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| 61. | nucleus | in the nervous system, a localized collection of neuron cell bodies that are functionally related; a "center" of neural function |
| 62. | oligodendrocyte | glial cell type in the CNS that provides the myelin insulation for axons in tracts |
| 63. | peripheral nervous system (PNS) | anatomical division of the nervous system that is largely outside the cranial and vertebral cavities, namely all parts except the brain and spinal cord |
| 64. | postsynaptic potential (PSP) | graded potential in the postsynaptic membrane caused by the binding of neurotransmitter to protein receptors |
| 65. | precentral gyrus of the frontal cortex | region of the cerebral cortex responsible for generating motor commands, where the upper motor neuron cell body is located |
| 66. | process | in cells, an extension of a cell body; in the case of neurons, this includes the axon and dendrites |
| 67. | propagation | movement of an action potential along the length of an axon |
| 68. | receptor potential | graded potential in a specialized sensory cell that directly causes the release of neurotransmitter without an intervening action potential |
| 69. | refractory period | time after the initiation of an action potential when another action potential cannot be generated |
| 70. | relative refractory period | time during the refractory period when a new action potential can only be initiated by a stronger stimulus than the current action potential because voltage-gated K+ channels are not closed |
| 71. | repolarization | return of the membrane potential to its normally negative voltage at the end of the action potential |
| 72. | resistance | property of an axon that relates to the ability of particles to diffuse through the cytoplasm; this is inversely proportional to the fiber diameter |
| 73. | response | nervous system function that causes a target tissue (muscle or gland) to produce an event as a consequence to stimuli |
| 74. | resting membrane potential | the difference in voltage measured across a cell membrane under steady-state conditions, typically -70 mV |
| 75. | Schwann cell | glial cell type in the PNS that provides the myelin insulation for axons in nerves |
| 76. | saltatory conduction | quick propagation of the action potential along a myelinated axon owing to voltage-gated Na+ channels being present only at the nodes of Ranvier |
| 77. | satellite cell | glial cell type in the PNS that provides support for neurons in the ganglia |
| 78. | sensation | nervous system function that receives information from the environment and translates it into the electrical signals of nervous tissue |
| 79. | size exclusion | principle of selectively allowing ions through a channel on the basis of their relative size |
| 80. | soma | in neurons, that portion of the cell that contains the nucleus; the cell body, as opposed to the cell processes (axons and dendrites) |
| 81. | somatic nervous system (SNS) | functional division of the nervous system that is concerned with conscious perception, voluntary movement, and skeletal muscle reflexes |
| 82. | spatial summation | combination of graded potentials across the neuronal cell membrane caused by signals from separate presynaptic elements that add up to initiate an action potential |
| 83. | spinal cord | organ of the central nervous system found within the vertebral cavity and connected with the periphery through spinal nerves; mediates reflex behaviors |
| 84. | stimulus | an event in the external or internal environment that registers as activity in a sensory neuron |
| 85. | summate | to add together, as in the cumulative change in postsynaptic potentials toward reaching threshold in the membrane, either across a span of the membrane or over a certain amount of time |
| 86. | synapse | narrow junction across which a chemical signal passes from neuron to the next, initiating a new electrical signal in the target cell |
| 87. | synaptic cleft | small gap between cells in a chemical synapse where neurotransmitter diffuses from the presynaptic element to the postsynaptic element |
| 88. | synaptic end bulb | swelling at the end of an axon where neurotransmitter molecules are released onto a target cell across a synapse |
| 89. | temporal summation | combination of graded potentials at the same location on a neuron resulting in a strong signal from one input |
| 90. | thalamus | region of the central nervous system that acts as a relay for sensory pathways |
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