Physiology, Action Potential

Excerpt

An action potential is a rapid sequence of changes in the voltage across a membrane. The membrane voltage, or potential, is determined at any time by the relative ratio of ions, extracellular to intracellular, and the permeability of each ion. In neurons, the rapid rise in potential, depolarization, is an all-or-nothing event that is initiated by the opening of sodium ion channels within the plasma membrane. The subsequent return to resting potential, repolarization, is mediated by the opening of potassium ion channels. To reestablish the appropriate balance of ions, an ATP-driven pump (Na/K-ATPase) induces movement of sodium ions out of the cell and potassium ions into the cell.