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Skeletal striated muscle tissue


Skeletal striated muscle tissue constitutes most of the vertebrate body musculature, forming what is popularly called meat.

This musculature completely covers the skeleton and is attached to the bones, hence it is called skeletal. This type of fabric features voluntary contraction (which depends on the will of the individual).

A skeletal muscle is a bundle of long fibers. Each is a cell with many nuclei called multinucleated myocytes. A muscle fiber can measure several inches long by 50 mm thick.

The striated muscle cell has, in its cytoplasm, bundles of very thin contractile fibers, the myofibrils, arranged longitudinally. Each myofibril corresponds to a set of two main types of proteins: the myosin, thick, and the actins, thin. These proteins are organized in such a way that they originate transverse bands, light and dark, characteristic of striated muscle cells, both skeletal and cardiac.

The filaments of myosin form dark bands called anisotropic (band A), and those of actin, clear bands, called isotropic (band I).

In the center of each band I a darker line appears, called Z line. The interval between two consecutive Z lines constitutes a myometer or sarcomere and corresponds to the contractile unit of the muscle cell.

At the center of each band A is a lighter band called band H, clearly visible in the relaxed muscle cells and disappearing as the muscle contraction occurs.

In muscle contraction, the myofilaments do not shrink, but the sarcomeres become shorter and the entire muscle cell contracts.

Sarcomer shortening occurs as a result of the slippage of thin myofilaments over the thick ones, with greater overlap between them: band I decreases in size, as actin filaments slide over those of myosin, penetrate band A and reduce bandwidth. H.

The plasma membrane of the skeletal striated muscle cell is often called sarcolemma (Greek, sarcos, meat).