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KEY CONCEPTS

KEY CONCEPTS

  • Neurons are the principal cells in the brain that process information. There is a great diversity of neuronal cell types based on morphology, molecular constituents, location, and connections.

  • The nucleus and major cytoplasmic organelles in the cell body of neurons synthesize and process proteins, which are subsequently transported within the soma or along axons and dendrites to their appropriate locations.

  • The axon conducts action potentials to presynaptic terminals to initiate communication with other neurons, which occurs at synapses.

  • Dendrites, multiple fine processes that extend from the neuronal cell body, together with the cell body, serve as the primary structure for the reception of synaptic contacts from other neurons.

  • The cytoskeleton—the inner scaffold of a neuron formed by a system of interconnected protein filaments called microtubules, intermediate filaments, and actin filaments—plays a key role in the structure of neurons and in the transport of various proteins and organelles from the cell body to axonal and dendritic processes.

  • Three major classes of glia—astrocytes, microglia, and oligodendrocytes—play important roles in brain function.

  • Astrocytes have diverse functions, including maintenance of the extracellular milieu, metabolism of certain neurotransmitters, formation of the blood–brain barrier, and response to brain injury.

  • Microglia are essential components of the brain’s immune system, but function more broadly by sculpting synaptic connections between neurons.

  • Oligodendrocytes are the source of myelin sheaths that insulate many axons in the brain, a requirement for rapid transduction of electrical impulses.

  • The blood–brain barrier—formed by capillary endothelial cells, connections between which are sealed by tight junctions and then wrapped by astrocyte end–feet and pericytes—allows only small lipophilic substances to enter the brain from the general circulation.

  • In their resting state, neurons maintain a negative electrical potential in relation to the extracellular environment. This results primarily from differences between the intracellular and extracellular concentrations of K+, Na+, and Cl and the relative permeability of the cell membrane to these and other ions. The energy–consuming Na+–K+ pump helps to maintain appropriate ionic gradients across the membrane.

  • The generation of all-or-none action potentials relies on the activities of voltage–dependent ion channels, highly specialized proteins that allow the flow of a specific ion (K+, Na+, or Ca2+) across neuronal membranes in response to changes in neuronal membrane potential.

  • Sodium channels are the targets of many important drugs including local anesthetics and some antiseizure medications.

  • Potassium channels are a large and diverse family of proteins that regulate neuronal excitability and control the shape of the action potential.

  • Entry of Ca2+ into neurons through voltage–dependent Ca2+ channels, of which there are three major classes—CaV1 (L-type), CaV2 (P/Q-, N-, and R-type), and CaV3 (T-type)—is important for neurotransmitter release and activation of intracellular signaling cascades.

  • Blockers of CaV1 Ca2+ channels are used to treat ischemic heart disease and hypertension.

  • Mutations in ion channels are the cause of several neurologic ...

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