APA Dictionary of Psychology

the change in electric potential that propagates along the axon of a neuron during the transmission of a nerve impulse or the contraction of a muscle. It is marked by a rapid, transient depolarization of the cell’s plasma membrane, from a resting potential of about –70 mV (inside negative) to about +30 mV (inside positive), and back again, after a slight hyperpolarization, to the resting potential. Each action potential takes just a few milliseconds. Also called spike potential.