The membrane potential becomes positive. The membrane becomes more negative than it is at rest. The voltage at which an action potential is initiated. Different neurons have different resting potentials, but for humans it is typically around -70 mv. An action potential is initiated if the membrane potential of a neuron reaches threshold .
Different neurons have different threshold.
This phase is termed the depolarization stage. This returns the inside of the membrane to negative value. This is termed the repolarization stage . At the end of this stage the inside of the membrane may be even more negative than it is at rest. Refer to the Table Below to help understand why a typical human neuron is negative at rest.