In healthy myofibers (fully differentiated muscle cells) nuclei are positioned around the cell periphery. ... Multi-nucleated muscle cells form by the iterative fusion of myoblasts (mononucleated muscle precursor cells) to the growing myotube.

What are Myofibrils made of?

Myofibrils are composed of overlapping thick and thin myofilaments organized into distinct, repeating units called sarcomeres. Z-discs (also called Z-lines; Z in Figures 5.1, 5.2), comprised largely of α-actinin, form the boundaries of sarcomeres and provide an attachment site for thin filaments.

Do muscle cells have a nucleus?

Skeletal muscle fibers are cylindrical, multinucleated, striated, and under voluntary control. Smooth muscle cells are spindle shaped, have a single, centrally located nucleus, and lack striations. ... Cardiac muscle has branching fibers, one nucleus per cell, striations, and intercalated disks.