Cellular Action Potential

Action potential is used to refer to what happens in a cell when it fires. There are five phases to action potentials, numbered 0 through 4, and the electrolytes sodium and potassium are the two electrolytes responsible for it. Calcium also plays a role although not in conduction but in mainting the duration of sodium's action.

This entire sequence takes a few milliseconds.

In general sodium conducts and fires, calcium calms and extends, potassium chills and trys to stay away from sodium.

Phases
Phase 4

This is the resting phase. It is state the cell is in before anything starts to happen and state it returns to at the end. There is more sodium outside of the cell and more potassium on the inside. The electrical charge is -80 mV. This is considered polarized.

Phase 0

Fast sodium ion channels open and Na+ rishes into the cell. The cell depolarizes (gains electrical charge) up to about +20 mV. This is what allows the cell to fire.

Phase 1

Na+ fast channels close, K+ fast channels open and K+ leaves cell. Result is a slight repolarization of cell.

Phase 2

Slow channels for Na+ and K+ open, Calcium channels open; calcium has a calming effect on cellur activity. Result is a plateau where charge remains about the same.

Phase 3

All channels close and cell return to it's resting state.

Videos
Two really short videos for the visual.