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The Major Components of the Muscular System

The human body is composed of several systems, among which are the endocrine, nervous, lymphatic, and immune, and muscular. The muscular system not only allows for movement but also the circulation of the blood and the function of organs. Without this system, life would not be possible. The body is composed of several hundred individual muscles, but they may all be understood and categorized into three types or components: skeletal, cardiac, and smooth.

  1. Skeletal Muscle

    • Skeletal muscles are directly or indirectly attached to the bones of the body. Using voluntary contraction, most of these muscles pull on tendons and move the bones of the skeleton. The resulting motions can range from simple movements like extending the arm to more complex actions such as playing the violin. Additionally, skeletal muscles maintain posture and body position through coordinated tension. (Otherwise, you would fall over in a heap.) The muscles found at the abdominal wall and pelvic cavity support the weight of the internal organs, and protects them from injury. The skeletal muscles at the openings of the digestive and urinary tracts provide voluntary control over swallowing, urination, and defecation. Finally, the actions of all of these muscles use energy, the expenditure of which keeps body temperature in a range required for normal functioning.

    Cardiac Muscle

    • The cardiac muscles---the muscles of the heart---allow blood to pump through the circulatory system. Unlike skeletal muscles, they are not activated voluntarily, but controlled by the lower section of the brain, known as the medulla oblongata. Additionally, the muscles are composed of interlocking branches, creating strong junctions that enable the heart to contract forcefully without ripping the fibers apart. This interconnectedness allows the muscle fibers to contract in synchronous waves that sweep from the atria down through the ventricles to pump blood. Anything that prevents this wave (such as muscle damage from a heart attack) results in a lethal condition known as fibrillation.

    Smooth Muscle

    • Smooth muscle is distinct from its cardiac and skeletal counterparts in that it possesses no visible striations---elongated fibers marked by transverse dark and light bands. However, smooth muscle does possess thick and thin filaments that slide against each other to produce involuntary contractions. Smooth muscles assume many of the "housekeeping" functions of the body, like pushing food through your intestines, urine through your bladder, and, in females, uterine muscles that are employed during childbirth. Notably, a smooth sphincter muscle in your eye controls the size of its pupil.

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