S overview and classification of muscle

Muscle tissue is responsible for movement of the body and its parts and for changes in the size and shape of internal organs. This tissue is characterized by aggregates of specialized, elongated cells arranged in parallel array, whose primary role is contraction (Fig. 10.1).

Myofilament interaction is responsible for muscle cell contraction

Two types of myofilaments are associated with cell contraction:

• Thin filaments (6 to 8 nm in diameter, 1.0 /xm long), composed primarily of the protein actin. Each thin filament of fibrous actin (F-actin) is a polymer formed from globular actin molecules (G-actin).

• Thick filaments (-15 nm in diameter, 1.5 fxm long), composed of the protein myosin II. Each thick filament consists of 200 to 300 myosin II molecules. The long, rod-shaped tail portion of each molecule aggregates in a regular parallel but staggered array, while the head portions project out in a regular helical pattern.

The two types of myofilaments occupy the bulk of the cytoplasm, which in muscle cells is also called sarcoplasm [Gr. sarcos, flesh;plasma, thing]. Actin and myosin are also present in most other cell types (although in considerably smaller amounts), where they play a role in cellular activities such as cytokinesis, exocytosis, and cell migration. In contrast, muscle cells contain a large number of aligned contractile filaments that the cells use for the single purpose of producing mechanical work.

0 0

Post a comment