Question

what is the specialized smooth endoplasmic reticulum in muscle fibers that stores, releases, and retrieves calcium ions (ca++)?
a.) sarcolemma
b.) sarcoplasmic reticulum (sr)
c.) myoblast
d.) sarcoplasm

Explanation:

• Sarcolemma: It is the cell membrane of a muscle fiber, not related to calcium ion storage.
• Sarcoplasmic reticulum (SR): This is the specialized smooth endoplasmic reticulum in muscle fibers that stores, releases, and retrieves calcium ions (\(Ca^{++}\)).
• Myoblast: These are embryonic cells that develop into muscle cells, not involved in calcium ion handling as described.
• Sarcoplasm: It is the cytoplasm of a muscle fiber, not the structure for calcium ion storage.

Answer:

B. Sarcoplasmic reticulum (SR)