musklene

Musklene, in Norwegian usage, refers to the muscles in general and is the definite plural form of muskel. In humans and many other animals, the muscular system is responsible for movement, posture, joint stabilization, and heat production through contraction and relaxation of muscle tissue.

The muscular system includes three main types of muscle tissue. Skeletal muscles attach to bones and are typically under voluntary control, enabling deliberate movement. Smooth muscles line the walls of hollow organs and blood vessels and operate involuntarily. Cardiac muscle makes up the heart and also contracts involuntarily. Skeletal muscles are organized into fibers bundled into fascicles, wrapped by connective tissue layers. Each muscle fiber contains myofibrils, which consist of repeating sarcomeres—the contractile units formed by actin and myosin filaments.

Contraction is driven by the sliding filament mechanism. When a motor neuron stimulates a muscle, calcium ions are released, causing cross-bridge cycling between actin and myosin that shortens the sarcomere. ATP provides the energy for this process. Muscles require a blood supply for oxygen and nutrients and nerves for activation, with specialized neuromuscular junctions coordinating signals.

Energy for muscle activity comes from aerobic metabolism and, for short bursts, anaerobic pathways and stored phosphocreatine. Training can induce hypertrophy, improve endurance, and alter fiber characteristics, while disuse leads to atrophy. Common clinical topics related to muscles include muscular dystrophies, myopathies, cramps, and injuries, as well as rehabilitation and physical therapy approaches that aim to restore strength and function.