Human Anatomy and Physiology - N. I. Fedyukovich 2003

The Muscular System

The Muscular System is the active component of the human Musculoskeletal System, while bones and ligaments constitute its passive part. Together, the muscular system and bones enable changes in body position in space, facilitate respiratory and swallowing movements, and shape facial expressions. Skeletal Muscles (Fig. 53) participate in forming the oral, thoracic, abdominal, and pelvic cavities; they comprise the walls of hollow Organs (Pharynx, Larynx, etc.); they alter THE POSITION OF the Eyeball within the Orbit; and they act upon the auditory ossicles in the tympanic cavity of the Middle ear. Muscular activity not only enables movement but also influences Blood Circulation, as well as the development and shape of bones. Regular muscular exertion promotes the growth of Muscle mass by increasing the structures that compose the muscles.

Class="center">

Fig. 53. Diagram of a Skeletal Muscle:

A — muscle fibers attached to tendons; B — an individual fiber consisting of myofibrils; C — an individual myofibril: alternating light Actin I-bands and dark Myosin A-bands; presence of the H-zone and M-line; D — cross-bridges between thick myosin and thin actin filaments

Skeletal muscles in newborns and children account for about 20—25 % of body weight, whereas in adults they make up to 40 %, and in elderly and aged people — up to 25—30 %. More than half of all muscles are located in the HEAD and trunk region, and 20 % are in the upper limbs. There are about 400 muscles in The Human Body, which consist of Striated Muscle tissue and are under voluntary control.