Skeletal muscle tissue is composed of groups of muscle fibers in an orderly arrangement. A small muscle may be only a few bundles of fibers, while the major muscles in the body, such as the gluteus maximus that forms the bulk of the buttock, are made up of hundreds of bundles. Movement of the skeletal muscle is under the control of the brain. Each muscle fiber has a nerve ending that receives impulses from the brain and then stimulates the muscle, resulting in the filaments of myosin sliding over the actin filaments in about the same way as an extendable ladder moves when it is closed. This movement causes the muscle to shorten in length.