Action Potential

Rapid depolarization; Sodium rushes into cell making cell more positive. Action produces characteristic upstroke in action potential

Initial repolarization; Rapid influx of chlo-ride inactiviates inward pumping of sodium.

The plateu. Slow inward flow of calcium occurs and flow of potassium is slowed considerably.

Final rapid deploarization; sudden acceleration of repoloarization as the slow calicum current is inactivated and the outward flow of potassium is accelerated.

Diastolic depolarization is very rapid; Pacemaker cells have fall in outward potassium current with a rapid sodium influx. Nonpacemaker cells remain in the steady state until their membranes are acted on by another stimulus.