Nerve action potentials are the electrical signals sent out by the body to control bodily processes such as muscular movement. They are controlled by ions and their concentrations around the nerve cell. They propagate uniformly along the nerve cell and are governed by the all-or-none phenomena. This means that a nerve action potential will not occur unless the depolarization threshold is met. The depolarization threshold is the potential that must be reached before depolarization of the nerve cell will occur. As a nerve action potential propagates along a neuron it goes through several phases which are shown in the graph below.
where
(A) Resting state = the membrane potential at rest(before the nerve action potential occurs)
(B) Depolarization = occurs when there is a drastic reversal in membrane potential
(C) Repolarization = occurs when the membrane potential is returning to the resting state
(D) Undershoot = occurs because the potassium gate stays open too long