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Skeletal Muscles
The muscles that are attached to the skeleton and are associated with the movement of bones are called skeletal muscles. The skeletal muscles are consciously controlled and therefore, are called voluntary muscles. Skeletal muscles are also called striped or striated muscles because they show alternate light and dark bands, e.g., triceps and biceps. Generally, each end of the entire muscle is attached to bone by a bundle of collagen, non-elastic ibres, known as tendons.
Skeletal Muscle Fibre : Each muscle consists of muscle bundles, which are further composed of muscle ibres or cells. Each muscle ibre is a long cylindrical cell with multiple oval nuclei arranged just beneath its sarcolemma. Skeletal muscle ibres are huge cells. Their diameter is 10 - 100 mm.Sarcoplasm of the muscle ibre is similar to the cytoplasm of other cells but it contains usually large amount of stored glycogen and unique oxygen bonding protein myoglobin, a red pigment that stores oxygen.
When viewed in high magniication, each muscle ibre is seen to contain a large number of myoibrils 1-2 mm in diameter that run in parallel fashion and extend entire length of the cell. Bundles of these fibrils are enclosed by the muscle cell membrane or sarcolemma. The myofibrils consist of smaller contractile units called sarcomere. In each sarcomere a series of dark and light band are evident along the length of each myoibril. Each dark band is called A band, because it is anisotropic, i.e it can polarize visible light. The light band called I band is isotropic or non-polarizing. It gives the cell as a whole its striped appearance. Each A band has a lighter stripe in its mid section called H - zone