Final answer:
The plateau phase in cardiac muscle is attributed to the slow influx of calcium ions, but it lasts approximately 175 ms, not 250 ms, making the statement false.
Step-by-step explanation:
The plateau phase in cardiac muscle is indeed due to the slow influx of calcium ions (Ca²⁺) through the slow calcium channels, which is critical for maintaining the membrane in a state of depolarization for an extended period. This plateau phase is responsible for the cardiac muscle's ability to ensure a proper contraction and for establishing an absolute refractory period, during which the muscle cannot be re-excited, allowing the heart to function properly. The action potential of cardiac muscle cells involves a rapid depolarization, followed by a plateau phase where the membrane potential declines relatively slowly due to Ca²⁺ entry and decreased K⁺ exit, resulting in an extended contraction period compared to skeletal muscle, and finally, repolarization. The plateau phase typically lasts approximately 175 ms, which is less than the 250 msec mentioned in the question, making the statement False.