APA Dictionary of Psychology

n. a reduction in the electric potential across the plasma membrane of a cell, especially a neuron, such that the inner surface of the membrane becomes less negative in relation to the outer surface. Depolarization occurs when the membrane is stimulated and sodium ions (Na⁺) flow into the cell. If the stimulus intensity exceeds the excitatory threshold of the neuron, an action potential is created and a nerve impulse propagated. Compare hyperpolarization.