An action potential, also called a spike, nerve impulse, and discharge, is the rapid reversal of charge of the cell membrane. These changes in charge occur within milliseconds, meaning the action potential travels very quickly down the axon in order to convey information over long distances. This transfer of information occurs within six phases and requires the presence of multiple pumps and channels embedded in the membrane to control ion concentration.
Phase 1: The Resting Phase
The first phase of the action potential is the resting phase. A neuron at rest has a membrane potential of -65 mV. The resting potential is established through the movement of ions across the membrane, which allows the cell to have the ability …show more content…
All sodium channels are inactive at this point, meaning that the current, conductance, and driving force of sodium is equal to zero. Potassium’s conductance, however, is greater than zero, and potassium has a high driving force and current during the falling phase. This is due to the opening of voltage-gated potassium channels, which are delayed rectifiers. During the repolarization of the membrane, the cell enters a relative refractory period. This begins two to three milliseconds after the action potential is generated. Action potentials can be generated if the stimulus is large enough during the relative refractory period. The membrane potential, in contrast to the resting phase, is now -80 mV. This is the equilibrium potential for potassium; this occurs because the membrane is more permeable to potassium once again. Ion concentrations are restored in the next phase, which is called the undershoot.
Phases 5 and 6: The Undershoot and the Return to Rest
There is a small capacitive current during the undershoot, and potassium is leaving the cell because leak channels are still active. The membrane potential returns to rest, the sixth phase of the action potential. At this time, concentration gradients are restored because of the sodium-potassium pump’s hard work. After the return to rest, the cycle begins all over again, starting with the resting phase and so on.
The Propagation of the Action