Question

the area of a muscle fiber that stores calcium ions (ca²⁺) is called the:
a myofibril
b nucleus
c sarcoplasmic reticulum
d endomysium

Explanation:

• Myofibrils are the contractile elements of muscle fibers, composed of actin and myosin filaments.
• The nucleus contains the cell's genetic material.
• The sarcoplasmic reticulum is a specialized endoplasmic reticulum in muscle cells that stores calcium ions (\(Ca^{2+}\)). When a muscle is stimulated to contract, calcium is released from the sarcoplasmic reticulum.
• The endomysium is a connective - tissue sheath that surrounds individual muscle fibers.

Answer:

C. sarcoplasmic reticulum