Role of Na⁺ in the generation of action potential : Stimulation of an axon increases its membrane permeability to Na⁺. As a result Na⁺ ions diffuse across he membrane from the extra cellular fluid (ECF) where their concentration is higher to the interior of the fibre where the concentraion is much lower. The membrane permeability to K⁺ starts rising so there is simultanous rise in the outward diffusion of K⁺ from the cell interior having a higher K⁺concentration. These effects lower the overall cation concentration outside than inside the membrane. Thus, depolarization i.e. charge is reversed in the membrane.

The wave of depolarization spreads. It stimulates adjacent Na⁺ channel to get activated, so that next part is depolarized but previous part is repolarized. The wave of depolarization spreads in all directions.