Final answer:
The hyperpolarization undershoot in a neuron happens because potassium ion gates are slow to close, leading to an extended outflow of K+ and a more negative membrane potential before returning to the resting state.
Step-by-step explanation:
The hyperpolarization undershoot occurs in a neuron due to the fact that potassium ion (K+) gates are slow to close. During an action potential, after the depolarization phase, potassium channels open to allow K+ ions to exit the neuron, which repolarizes the membrane. As repolarization occurs, these channels begin to close but with a delay. This delay means that potassium continues to leave the cell slightly longer than necessary, driving the membrane potential to become even more negative than the resting state, thus creating the hyperpolarization undershoot. Eventually, the channels close, and the membrane potential returns to the resting level due to the activity of non-gated channels and the Na+/K+ pump.