Action Potential

Neuronal firing is an all-or-nothing response: nothing happens before the threshold is reached, then the event fires entirely at once. The resting membrane potential is the difference in electrical charge between the inside and outside of a neuron's cell membrane, analogous to a battery charge. The threshold principle is critical because it explains how the nervous system regulates sensitivity. A neuron resting too close to its firing threshold may react to very small inputs, while one too far below threshold may fail to respond when it should.