Structure of a Skeletal Muscle page 298

Skeletal muscles are composed of nervous, vascular, and various connective tissues, as well as skeletal muscle tissue.

1. Connective tissue coverings a. Fascia covers each skeletal muscle.

b. Other connective tissues surround cells and groups of cells within the muscle's structure.

c. Fascia is part of a complex network of connective tissue that extends throughout the body.

2. Skeletal muscle fibers a. Each skeletal muscle fiber is a single muscle cell, which is the unit of contraction.

b. Muscle fibers are cylindrical cells with many nuclei.

c. The cytoplasm contains mitochondria, sarcoplasmic reticulum, and myofibrils of actin and myosin.

d. The arrangement of the actin and myosin filaments causes striations. (I bands, Z lines, A bands, H zone and M line.)

e. Cross-bridges of myosin filaments form linkages with actin filaments. The reaction between actin and myosin filaments provides the basis for contraction.

f. When a fiber is at rest, troponin and tropomyosin molecules interfere with linkage formation. Calcium ions remove the inhibition.

g. Transverse tubules extend from the cell membrane into the cytoplasm and are associated with the cisternae of the sarcoplasmic reticulum.

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