Britannica Sources used in this answer

Why do skeletal muscle fibers contain many nuclei?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Diagram showing the structure of human striated or skeletal muscle, with labeled cross-sections from whole muscle to fascicle, muscle fiber, myofibril, and sarcomere, highlighting actin and myosin filaments. — muscle The structure of striated, or skeletal, muscle. Striated muscle tissue, such as the tissue of the human biceps muscle, consists of long fine fibers, each of which is in effect a bundle of finer myofibrils. Within each myofibril are filaments of the proteins myosin and actin; these filaments slide past one another as the muscle contracts and expands. On each myofibril, regularly occurring dark bands, called Z lines, can be seen where actin and myosin filaments overlap. The region between two Z lines is called a sarcomere; sarcomeres can be considered the primary structural and functional unit of muscle tissue.

Skeletal muscle fibers contain many nuclei because they are formed through the fusion of individual, singly nucleated cells during embryonic development. Once these cells fuse to create the long, multinucleated muscle fibers, they do not divide again.1