myocytter

Myocytter, or myocytes, are the muscle cells responsible for contraction in vertebrates. They include skeletal muscle fibers, cardiac myocytes, and smooth muscle cells. Skeletal muscle fibers are long, multinucleated cells formed by fusion of myoblasts and organized into repeating units called sarcomeres. Cardiac myocytes are smaller, branched cells with a single nucleus connected by intercalated discs that coordinate contraction. Smooth muscle cells are spindle-shaped, usually with a single nucleus, and occur in walls of hollow organs and blood vessels.

All myocytes share the general aim of converting chemical energy into mechanical work. The contractile apparatus consists of myofibrils arranged in sarcomeres, containing actin and myosin filaments that slide past one another during contraction (the sliding filament theory). Excitation-contraction coupling in skeletal and cardiac muscle relies on calcium ions released from the sarcoplasmic reticulum and, in skeletal muscle, propagated by transverse tubules. Energy is supplied primarily by mitochondria, with varying reliance on oxidative versus glycolytic metabolism depending on fiber type.

Development and regeneration involve myogenesis, where undifferentiated myoblasts fuse to form mature fibers. Satellite cells on muscle fibers contribute to growth and repair. Aging and disuse can lead to atrophy, while training can induce hypertrophy and shifts in metabolic profiles. Fiber-type composition varies by muscle and species, with slow-twitch (Type I) fibers being more oxidative and fatigue-resistant, and fast-twitch (Type II) fibers more glycolytic and powerful but fatigue-prone.

Pathologies affecting myocytes include muscular dystrophies, inflammatory myopathies, and smooth muscle dysfunctions in vascular or gastrointestinal systems. Myocytter are essential for movement, circulation, and organ function, making them central to physiology and medicine.