What occurs during the second phase of the myocardial action potential?

The second phase of the myocardial action potential is characterized by a slow influx of calcium ions into the cardiac muscle cells. This phase is often referred to as the plateau phase and is crucial for maintaining the depolarized state of the cell membrane. During this period, calcium channels open and allow calcium to enter the cells, which not only sustains the contraction of the heart muscle but also plays a vital role in the excitation-contraction coupling process that leads to muscle contraction.

The influx of calcium during this plateau phase prevents further rapid depolarization and allows the heart muscle to contract effectively. This extended phase is essential for proper cardiac function, as it provides sufficient time for the heart to pump blood before the cells return to their resting state through repolarization.

Understanding the role of calcium during this phase is vital in recognizing the significance of calcium channel blockers in clinical practice, as they can influence heart rate and contractility. The plateau phase stands out as a unique feature of myocardial action potentials compared to those in other tissues, where rapid repolarization occurs without a prolonged plateau.