ABSTRACT
The term action potential (AP) describes the depolarisation above threshold potential, and subsequent repolarisation of a nerve axon resulting in the propagation of a nerve impulse along that axon. In an unmyelinated axon the AP moves rather like a wave; local currents spreading in front of the AP cause a change in membrane potential and bring the membrane to threshold potential to spark the propagation of the AP. The AP can only flow in one direction as the axon behind it will be refractory. The myelin increases the AP’s velocity, and its insulating effect allows axons to be of smaller diameter. The Nernst equation calculates the electrical potential for an individual ion, thus helping to predict how each ion affects the cell membrane potential. It represents the electrical potential required to balance a given ionic concentration gradient across a membrane so that there is no net flux.
