Final answer:
During an action potential, sodium ions rush into the cell, causing depolarization, while potassium ions leave the cell, repolarizing it. This enables the transmission of the electrical impulse down the axon.
Step-by-step explanation:
During an action potential, the neuron undergoes depolarization and repolarization. Initially, sodium ions rush into the cell, causing depolarization and a reversal of the membrane potential. As a result, voltage-gated potassium channels open, allowing potassium ions to leave the cell and repolarize it. At the resting potential, potassium channels close and sodium channels reset. This process enables the depolarization of the membrane to travel down the axon in one direction.