College of Massage Therapists of British Columbia (CMTBC) Practice Exam

What is the role of the sarcoplasmic reticulum in muscle cells?

1. Regulates intracellular calcium levels

2. Stores glycogen for energy

3. Facilitates protein synthesis

4. Stimulates muscle contraction

The correct answer is: Regulates intracellular calcium levels

The sarcoplasmic reticulum plays a crucial role in muscle cells by regulating intracellular calcium levels. This specialized organelle acts as a reservoir for calcium ions, which are essential for muscle contraction. When a muscle is stimulated to contract, calcium is released from the sarcoplasmic reticulum into the cytoplasm of the muscle cell. The increase in calcium concentration triggers the interaction between actin and myosin filaments, leading to muscle contraction. In the absence of adequate calcium levels, muscle contraction cannot occur effectively, highlighting the importance of the sarcoplasmic reticulum in muscle physiology. Its ability to uptake and release calcium ions is a key part of the muscle contraction cycle, allowing for proper muscle function and coordination. Other choices, while related to muscle cell function, do not accurately reflect the primary role of the sarcoplasmic reticulum. For example, glycogen storage is primarily managed by other organelles, such as granules within the cytoplasm, rather than the sarcoplasmic reticulum. Moreover, protein synthesis occurs mainly in the ribosomes and the endoplasmic reticulum, while stimulation of muscle contraction is directly related to the release of calcium rather than a function of the sarcoplasmic reticulum itself.