Glossary

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

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

external capsule: white matter region between the putamen and the claustrum; contains primarily cortical association fibers

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

external segment of the globus pallidus: contains neurons that project to the subthalamic nucleus; part of the indirect basal ganglia path

extrastriate cortex: visual cortical areas excluding the primary (or striate) cortex

extreme capsule: white matter region between the claustrum and insular cortex; contains primarily cortical association fibers

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

facial colliculus: surface landmark on ventricular (dorsal) surface of the pons; overlies the genu of the facial nerve and the abducens nucleus

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

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

falx cerebri: dural flap between the two cerebral hemi-spheres; extension of the meningeal layer of the dura

fastigial nucleus: one of the deep cerebellar nuclei; transmits the output of the vermis to the medial descending motor pathways

fenestrated capillaries: contain pores through which substances can diffuse from within the capillary to surrounding tissue

fimbria: portion of the fornix that covers part of the hippocampal formation

first lumbar vertebra: marks the approximate location of the caudal end of the spinal cord within the vertebral canal

fissure: groove in the cortical surface; more consistent in shape and depth than a sulcus

flaccid paralysis: inability to contract a muscle, together with a profound loss of muscle tone

FLAIR: MRI pulse sequence that suppresses signal related to cerebrospinal fluid; abbreviation for fluid attenuated inversion recovery

flexure: bend in the axis of the central nervous system or axis of the embryo

flocculonodular lobe: portion of the cerebellar cortex involved in eye movement control and balance

flocculus: see flocculonodular lobe

floor plate: ventral surface of the developing central nervous system; key site for organizing the dorsoventral patterning of the spinal cord during development

folia: thin folds of the cerebellar cortex

foramen of Magendie: opening in the fourth ventricle where cerebrospinal fluid can pass into the subarachnoid space; located on the midline

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

forebrain: most rostral primary brain vesicle; divides into the telencephalon and diencephalon

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

form pathway (for vision): circuit specialized for discriminating features of the shapes of visual stimuli; information in this path is used for object recognition

fornix: a major output tract from the hippocampal formation

fourth ventricle: portion of the ventricular system located in the brain stem; separates medulla and pons from the cerebellum

fovea: portion of the retina with the greatest visual acuity, where only cone receptors are located; located in the center of the macula

fractionate movements: ability to isolate one movement from another, such as move one finger while keeping the other fingers still

fractionation (of movement): ability to move one finger or limb segment independent of the other fingers or limb segments; often termed individuation

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

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

frontal: close to the forehead

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

frontal eye fields: portion of the lateral frontal lobe important in the control of eye movements

frontal lobe: one of the lobes of the cerebral hemisphere

functional localization: identification of brain regions that participate in particular functions

functional magnetic resonance imaging (fMRI): a form of magnetic resonance imaging that can monitor blood oxygenation, which correlates with neuronal activity

functional neuroanatomy: examines those parts of the nervous system that work together to accomplish a particular task

GABA: γ-aminobutyric acid; principal inhibitory neurotransmitter in the central nervous system

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

ganglion: collections of neuronal cell bodies outside the central nervous system

ganglion cell layer: innermost retinal cell layer; contains cell bodies of ganglion cells

ganglion cells: retinal projection neurons; axons course in the optic nerve and terminate in the diencephalon and midbrain

geniculate ganglion: location of cell bodies of primary sensory neurons that project in the intermediate nerve (cranial nerve VII)

genu: Latin for knee; used to describe structures with an acute bend, such as the corpus callosum and facial nerve

genu of the internal capsule: separates the anterior and posterior limbs of the internal capsule

ghrelin: protein secreted by enteroendocrine cells of the stomach; promotes food intake

girdle muscles: striated muscles that insert proximally and attach on parts of the shoulder or hip

glial cells: major cell type in the nervous system; outnumber neurons about 10 to 1; also termed glia

globose nucleus: deep cerebellar nucleus; together with the emboliform nucleus comprise the interposed nuclei, which transmit information from the intermediate cerebellar hemisphere

globus pallidus: basal ganglia nucleus; comprises distinct internal and external divisions

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

glossopharyngeal (IX) nerve: cranial nerve; located in the medulla

glutamate: principal excitatory neurotransmitter of neurons in the central nervous system

Golgi neurons: inhibitory interneurons of the cerebellar cortex

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

gracile fascicle: medial component of the dorsal column; transmits mechanoreceptive information from the legs and lower trunk to the ipsilateral gracile nucleus

gracile nucleus: target of the axons of the gracile fascicle; transmits information to the contralateral thalamus via the medial lemniscus

granular layer: innermost cell layer of the cerebellum; primarily contains granule and Golgi neurons and the axon terminals of mossy fibers

granule cell: cerebellar excitatory interneuron; cell of origin of parallel fibers

granule neurons: the only excitatory interneuron of the cerebellar cortex

gray matter: portions of the central nervous system that contain predominantly neuronal cell bodies

great cerebral vein (of Galen): major vein; carries venous drainage from the diencephalon and deep telencephalic structures

gyri: grooves in the cerebral cortex

gyrus rectus: located on the inferior frontal lobe; runs parallel to the olfactory tract

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

hair cells: auditory receptor neurons

hearing: one of the five major senses

hemiballism: movement disorder produced by damage to the subthalamic nucleus; characterized by involuntary rapid (ballistic) limb movements

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

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

Heschl's gyri: location of primary auditory cortex

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)

hindbrain: most caudal portion of the brain; includes the medulla, pons, and cerebellum

hippocampal formation: telencephalic structure located primarily within the temporal lobe; comprises the dentate gyrus, hippocampus, and subiculum; involved in learning and memory

hippocampal sulcus: separates the dentate gyrus from the subiculum; largely obscured in the mature brain

hippocampus: component of the hippocampal formation

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

horizontal localization of sound: ability to identify the position of the source of a sound in the horizontal plane

Horner syndrome: constellation of neurological signs associated with dysfunction of the sympathetic innervation of the head

Huntington disease: genetic autosomal dominant disorder; produces hyperkinetic motor signs

hydrocephalus: buildup of cerebrospinal fluid within the brain

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

hypoglossal motor neurons: innervate intrinsic tongue muscles

hypoglossal (XII) nerve: cranial nerve located in the medulla

hypoglossal nucleus: location of hypoglossal motor neurons

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

hypothalamic sulcus: roughly separates the hypothalamus and thalamus on the medial brain surface

hypothalamus: major brain division; part of diencephalon

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

indirect cortical pathways: motor pathway from the cerebral cortex that synapses first in the brain stem before synapsing on spinal neurons

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

infarction: death of tissue because of cessation of blood flow

inferior cerebellar peduncle: predominantly an input pathway to the cerebellum

inferior colliculus: located in the caudal midbrain, on its dorsal surface; contains neurons that are part of the ascending auditory pathway

inferior ganglia: location of primary somatic sensory cell bodies of vagus and glossopharyngeal nerves that innervate visceral tissues

inferior oblique muscle: extraocular muscle that depresses the eye, mostly when the eye is adducted

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

inferior parietal lobule: located dorsal to the lateral sulcus; important for a variety of higher brain functions, including language and perception

inferior petrosal sinus: major dural sinus

inferior rectus muscle: extraocular muscle that depresses the eye, especially when eye is abducted

inferior sagittal sinus: major dural sinus

inferior salivatory nuclei: location of parasympathetic preganglionic neurons that innervate cranial glands

inferior temporal gyrus: important in visual form perception

inferior vestibular nucleus: receives direct input from the vestibular organs; projects to various brain stem and spinal targets for eye movement control and balance

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

inner hair cells: principal auditory receptor neuron

inner nuclear layer: retinal layer that contains the cell bodies and proximal processes of the retinal interneurons: bipolar, horizontal, and amacrine cells

inner synaptic (or plexiform) layer: where synaptic connections between the bipolar cells and the ganglion cells are made

input nuclei (of basal ganglia): consisting of the striatum; receive input from cerebral cortex

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

insulin: hormone secreted by the pancreatic islet cells; can inhibit food intake through hypothalamic circuits

intention tremor: slow oscillatory movement of the distal limb as it approaches the endpoint of the movement; results from cerebellar dysfunction or damage

interaural intensity difference: a mechanism for determining the horizontal location of high-frequency sounds

interaural time difference: a mechanism for determining the horizontal location of low-frequency sounds

intermediate hemisphere: portion of the cerebellar cortex involved in limb and trunk control

intermediate horn: the lateral intermediate zone of the spinal cord; location of sympathetic preganglionic neurons

intermediate nerve: sensory and parasympathetic branch of cranial nerve VII

intermediate zone: portion of spinal gray matter located between the dorsal and ventral horns

intermediolateral cell column: see intermediolateral nucleus

intermediolateral nucleus: location of sympathetic preganglionic neurons; present from about T1 to about L2

internal arcuate fibers: decussating fibers of the dorsal column nuclei

internal capsule: location of axons coursing to and from the cerebral cortex; present between the thalamus and parts of the basal ganglia

internal carotid artery: major cerebral artery; supplies blood to the cerebral cortex and many deep structures excluding the brain stem and cerebellum

internal medullary laminae: bands of white matter that divide the thalamus into several nuclear divisions

internal segment of the globus pallidus: one of the principal output nuclei of the basal ganglia

interneurons: neurons with an axon that remains locally within the nucleus or cortical region where the cell body is located

internuclear neurons: neurons located in the abducens nucleus that project to the contralateral oculomotor nucleus to transmit control signals for horizontal saccadic eye movements

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

interpeduncular cistern: where cerebrospinal fluid collects between the cerebral peduncles

interpeduncular fossa: space between the cerebral peduncles

interpolar nucleus: component of the spinal trigeminal nucleus; important for facial pain, especially within the mouth and teeth

interposed nuclei: deep cerebellar nuclei; comprises the globose and emboliform nuclei

intersegmental neurons: spinal interneurons that interconnect neurons in different segments; also termed propriospinal neurons

interstitial nucleus of Cajal: involved in eye and head control; located in rostral midbrain; gives rise to a small descending motor pathway

interstitial nucleus of the MLF: center for control of vertical eye movements; located in rostral midbrain

interventricular foramen (of Monro): conduit through which cerebrospinal fluid and choroid plexus passes from the lateral ventricles to the third ventricle

interventricular foramina: see interventricular foramen

intracavernous segment: portion of internal carotid artery as it passes through the cavernous sinus

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

intrapetrosal segment: portion of the carotid artery as it travels through the petrous bone

intrasegmental neurons: local spinal interneurons; their axons remain with the segment of the cell body

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

ipsilateral: on the same side; term used relative to a particular landmark or event

ischemia: decreased delivery of oxygenated blood to the tissue

ischemic stroke: occlusion of an artery that results in downstream cessation of blood flow

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

itch: sensory experience produced by histamine

itch-sensitive receptors: activation leads to the sensation itch; also termed pruritic receptor

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

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

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

knee-jerk reflex: automatic extension of the leg upon stimulation of the patella tendon; the stimulus stretches muscle spindle receptors in the quadriceps muscle

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

lacrimal gland: tear gland

lamina terminalis: rostral wall of the third ventricle; marks location of most anterior portion of the neural tube

laminated: morphological feature in which neuronal cell bodies or axons form discrete layers

large-diameter axon: mechanoreceptive sensory axons

large-diameter fiber entry zone: site at which large-diameter axons enter the spinal cord; located medial to Lissauer's tract

laryngeal closure reflex: automatic contraction of laryngeal adductor muscles to prevent food and fluids from entering the trachea

lateral cerebellar hemisphere: cortical component of the cerebrocerebellum; involved primarily in motor planning

lateral column: portion of the spinal white matter; contains diverse somatic sensory, cerebellar, and motor control pathways

lateral corticospinal tract: pathway in which descending axons for voluntary limb control descend; originates primarily from the motor areas of the frontal lobe

lateral descending pathways: motor pathways for controlling limb muscles

lateral gaze palsy: see internuclear ophthalmoplegia

lateral geniculate nucleus: thalamic visual relay nucleus

lateral hypothalamus (or hypothalamic zone): important for feeding and sleep-wakefulness; orexin-containing neurons are unique to this brain region

lateral intermediate zone: portion of spinal gray matter that plays a role in limb muscle control

lateral lemniscus: ascending brain stem auditory pathway

lateral medullary lamina: band of axons that separates the external segment of the globus pallidus and the putamen

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

lateral olfactory stria: pathway by which axons from the olfactory tract project to the olfactory cortical areas

lateral posterior nucleus: thalamic nucleus with projections to the posterior parietal lobe

lateral rectus muscle: ocular abductor muscle; moves eye laterally

lateral reticular nucleus: precerebellar nucleus; transmits information from the cerebral cortex and spinal cord to the intermediate cerebellum

lateral septal nucleus: telencephalic nucleus; part of limbic system

lateral sulcus: separates the temporal lobe from the frontal and parietal lobes

lateral superior olivary nucleus: contains neurons sensitive to interaural intensity differences; plays role in horizontal localization of high-frequency sounds

lateral ventral horn: contains motor neurons that innervate limb muscles

lateral ventricle: telencephalic component of the ventricular system; bilaterally paired, with four components (anterior horn, body, atrium, posterior horn, and inferior horn)

lateral vestibular nucleus: key brain stem nucleus for control of proximal muscles; important in balance; gives rise to the lateral vestibulospinal tract

lateral vestibulospinal tract: ipsilateral pathway; component of the medial descending pathways

laterality: pertains to one side or the other

L-dopa: precursor to dopamine; used in the treatment of Parkinson disease

lenticular fasciculus: region of the white matter through which axons from the internal segment of the globus pallidus course en route to the thalamus

lenticular nucleus: globus pallidus (both internal and external segments) and putamen

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

leptin: hormone produced by adipocytes in proportion to the amount of body fat; suppresses feeding

levator palpebrae superioris muscle: principal eyelid elevator

limb position sense: ability to judge the position of one's limbs without using vision

limbic association cortex: diverse regions of primarily the frontal and temporal lobes; involved in emotions, learning, and memory

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

limbic system: brain structures and their interconnections that collectively mediate emotions, learning, and memory

Lissauer's tract: location of central branches of small-diameter afferent fibers prior to termination in the superficial dorsal horn

lobe: major division of the cerebral cortex

lobule: a division of a lobe

locus ceruleus: principal noradrenergic brain stem nucleus; located in the rostral pons

long circumferential branches: brain stem arterial branches that supply the most dorsolateral portions; also supply the cerebellum

longitudinal axis: the head-to-tail (or head-to-coccyx) axis of the nervous system

lumbar: spinal cord segment; there are five in total

lumbar cistern: space within the vertebral canal where cerebrospinal fluid pools; commonly used for withdrawing cerebrospinal fluid from patients

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

M cell: retinal ganglion neuron with a large dendritic arbor; plays a preferential role in sensing of visual motion; magnocellular

macroglia: glial cell class that comprises oligodendrocytes, Schwann cells, astrocytes, and ependymal cells; serve a variety of support and nutritive functions; contrast with microglia

macula lutea: portion of the central retina that contains the fovea

macular region: portion of the retina surrounding the macula lutea

macular sparing: maintenance of vision around the fovea after visual cortex damage that produces a loss of parafoveal and peripheral vision

magnetic resonance angiography: application of magnetic resonance imaging to study vasculature by monitoring motion of water molecules in blood vessels

magnetic resonance imaging: radiological technique to examine brain structure; uses primarily the water content of tissue to provide a structural image

magnocellular division (of red nucleus): component of the red nucleus that contains large neurons that project to the spinal cord as the rubrospinal tract

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

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

main (or principal) trigeminal sensory nucleus: brain stem relay nucleus for mechanosensory information from the face and oral cavity

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

mammillary bodies: hypothalamic nuclear complex; contains the medial and lateral mammillary nuclei; the mammillary bodies give rise to the mammillothalamic and mammillotegmental tracts

mammillotegmental tract: originates from the lateral mammillary nucleus; terminates in the pontine tegmentum

mammillothalamic tract: originates from both the medial and lateral mammillary nuclei; terminates in the anterior thalamic nuclei

mandibular division: trigeminal sensory nerve root that innervates primarily the lower face and parts of the oral cavity

marginal zone: outermost layer of the dorsal horn

mastication: chewing

maxillary division: trigeminal sensory nerve root that innervates primarily the lips, cheek, and parts of the oral cavity

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

medial dorsal nucleus (of the thalamus): principal thalamic nucleus projecting to the frontal lobe

medial forebrain bundle: pathway that carries functionally diverse brain stem pathways to subcortical nuclei and the cerebral cortex, including the monoaminergic pathways

medial geniculate nucleus: thalamic auditory relay nucleus

medial lemniscus: brain stem tract that contains axons traveling from the dorsal column nuclei to the thalamus

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

medial mammillary nucleus: principal nucleus of the mammillary body; projects to the anterior nuclei of the thalamus

medial medullary lamina: band of myelinated axons that separates the internal and external segments of the globus pallidus

medial olfactory stria: small tract that contains axons from other brain regions that project to the olfactory bulb

medial orbital gyri: see medial orbitofrontal gyri

medial orbitofrontal gyri: part of the limbic association cortex

medial prefrontal cortical areas: portion of the prefrontal cortex one function of which is object recognition

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)

medial septal nucleus: telencephalic nucleus; important projections to the hippocampal formation; gives rise to cholinergic and GABA-ergic projections

medial superior olivary nucleus: contains neurons sensitive to interaural timing differences; plays role in horizontal localization of low-frequency sounds

medial ventral horn: contains motor neurons that innervate proximal limb and axial muscles; controlled by the medial descending pathways

medial vestibular nucleus: part of the vestibular nuclear complex; gives rise to the medial vestibulospinal tract for head and eye coordination

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

median raphe nuclei: located along or close to the brain stem midline; use serotonin as neurotransmitter

medium spiny neurons: major class of striatal neuron; projects to the globus pallidus

medulla: major brain division; part of hindbrain

medullary dorsal horn: extension of dorsal horn into the medulla; also termed caudal nucleus

Meissner's corpuscle: mechanoreceptor

melanin-concentrating hormone: peptide that affects food intake

membranous labyrinth: cavity within which the vestibular apparatus are located; contains endolymph

meninges: membranes that cover the central nervous system; comprises dura, arachnoid, and pia

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

mesoderm: middle layer of the embryo

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

microglia: class of glial cell that subserves a phagocytic or scavenger role; responds to nervous system infection or damage; contrasts with macroglia

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

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

middle ear ossicles: three bones that conduct sound pressure waves from the tympanic membrane to the oval window

middle temporal gyrus: located on the lateral temporal lobe; important in higher visual functions, especially object recognition

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

mitral cells: projection neuron of the olfactory bulb

mixed nerve: peripheral nerve composed of somatic sensory and motor axons

modality: sensory attribute that corresponds to quality (eg, pain)

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

motion pathway (for vision): circuit specialized for discriminating the speed and direction of moving visual stimuli

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

motor homunculus: representation of body musculature in the primary motor cortex; organization is similar to the form of the body

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)

motor unit: a single alpha-motor neuron and all of the muscle fibers that it innervates

Müller cell: retinal glial cell that stretches from the outer to the inner limiting membranes; have important structural and metabolic functions

multipolar neurons: neurons with a complex dendritic array and a single axon; principal neuron class in the central nervous system

muscarinic receptors: membrane proteins that transduce acetylcholine into neuronal depolarization; named for agonist muscarine

muscle spindle receptor: stretch receptor in muscle; has efferent sensitivity control

myelencephalon: secondary brain vesicle; forms the medulla of the mature brain

myelin: fatty substance that contains numerous myelin proteins

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

myelin stains: methods to reveal the presence of the myelin sheath

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)

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

nasal hemiretina: portion of the retina medial to a vertical line that runs through the macula

nasal mucosal glands: located in the nasal cavity, secrete mucous, which is rich in glycoproteins; protects the nasal epithelium

neocortex: phylogenetically most recent portion of the cerebral cortex; most abundant form of cortex; has six or more layers

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

neural degeneration: deterioration in neuron structure and function

neural groove: midline region of the neural tube where neurons and glial cells do not proliferate; where the floor plate forms

neural induction: process by which a portion of the dorsal ectoderm of the embryo becomes committed to form the nervous system

neural plate: dorsal ectoderm region from which the nervous system forms

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

neuraxis: principal axis of the central nervous system

neuroactive compounds: chemicals that alter neuronal function

neuroectoderm: portion of the ectoderm that gives rise to the nervous system; corresponds to the neural plate

neurohypophysis: portion of the pituitary that develops from the neuroectoderm; where vasopressin and oxytocin are released into the systemic circulation

neuromelanin: polymer of the catecholamine precursor dihydroxyphenylalanine (or dopa), which is contained in the neurons in the pars compacta

neuromeres: segments of the developing hindbrain

neuron: nerve cell

neurophysins: protein that derives from the prohormone that gives rise to oxytocin and vasopressin; coreleased with oxytocin and vasopressin

neurotransmitter: typically small molecular weight compounds (eg, glutamate and γ-aminobutyric acid, and acetylcholine) that excite or inhibit neurons

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

nigrostriatal tract: pathway in which nigrostriatal axons course

nociceptors: somatic sensory receptors that are selectively activated by noxious or damaging stimuli

nodulus: portion of the cerebellum critical for vestibular control of eye and head movements

nondeclarative memory: memory of procedures and actions

noradrenalin: neurotransmitter; also termed norepinephrine

noradrenergic: neuron that uses noradrenalin as a neurotransmitter

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

noxious: tissue damaging

noxious stimuli: a tissue-damaging stimulus; can be mechanical, thermal, or in response to various forms of trauma

nucleus: collection of neuronal cell bodies within the central nervous system

nucleus accumbens: component of the striatum located ventrally and medially; key structure in drug addiction

nucleus ambiguus: contains primarily motor neurons that innervate the pharynx and larynx; also contains parasympathetic preganglionic neurons; located in the medulla

nucleus of the diagonal band of Broca: cholinergic telencephalic nucleus with diverse cortical projections; located in the basal forebrain

nucleus of the lateral lemniscus: auditory projection nucleus; located in the rostral pons

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

nucleus proprius: contains neurons that process somatic sensory information; corresponds to laminae III–IV of the dorsal horn

nystagmus: rhythmical oscillations of the eyeball

occipital lobe: one of the lobes of the cerebral hemisphere

occipital somites: somites from which neck and cranial structures develop

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

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

oculomotor loop: basal ganglia circuit that engages frontal eye movement control areas

oculomotor nucleus: contains motor neurons that innervate the medial rectus, superior rectus, inferior rectus, inferior oblique, and levator palpebrae muscles

odorants: chemicals that produce odors

olfactory bulb: telencephalic structure that receives input from olfactory sensory neurons and projects to the olfactory cortical areas

olfactory discrimination: ability to discriminate one odorant from another

olfactory epithelium: portion of the olfactory mucosa that contains olfactory sensory neurons

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

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

olfactory sulcus: groove on the inferior frontal lobe surface in which the olfactory bulb and tract course

olfactory tract: contains axons that interconnect the olfactory bulb with the other olfactory nuclear regions of the brain

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

oligodendrocytes: class of glial cell that forms the myelin sheath around axons within the central nervous system

olive: landmark on ventral surface of the medulla under which the inferior olivary nucleus is located

olivocochlear bundle: efferent projection from the inferior olivary nucleus to hair cells in the cochlea

olivocochlear projection: see olivocochlear bundle

Onuf's nucleus: located in sacral spinal cord; contains motor neurons that innervate anal and urethral sphincters

operculum: portions of frontal, parietal, and temporal lobes that overlie the insular cortex

ophthalmic artery: supplies the eye; can be a pathway for collateral brain circulation after occlusion of the internal carotid artery

ophthalmic division: trigeminal sensory nerve root that innervates primarily the upper face

optic chiasm: site of decussation of ganglion cell axons from the nasal hemiretinae

optic disk: site on retina where ganglion cell axons exit from the eye

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

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

optic tectum: also termed the superior colliculus

optic tract: retinal ganglion cell axon pathway between the optic chiasm and the lateral geniculate nucleus

optokinetic reflexes: ocular reflexes that use visual information; supplements the actions of vestibulo-ocular reflexes

oral nucleus: rostral component of the spinal trigeminal nucleus

orbitofrontal (or orbital) gyri: portion of the inferior frontal lobe that contains the orbital gyri; overlie the bony orbits

orbitofrontal cortex: part of prefrontal cortex; important for emotion and personality

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

organ of Corti: component of the inner ear for transducing sound into neural signals

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

orientation column: cluster of neurons in the primary visual cortex that processes information about the orientation of a visual stimulus

orthonasal olfaction: when molecules travel from the external environment, through the nostrils (nares), to activate olfactory neurons in the olfactory epithelium

orthostatic hypotension: sudden reduction in systemic blood pressure upon standing upright; sometimes termed postural hypotension

otic ganglion: contains parasympathetic postganglionic neurons that innervate the parotid gland, which secretes saliva

otolith organs: the utricle and saccule; sensitive to linear acceleration

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

outer nuclear layer: retinal layer that contains the cell bodies of photoreceptors (rods and cones)

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)

output nuclei (of basal ganglia): consisting of the globus pallidus-internal part, part of the ventral pallidum, and the substantia nigra pars reticulata

oxytocin: peptide released by magnocellular neurons in the paraventricular and supraoptic nuclei

P cell: retinal ganglion neurons with a small dendritic arbor; plays a preferential role in sensing of form and color; parvocellular

pacinian corpuscle: rapidly adapting mechanoreceptor sensitive to high-frequency vibration

pain: sensation evoked by noxious stimulation

palate: arch-shaped portion of the superior oral cavity

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

pallidotomy: therapeutic lesion of a portion of the globus pallidus to alleviate dyskinesias

parabrachial nucleus: transmits viscerosensory information from the solitary nucleus to the diencephalon; located in the rostral pons

parafascicular nucleus: thalamic diffuse-projecting nucleus with widespread projections to the frontal lobe and striatum

parahippocampal gyrus: located on medial temporal lobe; contains cortical association areas that project to the hippocampal formation

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

parallel organization: property of neural systems in which pathways with similar anatomical organizations serve distinct functions

parallel sensory pathways: two or more sensory pathways that have similar anatomical projections and overlapping sets of functions

paramedian arterial branches: supply the most medial portions of the brain stem; originate primarily from the basilar artery

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

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

parasympathetic nervous system: component of the autonomic nervous system; originates from the brain stem and the caudal sacral spinal cord

parasympathetic preganglionic neurons: autonomic neurons located in the central nervous system; project to parasympathetic postganglionic neurons, which are located in the periphery

paraterminal gyrus: located anterior to the rostral wall of the third ventricle and ventral to the rostrum of the corpus callosum

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

paravertebral ganglia: contain sympathetic postganglionic neurons

parietal lobe: one of the lobes of the cerebral hemisphere

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

parietooccipital sulcus: separates the parietal and occipital lobes

Parkinson disease: results from loss of dopaminergic neurons in the substantia nigra pars compacta; characterized by slowing or absence of movement (bradykinesia) and tremor

parotid gland: salivary gland; innervated by axons of the glossopharyngeal (IX) nerve

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

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

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

peduncles: a large collection of axons

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

perforant pathway: projection from the entorhinal cortex to the dentate gyrus

periamygdaloid cortex: one of the olfactory cortical areas; receives a direct projection from the olfactory tract; located on the rostromedial temporal lobe

periaqueductal gray matter: central region of the midbrain that surrounds the cerebral aqueduct; participates in diverse functions, including pain suppression

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

perilymph: fluid that fills the space between the membranous labyrinth and the temporal bone; resembles extracellular fluid and cerebrospinal fluid

peripheral autonomic ganglia: clusters of sympathetic and parasympathetic postganglionic neurons

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

periventricular nucleus: contains parvocellular neurosecretory neurons; located in the hypothalamus, beneath the walls of the third ventricle

periventricular zone: portion of the hypothalamus that contains most of the parvocellular neurosecretory neurons; located beneath the walls and floor of the third ventricle

pharynx: the portion of the digestive tube between the esophagus and mouth; the throat

pheromones: a chemical produced and secreted by an animal that influences the behavior and development of other members of the same species

pia mater: inner meningeal layer; adheres closely to the surface of the central nervous system

pigment epithelium: external to the photoreceptor layer; it serves a phagocytic role during renewal of rod outer segment disks

pineal gland: endocrine gland located dorsal to the superior colliculus that is involved in the sleep/wake cycle; secretes melatonin

piriform cortex: one of the olfactory cortical areas; receives a direct projection from the olfactory tract; located on the rostromedial temporal lobe

pituitary portal circulation: connects capillary beds of the median eminence and anterior lobe of the pituitary; portal vein

pons: one of the major brain divisions; Latin for bridge

pontine cistern: site of accumulation of cerebrospinal fluid at the pontomedullary junction

pontine flexure: bend in the developing nervous system at the pons

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

pontomedullary junction: where the pons and medulla join

pontomedullary reticular formation: contains diverse motor, sensory, and integrative nuclei; especially important in arousal and visceral and skeletal muscle control

portal circulation: contains two capillary beds joined by portal veins; present in the pituitary gland and the liver

portal veins: join the two capillary beds of a portal circulation

positron emission tomography: functional imaging technique based on the emission of positively charged unstable subatomic particles (positrons); PET

postcentral gyrus: important for mechanical sensations, including position sense; located in the parietal lobe

postcommissural fornix: principal division of the fornix; contains axons principally from the subiculum that terminate in the mammillary bodies

posterior: toward the abdomen

posterior cerebellar incisure: shallow groove in the posterior lobe of the cerebellum

posterior cerebral artery: supplies portions of the occipital and temporal lobes as well as the diencephalon

posterior circulation: arterial supply provided by the vertebral and basilar arteries

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

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

posterior inferior cerebellar artery (PICA): supplies the dorsolateral medulla and portions of the inferior (posterior) cerebellum

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

posterior lobe of cerebellum: portion of cerebellar cortex between the anterior and flocculonodular lobes; comprises lobules VI–IX

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

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

posterior spinal arteries: supply blood to the dorsal columns and dorsal horn predominantly

posterolateral fissure: separates the posterior and flocculonodular cerebellar lobes

posteroventral cochlear nucleus: contributes to a system of connections that regulate hair cell sensitivity

postganglionic neuron: autonomic neuron that projects to a peripheral motor target, such as a smooth muscle or a gland

postsynaptic neuron: component of a synapse; contacted by a presynaptic neuron

precentral gyrus: contains the primary motor cortex and the caudal portion of the premotor cortex; located in the frontal lobe

precommissural fornix: small division of the fornix that contains axons primarily from the hippocampus that terminate in the septal nuclei

prefrontal association cortex: involved in diverse functions, including thought and working memory

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

prefrontal cortex: see prefrontal association cortex

preganglionic neuron: autonomic neuron located in the central nervous system

premotor areas: participate in the planning of movements; located in the frontal lobe, in areas 6, 23, and 24

premotor cortex: specific premotor region located in the lateral portion of area 6

preoccipital notch: surface landmark that forms part of the boundary between the temporal and occipital lobes on the lateral surface

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

preoptic sleep center: hypothalamic center that regulates transition from wakefulness to sleep

prepositus nucleus: participates in eye position control; receives abundant inputs from the vestibular nuclei; located in the medulla

presynaptic neuron: component of the synapse; transmits information to the postsynaptic neuron

presynaptic terminal: axon terminal

pretectal nuclei: involved in pupillary light reflex; located in the junction between the midbrain and diencephalon

prevertebral ganglia: sympathetic ganglia that lie along the vertebral column

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

primary fissure: separates the anterior and posterior lobes of the cerebellum

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

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

primary olfactory neurons: transduce odorant molecules into neural signals; located within the olfactory epithelium

primary sensory (or afferent) fibers: somatic sensory receptor; dorsal root ganglion neuron

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

primary vestibular afferents: innervate vestibular hair cells; terminate primarily in the vestibular nuclei and cerebellum

primary visual cortex: participates in visual perceptions; located in the occipital lobe

projection neurons: cortical pyramidal neurons that project their axons to subcortical sites

proopiomelanocortin: a large peptide from which β-endorphin is cleaved

proprioception: sense of the position of the body; usually that of a limb or one limb segment relative to another

propriospinal neurons: spinal interneurons that interconnect neurons in different segments; also termed intersegmental neurons

prosencephalon: most rostral brain vesicle; gives rise to the telencephalon and diencephalon, which are the forebrain structures

prosopagnosia: inability to recognize faces

proximal limb muscles: muscles that innervate the shoulder or hip

pruritic: related to itch

pruritic receptor: sensory receptors responsible for the sensation of itch; activated by histamine

pseudoptosis: partial dropping of the eyelid

pseudounipolar neurons: neuron type that has a single axon and few or no dendrites in maturity (eg, the dorsal root ganglion neuron)

pterygopalatine ganglion: peripheral ganglion containing the cell bodies of parasympathetic postganglionic neurons that innervate nasal and oropharyngeal mucosal glands and lacrimal glands

pulmonary aspiration: the presence of food or consumed fluids in the lungs

pulvinar nucleus: major thalamic nucleus that has diverse projections to the parietal, temporal, and occipital lobes; involved in perception and linguistic functions

pupillary constriction: reduction in pupil diameter

pupillary dilation: increase in pupil diameter

pupillary light reflex: closure of the pupil with visual stimulation of the retina; used to test midbrain function in comatose patients

pupillary reflexes: changes in pupil diameter that occur without voluntary control; usually occur together with other ocular reflexes

Purkinje layer: location of Purkinje cell bodies

Purkinje neuron (or cell): output neuron of the cerebellar cortex; makes GABAergic inhibitory synapses on neurons of deep cerebellar nuclei and vestibular nuclei

putamen: component of the striatum; important in limb and trunk control

pyramid: tract on ventral surface of medial medulla; contains descending cortical axons, including the corticobulbar and corticospinal tracts

pyramidal neuron (or cell): cortical projection neuron class with characteristic pyramidal-shaped cell body

pyramidal decussation: where pyramidal cell axons from the motor and premotor areas cross the midline; located in the medulla

pyramidal signs: motor impairments that follow lesion of the corticospinal system

pyramidal tract: location of descending motor control pathway that originates in the motor and somatic sensory areas

quadrigeminal bodies: another name for the superior and inferior colliculi

quadrigeminal cistern: portion of the subarachnoid space that overlies the superior and inferior colliculi

radial glia: type of astrocyte that plays a role in organizing neural development; form scaffold for neuron growth and migration

radicular arteries: segmental arteries that supply the spinal cord, together with anterior and posterior spinal arteries

radicular pain: pain localized to the distribution of a single dermatome or several adjoining dermatomes

raphe nuclei: contain serotonin; located along the midline throughout most of the brain stem

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

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

receptive membrane: portion of a neuron's membrane that contains receptors sensitive to neuroactive compounds or a particular stimulus

red nucleus: plays a role in limb movement control; gives rise to the rubrospinal and rubroolivary tracts

reduced myotatic reflexes: a condition in which the strength of muscle stretch or tendon reflexes are diminished

regional neuroanatomy: examines the spatial relations between brain structures within a portion of the nervous system

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

relay nuclei: contain neurons that transmit (or relay) incoming information to other sites in the central nervous system

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

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

REM sleep: abbreviation for rapid eye movement characterized by dreaming, low limb and trunk muscle tone, and low-amplitude high-frequency electroencephalographic activity

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

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

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

reticular nucleus: a thalamic nucleus that projects to other thalamic nuclei; plays a role in regulating thalamic neuronal activity

reticulospinal tract: descending motor pathway that originates from the reticular formation, primarily in the pons and medulla, and synapses in the spinal cord

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

retinitis pigmentosa: disease in which breakdown products accumulate at the pigment epithelium of the retina

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

retroinsular cortex: location of a vestibular cortical area; junction of the posterior insular cortex with the cortex on the lateral brain surface.

retronasal olfaction: when molecules travel from the oropharynx to activate olfactory neurons in the olfactory epithelium

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

rhinal sulcus: rostral extension of the collateral sulcus, which separates the parahippocampal gyrus from more lateral temporal lobe regions

rhodopsin: photopigment in rod cells

rhombencephalon: most caudal primary brain vesicle; gives rise to the pons and medulla

rhombic lip: portion of the developing pons that gives rise to most of the cerebellum

rhombomeres: segments in the developing pons and medulla; eight in total

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

rod bipolar cells: retinal interneurons that transmit signals from rod cells to ganglion cells

rods: photoreceptors for vision under low light conditions (scotopic vision); located away from the macula portion of the retina

rostral: toward the nose

rostral interstitial nucleus of the medial longitudinal fasciculus: plays a role in control of vertical saccades

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

rostrocaudal axis: from the nose to the coccyx; the long axis of the central nervous system

rubrospinal tract: projection from the magnocellular portion of the red nucleus to the spinal cord

Ruffini's corpuscle: type of mechanoreceptor; distal process of large-diameter myelinated afferent fibers (A-β)

saccades: rapid, darting movements of the eye from one site of gaze to another

saccadic eye movements: see saccades

saccule: vestibular sensory organ (or otolith organ) sensitive to linear acceleration

sacral: spinal cord segment; there are five in total

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

scala media: inner ear fluid compartment

scala tympani: inner ear fluid compartment

scala vestibuli: inner ear fluid compartment; conducts pressure waves from the tympanic membrane to the other fluid compartments

Schaefer collaterals: collateral axon branch of neurons in the CA3 region of the hippocampus that synapse on neurons in the CA1 region

schizophrenia: psychiatric disease characterized by disordered thoughts, often associated with hallucinations

Schwann cells: glial cells that form the myelin sheath around peripheral axons

sclera: nonneural cover over the eye

scotoma: blind spot

seasonal affective disorder (SAD): form of depression during periods when days are short and nights are long

secondary auditory areas: cortical areas that process auditory information from the primary area

secondary somatic sensory cortex: cortical areas that process somatic sensory information from the primary area

segmental interneurons: neurons whose axons remain within a single spinal cord segment

segmental: pertaining to the segmental organization of the spinal cord

semantic memory: memory and knowledge of facts, people, and objects, including new word meaning

semicircular canals: vestibular organs sensitive to angular acceleration; there are three semicircular canals, each sensitive to acceleration in a different plane

semilunar ganglion: contains cell bodies of primary trigeminal sensory neurons

sensory: related to any of a wide range of stimuli from the environment or from within the body

sensory cranial nerve nuclei: process sensory information from the cranial nerves

sensory homunculus: form of somatic sensory representation in the postcentral gyrus (primary somatic sensory cortex)

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

septum pellucidum: forms the medial walls of the anterior horn and part of the body of the lateral ventricle

serotonergic: neurons that use serotonin as a neurotransmitter

serotonin: neuroactive compound; also termed 5-HT (5-hydroxytryptamine)

short circumferential branches: supply ventral portions of the brain stem away from the midline; primarily from the basilar artery

sigmoid: S-shaped

sigmoid sinus: dural blood sinus that drains the transverse sinus and flows into the inferior petrosal sinus; located bilaterally

six layers: describes laminar pattern of neocortex

skeletal somatic motor: neuron class in which axons synapse on skeletal muscle that derives from the somites

skeletomotor loop: basal ganglia circuit that engages the motor and premotor areas

slowly adapting: response characteristic of neurons to an enduring stimulus in which a prolonged series of action potentials decrement slowly or not at all

small-diameter axons: afferent fibers that are sensitive to pain, temperature, and itch (ie, histamine)

smell: one of the five major senses

smooth pursuit eye movements: slow eye movements that follow visual stimuli

soft palate: caudal, arch-shaped, portion of superior oral cavity formed by muscle

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

solitary tract: where the central branches of gustatory and viscerosensory axons collect before synapsing in the solitary nucleus

somatic: related to the body

somatic motor systems: pathways and neurons that participate in limb and trunk muscle control

somatic sensory: body sense; includes pain, temperature sense, itch, touch, and limb position sense

somatic skeletal motor column: motor nuclei in the spinal cord that contain motor neurons that innervate somatic skeletal muscle

somatotopy: organization of central sensory and motor representations based on the shape and spatial characteristics of the body

somites: para-axial mesoderm that organizes development of muscles, bones, and other structures of the neck, limbs, and trunk

spastic paralysis: condition in which the presence of spasticity produces an inability to voluntarily control striated muscle

spasticity: velocity-dependent increase in muscle tone; occurs after damage to the corticospinal system during development or in maturity

spina bifida: neural tube defect; failure of the caudal neural tube to close, producing impairments in lumbosacral spinal cord functions

spinal accessory (XI) nerve: cranial motor nerve that innervates the sternocleidomastoid muscle and parts of the trapezius muscle

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

spinal border cells: neurons that contribute axons to the ventral spinocerebellar tract

spinal cord: major division of the central nervous system

spinal nerves: mixed nerves present at each spinal segment

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

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

spinal trigeminal tract: pathway in which trigeminal afferent fibers course before synapsing in the spinal trigeminal nucleus

spinocerebellar tracts: paths transmitting somatic sensory information from the limbs and trunk to the cerebellum for movement control

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

spinomesencephalic tract: transmits somatic sensory information from the limbs and trunk to the midbrain

spinoreticular tract: transmits somatic sensory information from the limbs and trunk to the reticular formation

spinotectal tract: transmits somatic sensory information from the limbs and trunk to the dorsal midbrain; term often used interchangeably with spinomesencephalic tract

spinothalamic tract: transmits somatic sensory information from the limbs and trunk to the thalamus

spiral ganglion: where the cell bodies of auditory primary sensory neurons are located

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

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

stem cells: multipotential cell that can develop into nerve, glial, or other cell types

sternocleidomastoid muscle: flexes the head and rotates head to opposite side

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

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

stria medullaris: pathway that courses along the lateral walls of the third ventricle; contains axons from the septal nuclei to the habenula

stria terminalis: C-shaped pathway from the amygdala to portions of the diencephalon and cerebral hemispheres; also contains neurons

striasome: an anatomical compartment of the striatum that contains patch-like distributions of particular neurochemicals (eg, acetylcholinesterase; encephalin)

striatal cell bridges: places of continuity of the caudate nucleus and putamen that span the internal capsule

striate cortex: another term for the primary visual cortex based on the location of the stria of Gennari

striatum: component of the basal ganglia; comprises the caudate nucleus, putamen, and nucleus accumbens

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

subcommissural organ: a circumventricular organ; located near the posterior commissure

subdural hematoma: hemorrhage of blood into the potential space between the dura and the arachnoid

subdural space: potential space between the dura and the arachnoid

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

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

subiculum: component of the hippocampal formation

submandibular ganglion: contain postganglionic neurons that innervate the oral mucosa and the submandibular and sublingual glands

submodality: category of a sensory modality, such as color vision, bitter, or pain

substance P: neuroactive compound; present in neurons that process painful stimuli

substantia gelatinosa: laminae II and III of the dorsal horn; process pain, temperature, and itch

substantia nigra pars compacta: portion of the substantia nigra where neurons contain dopamine and project widely to the striatum

substantia nigra pars reticulata: portion of the substantia nigra where neurons contain GABA and project to the thalamus primarily

substantia nigra: component of the basal ganglia; comprises the pars reticulata and the pars compacta

subthalamic nucleus: basal ganglia nucleus involved in limb control; when damaged, can produce hemiballism; part of the indirect basal ganglia circuit

sulci: grooves

sulcus limitans: groove that separates developing sensory and motor structures in the spinal cord and brain stem

sulcus: groove

superior cerebellar artery: supplies rostral pons and cerebellum; long circumferential branch of the basilar artery

superior cerebellar peduncle: tract that primarily carries axons from the deep cerebellar nuclei to the brain stem and thalamus

superior colliculus: plays a key role in controlling saccades; located in the rostral midbrain

superior ganglion: of the vagus and glossopharyngeal nerves, contains cell bodies of somatic sensory afferent fibers

superior oblique muscle: depresses the eye when the eye is adducted and intorts the eye when it is abducted

superior olivary nuclear complex: involved in processing incoming auditory signals; especially important for horizontal localization of sounds

superior olivary nuclei: auditory relay nuclei predominantly important in the horizontal localization of sounds

superior parietal lobule: important for spatial localization

superior petrosal sinus: dural sinus; drains into the sigmoid sinus

superior rectus muscle: elevates the eye

superior sagittal sinus: dural sinus; drains into the straight sinus

superior salivatory nucleus: contains parasympathetic preganglionic neurons whose axons course in the intermediate (VII) nerve

superior temporal gyrus: involved in hearing and speech

superior vestibular nucleus: one of four vestibular nuclei; located in the pons

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

supplementary motor area: portion of the medial frontal lobe important in the control of eye movements

supporting cells: provide structural and possibly trophic support for taste buds

suprachiasmatic nucleus: hypothalamic nucleus important for circadian rhythms; center of the biological clock

supraoptic nucleus: contains magnocellular neurosecretory neurons; secretes oxytocin and vasopressin into the systemic circulation in the posterior pituitary gland

Sylvian fissure: separates the temporal lobe from the parietal and frontal lobes; also termed the lateral sulcus

sympathetic nervous system: component of the autonomic nervous system

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

synapses: specialized sites of contact where neurons communicate and where neurotransmitters are released; comprise three components—presynaptic axon terminal, synaptic cleft, and postsynaptic membrane

synaptic cleft: narrow intercellular space between the neurons at synapses

syringomyelia: cavity

T1 relaxation time: proton relaxation time related to the overall tissue environment; also termed spin-lattice relaxation time

T2 relaxation time: proton relaxation time related to interactions between protons; also termed spin-spin relaxation time

tabes dorsalis: degenerative loss of large-diameter mechanoreceptive fibers; associated with end-stage neurosyphilis

tarsal muscle: a smooth muscle that assists the actions of the levator palpebrae muscle; under control of the sympathetic nervous system

tastants: chemicals that produce tastes

taste: one of the five major senses

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

taste receptor cells: component of taste buds; transduce oral chemicals into gustatory signals

tectorial membrane: component of the organ of Corti; stereocilia of hair cells embed within the tectorial membrane

tectospinal tract: projection from the deep layers of the superior colliculus to the spinal cord

tectum: most dorsal portion of the brain stem; present only in midbrain in maturity

tegmentum: portion of the brain stem between the tectum and the base; present throughout the brain stem; Latin for cover

telencephalon: secondary brain vesicle that gives rise to structures of the cerebral hemisphere; derives from the prosencephalon

temporal hemiretina: temporal hall of the retina

temporal lobe: one of the lobes of the cerebral hemisphere

temporal pole: most rostral portion of the temporal lobe

tentorium cerebelli: dural flap between the occipital lobes and the cerebellum

terminal ganglia: parasympathetic ganglia that contain postganglionic neurons; receive input from the vagus nerve; located on the structure their axons innervate

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

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

thalamic radiations: axons of thalamic nuclei that project to the cerebral cortex

thalamostriate vein: follows C-shaped course of caudate nucleus and stria terminalis

thalamus: major site of relay nuclei that transmit information to the cerebral cortex; component of the diencephalon

thermoreceptors: primary sensory neurons sensitive to thermal changes

third ventricle: component of the ventricular system; located between the two halves of the diencephalon

thoracic: spinal cord segment; there are 12 in humans

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

touch: one of the five major senses

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)

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

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

tract: collection of axons within the central nervous system

transverse plane: perpendicular to the longitudinal axis of the central nervous system, between the dorsal and ventral surfaces

transverse sinus: dural sinus that carries blood into the systemic circulation

trapezius muscle: contains several functional regions that support the weight of the arm and act on the scapula

trapezoid body: site of decussation of auditory fibers

tremor: trembling or shaking movement

trigeminal ganglion: location of cell bodies of all trigeminal afferent fibers except those afferents innervating muscle spindle receptors; also termed semilunar ganglion

trigeminal lemniscus: tract in which axons from the main trigeminal sensory nucleus ascend to the thalamus

trigeminal mesencephalic nucleus: contains cell bodies of primary sensory neurons innervating stretch receptors in jaw muscles

trigeminal motor nucleus: contains motor neurons that innervate jaw muscles

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

trigeminocerebellar pathways: projection from spinal trigeminal nuclei to the cerebellum

trigeminothalamic tract: projection from spinal trigeminal nuclei to the thalamus

trochlear (IV) nerve: cranial nerve that contains the axons of trochlear motor neurons, which innervate the superior oblique muscle

trochlear nucleus: contains motor neurons that innervate the superior oblique muscle

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

tuberomammillary nucleus: hypothalamic nucleus; contains neurons that use histamine as a neurotransmitter; diverse projections to activate forebrain neurons

tufted cells: olfactory bulb projection neurons

tympanic membrane: ear drum; oscillates in response to environmental pressure changes associated with sounds; coupled to middle ear ossicles

uncal herniation: displacement of the uncus medially due to an expanding space-occupying lesion above the cerebellar tentorium

uncinate fasciculus: association pathway interconnecting frontal and anterior temporal cortical areas

uncus: bulge on the medial temporal lobe; overlies the anterior hippocampal formation and amygdala

unipolar neuron: neuron with a cell body and axon but few dendrites

urination: release of urine from the bladder

utricle: vestibular sensory organ (or otolith organ) sensitive to linear acceleration

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

vascular organ of the lamina terminalis: a circumventricular organ; located in the rostral wall of the third ventricle

vasopressin: neuroactive peptide that also acts on peripheral structures, including promoting fluid reabsorption in the kidney; also termed antidiuretic hormone (ADH)

venogram: radiological image of veins

ventral: toward the abdomen; synonymous with anterior

ventral (anterior) commissure: see ventral spinal commissure

ventral (or anterior) corticospinal tract: pathway for control of axial and proximal limb muscles of the neck and upper body

ventral amygdalofugal pathway: output pathway from the basolateral and central nuclei of the amygdala

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

ventral cochlear nucleus: concerned with processing the horizontal sound localization; division of cochlear nucleus

ventral column: portion of spinal cord white matter medial to the ventral horn; contains primarily descending fibers for controlling axial and proximal limb musculature

ventral horn: laminae VIII and IX of the spinal gray matter; location of neurons for somatic motor control

ventral lateral thalamic nucleus: part of the motor thalamus; receiving primarily information from the deep cerebellar nuclei; projects to cortical motor and premotor areas

ventral medial nucleus (of the hypothalamus): participates in appetitive behaviors, such as feeding

ventral pallidum: output nucleus of the limbic circuit of the basal ganglia; located ventral to the anterior commissure

ventral posterior lateral nucleus: division of the ventral posterior nucleus where information from the dorsal column nuclei is processed

ventral posterior medial nucleus: division of the ventral posterior nucleus where trigeminal information is processed

ventral posterior nucleus: thalamic nucleus for processing somatic sensory information; projects to the primary somatic sensory cortex

ventral root: where motor axons leave the spinal cord

ventral spinal commissure: where axons of the anterolateral system decussate; located ventral to lamina X and the central canal

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

ventral striatum: consists of the ventromedial portions of the caudate nucleus and putamen and the nucleus accumbens

ventral tegmental area: contains dopaminergic neurons that project to the ventromedial portion of the striatum and the prefrontal cortex; located in the rostral midbrain

ventricles: dilated channels within the ventricular system; contain choroid plexus

ventricular system: cavities within the central nervous system that contain cerebrospinal fluid

ventricular zone: innermost layer of the developing central nervous system; layer from which nerve cells are generated

ventrolateral medulla: contains neurons that participate in blood pressure regulation through projections to the intermediolateral cell column

ventrolateral nucleus: principal motor control nucleus of the thalamus; receives cerebellar input and projects to primary and premotor cortical areas

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

ventromedial hypothalamic nucleus: important in regulating appetite and other consummatory behaviors; receives input from limbic system structures

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

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

vermis: midline portion of the cerebellar cortex; plays a role in axial and proximal limb control

vertebral arteries: branch from the subclavian artery; two vertebral arteries converge to form the basilar artery

vertebral canal: cavity within the vertebral column within which the spinal cord is located

vertebral-basilar circulation: arterial supply to the brain stem and parts of the temporal and occipital lobes

vertigo: the sense of the world spinning around or that of an individual whirling around

vestibular ganglion: location of cell bodies of primary vestibular neurons; also termed Scarpa's ganglion

vestibular labyrinth: fluid-filled cavities within the temporal bone within which the vestibular organs are located

vestibular division of CN VIII: component of CN VIII that supplies the semicircular canals, utricle, and saccule

vestibular nuclei: major termination site of vestibular sensory fibers

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

vestibulocochlear (VIII) nerve: contains afferent fibers that innervate the auditory and vestibular structures of the inner ear

vestibuloocular reflex: automatic control of eye position by vestibular sensory information

vestibulospinal tract: axons that originate from the vestibular nuclei and project to the brain stem

vibration sense: the capacity to detect and distinguish mechanical vibration of the body

visceral: related to the internal organs of the body

visceral (autonomic) motor fibers: axons of autonomic preganglionic or postganglionic neurons as they course in the periphery

visceral motor nuclei: contain autonomic preganglionic neurons

viscerosensory: related to the sensory innervation of the internal organs of the body

vision: one of the five major senses

visual field: the total area that is seen

visual field defect: loss of vision within a portion of the visual field

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

vomeronasal organ: peripheral olfactory organ important for detecting pheromones; well-documented as a functional structure in animals, but its function in humans is controversial

Wallenberg syndrome: see lateral medullary syndrome

Wallerian degeneration: deterioration of the structure and function of the distal portion of an axon, when cut; also termed anterograde generation

Wernicke's area: important for understanding speech; located in the posterior superior temporal gyrus (area 22)

what pathway: corticocortical circuits important for identifying an object using vision, touch, or sound

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

white matter: location of predominantly myelinated axons

working memory: the temporary storing of information used to plan and shape upcoming behaviors

zona incerta: contains GABA-ergic neurons that project widely to the cerebral cortex; nuclear region of the diencephalon

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