| action potential | the all-or-none electrical event in the neuron or muscle cell in which the polarity of the cell membrane is rapidly reversed and then reestablished.
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| afferent fibers | nerve fibers (sensory fibers) that carry neural information back to the central nervous system.
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| autonomic nervous system | portion of the nervous system that controls the actions of visceral organs.
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| axon | a nerve fiber that conducts a nerve impulse away from the neuron cell body.
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| brain stem | portion of the brain that includes midbrain, pons, and medulla.
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| cell body | the soma, or major portion of the body of a nerve cell. Contains the nucleus.
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| central nervous system (CNS) | portion of the nervous system that consists of the brain and spinal cord.
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| cerebellum | portion of the brain that is concerned with fine coordination of skeletal muscles during movement.
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| cerebrum | superior aspect of the brain that occupies the upper cranial cavity. Contains the motor cortex.
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| conductivity | capacity for conduction.
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| dendrites | portion of the nerve fiber that transmits action potentials toward a nerve cell body.
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| efferent fibers | nerve fibers (motor fibers) that carry neural information from the central nervous system to the periphery.
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| EPSP | excitatory post-synaptic potential. A graded depolarization of a post-synaptic membrane by a neurotransmitter.
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| IPSP | inhibitory post-synaptic potential that moves the post-synaptic membrane further from threshold.
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| irritability | a trait of certain tissues that enables them to respond to stimuli (e.g., nerve and muscle).
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| kinesthesia | a perception of movement obtained from information about the position and rate of movement of the joints.
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| motor cortex | portion of the cerebral cortex containing large motor neurons whose axons descend to lower brain centers and spinal cord; associated with the voluntary control of movement.
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| neuron | nerve cell; composed of a cell body with dendrites (projections) that bring information to the cell body, and axons that take information away from the cell body to influence neurons, glands, or muscles.
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| parasympathetic nervous system | portion of the autonomic nervous system that primarily releases acetylcholine from its postganglionic nerve endings.
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| peripheral nervous system (PNS) | portion of the nervous system located outside the spinal cord and brain.
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| proprioceptors | receptors that provide information about the position and movement of the body; includes muscle and joint receptors as well as the receptors in the semicircular canals of the inner ear.
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| reciprocal inhibition | when extensor muscles (agonists) are contracted, there is a reflex inhibition of the motor neurons to the flexor muscles (antagonists), and vice versa.
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| resting membrane potential | the voltage difference measured across a membrane that is related to the concentration of ions on each side of the membrane and the permeability of the membrane to those ions.
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| Schwann cell | the cell that surrounds peripheral nerve fibers, forming the myelin sheath.
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| spatial summation | the additive effect of numerous simultaneous inputs to different sites on a neuron to produce a change in the membrane potential.
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| sympathetic nervous system | portion of the autonomic nervous system that releases norepinephrine from its postganglionic nerve endings; epinephrine is released from the adrenal medulla.
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| synapses | junctions between nerve cells (neurons) where the electrical activity of one neuron influences the electrical activity of the other neuron.
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| temporal summation | a change in the membrane potential produced by the addition of two or more inputs, occurring at different times (i.e., inputs are added together to produce a potential change that is greater than that caused by a single input).
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| vestibular apparatus | sensory organ, consisting of three semicircular canals, that provides needed information about body position to maintain balance.
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