This phase is known as the repolarization phase of an action potential. During an action potential, after the initial depolarization, the sodium channels that opened quickly during depolarization begin to inactivate. This inactivation prevents further influx of sodium ions.
Simultaneously, voltage-gated potassium channels, which have a slower response compared to sodium channels, start to open. As potassium ions exit the neuron, the inside of the cell becomes more negative again, moving back towards the resting membrane potential. This process is crucial as it helps reset the membrane potential back to its baseline level after the peak of the action potential.