Transmission of nerve impulses along axon involves the formation of action potentials. An action potential is divided into several phases which are resting phase, depolarisation phase and repolarisation phase.
Resting phase
During resting phase, the potential difference which exists across axon membrane at rest is called resting potential. The resting potential for human cell is about -70mV. Sodium potassium pumps actively pump three sodium ions out of the axon and pumps two potassium ions into the axoplasm, therefore more positive ions are pumped out that pump in.
Depolarisation phase
During depolarisation phase, sodium gates open, positively charged sodium ions diffuse into axon and the charge inside axon changes from negative to positive.
Repolarisation phase
During repolarisation phase, potassium gates open, positively charged potassium ions diffuse out from axon and the charge inside axon changes from positive to negative.