Structure and Function of Actin and Myosin.
Skeletal muscle comprises the largest single organ of the body. It is highly compartmentalized, and we often think of each compartment as a separate entity (such as the bicep muscle). Each of our individual muscles is composed of single cells or fibers embedded in a matrix of collagen. At either end of the muscle belly, this matrix becomes a tendon that attaches the muscle to the appropriate bone.
"Skeletal muscle is the most abundant tissue in the human body and also on of the most adaptable. Vigorous training with weights can double or triple a muscles size, whereas disuse, as in space travel, can shrink it by twenty percent in two weeks- (1).
Muscle cells contain most of the structures common to all cells. Each cell is enclosed by a cell membrane or plasmalemma; they contain mitochondria for the oxidative metabolism of nutrients; and all the machinery necessary for protein synthesis. Skeletal muscle fibers are multinucleated and can be as much as two centimeters long.
The principal force generating components are actin and myosin molecules. These myofilaments are arranged in interdigitating matrices capable of sliding across each other. To produce force, cross bridges from the myosin filaments associate with the actin filament, and then rotate slightly to pull the filaments across each other. "Muscle fibers, though, are just the building blocks for whole muscles- (6). .
"In chemical composition the fibers may be said, in round numbers, to consist of seventy five percent of water, about twenty percent of proteids, two percent of fat, one percent of nitrogenous extractives and carbohydrates, and two percent of salts, which are mainly potassium phosphate and carbonate-(3).
The Actin and Myosin System.
The ability of eucaryotic cells to adopt a variety of shapes and to carry out coordinated and direct movements depends on the cytoskeleton, a complex network of protein filaments that extends throughout the cytoplasm.