lihasrakud

Lihasrakud (Estonian for muscle cells) are the basic cellular units of muscle tissue. They are specialized for contraction and are responsible for producing force and movement. In vertebrates, three main categories of muscle tissue are recognized: skeletal muscle cells, cardiac muscle cells, and smooth muscle cells.

Skeletal muscle cells are long, cylindrical, multinucleated cells that form the voluntary muscles attached to bones. They contain organized contractile units called sarcomeres and can generate rapid, powerful contractions when activated by motor nerves.

Cardiac muscle cells are shorter, usually branched cells connected by intercalated discs. They form the heart muscle and contract rhythmically and involuntarily, coordinating through intrinsic pacemaker activity and electrical coupling.

Smooth muscle cells are spindle-shaped, non-striated cells found in the walls of hollow organs and blood vessels. They contract more slowly and autonomously, controlling the diameter of passages and the movement of contents through organs.

Structure and mechanism: Lihasrakud contain a plasma membrane (sarcolemma), cytoplasm (sarkoplasma), and numerous myofibrils arranged into sarcomeres, the basic contractile units. Contraction is driven by interactions between actin and myosin filaments, regulated by calcium ions and ATP and initiated by electrical or chemical signals.

Development and regeneration: Skeletal muscle has notable regenerative capacity due to satellite cells that can proliferate and fuse with damaged fibers. Cardiac muscle has limited regenerative ability, while smooth muscle can regenerate to a moderate extent.

Clinical relevance: Disorders of lihasrakud include muscular dystrophies and myopathies, which affect strength and movement. Aging, inactivity, and certain diseases can lead to muscle atrophy and functional decline.