Biological Systems MCAT Practice Exam

What is the primary function of voltage-gated Ca2+ channels in cardiac muscle?

1. Trigger relaxation of muscle fibers

2. Initiate action potential propagation

3. Prevent muscle fatigue

4. Maintain the resting potential

The correct answer is: Initiate action potential propagation

The primary function of voltage-gated Ca2+ channels in cardiac muscle is to initiate action potential propagation. In cardiac muscle cells, the action potential leading to muscle contraction begins when these channels open in response to depolarization caused by an influx of sodium ions. Once the membrane potential reaches a certain threshold, these calcium channels open, allowing Ca2+ ions to flow into the cell. The influx of calcium not only contributes to the depolarization and propagation of the action potential but also initiates the process of muscle contraction by triggering calcium release from the sarcoplasmic reticulum through a mechanism known as calcium-induced calcium release. This process is vital for the synchronous contraction of cardiac muscle cells, enabling the heart to function effectively as a pump. Other options, while related to muscle function in different contexts, do not accurately describe the primary role of voltage-gated Ca2+ channels in the cardiac muscle. Triggering relaxation of muscle fibers is primarily controlled by calcium re-uptake mechanisms, preventing muscle fatigue is more about metabolic processes and energy supply, and maintaining the resting potential involves other ionic channels and pumps rather than voltage-gated calcium channels. Thus, the role of these channels is foundational in propagating the action potential that is crucial for initiating