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There are several different components of the muscular system. The muscles within the muscular system contribute to proper organ function, help circulate blood, and allow for movement. The major components of this system include cardiac muscle, smooth muscle and skeletal muscle. Both cardiac and smooth muscles are activated involuntarily, while skeletal muscles are activated voluntarily. Contracting skeletal muscles pulls tendons, causes bones to move, and creates motion.
The majority of the components of the muscular system are skeletal muscles. These muscles serve several major functions and attach either directly or indirectly to the bones of the skeletal system. They are essential to most basic movements such as extending an arm or a leg. Complex activities such as running and swimming require the use of many of the body's skeletal muscles. These muscles are designed to produce skeletal movement, maintain body position and posture, support soft tissue, guard exits and entrances into and out of the body, and help maintain body temperature.
Tension within skeletal muscles allows people to stand up straight and maintain posture without falling to the ground. Certain skeletal muscles support and shield vital organs from injury. Urinary and digestive tract opening are also usually lined with skeletal muscle, providing voluntary control over urination, defecation and swallowing. At work, skeletal muscles release heat, which can help maintain a normal internal body temperature. Skeletal muscle cells contain multiple nuclei per cell and are also referred to as muscle fibers.
Cardiac muscles are more components of the muscular system. Heart muscles, which are a type of muscle only found in the heart, facilitate blood flow through the entire body. Unlike skeletal muscles, these muscles are activated involuntarily. The design of these muscles allows the heart to contract in a forceful manner without creating tears in the muscles themselves.
Smooth muscle differs from skeletal muscle and other components of the muscular system in that it offers no visible striations, which are are elongated fibers. Cells from smooth muscles are relatively small, shaped like an oval or spindle, and contain only one nucleus per cell. This type of muscle possesses thin and thick filaments that are designed to produce involuntary contractions by sliding in a back and forth motion against each other. Pushing food through the intestines and urine through the bladder are functions of smooth muscles. Small smooth muscles are also contained within the eyes to control the size of the pupil.