English: A diagram in three parts showing how an action potential propagates down a membrane, using the electrical membrane model as a guide. A local depolarization opens local sodium channels. Sodium current causes membrane depolarization (T1) which spreads to adjacent membrane, depolarizing it as well (T2). Sodium channels then open in this adjacent membrane, and the depolarization spreads further down the membrane (T4). Meanwhile, delayed rectifyer potassium current flows in the original membrane patch, causing the falling phase of the AP. T3 is not shown but can be imagined by interpolation.

Note that in T4, depolarization spreads in both directions down the membrane (i.e. also toward the place where the AP originated. A second action potential is not fired in that membrane because it is refractory, thus allowing for one-way AP conduction.

Diagram drawn by me in Corel Draw!