Final answer:
During repolarization, voltage-gated sodium channels close and potassium channels facilitate the exit of K+ ions, moving the membrane potential back towards the resting state. This process is crucial for re-establishing the conditions needed for the next action potential. In cardiac contractile cells, repolarization includes a unique plateau phase for effective blood pumping.
Step-by-step explanation:
Following the depolarization phase, during which voltage-gated sodium channels open allowing sodium ions to rush into the cell, a significant change called repolarization occurs. This stage is characterized by the closing of the sodium channels and the continued high conductance of potassium channels. The resultant movement of potassium ions out of the cell helps to bring the membrane potential back towards its resting state. During repolarization, the membrane potential moves back toward the negative resting membrane potential, generally around -70 mV. Importantly, the sodium-potassium ATPase continues to function throughout, maintaining the ion gradients essential for the resting potential and readiness for another action potential, as long as conditions permit.In cardiac contractile cells, repolarization is crucial for the resting periods that allow these cells to pump blood effectively. Unlike regular nerve cells, these cardiac cells experience a plateau phase before repolarization, thereby ensuring longer refractory periods essential for their function. This mechanism prevents the immediate firing of another action potential, allowing the heart muscle to relax and refill with blood before the next contraction.