Depolarisation phase of an axon is quickly followed by

Depolarisation phase of an axon is quickly followed by outward diffusion of potassium ions.

An action potential has two main phases: a depolarizing phase and a repolarizing phase. During the depolarising phase, the voltage-gated Na⁺ channels open and allow an influx of Na⁺ into the cell. During the repolarising phase, the voltage-gated K⁺ channels open, allowing K⁺ to flow out. Following the repolarising phase there may be an after-hyperpolarising phase, during which the voltage-gated K⁺ channels remain open even after the repolarising phase ends.