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| 1. | absolute refractory period | time during an action period when another action potential cannot be generated because the voltage-gated Na+ channel is inactivated |
| 2. | action potential | change in voltage of a cell membrane in response to a stimulus that results in transmission of an electrical signal; unique to neurons and muscle fibers |
| 3. | activation gate | part of the voltage-gated Na+ channel that opens when the membrane voltage reaches threshold |
| 4. | astrocyte | glial cell type of the CNS that provides support for neurons and maintains the blood-brain barrier |
| 5. | autonomic nervous system (ANS) | functional division of the nervous system that is responsible for homeostatic reflexes that coordinate control of cardiac and smooth muscle, as well as glandular tissue |
| 6. | axon hillock | tapering of the neuron cell body that gives rise to the axon |
| 7. | axon segment | single stretch of the axon insulated by myelin and bounded by nodes of Ranvier at either end (except for the first, which is after the initial segment, and the last, which is followed by the axon terminal) |
| 8. | axon terminal | end of the axon, where there are usually several branches extending toward the target cell |
| 9. | axon | single process of the neuron that carries an electrical signal (action potential) away from the cell body toward a target cell |
| 10. | axoplasm | cytoplasm of an axon, which is different in composition than the cytoplasm of the neuronal cell body |
| 11. | biogenic amine | class of neurotransmitters that are enzymatically derived from amino acids but no longer contain a carboxyl group |
| 12. | bipolar | shape of a neuron with two processes extending from the neuron cell bodythe axon and one dendrite |
| 13. | blood-brain barrier (BBB) | physiological barrier between the circulatory system and the central nervous system that establishes a privileged blood supply, restricting the flow of substances into the CNS |
| 14. | brain | the large organ of the central nervous system composed of white and gray matter, contained within the cranium and continuous with the spinal cord |
| 15. | central nervous system (CNS) | anatomical division of the nervous system located within the cranial and vertebral cavities, namely the brain and spinal cord |
| 16. | cerebral cortex | outermost layer of gray matter in the brain, where conscious perception takes place |
| 17. | cerebrospinal fluid (CSF) | circulatory medium within the CNS that is produced by ependymal cells in the choroid plexus filtering the blood |
| 18. | chemical synapse | connection between two neurons, or between a neuron and its target, where a neurotransmitter diffuses across a very short distance |
| 19. | cholinergic system | neurotransmitter system of acetylcholine, which includes its receptors and the enzyme acetylcholinesterase |
| 20. | choroid plexus | specialized structure containing ependymal cells that line blood capillaries and filter blood to produce CSF in the four ventricles of the brain |
| 21. | continuous conduction | slow propagation of an action potential along an unmyelinated axon owing to voltage-gated Na+ channels located along the entire length of the cell membrane |
| 22. | dendrite | one of many branchlike processes that extends from the neuron cell body and functions as a contact for incoming signals (synapses) from other neurons or sensory cells |
| 23. | depolarization | change in a cell membrane potential from rest toward zero |
| 24. | effector protein | enzyme that catalyzes the generation of a new molecule, which acts as the intracellular mediator of the signal that binds to the receptor |
| 25. | electrical synapse | connection between two neurons, or any two electrically active cells, where ions flow directly through channels spanning their adjacent cell membranes |
| 26. | electrochemical exclusion | principle of selectively allowing ions through a channel on the basis of their charge |
| 27. | enteric nervous system (ENS) | neural tissue associated with the digestive system that is responsible for nervous control through autonomic connections |
| 28. | ependymal cell | glial cell type in the CNS responsible for producing cerebrospinal fluid |
| 29. | excitable membrane | cell membrane that regulates the movement of ions so that an electrical signal can be generated |
| 30. | excitatory postsynaptic potential (EPSP) | graded potential in the postsynaptic membrane that is the result of depolarization and makes an action potential more likely to occur |
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