This tutorial is a very basic review of some basic physics and chemistry that plays a role in the generation and sustaining of the action potential. The goal of the tutorial is to give students some grasp of why the action potential acts as it does as opposed to simply a knowledge of what happens.

The first issue if that of diffusion. As would be described in any first semester chemistry book, molecules in solution move randomly. Examine Figure 1:
Figure 1. A solution of a substance, the purple dots, in solution. A membrane prevents movement of the water and the molecules from crossing from one side of the beaker to the other.

In this beaker full of water, a membrane divides the beaker in half. On the left side there is a collection of molecules. The black lines indicate the direction and speed of the movement of the molecules. The movements shows no coherent pattern. Click on the red barrier on the membrane to remove them and allow the water and molecules to move freely.