Question

During what part of the action potential will calcium ions enter the contractile cell?

A. Rapid depolarization phase
B. Plateau phase
C. Initial repolarization phase
D. Repolarization phase

Answer 1

Calcium ions enter the contractile cell during the plateau phase of the action potential, which follows rapid depolarization and is characterized by the opening of slow calcium channels.

Step-by-step explanation:

During the action potential of a cardiac contractile cell, calcium ions (Ca²⁺) enter the cell during the plateau phase. This phase follows the rapid depolarization and is characterized by the opening of slow Ca²⁺ channels, allowing these ions to enter the cell. This influx of calcium ions contributes to the prolonged plateau phase, which is significant because it enables cardiac muscle to function properly by prolonging the absolute refractory period and facilitating contraction.