CVS Practice Test

What is the function of terminal cisternae in muscle contraction?

1. They release calcium ions into the cytoplasm

2. They help in action potential propagation

3. They act as a storage site for ATP

4. They facilitate muscle fiber relaxation

The correct answer is: They release calcium ions into the cytoplasm

The terminal cisternae play a critical role in muscle contraction by releasing calcium ions into the cytoplasm. This release of calcium is essential because it triggers the interaction between the actin and myosin filaments, facilitating the contraction of the muscle fibers. The terminal cisternae are specialized areas of the sarcoplasmic reticulum that are closely associated with the transverse tubules. When an action potential travels along the muscle fiber and reaches the transverse tubules, it stimulates the terminal cisternae to release calcium ions. This influx of calcium allows for the binding of calcium to troponin, which initiates the process for muscle contraction. The correct functioning of terminal cisternae, therefore, is fundamental to the entire mechanism of muscle contraction, underscoring their importance in the physiology of muscles. The other options address functions that are not directly related to the primary role of terminal cisternae during muscle contraction. While action potential propagation occurs throughout the muscle fiber, it is primarily the terminal cisternae's release of calcium that directly initiates muscle shortening. ATP storage is managed by different cellular structures, as ATP is produced and utilized in a separate metabolic pathway. Lastly, muscle fiber relaxation requires a decrease in calcium levels, not a function