Action Potential

Synonyms

Discharge; Impulse; Spike

Definition

The action potential is the active electrical response of an excitable cell membrane to a stimulus, reflected in a fairly stereotyped change in membrane potential from a resting value (negative inside) to a depolarized (either positive or less negative inside) value and back. The durations of action potentials range from a few milliseconds in neurons to hundreds of milliseconds in cardiac, gastric and intestinal cells. The underlying mechanism consists of voltage-dependent opening of Na⁺, Ca²⁺ and K⁺ channels. The response is initially depolarizing due to opening of Na⁺ and/or Ca²⁺ channels, and subsequently repolarizing due to delayed opening of K⁺ channels.

Characteristics

The action potential represents membrane mechanisms, that yield an electrical signal, which propagates over long distances. The signal originates from an encoding process that converts graded, non-propagating receptor potentialsor synaptic potentials into action...