The muscular system is composed of specialized cells called muscle fibers. Their predominant function is contractibility. Muscles, 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 muscular system in vertebrates consists of three different types of muscles: cardiac, skeletal and smooth.
Cardiac muscle is a striated muscle that makes up the heart. It is the only type of muscle consisting of branching fibers.
Skeletal muscle consists of voluntary muscles attached to the frame of the skeletal system enabling bodily movement.
Smooth muscle is the involuntary muscle that enables the movement of internal organs.
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. without muscles we would not be able to move.
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% of the heat produced in the body is the result of muscle contraction.
There are about 70,000 muscles in the human body.