Exam 3 Review:  Chapter 11:  Impulse Transmission

refractory period (neuron) - The time interval, after a nerve fiber has been stimulated and an action potential has been achieved, which has to pass before the neuron can be stimulated again; this interval can be subdivided into absolute and relative refractory periods.

absolute refractory period (neuron) - The interval from the beginning of the action potential until the nerve fiber is able to conduct another action potential; during most of this interval the Na⁺ and K⁺ channels remain open.

relative refractory period (neuron) - The interval which follows the absolute refractory period and is the time period in which, although the neuron has not fully recovered, a small, weak action potential can be generated as the result of a strong input stimulus; the Na⁺ channels are closed and cannot easily reopen for a set period of time; during this interval the K⁺ channels remain open.

propagation = conduction (impulse) - The means or process by which an impulse = wave of depolarization = action potential  is spread over the surface of an excitable cell's membrane; the specific trigger is the opening of volted gated ion channels, usually Na⁺ channels.

continuous conduction - The step-by-step depolarization (the timed opening and then closing of sodium and potassium channels) of each adjacent area of the plasma membrane of an excitable cell, such as a muscle or gland cell or over the regions of the dendrites and cell bodies of neurons, and including unmyelinated axons.

saltatory conduction - The rapid sequential depolarization (the timed opening and then closing of sodium and potassium channels) of distant segments of a myelinated axon as the impulse jumps from neurofibrillar node to node; only the segments of the axolemma exposed at each node are depolarized to generate at local action potential, while the myelin sheath covered portions of the axon do not depolarize.

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