lihased

Lihased, the Estonian term for muscles, are tissues that generate force and enable movement, posture, and various bodily functions. In vertebrates they are classified into skeletal muscles, which attach to bones and are under voluntary control; smooth muscles, found in walls of hollow organs and vessels and acting involuntarily; and cardiac muscle, which forms the heart and contracts rhythmically without conscious input. They vary in size and distribution.

Skeletal muscles are striated and consist of fibers grouped into fascicles, surrounded by connective tissue. Each fiber contains myofibrils made of sarcomeres—the contractile units built from actin and myosin. Contraction occurs by the sliding filament mechanism, driven by calcium released from the sarcoplasmic reticulum and powered by ATP.

Nerves control muscles via motor neurons at neuromuscular junctions, initiating contraction. Energy sources include immediate ATP and phosphocreatine, anaerobic glycolysis, and aerobic respiration, depending on intensity and duration. Blood supply delivers oxygen and nutrients and removes waste products.

Functions include voluntary movement, posture maintenance, joint stabilization, and heat production. Muscles adapt to training with growth (hypertrophy) and metabolic changes, while disuse leads to atrophy. Aging, injury, and disease can impair strength and function.