Functions of the Muscular System
The muscular system is composed of specialized cells called muscle fibers. Their
predominant function is contractibility. Muscles, where attached to bones or internal
organs and blood vessels, are responsible for movement. Nearly all movement in the
body is the result of muscle contraction. Exceptions to this are the action of cilia, the
flagellum on sperm cells, and amoeboid movement of some white blood cells.
The integrated action of joints, bones, and skeletal muscles produces obvious movements
such as walking and running. Skeletal muscles also produce more subtle movements that
result in various facial expressions, eye movements, and respiration.
In addition to movement, muscle contraction also fulfills some other important functions
in the body, such as posture, joint stability, and heat production. Posture, such as sitting
and standing, is maintained as a result of muscle contraction. The skeletal muscles are
continually making fine adjustments that hold the body in stationary positions. The
tendons of many muscles extend over joints and in this way contribute to joint stability.
This is particularly evident in the knee and shoulder joints, where muscle tendons are a
major factor in stabilizing the joint. Heat production, to maintain body temperature, is an
important by-product of muscle metabolism. Nearly 85 percent of the heat produced in
the body is the result of muscle contraction.
Structure of Skeletal Muscle
A whole skeletal muscle is considered an organ of the muscular system. Each organ or
muscle consists of skeletal muscle tissue, connective tissue, nerve tissue, and blood or
Skeletal muscles vary considerably in size, shape, and arrangement of fibers. They range
from extremely tiny strands such as the stapedium muscle of the middle ear to large
masses such as the muscles of the thigh. Some skeletal muscles are broad in shape and
some narrow. In some muscles the fibers are parallel to the long axis of the muscle, in
some they converge to a narrow attachment, and in some they are oblique.