Physiology of Muscle Contraction

The essential function of the skeletal muscle is contraction and relaxation in response to a command from a motor neuron. The muscle is very unique organ and is capable converting stored chemical energy into mechanical energy through metabolic processes. The skeletal muscles constitute from 40 to 45 percent of the body weight in an adult. There are 434 voluntary muscles in our body and about 250 million muscle fibers constitute these muscles. The muscle cells or sarcomeres are very complex in structure, metabolism and functions.

All voluntary muscle have innervation by motor neurons. The muscle fibers are composed of myofibrils within the sarcoplasm. The myofibrils appear to be the ultimate functional units of the muscle and have alternate light and dark bands. The contractile protein of the muscle is called actomycin (AM) and is composed of two components: (1) actin and (2) myosin. The actomycin is considered to be the structural protein of the resting myofibrils and contain many enzymes necessary the muscle metabolism. The organic phosphate compound called adenosine triphosphate (ATP) is an energy rich compound and is attached to actomycin of myofibrils. The neuronal spark of the motor neurons fires the ATP-AM linkage and breaks it. The ATP is liberated and its breakdown provides energy for the muscle contraction. During contraction of the muscle, the actin threads could be shortened to 40% of its original relaxed phase size. Physiology of muscle contraction involves a series of molecular interactions and rearrangements within the system composed of actin, myosin, and adenosine triphosphate.