Skeletilihaseid

Skeletilihaseid are muscles attached to the skeleton that enable voluntary movement, stabilize joints, and help maintain posture. They are the largest group of muscles in the body and are characterized by their striated appearance under a microscope, due to the organized arrangement of contractile proteins.

Anatomically, skeletal muscles consist of muscle fibers organized into fascicles, surrounded by connective tissue layers called endomysium, perimysium, and epimysium. Each muscle fiber is a long, multinucleated cell containing myofibrils, which in turn are made of repeating sarcomeres—the functional units of contraction. The sarcomeres contain actin (thin) and myosin (thick) filaments, whose interactions produce muscle shortening through the sliding filament mechanism.

Contraction is initiated by the nervous system. Motor neurons stimulate the neuromuscular junction, releasing acetylcholine and triggering an action potential that travels along the muscle fiber. Calcium is released from the sarcoplasmic reticulum, enabling cross-bridge cycling between actin and myosin and ATP-driven contraction. Energy for sustained activity comes from aerobic respiration, anaerobic glycolysis, and phosphocreatine, with fiber metabolism influencing fatigue resistance.

Skeletal muscle fibers are broadly classified by their metabolic and contractile properties into Type I (slow-twitch, oxidative), Type IIa (fast-oxidative), and Type IIx/IIb (fast-glycolytic). These distributions vary with training and genetics, contributing to differences in endurance and strength. Regeneration relies on satellite cells and, in response to training, muscles can undergo hypertrophy. Clinically, skeletal muscles are involved in conditions such as strains, myopathies, and muscular dystrophies, and they play a central role in thermogenesis and glucose metabolism.