Propagation of Action Potentials

The Propagation of an action potential is the process by which a nerve impulse is transmitted along the axon. It is a self-propagating process; once initiated, an action potential propagates with constant velocity.

When the membrane at the trigger zone is depolarized to a threshold, the voltage-gated sodium channels open to initiate an action potential.

These sodium ions move down the axon, depolarizing the adjacent region. This triggers the opening of sodium channels in that part of the membrane, propagating the action potential.

This type of propagation is called continuous propagation because the depolarization and repolarization of each segment happen continuously in a series of small steps. This mode of propagation is seen in unmyelinated axons.

In contrast, in the myelinated axons, the action potential propagates by saltatory propagation. Here, the first action potential at a node creates an ionic current that opens the ion channels at the next node.

Since the action potential can jump from one node to another, saltatory conduction allows the impulse to propagate faster in a myelinated axon than in an unmyelinated axon.