Answer
In the depolarization phase, voltage-gated Na+ channels are open.
This allows an influx of Na+ ions to flow down their concentration gradient into the neuron.
In the repolarization phase, the K+ voltage-gated channels are open, while the Na+ channel gates are inactivating.
Work Step by Step
If the K+ channels remain open after the Na+ gates have inactivated, the membrane potential may hyperpolarize, with the membrane potential going to -80 mV, or even 90 mV.
