An action potential can be propagated along the length of an axon. (A) The voltages that would be recorded from a set of intracellular electrodes placed at intervals along the axon, whose width is greatly exaggerated in this schematic figure. Note that the action potential does not weaken as it travels. (B) The current changes in the Na⁺ channels and the current flows (orange arrows) that give rise to the traveling disturbance of the membrane potential. The region of the axon with a depolarized membrane is shaded in blue. Note that an action potential can travel only away from the site of depolarization because NA⁺-channel inactivation prevents the depolarization from spreading backward. In myelinated axons, clusters of NA⁺ channels can be millimeters apart from each other.  Fair Use and Copyright info