action potential

An all-or-nothing change in electrical potential that occurs across a plasma membrane of a nerve cell during the passage of a nerve impulse. As an impulse travels along the axon of a nerve cell, it causes a localized and transient switch in potential across the membrane from about -60 millivolts (the so-called resting potential) to +45 millivolts. The change in potential is caused by an influx of sodium ions (see sodium-potassium pump). Nervous stimulation of muscle cells and some glandular cells has a similar effect.

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• ANATOMY AND PHYSIOLOGY

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