What roles do satellite cells play in muscle growth and repair?

• A. They are mature muscle fibers that contract.
• B. They are cholesterol regulators in muscle membranes.
• C. They are immune cells that repair tissue.
• D. They are muscle stem cells that activate after injury, proliferate, and fuse with damaged fibers to repair or contribute to growth.

Answer: (D)

Satellite cells are muscle stem cells located just beneath the muscle fiber membrane. When a muscle is damaged or stimulated to grow, they exit quiescence, proliferate, and then fuse with damaged fibers (or with each other to form new fibers). This fusion donates new nuclei to existing fibers, boosting their capacity to synthesize proteins and thereby supporting repair and hypertrophy. They are not mature contractile fibers, not cholesterol regulators, and not immune cells; instead they serve as the resident pool of progenitor cells that drive muscle regeneration and growth.