A momentary change in electrical potential on the surface of a neuron or muscle cell. Nerve impulses are action potentials. They either stimulate a change in polarity in another neuron or cause a muscle cell to contract.
The rapid change in electric potential that parts of a nerve cell undergo when a nerve impulse is generated. Unlike ordinary electric current (see also current), which consists of the flow of electrons, the action potential involves the movement of sodium and potassium ions across the cell membrane.