Final answer:
The long cardiac action potential, lasting 200-300 msec, allows the heart to fill with blood and ensures effective pumping by providing a complete and efficient contraction before the next heartbeat.
Step-by-step explanation:
The long duration of the cardiac action potential, which ranges from 200-300 milliseconds, primarily serves to allow an opportunity for the heart to fill with blood, ensuring effective pumping during each cardiac cycle. This extended period is known as the plateau phase and is marked by the influx of calcium ions through voltage-gated calcium channels. The sustained depolarization coupled with the influx of calcium ions leads to a prolonged contraction compared to skeletal muscle, which is essential for maintaining heart function and preventing premature contractions that would be incompatible with life.
The longer refractory period of cardiac muscle cells, contributed to by the plateau phase of the action potential, prevents the myocardium from being stimulated again too quickly, thereby guaranteeing that each contraction is complete before the next one begins. This orchestration ensures the efficient circulation of blood throughout the body and maintains cardiac health.