When an action potential is produced in a polarized nerve membrane, local currents from the action potential spread to the adjacent membrane area and depolarize it to the threshold level, triggering another action potential and the process continues.
Thus, there are two essential components of action potential propagation-
(a) the flow of local currents, which depolarizes the adjacent membrane. This electro tonic conduction of membrane depolarization, however, tends to fade out very quickly.
(b) The triggering of a fresh action potential in the adjacent membrane.
The new action potential depolarizes the membrane maximally, and thereby restates the depolarization to its original magnitude of ~ 110 mV. Without the first conductive component, an action potential cannot be conducted at all. Without the second regenerative component, an action potential can be conducted only up to a limited distance beyond which it will fade out. Before the local currents fade out completely, a fresh action potential must be generated for the action potential to be propagated.
The conductive component is very fast and depends on the electrical characteristics of the membrane (called the cable properties of the membrane). The regenerative component is much slower. Frequent action potentials along the neuron tend to slow down the conduction velocity.