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Troponin

Tropomyosin Myosin molecule

Actin molecule

Figure

Thick filaments are composed of the protein myosin, and thin filaments are composed of actin. Myosin molecules have cross-bridges that extend toward nearby actin filaments.

with the sarcolemma and thus contain extracellular fluid. Each transverse tubule lies between two enlarged portions of the sarcoplasmic reticulum called cisternae, and these three structures form a triad near the region where the actin and myosin filaments overlap (fig. 9.7).

Although muscle fibers and the connective tissues associated with them are flexible, they can tear if overstretched. This type of injury is common in athletes and is called a muscle strain. The seriousness of the injury depends on the degree of damage the tissues sustain. In a mild strain, only a few muscle fibers are injured, the fascia remains intact, and little function is lost. In a severe strain, many muscle fibers as well as fascia tear, and muscle function may be lost completely. A severe strain is very painful and is accompanied by discoloration and swelling of tissues due to ruptured blood vessels. Surgery may be required to reconnect the separated tissues.

Describe how connective tissue is associated with a skeletal muscle.

Describe the general structure of a skeletal muscle fiber.

Explain why skeletal muscle fibers appear striated.

Explain the physical relationship between the sarcoplasmic reticulum and the transverse tubules.

Ske Con

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