The primary role of the muscular system is to make other body organs move through the use of muscles. The muscular system also plays an important role in digestion, heart contraction and blood flow, organ protection, heat production, and maintenance of the body’s shape. Muscles have been assigned with Latin names in order to describe their shape, location, action, and size. For instance, deltoid means triangular muscle, abdominis means abdominal muscle, flexor means flexion muscle, and minimus means smallest muscle.
The contraction of cells that make up the muscles is responsible for the production of movement. Most muscles accomplish their function in pairs, each muscle with an action that opposes the action of another muscle. This means that the contraction of one muscle results in the relaxation of another muscle. In bending the knee, for instance, the hamstring muscle contracts as the quadriceps relaxes. When the knee is straightened, the quadriceps contracts as the hamstring relaxes.
Three types of muscles – skeletal, cardiac, and smooth muscles – make up the muscular system. The role of more than 640 skeletal muscles is to produce voluntary bone movement and, together with bones, to give the general shape of the body. Skeletal muscles, which constitute 40% of the weight of the body, are also known as striated muscles because of the stripes or striations that mark the skeletal muscle fibers. Bones are attached to the origin and insertion of skeletal muscles by means of tendons. Origin is the end of the skeletal muscle that has little or no movement, while insertion is the end that moves.
Cardiac muscles produce involuntary movement in the heart. This means cardiac muscles contract automatically even without any stimulus from the nervous system. Moreover, cardiac muscles continuously contract throughout a person’s lifetime. The striations in cardiac muscle fibers are not as clear as those in skeletal muscle fibers. Cardiac muscle contractions pump blood to all parts of the body.
Involuntary contractions of smooth muscles enable food to pass along the digestive tract during digestion. Therefore, smooth muscles can be found lining the esophagus, stomach, and intestines, although they are also present in blood vessels and the urinary bladder. Unlike the skeletal and cardiac muscles, striations cannot be found in smooth muscles. The contraction of smooth muscles is much slower than that of skeletal muscles.
The muscular system and skeletal system work together to produce body movements; one will not be able to do its job without the other. Bones are responsible for the movement of the body into various positions, but they cannot move by themselves. Only muscles can move bones through contractions.