Action Potential
An action potential, abbreviated AP, is a generalized membrane depolarization of a cell.
The membrane potential reaches a threshold value due to changes in the ion fluxes by extracellular chemical or physical signals or by intracellular metabolic processes.
In the heart, the AP appears at the pacemaker cells, the Purkinje fibers and the working myocardium, where it initiates contraction. The AP of the heart muscle cells differs from the AP of the nerve cells by a pronounced plateau as a result of a strong calcium influx that begins with depolarization.