automatic closure of the jaw upon stimulation of muscle spindle afferents in jaw muscles; analogous to the knee-jerk reflex
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jaw proprioception: the ability to sense jaw angle; more commonly used to describe the sensory events signaled by primary sensory neurons whose cell bodies are located within the mesencephalic trigeminal nucleus
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juxtarestiform body: efferent pathway from the cerebellum to the caudal brain stem; principal location of axons from the fastigial nucleus to vestibular and other brain stem neurons
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knee-jerk reflex: automatic extension of the leg upon stimulation of the patella tendon; the stimulus stretches muscle spindle receptors in the quadriceps muscle
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Korsakoff syndrome: a form of memory loss in patients with alcoholism or thiamine deficiency; produced by degeneration of the mammillary bodies and parts of the medial thalamus
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lacrimal gland: tear gland
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lamina terminalis: rostral wall of the third ventricle; marks location of most anterior portion of the neural tube
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laminated: morphological feature in which neuronal cell bodies or axons form discrete layers
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large-diameter axon: mechanoreceptive sensory axons
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large-diameter fiber entry zone: site at which large-diameter axons enter the spinal cord; located medial to Lissauer's tract
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laryngeal closure reflex: automatic contraction of laryngeal adductor muscles to prevent food and fluids from entering the trachea
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lateral cerebellar hemisphere: cortical component of the cerebrocerebellum; involved primarily in motor planning
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lateral column: portion of the spinal white matter; contains diverse somatic sensory, cerebellar, and motor control pathways
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lateral corticospinal tract: pathway in which descending axons for voluntary limb control descend; originates primarily from the motor areas of the frontal lobe
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lateral descending pathways: motor pathways for controlling limb muscles
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lateral gaze palsy: see internuclear ophthalmoplegia
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lateral geniculate nucleus: thalamic visual relay nucleus
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lateral hypothalamus (or hypothalamic zone): important for feeding and sleep-wakefulness; orexin-containing neurons are unique to this brain region
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lateral intermediate zone: portion of spinal gray matter that plays a role in limb muscle control
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lateral lemniscus: ascending brain stem auditory pathway
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lateral medullary lamina: band of axons that separates the external segment of the globus pallidus and the putamen
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lateral medullary syndrome: set of neurological signs associated with occlusion of the posterior inferior cerebellar artery; signs include difficulty in swallowing, vertigo, loss of pain and temperature sense on the ipsilateral face and contralateral limbs and trunk, ataxia, and Horner syndrome
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lateral olfactory stria: pathway by which axons from the olfactory tract project to the olfactory cortical areas
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lateral posterior nucleus: thalamic nucleus with projections to the posterior parietal lobe
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lateral rectus muscle: ocular abductor muscle; moves eye laterally
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lateral reticular nucleus: precerebellar nucleus; transmits information from the cerebral cortex and spinal cord to the intermediate cerebellum
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lateral septal nucleus: telencephalic nucleus; part of limbic system
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lateral sulcus: separates the temporal lobe from the frontal and parietal lobes
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lateral superior olivary nucleus: contains neurons sensitive to interaural intensity differences; plays role in horizontal localization of high-frequency sounds
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lateral ventral horn: contains motor neurons that innervate limb muscles
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lateral ventricle: telencephalic component of the ventricular system; bilaterally paired, with four components (anterior horn, body, atrium, posterior horn, and inferior horn)
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lateral vestibular nucleus: key brain stem nucleus for control of proximal muscles; important in balance; gives rise to the lateral vestibulospinal tract
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lateral vestibulospinal tract: ipsilateral pathway; component of the medial descending pathways
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laterality: pertains to one side or the other
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L-dopa: precursor to dopamine; used in the treatment of Parkinson disease
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lenticular fasciculus: region of the white matter through which axons from the internal segment of the globus pallidus course en route to the thalamus
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lenticular nucleus: globus pallidus (both internal and external segments) and putamen
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lenticulostriate arteries: branches of the middle cerebral artery and anterior cerebral artery that supply deep structures of the cerebral hemispheres, including parts of the internal capsule and basal ganglia; originate from the proximal portions of the arteries
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leptin: hormone produced by adipocytes in proportion to the amount of body fat; suppresses feeding
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levator palpebrae superioris muscle: principal eyelid elevator
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limb position sense: ability to judge the position of one's limbs without using vision
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limbic association cortex: diverse regions of primarily the frontal and temporal lobes; involved in emotions, learning, and memory
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limbic loop (of basal ganglia): the basal ganglia circuit that receive input from limbic cortical areas, basolateral amygdala, and the hippocampal formation and projects to the orbitofrontal cortex and anterior cingulate cortex
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limbic system: brain structures and their interconnections that collectively mediate emotions, learning, and memory
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Lissauer's tract: location of central branches of small-diameter afferent fibers prior to termination in the superficial dorsal horn
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lobe: major division of the cerebral cortex
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lobule: a division of a lobe
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locus ceruleus: principal noradrenergic brain stem nucleus; located in the rostral pons
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long circumferential branches: brain stem arterial branches that supply the most dorsolateral portions; also supply the cerebellum
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longitudinal axis: the head-to-tail (or head-to-coccyx) axis of the nervous system
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lumbar: spinal cord segment; there are five in total
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lumbar cistern: space within the vertebral canal where cerebrospinal fluid pools; commonly used for withdrawing cerebrospinal fluid from patients
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lumbar tap: process of removing cerebrospinal fluid from the lumbar cistern; needle is inserted into the intervertebral space between the third and fourth (or the fourth and fifth) lumbar vertebrae
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M cell: retinal ganglion neuron with a large dendritic arbor; plays a preferential role in sensing of visual motion; magnocellular
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macroglia: glial cell class that comprises oligodendrocytes, Schwann cells, astrocytes, and ependymal cells; serve a variety of support and nutritive functions; contrast with microglia
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macula lutea: portion of the central retina that contains the fovea
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macular region: portion of the retina surrounding the macula lutea
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macular sparing: maintenance of vision around the fovea after visual cortex damage that produces a loss of parafoveal and peripheral vision
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magnetic resonance angiography: application of magnetic resonance imaging to study vasculature by monitoring motion of water molecules in blood vessels
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magnetic resonance imaging: radiological technique to examine brain structure; uses primarily the water content of tissue to provide a structural image
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magnocellular division (of red nucleus): component of the red nucleus that contains large neurons that project to the spinal cord as the rubrospinal tract
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magnocellular neurosecretory system: hypothalamic neurons in the supraoptic and paraventricular nuclei that project their axons to the posterior lobe of the pituitary, where they release oxytocin and vasopressin
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magnocellular visual system: components of the visual system in the retina, lateral geniculate, and visual cortical areas that originate from M-type ganglion cells; sensitive primarily to moving stimuli
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main (or principal) trigeminal sensory nucleus: brain stem relay nucleus for mechanosensory information from the face and oral cavity
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malleus: one of the middle ear ossicles (bones); essential for conducting changes in air pressure from the tympanic membrane to the oval window; attaches to the tympanic membrane
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mammillary bodies: hypothalamic nuclear complex; contains the medial and lateral mammillary nuclei; the mammillary bodies give rise to the mammillothalamic and mammillotegmental tracts
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mammillotegmental tract: originates from the lateral mammillary nucleus; terminates in the pontine tegmentum
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mammillothalamic tract: originates from both the medial and lateral mammillary nuclei; terminates in the anterior thalamic nuclei
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mandibular division: trigeminal sensory nerve root that innervates primarily the lower face and parts of the oral cavity
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marginal zone: outermost layer of the dorsal horn
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++
maxillary division: trigeminal sensory nerve root that innervates primarily the lips, cheek, and parts of the oral cavity
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mechanoreceptive afferent fibers: sensory axons that have mechanoreceptive terminals
++
mechanoreceptors: sensory receptors sensitive to mechanical stimulation
++
medial descending pathways: motor pathways for controlling axial and other proximal muscles
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medial dorsal nucleus (of the thalamus): principal thalamic nucleus projecting to the frontal lobe
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medial forebrain bundle: pathway that carries functionally diverse brain stem pathways to subcortical nuclei and the cerebral cortex, including the monoaminergic pathways
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medial geniculate nucleus: thalamic auditory relay nucleus
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medial lemniscus: brain stem tract that contains axons traveling from the dorsal column nuclei to the thalamus
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medial longitudinal fasciculus: brain stem tract that contains axons from the vestibular nuclei, extraocular motor nuclei, and various brain stem nuclei; primarily for control of eye movements
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medial mammillary nucleus: principal nucleus of the mammillary body; projects to the anterior nuclei of the thalamus
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medial medullary lamina: band of myelinated axons that separates the internal and external segments of the globus pallidus
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medial olfactory stria: small tract that contains axons from other brain regions that project to the olfactory bulb
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medial orbital gyri: see medial orbitofrontal gyri
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medial orbitofrontal gyri: part of the limbic association cortex
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medial prefrontal cortical areas: portion of the prefrontal cortex one function of which is object recognition
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medial preoptic area: portion of the anterior hypothalamus that contains parvocellular neurosecretory neurons; sexually dimorphic
++
medial rectus muscle: extraocular muscle that adducts eye (ie, moves toward the nose); innervated by the oculomotor nerve (cranial nerve III)
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medial septal nucleus: telencephalic nucleus; important projections to the hippocampal formation; gives rise to cholinergic and GABA-ergic projections
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medial superior olivary nucleus: contains neurons sensitive to interaural timing differences; plays role in horizontal localization of low-frequency sounds
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medial ventral horn: contains motor neurons that innervate proximal limb and axial muscles; controlled by the medial descending pathways
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medial vestibular nucleus: part of the vestibular nuclear complex; gives rise to the medial vestibulospinal tract for head and eye coordination
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medial vestibulospinal tract: motor pathway for coordinating head and eye movements
++
median eminence: contains the primary capillaries of the hypophyseal portal system; located in the proximal portion of the infundibular stalk; lacks blood-brain barrier
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median raphe nuclei: located along or close to the brain stem midline; use serotonin as neurotransmitter
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medium spiny neurons: major class of striatal neuron; projects to the globus pallidus
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medulla: major brain division; part of hindbrain
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medullary dorsal horn: extension of dorsal horn into the medulla; also termed caudal nucleus
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Meissner's corpuscle: mechanoreceptor
++
melanin-concentrating hormone: peptide that affects food intake
++
membranous labyrinth: cavity within which the vestibular apparatus are located; contains endolymph
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meninges: membranes that cover the central nervous system; comprises dura, arachnoid, and pia
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Merkel's receptor: mechanoreceptor
++
mesencephalic trigeminal nucleus: contains cell bodies of jaw muscle stretch receptors; only site in the central nervous system that contains cell bodies of sensory receptor neurons; more similar to a ganglion than a nucleus
++
mesencephalic trigeminal tract: contains the axons of jaw muscle stretch receptors
++
mesencephalon: secondary brain vesicle; major brain division; also termed midbrain
++
mesocorticolimbic dopaminergic system: dopaminergic projection to the frontal lobe and ventral striatum; primarily originates from the ventral tegmental area
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mesoderm: middle layer of the embryo
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mesolimbic dopaminergic system: originates from the ventral tegmental nucleus; supplies dopamine to nucleus accumbens and parts of frontal lobe; sometimes termed mesocorticolimbic dopaminergic system
++
metencephalon: secondary brain vesicle; gives rise to the pons and cerebellum
++
Meyer's loop: component of the optic radiation from the lateral geniculate nucleus to the occipital lobe that courses through the rostral temporal lobe; axons transmit visual information from the contralateral upper visual field
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microglia: class of glial cell that subserves a phagocytic or scavenger role; responds to nervous system infection or damage; contrasts with macroglia
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microzones (of cerebellum): small clusters of Purkinje neurons receive climbing fiber inputs that have similar physiological characteristics, such as processing somatic sensory information from the same body part
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midbrain: major brain division
++
midbrain dopaminergic neurons: correspond to dopaminergic neurons in the substantia nigra pars compacta and the ventral tegmental area
++
midbrain tectum: region dorsal to the cerebral aqueduct; corresponds to the superior and inferior colliculi
++
middle cerebellar peduncle: major input pathway to the cerebrocerebellum; consists of axons of pontine nuclei
++
middle cerebral artery: supplies blood to the lateral surface of the cerebral cortex and deep structures of the cerebral hemisphere and diencephalon
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middle ear ossicles: three bones that conduct sound pressure waves from the tympanic membrane to the oval window
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middle temporal gyrus: located on the lateral temporal lobe; important in higher visual functions, especially object recognition
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midline thalamic nuclei: diffuse-projecting nuclei; one of its major targets is the hippocampal formation
++
midsagittal: anatomical or imaging plane through the midline that is parallel both to the longitudinal axis of the central nervous system and to the midline, between the dorsal and ventral surfaces
++
miosis: pupillary constriction
++
mirror neurons: discharge when an animal preforms a movement or sees movements being performed by another
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mitral cells: projection neuron of the olfactory bulb
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mixed nerve: peripheral nerve composed of somatic sensory and motor axons
++
modality: sensory attribute that corresponds to quality (eg, pain)
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molecular layer: outermost cerebellar layer; contains stellate and basket neurons, Purkinje cell dendrites, climbing fibers, and parallel fibers
++
mossy fiber terminal: enlarged axon terminal; one of the principal components of the cerebellar glomerulus
++
mossy fibers: in the cerebellum, major input to the cortex that originates from diverse structures, including the spinal cord and pontine nuclei; in the hippocampus, axon branch of granule cells in the dentate gyrus that synapse on neurons in the CA3 region
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motion pathway (for vision): circuit specialized for discriminating the speed and direction of moving visual stimuli
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motor cranial nerve nuclei: contain cell bodies of somatic and branchiomeric motor neurons; nuclei containing parasympathetic preganglionic motor neurons are typically termed autonomic motor nuclei or columns
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motor homunculus: representation of body musculature in the primary motor cortex; organization is similar to the form of the body
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motor neurons: central nervous system neurons that have an axon that projects to the periphery, to synapse on striated muscles (somatic or branchiomeric motor neurons) or autonomic postganglionic neurons and adrenal cells (autonomic motor neurons)
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motor unit: a single alpha-motor neuron and all of the muscle fibers that it innervates
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Müller cell: retinal glial cell that stretches from the outer to the inner limiting membranes; have important structural and metabolic functions
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multipolar neurons: neurons with a complex dendritic array and a single axon; principal neuron class in the central nervous system
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muscarinic receptors: membrane proteins that transduce acetylcholine into neuronal depolarization; named for agonist muscarine
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muscle spindle receptor: stretch receptor in muscle; has efferent sensitivity control
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myelencephalon: secondary brain vesicle; forms the medulla of the mature brain
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myelin: fatty substance that contains numerous myelin proteins
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myelin sheath: covering around peripheral and central axons to speed action potential conduction; formed by Schwann cells in the periphery and oligodendrocytes in the central nervous system
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myelin stains: methods to reveal the presence of the myelin sheath
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myotatic reflexes: mechanoreceptors in muscle excite or inhibit motor neurons at short latency with only one or just a few synapses (eg, the knee-jerk [stretch] reflex)
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narcolepsy: disease in which the patient experiences persistent daytime sleepiness; often associated with cataplexy, which is the transient loss of muscle tone without a loss of consciousness
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nasal hemiretina: portion of the retina medial to a vertical line that runs through the macula
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nasal mucosal glands: located in the nasal cavity, secrete mucous, which is rich in glycoproteins; protects the nasal epithelium
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neocortex: phylogenetically most recent portion of the cerebral cortex; most abundant form of cortex; has six or more layers
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neural crest: collection of dorsal neural tube cells that migrate peripherally and give rise to all of the neurons whose cell bodies are outside of the central nervous system; also gives rise to Schwann cells and the arachnoid and pial meningeal layers
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neural degeneration: deterioration in neuron structure and function
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neural groove: midline region of the neural tube where neurons and glial cells do not proliferate; where the floor plate forms
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neural induction: process by which a portion of the dorsal ectoderm of the embryo becomes committed to form the nervous system
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neural plate: dorsal ectoderm region from which the nervous system forms
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neural tube: embryonic structure that gives rise to the central nervous system; cells in the walls of the neural tube form neurons and glial cells, whereas the cavity within the tube forms the ventricular system
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neuraxis: principal axis of the central nervous system
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neuroactive compounds: chemicals that alter neuronal function
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neuroectoderm: portion of the ectoderm that gives rise to the nervous system; corresponds to the neural plate
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neurohypophysis: portion of the pituitary that develops from the neuroectoderm; where vasopressin and oxytocin are released into the systemic circulation
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neuromelanin: polymer of the catecholamine precursor dihydroxyphenylalanine (or dopa), which is contained in the neurons in the pars compacta
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neuromeres: segments of the developing hindbrain
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neurophysins: protein that derives from the prohormone that gives rise to oxytocin and vasopressin; coreleased with oxytocin and vasopressin
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neurotransmitter: typically small molecular weight compounds (eg, glutamate and γ-aminobutyric acid, and acetylcholine) that excite or inhibit neurons
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nigrostriatal dopaminergic system: originates from the substantia nigra pars compacta and terminates primarily in the dorsal and lateral portions of the putamen and caudate nucleus
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nigrostriatal tract: pathway in which nigrostriatal axons course
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nociceptors: somatic sensory receptors that are selectively activated by noxious or damaging stimuli
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nodulus: portion of the cerebellum critical for vestibular control of eye and head movements
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nondeclarative memory: memory of procedures and actions
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noradrenalin: neurotransmitter; also termed norepinephrine
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noradrenergic: neuron that uses noradrenalin as a neurotransmitter
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notochord: releases substances important for organizing the ventral neural tube, such as determining whether a developing neuron becomes a motor neuron; located ventral to the developing nervous system
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noxious stimuli: a tissue-damaging stimulus; can be mechanical, thermal, or in response to various forms of trauma
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nucleus: collection of neuronal cell bodies within the central nervous system
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nucleus accumbens: component of the striatum located ventrally and medially; key structure in drug addiction
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nucleus ambiguus: contains primarily motor neurons that innervate the pharynx and larynx; also contains parasympathetic preganglionic neurons; located in the medulla
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nucleus of the diagonal band of Broca: cholinergic telencephalic nucleus with diverse cortical projections; located in the basal forebrain
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nucleus of the lateral lemniscus: auditory projection nucleus; located in the rostral pons
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nucleus of the trapezoid body: contains inhibitory neurons that receive input from the anteroventral cochlear nucleus and project to the lateral superior olivary nucleus; may participate in shaping the interaural timing sensitivity of neurons in the lateral superior olivary nucleus located in the pons
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nucleus proprius: contains neurons that process somatic sensory information; corresponds to laminae III–IV of the dorsal horn
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nystagmus: rhythmical oscillations of the eyeball
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occipital lobe: one of the lobes of the cerebral hemisphere
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occipital somites: somites from which neck and cranial structures develop
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ocular dominance columns: clusters of neurons in the primary visual cortex that receive and process information predominantly from either the ipsilateral or the contralateral eye
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oculomotor (III) nerve: motor cranial nerve; contains axons that innervate the medial rectus, superior rectus, inferior rectus, inferior oblique, and levator palpebrae muscles, as well as axons of parasympathetic preganglionic neurons
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oculomotor loop: basal ganglia circuit that engages frontal eye movement control areas
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oculomotor nucleus: contains motor neurons that innervate the medial rectus, superior rectus, inferior rectus, inferior oblique, and levator palpebrae muscles
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odorants: chemicals that produce odors
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olfactory bulb: telencephalic structure that receives input from olfactory sensory neurons and projects to the olfactory cortical areas
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olfactory discrimination: ability to discriminate one odorant from another
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olfactory epithelium: portion of the olfactory mucosa that contains olfactory sensory neurons
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olfactory (I) nerve: central branches of olfactory sensory neurons; travels the short distance between the olfactory. mucosa, through the cribriform plate, to synapse in the olfactory bulb
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olfactory receptor: transmembrane protein complex in an olfactory sensory neuron; transduces a particular set of odorants into a neural potential; any given olfactory sensory neurons contains a single (or just a few) olfactory receptor types
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olfactory sulcus: groove on the inferior frontal lobe surface in which the olfactory bulb and tract course
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olfactory tract: contains axons that interconnect the olfactory bulb with the other olfactory nuclear regions of the brain
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olfactory tubercle: region on the ventral brain surface that receives input from the olfactory tract; may play a role in emotions in addition to olfaction
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oligodendrocytes: class of glial cell that forms the myelin sheath around axons within the central nervous system
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olive: landmark on ventral surface of the medulla under which the inferior olivary nucleus is located
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olivocochlear bundle: efferent projection from the inferior olivary nucleus to hair cells in the cochlea
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olivocochlear projection: see olivocochlear bundle
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Onuf's nucleus: located in sacral spinal cord; contains motor neurons that innervate anal and urethral sphincters
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operculum: portions of frontal, parietal, and temporal lobes that overlie the insular cortex
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ophthalmic artery: supplies the eye; can be a pathway for collateral brain circulation after occlusion of the internal carotid artery
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ophthalmic division: trigeminal sensory nerve root that innervates primarily the upper face
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optic chiasm: site of decussation of ganglion cell axons from the nasal hemiretinae
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optic disk: site on retina where ganglion cell axons exit from the eye
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optic (II) nerve: sensory cranial nerve that contains axons of retinal ganglion cells; major projections are to the lateral geniculate nucleus, superior colliculus, and pretectal nuclei
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optic radiations: pathway from the lateral geniculate nucleus to the primary visual cortex; forms the lateral wall of the posterior horn of the lateral ventricle
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optic tectum: also termed the superior colliculus
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optic tract: retinal ganglion cell axon pathway between the optic chiasm and the lateral geniculate nucleus
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optokinetic reflexes: ocular reflexes that use visual information; supplements the actions of vestibulo-ocular reflexes
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oral nucleus: rostral component of the spinal trigeminal nucleus
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orbitofrontal (or orbital) gyri: portion of the inferior frontal lobe that contains the orbital gyri; overlie the bony orbits
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orbitofrontal cortex: part of prefrontal cortex; important for emotion and personality
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orexin: peptide that is essential for the proper maintenance of the aroused state; loss of orexin is implicated in the sleep disorder narcolepsy; may also participate in feeding; also termed hypocretin
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organ of Corti: component of the inner ear for transducing sound into neural signals
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organum vasculosum of the lamina terminalis: one of the circumventricular organs; region in which the bloodbrain barrier is absent; axons project to magnocellular neurons of the paraventricular nucleus
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orientation column: cluster of neurons in the primary visual cortex that processes information about the orientation of a visual stimulus
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orthonasal olfaction: when molecules travel from the external environment, through the nostrils (nares), to activate olfactory neurons in the olfactory epithelium
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orthostatic hypotension: sudden reduction in systemic blood pressure upon standing upright; sometimes termed postural hypotension
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otic ganglion: contains parasympathetic postganglionic neurons that innervate the parotid gland, which secretes saliva
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otolith organs: the utricle and saccule; sensitive to linear acceleration
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outer hair cells: class of auditory receptor neurons; may be more important in regulating the sensitivity of the organ of Corti than in auditory signal transduction
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outer nuclear layer: retinal layer that contains the cell bodies of photoreceptors (rods and cones)
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outer synaptic (or plexiform) layer: retinal layer in which connections are made between photoreceptors and two classes of retinal interneurons (horizontal cells and bipolar neurons)
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output nuclei (of basal ganglia): consisting of the globus pallidus-internal part, part of the ventral pallidum, and the substantia nigra pars reticulata
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oxytocin: peptide released by magnocellular neurons in the paraventricular and supraoptic nuclei
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P cell: retinal ganglion neurons with a small dendritic arbor; plays a preferential role in sensing of form and color; parvocellular
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pacinian corpuscle: rapidly adapting mechanoreceptor sensitive to high-frequency vibration
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pain: sensation evoked by noxious stimulation
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palate: arch-shaped portion of the superior oral cavity
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paleocortex: type of cerebral cortex with fewer than six layers; commonly associated with processing of olfactory stimuli; located on the basal surface of the cerebral hemispheres, in part of the insular cortex, and caudally along the parahippocampal gyrus and retrosplenial cortex
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pallidotomy: therapeutic lesion of a portion of the globus pallidus to alleviate dyskinesias
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parabrachial nucleus: transmits viscerosensory information from the solitary nucleus to the diencephalon; located in the rostral pons
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parafascicular nucleus: thalamic diffuse-projecting nucleus with widespread projections to the frontal lobe and striatum
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parahippocampal gyrus: located on medial temporal lobe; contains cortical association areas that project to the hippocampal formation
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parallel fibers: axons of cerebellar granule cells that course along the long axis of the folia; a single parallel fiber makes synapses with many Purkinje cells
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parallel organization: property of neural systems in which pathways with similar anatomical organizations serve distinct functions
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parallel sensory pathways: two or more sensory pathways that have similar anatomical projections and overlapping sets of functions
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paramedian arterial branches: supply the most medial portions of the brain stem; originate primarily from the basilar artery
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paramedian pontine reticular formation: transmits control signals from the contralateral cerebral cortex to brain stem centers for controlling horizontal saccades; major target of neurons in this structure is the abducens nucleus
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parasagittal: anatomical or imaging plane off the midline that is parallel both to the longitudinal axis of the central nervous system and to the midline, between the dorsal and ventral surfaces
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parasympathetic nervous system: component of the autonomic nervous system; originates from the brain stem and the caudal sacral spinal cord
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parasympathetic preganglionic neurons: autonomic neurons located in the central nervous system; project to parasympathetic postganglionic neurons, which are located in the periphery
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paraterminal gyrus: located anterior to the rostral wall of the third ventricle and ventral to the rostrum of the corpus callosum
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paraventricular nucleus: hypothalamic nucleus that contains magnocellular neurosecretory neurons, parvocellular neurosecretory neurons, and descending projection neurons that regulate the functions of the autonomic nervous system
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paravertebral ganglia: contain sympathetic postganglionic neurons
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parietal lobe: one of the lobes of the cerebral hemisphere
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parietal-temporal-occipital association area: association cortex at the junction of the parietal, temporal, and occipital lobes; important for linguistics, perception, and other higher brain functions
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parietooccipital sulcus: separates the parietal and occipital lobes
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Parkinson disease: results from loss of dopaminergic neurons in the substantia nigra pars compacta; characterized by slowing or absence of movement (bradykinesia) and tremor
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parotid gland: salivary gland; innervated by axons of the glossopharyngeal (IX) nerve
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parvocellular division (of red nucleus): component of the red nucleus that contains small neurons that project to the inferior olivary nucleus as the rubroolivary tract
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parvocellular neurosecretory system: hypothalamic neurons located predominantly in the periventricular zone; neurons project to the median eminence where they make neurovascular contacts with capillaries and release factors into the blood that are carried to the anterior lobe by the portal veins
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parvocellular visual system: components of the visual system in the retina, lateral geniculate, and visual cortical areas that originate from P-type ganglion cells; sensitive primarily to color, size, and the shapes of stimuli
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peduncles: a large collection of axons
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pedunculopontine nucleus: a pontine nucleus that receives a projection from the internal segment of the globus pallidus; participates in diverse functions, including regulating arousal and movement control; contains cholinergic neurons
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perforant pathway: projection from the entorhinal cortex to the dentate gyrus
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periamygdaloid cortex: one of the olfactory cortical areas; receives a direct projection from the olfactory tract; located on the rostromedial temporal lobe
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periaqueductal gray matter: central region of the midbrain that surrounds the cerebral aqueduct; participates in diverse functions, including pain suppression
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periglomerular cell: an inhibitory interneuron in the olfactory bulb that receives input from olfactory sensory neurons and inhibits mitral cells in the same and adjacent glomeruli
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perilymph: fluid that fills the space between the membranous labyrinth and the temporal bone; resembles extracellular fluid and cerebrospinal fluid
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peripheral autonomic ganglia: clusters of sympathetic and parasympathetic postganglionic neurons
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peripheral nervous system: contains the axons of motor neurons, the peripheral axons and cell bodies of dorsal root ganglion neurons, the axon of autonomic preganglionic neurons, and the cell body and axon of autonomic postganglionic neurons
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periventricular nucleus: contains parvocellular neurosecretory neurons; located in the hypothalamus, beneath the walls of the third ventricle
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periventricular zone: portion of the hypothalamus that contains most of the parvocellular neurosecretory neurons; located beneath the walls and floor of the third ventricle
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pharynx: the portion of the digestive tube between the esophagus and mouth; the throat
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pheromones: a chemical produced and secreted by an animal that influences the behavior and development of other members of the same species
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pia mater: inner meningeal layer; adheres closely to the surface of the central nervous system
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pigment epithelium: external to the photoreceptor layer; it serves a phagocytic role during renewal of rod outer segment disks
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pineal gland: endocrine gland located dorsal to the superior colliculus that is involved in the sleep/wake cycle; secretes melatonin
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piriform cortex: one of the olfactory cortical areas; receives a direct projection from the olfactory tract; located on the rostromedial temporal lobe
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pituitary portal circulation: connects capillary beds of the median eminence and anterior lobe of the pituitary; portal vein
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pons: one of the major brain divisions; Latin for bridge
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pontine cistern: site of accumulation of cerebrospinal fluid at the pontomedullary junction
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pontine flexure: bend in the developing nervous system at the pons
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pontine nuclei: relay information from the ipsilateral cerebral cortex to the contralateral cerebellar cortex and deep nuclei, principally the lateral cerebellar cortex and the dentate nucleus
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pontomedullary junction: where the pons and medulla join
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pontomedullary reticular formation: contains diverse motor, sensory, and integrative nuclei; especially important in arousal and visceral and skeletal muscle control
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portal circulation: contains two capillary beds joined by portal veins; present in the pituitary gland and the liver
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portal veins: join the two capillary beds of a portal circulation
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positron emission tomography: functional imaging technique based on the emission of positively charged unstable subatomic particles (positrons); PET
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postcentral gyrus: important for mechanical sensations, including position sense; located in the parietal lobe
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postcommissural fornix: principal division of the fornix; contains axons principally from the subiculum that terminate in the mammillary bodies
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posterior: toward the abdomen
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posterior cerebellar incisure: shallow groove in the posterior lobe of the cerebellum
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posterior cerebral artery: supplies portions of the occipital and temporal lobes as well as the diencephalon
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posterior circulation: arterial supply provided by the vertebral and basilar arteries
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posterior commissure: interconnects midbrain structures in the two halves of the brain stem; axons that mediate the pupillary light reflex in the nonilluminated eye course within the anterior commissure
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posterior communicating artery: branch of the internal carotid artery that joins the posterior cerebral arteries; connects the anterior and posterior circulations, thereby providing a pathway for collateral circulation; part of the circle of Willis
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posterior inferior cerebellar artery (PICA): supplies the dorsolateral medulla and portions of the inferior (posterior) cerebellum
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posterior limb of the internal capsule: component of the internal capsule that lies lateral to the thalamus; carries axons from various sources including those coursing to and from the primary motor and somatic sensory cortical areas
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posterior lobe of cerebellum: portion of cerebellar cortex between the anterior and flocculonodular lobes; comprises lobules VI–IX
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posterior lobe (of pituitary gland): contains axons and terminations of the paraventricular and supraoptic nuclei of the hypothalamus; axon terminations release vasopressin (ADH) and oxytocin at neurovascular contacts with systemic capillaries
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posterior parietal lobe (or cortex): caudal to the primary somatic sensory cortex; important for proprioception, spatial awareness, attention and visually guided limb and eye movements; part of the where pathway for visual motion and actions
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posterior spinal arteries: supply blood to the dorsal columns and dorsal horn predominantly
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posterolateral fissure: separates the posterior and flocculonodular cerebellar lobes
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posteroventral cochlear nucleus: contributes to a system of connections that regulate hair cell sensitivity
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postganglionic neuron: autonomic neuron that projects to a peripheral motor target, such as a smooth muscle or a gland
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postsynaptic neuron: component of a synapse; contacted by a presynaptic neuron
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precentral gyrus: contains the primary motor cortex and the caudal portion of the premotor cortex; located in the frontal lobe
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precommissural fornix: small division of the fornix that contains axons primarily from the hippocampus that terminate in the septal nuclei
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prefrontal association cortex: involved in diverse functions, including thought and working memory
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prefrontal cortex loop: circuit of the basal ganglia that projects to the prefrontal cortex; involved in higher brain functions, such as thought and working memory
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prefrontal cortex: see prefrontal association cortex
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preganglionic neuron: autonomic neuron located in the central nervous system
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premotor areas: participate in the planning of movements; located in the frontal lobe, in areas 6, 23, and 24
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premotor cortex: specific premotor region located in the lateral portion of area 6
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preoccipital notch: surface landmark that forms part of the boundary between the temporal and occipital lobes on the lateral surface
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preoptic area: serves diverse functions including the control of sex hormone release from the anterior pituitary gland and regulation of sleep and wakefulness; located in the most rostral part of the hypothalamus
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preoptic sleep center: hypothalamic center that regulates transition from wakefulness to sleep
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prepositus nucleus: participates in eye position control; receives abundant inputs from the vestibular nuclei; located in the medulla
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presynaptic neuron: component of the synapse; transmits information to the postsynaptic neuron
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presynaptic terminal: axon terminal
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pretectal nuclei: involved in pupillary light reflex; located in the junction between the midbrain and diencephalon
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prevertebral ganglia: sympathetic ganglia that lie along the vertebral column
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primary auditory cortex: first cortical processing site for auditory information; located in the transverse temporal gyri (of Heschl) in the temporal lobe; corresponds to cytoarchitectonic area 41
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primary fissure: separates the anterior and posterior lobes of the cerebellum
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primary motor cortex: contains neurons that participate in the control of limb and trunk movements; contains neurons that synapse directly on motor neurons; consists of area 4
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primary olfactory cortex: defined as the target areas of olfactory tract axons; located in the rostromedial temporal lobe and the basal surface of the frontal lobes; corresponds to the paleocortex
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primary olfactory neurons: transduce odorant molecules into neural signals; located within the olfactory epithelium
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primary sensory (or afferent) fibers: somatic sensory receptor; dorsal root ganglion neuron
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primary somatic sensory cortex: participates in somatic sensations, principally mechanical sensations and limb position sense; corresponds to cytoarchitectonic areas 1, 2, and 3; located in the postcentral gyrus
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primary vestibular afferents: innervate vestibular hair cells; terminate primarily in the vestibular nuclei and cerebellum
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primary visual cortex: participates in visual perceptions; located in the occipital lobe
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projection neurons: cortical pyramidal neurons that project their axons to subcortical sites
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proopiomelanocortin: a large peptide from which β-endorphin is cleaved
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proprioception: sense of the position of the body; usually that of a limb or one limb segment relative to another
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propriospinal neurons: spinal interneurons that interconnect neurons in different segments; also termed intersegmental neurons
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prosencephalon: most rostral brain vesicle; gives rise to the telencephalon and diencephalon, which are the forebrain structures
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prosopagnosia: inability to recognize faces
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proximal limb muscles: muscles that innervate the shoulder or hip
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pruritic: related to itch
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pruritic receptor: sensory receptors responsible for the sensation of itch; activated by histamine
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pseudoptosis: partial dropping of the eyelid
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pseudounipolar neurons: neuron type that has a single axon and few or no dendrites in maturity (eg, the dorsal root ganglion neuron)
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pterygopalatine ganglion: peripheral ganglion containing the cell bodies of parasympathetic postganglionic neurons that innervate nasal and oropharyngeal mucosal glands and lacrimal glands
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pulmonary aspiration: the presence of food or consumed fluids in the lungs
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pulvinar nucleus: major thalamic nucleus that has diverse projections to the parietal, temporal, and occipital lobes; involved in perception and linguistic functions
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pupillary constriction: reduction in pupil diameter
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pupillary dilation: increase in pupil diameter
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pupillary light reflex: closure of the pupil with visual stimulation of the retina; used to test midbrain function in comatose patients
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pupillary reflexes: changes in pupil diameter that occur without voluntary control; usually occur together with other ocular reflexes
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Purkinje layer: location of Purkinje cell bodies
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Purkinje neuron (or cell): output neuron of the cerebellar cortex; makes GABAergic inhibitory synapses on neurons of deep cerebellar nuclei and vestibular nuclei
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putamen: component of the striatum; important in limb and trunk control
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pyramid: tract on ventral surface of medial medulla; contains descending cortical axons, including the corticobulbar and corticospinal tracts
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pyramidal neuron (or cell): cortical projection neuron class with characteristic pyramidal-shaped cell body
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pyramidal decussation: where pyramidal cell axons from the motor and premotor areas cross the midline; located in the medulla
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pyramidal signs: motor impairments that follow lesion of the corticospinal system
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pyramidal tract: location of descending motor control pathway that originates in the motor and somatic sensory areas
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quadrigeminal bodies: another name for the superior and inferior colliculi
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quadrigeminal cistern: portion of the subarachnoid space that overlies the superior and inferior colliculi
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radial glia: type of astrocyte that plays a role in organizing neural development; form scaffold for neuron growth and migration
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radicular arteries: segmental arteries that supply the spinal cord, together with anterior and posterior spinal arteries
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radicular pain: pain localized to the distribution of a single dermatome or several adjoining dermatomes
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raphe nuclei: contain serotonin; located along the midline throughout most of the brain stem
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rapidly adapting: response characteristic of neurons to a sudden stimulus in which a brief series of action potentials decrement rapidly to few or no action potentials
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Rathke's pouch: an ectodermal diverticulum in the roof of the developing oral cavity from which the anterior and intermediate lobes of the pituitary develop
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receptive membrane: portion of a neuron's membrane that contains receptors sensitive to neuroactive compounds or a particular stimulus
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red nucleus: plays a role in limb movement control; gives rise to the rubrospinal and rubroolivary tracts
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reduced myotatic reflexes: a condition in which the strength of muscle stretch or tendon reflexes are diminished
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regional neuroanatomy: examines the spatial relations between brain structures within a portion of the nervous system
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relaxation times: in magnetic resonance imaging, the times it takes protons to return to the energy state they were in before excitation by electromagnetic waves
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relay nuclei: contain neurons that transmit (or relay) incoming information to other sites in the central nervous system
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release-inhibiting hormones: chemicals that inhibit the release of a hormone from the anterior pituitary gland; usually neuroactive compounds secreted into the portal circulation at the median eminence
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releasing hormones: chemicals that promote the release of a hormone from the anterior pituitary gland; usually neuroactive compounds secreted into the portal circulation at the median eminence
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REM sleep: abbreviation for rapid eye movement characterized by dreaming, low limb and trunk muscle tone, and low-amplitude high-frequency electroencephalographic activity
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reproductive behaviors: relatively stereotypic behaviors between members of the same species that lead to a reproductive act; in animals, the hypothalamus plays an important role in promoting reproductive behaviors, often in response to pheromones
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restless legs syndrome: a disorder in which patients experience abnormal sensations in their legs that prompt the urge to move their legs to quell the sensation; abnormal sensations and movements are more common during rest and sleep than during activity
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reticular formation: a diffuse collection of nuclei in the central (medial) portion of the brain stem that play a role in a variety of functions, including regulation of arousal, motor control and vegetative functions
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reticular nucleus: a thalamic nucleus that projects to other thalamic nuclei; plays a role in regulating thalamic neuronal activity
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reticulospinal tract: descending motor pathway that originates from the reticular formation, primarily in the pons and medulla, and synapses in the spinal cord
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retina: peripheral portion of the visual system that contains photoreceptors as well as interneurons and projection neurons for the initial processing of visual information and transmission to several brain structures; develops from the diencephalon
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retinitis pigmentosa: disease in which breakdown products accumulate at the pigment epithelium of the retina
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retinohypothalamic tract: axons of retinal ganglion cells that project to the suprachiasmatic nucleus; information in this tract is used to synchronize circadian rhythms to the day-night cycle
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retroinsular cortex: location of a vestibular cortical area; junction of the posterior insular cortex with the cortex on the lateral brain surface.
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retronasal olfaction: when molecules travel from the oropharynx to activate olfactory neurons in the olfactory epithelium
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Rexed's laminae: thin sheets of neurons in the spinal cord, which are clearest in the dorsal horn; they are significant because neurons in different layers receive input from different afferent and brain sources and, in turn, project to different targets
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rhinal sulcus: rostral extension of the collateral sulcus, which separates the parahippocampal gyrus from more lateral temporal lobe regions
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rhodopsin: photopigment in rod cells
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rhombencephalon: most caudal primary brain vesicle; gives rise to the pons and medulla
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rhombic lip: portion of the developing pons that gives rise to most of the cerebellum
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rhombomeres: segments in the developing pons and medulla; eight in total
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rigidity: condition in patients with Parkinson disease in which there is resistance to passive movement about a joint; sometimes there are phasic decreases in this resistance, termed cog-wheel rigidity
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rod bipolar cells: retinal interneurons that transmit signals from rod cells to ganglion cells
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rods: photoreceptors for vision under low light conditions (scotopic vision); located away from the macula portion of the retina
++
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rostral interstitial nucleus of the medial longitudinal fasciculus: plays a role in control of vertical saccades
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rostral spinocerebellar tract: transmits information about the level of activation in cervical spinal interneuronal systems to the cerebellum; thought to relay internal signals from motor pathways, via spinal interneurons, to the cerebellum
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rostrocaudal axis: from the nose to the coccyx; the long axis of the central nervous system
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rubrospinal tract: projection from the magnocellular portion of the red nucleus to the spinal cord
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Ruffini's corpuscle: type of mechanoreceptor; distal process of large-diameter myelinated afferent fibers (A-β)
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saccades: rapid, darting movements of the eye from one site of gaze to another
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saccadic eye movements: see saccades
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saccule: vestibular sensory organ (or otolith organ) sensitive to linear acceleration
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sacral: spinal cord segment; there are five in total
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sagittal: anatomical or imaging plane that is parallel both to the longitudinal axis of the central nervous system and to the midline, between the dorsal and ventral surfaces
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scala media: inner ear fluid compartment
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scala tympani: inner ear fluid compartment
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scala vestibuli: inner ear fluid compartment; conducts pressure waves from the tympanic membrane to the other fluid compartments
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Schaefer collaterals: collateral axon branch of neurons in the CA3 region of the hippocampus that synapse on neurons in the CA1 region
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schizophrenia: psychiatric disease characterized by disordered thoughts, often associated with hallucinations
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Schwann cells: glial cells that form the myelin sheath around peripheral axons
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sclera: nonneural cover over the eye
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seasonal affective disorder (SAD): form of depression during periods when days are short and nights are long
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secondary auditory areas: cortical areas that process auditory information from the primary area
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secondary somatic sensory cortex: cortical areas that process somatic sensory information from the primary area
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segmental interneurons: neurons whose axons remain within a single spinal cord segment
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segmental: pertaining to the segmental organization of the spinal cord
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semantic memory: memory and knowledge of facts, people, and objects, including new word meaning
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semicircular canals: vestibular organs sensitive to angular acceleration; there are three semicircular canals, each sensitive to acceleration in a different plane
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semilunar ganglion: contains cell bodies of primary trigeminal sensory neurons
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sensory: related to any of a wide range of stimuli from the environment or from within the body
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sensory cranial nerve nuclei: process sensory information from the cranial nerves
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sensory homunculus: form of somatic sensory representation in the postcentral gyrus (primary somatic sensory cortex)
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septal nuclei: may participate in assessing the reward potential of events; receives input from the hippocampus and projects to the hypothalamus and other areas; located in rostral portion of the cerebral hemispheres
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septum pellucidum: forms the medial walls of the anterior horn and part of the body of the lateral ventricle
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serotonergic: neurons that use serotonin as a neurotransmitter
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serotonin: neuroactive compound; also termed 5-HT (5-hydroxytryptamine)
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short circumferential branches: supply ventral portions of the brain stem away from the midline; primarily from the basilar artery
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sigmoid sinus: dural blood sinus that drains the transverse sinus and flows into the inferior petrosal sinus; located bilaterally
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six layers: describes laminar pattern of neocortex
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skeletal somatic motor: neuron class in which axons synapse on skeletal muscle that derives from the somites
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skeletomotor loop: basal ganglia circuit that engages the motor and premotor areas
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slowly adapting: response characteristic of neurons to an enduring stimulus in which a prolonged series of action potentials decrement slowly or not at all
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small-diameter axons: afferent fibers that are sensitive to pain, temperature, and itch (ie, histamine)
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smell: one of the five major senses
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smooth pursuit eye movements: slow eye movements that follow visual stimuli
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soft palate: caudal, arch-shaped, portion of superior oral cavity formed by muscle
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solitary nucleus: contains neurons that receive and process gustatory and viscerosensory information and project to other brain stem and diencephalic nuclei, including the parabrachial nucleus and the thalamus
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solitary tract: where the central branches of gustatory and viscerosensory axons collect before synapsing in the solitary nucleus
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somatic: related to the body
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somatic motor systems: pathways and neurons that participate in limb and trunk muscle control
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somatic sensory: body sense; includes pain, temperature sense, itch, touch, and limb position sense
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somatic skeletal motor column: motor nuclei in the spinal cord that contain motor neurons that innervate somatic skeletal muscle
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somatotopy: organization of central sensory and motor representations based on the shape and spatial characteristics of the body
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somites: para-axial mesoderm that organizes development of muscles, bones, and other structures of the neck, limbs, and trunk
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spastic paralysis: condition in which the presence of spasticity produces an inability to voluntarily control striated muscle
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spasticity: velocity-dependent increase in muscle tone; occurs after damage to the corticospinal system during development or in maturity
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spina bifida: neural tube defect; failure of the caudal neural tube to close, producing impairments in lumbosacral spinal cord functions
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spinal accessory (XI) nerve: cranial motor nerve that innervates the sternocleidomastoid muscle and parts of the trapezius muscle
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spinal accessory nucleus: contains motor neurons whose axons course in the spinal accessory (XI) nerve to innervate the sternocleidomastoid muscle and parts of the trapezius muscle
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spinal border cells: neurons that contribute axons to the ventral spinocerebellar tract
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spinal cord: major division of the central nervous system
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spinal nerves: mixed nerves present at each spinal segment
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spinal tap: colloquial term for lumber puncture in which a needle is inserted into the lumbar cistern to collect a sample of cerebral spinal fluid; most commonly used for diagnostic testing
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spinal trigeminal nucleus: portion of the trigeminal sensory nuclear complex within the medulla and caudal pons; contains the caudal, interposed, and oral subnuclei; involved in diverse trigeminal functions, the most important of which are pain, temperature, and itch
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spinal trigeminal tract: pathway in which trigeminal afferent fibers course before synapsing in the spinal trigeminal nucleus
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spinocerebellar tracts: paths transmitting somatic sensory information from the limbs and trunk to the cerebellum for movement control
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spinocerebellum: portion of the cerebellum that plays a key role in limb and trunk control; includes the vermis and intermediate hemisphere of the cortex and the fastigial and interposed nuclei
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spinomesencephalic tract: transmits somatic sensory information from the limbs and trunk to the midbrain
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spinoreticular tract: transmits somatic sensory information from the limbs and trunk to the reticular formation
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spinotectal tract: transmits somatic sensory information from the limbs and trunk to the dorsal midbrain; term often used interchangeably with spinomesencephalic tract
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spinothalamic tract: transmits somatic sensory information from the limbs and trunk to the thalamus
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spiral ganglion: where the cell bodies of auditory primary sensory neurons are located
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stapes: one of the middle ear ossicles (bones); essential for conducting changes in air pressure from the tympanic membrane to the oval window; attaches to the oval window
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stellate cells: in the cerebellum, inhibitory interneurons located in the molecular layer; more generally, a class of small multipolar neuron in the central nervous system
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stem cells: multipotential cell that can develop into nerve, glial, or other cell types
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sternocleidomastoid muscle: flexes the head and rotates head to opposite side
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straight sinus: drains the inferior sagittal sinus and certain veins; empties into the confluence of sinuses; located where the falx cerebri and tentorium cerebelli meet; located on midline
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stria (or stripe) of Gennari: band of myelinated axons in layer 4B of the primary visual cortex; axons interconnect local areas of cortex for visual stimulus processing
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stria medullaris: pathway that courses along the lateral walls of the third ventricle; contains axons from the septal nuclei to the habenula
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stria terminalis: C-shaped pathway from the amygdala to portions of the diencephalon and cerebral hemispheres; also contains neurons
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striasome: an anatomical compartment of the striatum that contains patch-like distributions of particular neurochemicals (eg, acetylcholinesterase; encephalin)
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striatal cell bridges: places of continuity of the caudate nucleus and putamen that span the internal capsule
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striate cortex: another term for the primary visual cortex based on the location of the stria of Gennari
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striatum: component of the basal ganglia; comprises the caudate nucleus, putamen, and nucleus accumbens
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subarachnoid space: between the outer portion of the arachnoid and the pia; where cerebrospinal fluid accumulates over the surface of the brain and spinal cord
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subcommissural organ: a circumventricular organ; located near the posterior commissure
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subdural hematoma: hemorrhage of blood into the potential space between the dura and the arachnoid
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subdural space: potential space between the dura and the arachnoid
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subfornical organ: one of the circumventricular organs; region in which the blood-brain barrier is absent; axons project to magnocellular neurons of the paraventricular nucleus
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subgenual cortex: located ventral to the genu of the corpus callosum; associated with clinical depression and is a target of brain stimulation for intractable depression
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subiculum: component of the hippocampal formation
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submandibular ganglion: contain postganglionic neurons that innervate the oral mucosa and the submandibular and sublingual glands
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submodality: category of a sensory modality, such as color vision, bitter, or pain
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substance P: neuroactive compound; present in neurons that process painful stimuli
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substantia gelatinosa: laminae II and III of the dorsal horn; process pain, temperature, and itch
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substantia nigra pars compacta: portion of the substantia nigra where neurons contain dopamine and project widely to the striatum
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substantia nigra pars reticulata: portion of the substantia nigra where neurons contain GABA and project to the thalamus primarily
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substantia nigra: component of the basal ganglia; comprises the pars reticulata and the pars compacta
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subthalamic nucleus: basal ganglia nucleus involved in limb control; when damaged, can produce hemiballism; part of the indirect basal ganglia circuit
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sulcus limitans: groove that separates developing sensory and motor structures in the spinal cord and brain stem
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superior cerebellar artery: supplies rostral pons and cerebellum; long circumferential branch of the basilar artery
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superior cerebellar peduncle: tract that primarily carries axons from the deep cerebellar nuclei to the brain stem and thalamus
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superior colliculus: plays a key role in controlling saccades; located in the rostral midbrain
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superior ganglion: of the vagus and glossopharyngeal nerves, contains cell bodies of somatic sensory afferent fibers
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superior oblique muscle: depresses the eye when the eye is adducted and intorts the eye when it is abducted
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superior olivary nuclear complex: involved in processing incoming auditory signals; especially important for horizontal localization of sounds
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superior olivary nuclei: auditory relay nuclei predominantly important in the horizontal localization of sounds
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superior parietal lobule: important for spatial localization
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superior petrosal sinus: dural sinus; drains into the sigmoid sinus
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superior rectus muscle: elevates the eye
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superior sagittal sinus: dural sinus; drains into the straight sinus
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superior salivatory nucleus: contains parasympathetic preganglionic neurons whose axons course in the intermediate (VII) nerve
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superior temporal gyrus: involved in hearing and speech
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superior vestibular nucleus: one of four vestibular nuclei; located in the pons
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supplementary eye field: cortical eye movement control center located primarily on the medial wall of the frontal lobe; involved in more cognitive aspects of saccadic eye movement control
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supplementary motor area: portion of the medial frontal lobe important in the control of eye movements
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supporting cells: provide structural and possibly trophic support for taste buds
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suprachiasmatic nucleus: hypothalamic nucleus important for circadian rhythms; center of the biological clock
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supraoptic nucleus: contains magnocellular neurosecretory neurons; secretes oxytocin and vasopressin into the systemic circulation in the posterior pituitary gland
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Sylvian fissure: separates the temporal lobe from the parietal and frontal lobes; also termed the lateral sulcus
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sympathetic nervous system: component of the autonomic nervous system
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sympathetic preganglionic neurons: sympathetic nervous system neurons that are located in the central nervous system and synapse on sympathetic postganglionic neurons and cells in the adrenal medulla
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synapses: specialized sites of contact where neurons communicate and where neurotransmitters are released; comprise three components—presynaptic axon terminal, synaptic cleft, and postsynaptic membrane
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synaptic cleft: narrow intercellular space between the neurons at synapses
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T1 relaxation time: proton relaxation time related to the overall tissue environment; also termed spin-lattice relaxation time
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T2 relaxation time: proton relaxation time related to interactions between protons; also termed spin-spin relaxation time
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tabes dorsalis: degenerative loss of large-diameter mechanoreceptive fibers; associated with end-stage neurosyphilis
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tarsal muscle: a smooth muscle that assists the actions of the levator palpebrae muscle; under control of the sympathetic nervous system
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tastants: chemicals that produce tastes
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taste: one of the five major senses
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taste buds: gustatory organ, which consists of taste receptor cells, support cells, and basal cells, which may be stem cells for replenishing taste receptor cells
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taste receptor cells: component of taste buds; transduce oral chemicals into gustatory signals
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tectorial membrane: component of the organ of Corti; stereocilia of hair cells embed within the tectorial membrane
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tectospinal tract: projection from the deep layers of the superior colliculus to the spinal cord
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tectum: most dorsal portion of the brain stem; present only in midbrain in maturity
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tegmentum: portion of the brain stem between the tectum and the base; present throughout the brain stem; Latin for cover
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telencephalon: secondary brain vesicle that gives rise to structures of the cerebral hemisphere; derives from the prosencephalon
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temporal hemiretina: temporal hall of the retina
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temporal lobe: one of the lobes of the cerebral hemisphere
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temporal pole: most rostral portion of the temporal lobe
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tentorium cerebelli: dural flap between the occipital lobes and the cerebellum
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terminal ganglia: parasympathetic ganglia that contain postganglionic neurons; receive input from the vagus nerve; located on the structure their axons innervate
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thalamic adhesion: site of adhesion of the two halves of the thalamus; said to be present in approximately 80% of individuals; in humans, no axons decussate in the thalamic adhesion
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thalamic fasciculus: tract in which axons from the deep cerebellar nuclei and part of the internal segment of the globus pallidus course to the thalamus
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thalamic radiations: axons of thalamic nuclei that project to the cerebral cortex
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thalamostriate vein: follows C-shaped course of caudate nucleus and stria terminalis
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thalamus: major site of relay nuclei that transmit information to the cerebral cortex; component of the diencephalon
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thermoreceptors: primary sensory neurons sensitive to thermal changes
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third ventricle: component of the ventricular system; located between the two halves of the diencephalon
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thoracic: spinal cord segment; there are 12 in humans
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tonotopic organization: or tonotopy; where sounds of different frequencies are processed by different brain regions; sounds of similar frequencies are processed by neighboring brain regions, while sounds of very different frequencies are processed by brain regions that are farther apart
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touch: one of the five major senses
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tractography: an MRI approach (diffusion MRI) to identify the locations of tracts based on information about the local directions of brain water diffusion; a commonly used tractography method is diffusion tensor imaging (DTI)
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transcranial magnetic stimulation (TMS): noninvasive brain stimulation technique in which a pulse of magnetic energy is use to activate neurons; repetitive TMS (rTMS) uses a series of pulses
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transient ischemic attack (TIA): brief cessation of cerebral blood flow to a local brain region that produces transient dysfunction of the area; dysfunction lasts for a period of minutes to hours
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tract: collection of axons within the central nervous system
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transverse plane: perpendicular to the longitudinal axis of the central nervous system, between the dorsal and ventral surfaces
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transverse sinus: dural sinus that carries blood into the systemic circulation
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trapezius muscle: contains several functional regions that support the weight of the arm and act on the scapula
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trapezoid body: site of decussation of auditory fibers
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tremor: trembling or shaking movement
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trigeminal ganglion: location of cell bodies of all trigeminal afferent fibers except those afferents innervating muscle spindle receptors; also termed semilunar ganglion
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trigeminal lemniscus: tract in which axons from the main trigeminal sensory nucleus ascend to the thalamus
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trigeminal mesencephalic nucleus: contains cell bodies of primary sensory neurons innervating stretch receptors in jaw muscles
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trigeminal motor nucleus: contains motor neurons that innervate jaw muscles
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trigeminal (V) nerve: mixed cranial nerve containing sensory axons that innervate much of the head and oral cavity and motor axons that innervate jaw muscles
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trigeminocerebellar pathways: projection from spinal trigeminal nuclei to the cerebellum
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trigeminothalamic tract: projection from spinal trigeminal nuclei to the thalamus
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trochlear (IV) nerve: cranial nerve that contains the axons of trochlear motor neurons, which innervate the superior oblique muscle
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trochlear nucleus: contains motor neurons that innervate the superior oblique muscle
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tubercles: a round nodule or eminence that marks the location of an underlying nucleus or cortical region; cuneate and gracile tubercles are located on the dorsal medulla and the olfactory tubercle is located on the ventral surface of the basal forebrain
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tuberomammillary nucleus: hypothalamic nucleus; contains neurons that use histamine as a neurotransmitter; diverse projections to activate forebrain neurons
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tufted cells: olfactory bulb projection neurons
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tympanic membrane: ear drum; oscillates in response to environmental pressure changes associated with sounds; coupled to middle ear ossicles
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uncal herniation: displacement of the uncus medially due to an expanding space-occupying lesion above the cerebellar tentorium
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uncinate fasciculus: association pathway interconnecting frontal and anterior temporal cortical areas
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uncus: bulge on the medial temporal lobe; overlies the anterior hippocampal formation and amygdala
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unipolar neuron: neuron with a cell body and axon but few dendrites
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urination: release of urine from the bladder
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utricle: vestibular sensory organ (or otolith organ) sensitive to linear acceleration
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vagus (X) nerve: mixed cranial nerve; contains axons of branchiomeric motor neurons that innervate laryngeal and pharyngeal muscles, parasympathetic preganglionic fibers, gustatory and visceral afferent fibers, and somatic sensory afferents; located in the medulla
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vascular organ of the lamina terminalis: a circumventricular organ; located in the rostral wall of the third ventricle
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vasopressin: neuroactive peptide that also acts on peripheral structures, including promoting fluid reabsorption in the kidney; also termed antidiuretic hormone (ADH)
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venogram: radiological image of veins
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ventral: toward the abdomen; synonymous with anterior
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ventral (anterior) commissure: see ventral spinal commissure
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ventral (or anterior) corticospinal tract: pathway for control of axial and proximal limb muscles of the neck and upper body
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ventral amygdalofugal pathway: output pathway from the basolateral and central nuclei of the amygdala
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ventral anterior thalamic nucleus: part of the motor thalamus; receiving primarily information from the internal segment of the globus pallidus of the basal ganglia; projects to cortical motor and premotor areas
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ventral cochlear nucleus: concerned with processing the horizontal sound localization; division of cochlear nucleus
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ventral column: portion of spinal cord white matter medial to the ventral horn; contains primarily descending fibers for controlling axial and proximal limb musculature
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ventral horn: laminae VIII and IX of the spinal gray matter; location of neurons for somatic motor control
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ventral lateral thalamic nucleus: part of the motor thalamus; receiving primarily information from the deep cerebellar nuclei; projects to cortical motor and premotor areas
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ventral medial nucleus (of the hypothalamus): participates in appetitive behaviors, such as feeding
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ventral pallidum: output nucleus of the limbic circuit of the basal ganglia; located ventral to the anterior commissure
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ventral posterior lateral nucleus: division of the ventral posterior nucleus where information from the dorsal column nuclei is processed
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ventral posterior medial nucleus: division of the ventral posterior nucleus where trigeminal information is processed
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ventral posterior nucleus: thalamic nucleus for processing somatic sensory information; projects to the primary somatic sensory cortex
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ventral root: where motor axons leave the spinal cord
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ventral spinal commissure: where axons of the anterolateral system decussate; located ventral to lamina X and the central canal
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ventral spinocerebellar tract: transmits information about the level of activation in thoracic, lumbar, and sacral spinal interneuronal systems to the cerebellum; thought to relay internal signals from motor pathways, via spinal interneurons, to the cerebellum
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ventral striatum: consists of the ventromedial portions of the caudate nucleus and putamen and the nucleus accumbens
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ventral tegmental area: contains dopaminergic neurons that project to the ventromedial portion of the striatum and the prefrontal cortex; located in the rostral midbrain
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ventricles: dilated channels within the ventricular system; contain choroid plexus
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ventricular system: cavities within the central nervous system that contain cerebrospinal fluid
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ventricular zone: innermost layer of the developing central nervous system; layer from which nerve cells are generated
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ventrolateral medulla: contains neurons that participate in blood pressure regulation through projections to the intermediolateral cell column
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ventrolateral nucleus: principal motor control nucleus of the thalamus; receives cerebellar input and projects to primary and premotor cortical areas
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ventrolateral preoptic area: important in promoting REM and non-REM sleep, through inhibitory connections with other hypothalamic nuclei and brain stem nuclei that promote wakefulness
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ventromedial hypothalamic nucleus: important in regulating appetite and other consummatory behaviors; receives input from limbic system structures
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ventromedial posterior nucleus: thalamic nucleus important for processing noxious stimuli; projects to the posterior insular cortex; caudal to the thalamic region that processes viscerosensory information
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vergence movements: convergent or divergent eye movements; ensure that the image of an object of interest falls on the same place on the retina of each eye
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vermis: midline portion of the cerebellar cortex; plays a role in axial and proximal limb control
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vertebral arteries: branch from the subclavian artery; two vertebral arteries converge to form the basilar artery
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vertebral canal: cavity within the vertebral column within which the spinal cord is located
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vertebral-basilar circulation: arterial supply to the brain stem and parts of the temporal and occipital lobes
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vertigo: the sense of the world spinning around or that of an individual whirling around
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vestibular ganglion: location of cell bodies of primary vestibular neurons; also termed Scarpa's ganglion
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vestibular labyrinth: fluid-filled cavities within the temporal bone within which the vestibular organs are located
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vestibular division of CN VIII: component of CN VIII that supplies the semicircular canals, utricle, and saccule
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vestibular nuclei: major termination site of vestibular sensory fibers
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vestibulocerebellum: portion of the cerebellum that receives a monosynaptic projection from primary vestibular axons; processes this information for eye movement control and balance; includes primarily the flocculonodular lobe
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vestibulocochlear (VIII) nerve: contains afferent fibers that innervate the auditory and vestibular structures of the inner ear
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vestibuloocular reflex: automatic control of eye position by vestibular sensory information
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vestibulospinal tract: axons that originate from the vestibular nuclei and project to the brain stem
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vibration sense: the capacity to detect and distinguish mechanical vibration of the body
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visceral: related to the internal organs of the body
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visceral (autonomic) motor fibers: axons of autonomic preganglionic or postganglionic neurons as they course in the periphery
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visceral motor nuclei: contain autonomic preganglionic neurons
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viscerosensory: related to the sensory innervation of the internal organs of the body
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vision: one of the five major senses
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visual field: the total area that is seen
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visual field defect: loss of vision within a portion of the visual field
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visual motion pathway: originates primarily from the magnocellular ganglion cells of the retina and projects to V5 and ultimately to regions of the posterior parietal cortex
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vomeronasal organ: peripheral olfactory organ important for detecting pheromones; well-documented as a functional structure in animals, but its function in humans is controversial
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Wallenberg syndrome: see lateral medullary syndrome
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Wallerian degeneration: deterioration of the structure and function of the distal portion of an axon, when cut; also termed anterograde generation
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Wernicke's area: important for understanding speech; located in the posterior superior temporal gyrus (area 22)
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what pathway: corticocortical circuits important for identifying an object using vision, touch, or sound
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where-how pathway: corticocortical circuits important for identifying the location of an object using vision, touch, or sound and use of that information to help direct limb or eye movements
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white matter: location of predominantly myelinated axons
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working memory: the temporary storing of information used to plan and shape upcoming behaviors
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zona incerta: contains GABA-ergic neurons that project widely to the cerebral cortex; nuclear region of the diencephalon