The Organ System in Animals Responsible for Movement & Locomotion

Organization

• Skeletal muscle covers almost the entire body. For adult humans, it composes about 40 percent of the overall body weight. Major muscles cover the feet, legs, thighs, hips, belly, chest, back, shoulders, arms, hands, neck and head of animals. These are the most visible muscles, noticeable when animals flex their arms and legs in movement. When people work out, they are exercising skeletal muscle.

Movement

• Skeletal muscles derive their name from the fact that they cause the skeleton to move and attach to it with tendons. They work in pairs to move bones at joints. One muscle (tensor) contracts to pull, while another muscle (extensor) relaxes. This setup enables complex operations such as walking or grasping. Of the three types of muscles, skeletal muscles are the only voluntary muscles, meaning they are used consciously. The nervous system directs their movement.

Cell Structure

• Skeletal muscle cells, called fibers, are shaped like cylinders forming large strands. The fragile interiors of the cells are covered with thick protective layers that enable them to exert large amounts of force. Muscle fibers arrange in large clusters surrounded and protected by layers called the perimysium and epimysium. Like other cells, they are energized by blood vessels. Skeletal muscles also connect to the nervous system via nerves.

Types of Skeletal Muscles

• Skeletal muscles come in a variety of shapes and sizes. In some cases, the muscle strands form striations that run parallel to the length of the muscle. In others, the striations run obliquely. Some muscles have broad shapes, such as the central back muscles, while others are long and thin, such as on the forearm. Tiny muscles exist in the human ear called the stapedium, while large muscles move parts of the body such as the legs.