action potential

As an action potential (nerve impulse) travels down an axon, there is a change in electric polarity across the membrane of the axon. In response to a signal from another neuron, sodium- (Na) and potassium- (K)–gated ion channels open and close as the membrane reaches its threshold potential. Na channels open at the beginning of the action potential, and Na moves into the axon, causing depolarization. Repolarization occurs when K channels open and K moves out of the axon, creating a change in electric polarity between the outside of the cell and the inside. The impulse travels down the axon in one direction only, to the axon terminal where it signals other neurons.

An action potential (also known as a nerve impulse or "spike" when in a neuron) is a series of quick changes in voltage across a cell membrane. An action potential occurs when the membrane potential of a specific cell rapidly rises and falls. This "depolarization" (physically, a reversal of the polarization of the membrane) then causes adjacent locations to similarly depolarize. Action potentials occur in several types of excitable cells, which include animal cells like neurons and muscle cells, as well as some plant cells. Certain endocrine cells such as pancreatic beta cells, and certain cells of the anterior pituitary gland are also excitable cells.