Final answer:
The period after repolarization of a myocardial cell with a negative interior and a positive exterior is known as the refractory period, which includes hyperpolarization due to prolonged opening of K+ channels. This phase is critical for restoring the resting membrane potential of the cardiac cells and preparing for the next heartbeat.
Step-by-step explanation:
The period of time following repolarization of a myocardial cell when the outside is positive and the inside is negative is known as the resting phase. However, repolarization often overshoots the resting membrane potential causing a period known as hyperpolarization. This is due to K+ channels remaining open longer than necessary, which allows for an excess outward flow of K+, resulting in a membrane potential that is temporarily even more negative than the usual resting potential. This hyperpolarization contributes to the refractory period during which myocardial cells cannot generate another action potential, effectively preventing premature or additional depolarizations and providing time for the heart chambers to refill with blood. The refractory period is crucial to the function of cardiac contractile cells as this time allows the sodium-potassium ATPase to transport ions and restore the ion concentration gradients, setting the stage for future action potentials to trigger subsequent heartbeats.