The human muscular system anatomy comprises specialized cells known as muscle fibers. Their main function is contractility. Movement is controlled by muscles attached to bones or internal organs and blood vessels. Muscle contraction causes nearly all activity in the body. The action of cilia, the flagellum on sperm cells, and the amoeboid movement of some white blood cells are exceptions to this rule. Walking and running are obvious movements produced by the coordinated action of joints, bones, and skeletal muscles. As shown in this human muscular system anatomy, skeletal muscles also produce more subtle movements that result in various facial expressions, eye movements, and respiration.
