Action Potential

An action potential is a rapid rise and subsequent fall in voltage or membrane potential across a cellular membrane with a characteristic pattern. Sufficient current is required to initiate a voltage response in a cell membrane; if the current is insufficient to depolarize the membrane to the threshold level, an action potential will not fire. Examples of cells that signal via action potentials are neurons and muscle cells. 

1. Stimulus starts the rapid change in voltage or action potential. In patch-clamp mode, sufficient current must be administered to the cell in order to raise the voltage above the threshold voltage to start membrane depolarization.
2. Depolarization is caused by a rapid rise in membrane potential opening of sodium channels in the cellular membrane, resulting in a large influx of sodium ions.
3. Membrane Repolarization results from rapid sodium channel inactivation as well as a large efflux of potassium ions resulting from activated potassium channels.
4. Hyperpolarization is a lowered membrane potential caused by the efflux of potassium ions and closing of the potassium channels.
5. Resting state is when membrane potential returns to the resting voltage that occurred before the stimulus occurred.