Final answer:
During rapid depolarization, voltage-gated Na+ channels open causing an influx of sodium ions and depolarization. Soon after, K+ channels open allowing potassium to leave, starting the repolarization process. Sodium-potassium ATPase then restores the resting potential.
Step-by-step explanation:
Ion Movement During Rapid Depolarization
During rapid depolarization, significant changes occur involving ion channels and the movement of ions. Initially, electrical stimulation opens voltage-gated sodium (Na+) channels, allowing Na+ ions to rush into the cell, thus reducing the membrane potential from a resting state. This causes the inside of the cell to become more positive, resulting in depolarization. Subsequently, the membrane potential increases to approximately +30 mV, leading to the closing of Na+ channels.
Simultaneously, voltage-gated potassium (K+) channels open, permitting K+ ions to exit the cell. This outflow of positive charges initiates repolarization, where the cell membrane potential moves toward the negative resting potential. After repolarization, the resting potential is restored, owing to the sodium-potassium ATPase which transports ions to maintain the usual negative interior polarity.
Furthermore, during the plateau phase of a cardiac action potential, slow calcium (Ca2+) channels open, allowing calcium to enter and contribute to the longer depolarization period, while K+ ions continue to exit the cell. After the plateau, Ca2+ channels close and more K+ channels open, further facilitating repolarization.