A voluntary muscle, often called a skeletal muscle, is one of three types of muscle in the body. Most voluntary muscles are used to move bones, though some, such as the muscles in the face, are used to create movements below the skin. Unlike cardiac or smooth muscle, these muscles can be controlled by the conscious mind.
As a part of the musculoskeletal system, each voluntary muscle is used to help a person move around. Most are connected to bones by connective tissue called tendons. The muscle is attached to a bone at a location called its origin. It then runs along the length of the entire bone and is attached to a bone on the other side of the joint at the insertion. The muscle moves the bone here at the insertion,
Muscles contract when a part of the body is moved. It is not possible for a voluntary muscle to extend on its own, so muscles work in opposing pairs. In each opposing pair, the muscle that contracts is known as the extensor, while the muscle that expands is known as the flexor. Switching the roles of extensor and flexor in an opposing pair of muscles causes the opposite movement to happen. For example, contracting the bicep in the upper arm causes the elbow to bend, while contracting the triceps, on the opposite side of the upper arm, causes the elbow to straighten out again.
There are some muscles that are not used to move bones. The muscles in the face are attached to the underside of the skin, which allows them to create a variety of different facial expressions. A slight movement by one or more of the 43 facial muscles results in one of the many different expressions that human beings are able to make. The tongue is also a voluntary muscle and is attached to the body at only one end. The wide range of movement in the tongue is possible because it is made up of a group of muscles that work closely together.
Each muscle is made up of muscle cells. These cells are fused together into fibers that run the entire length of the muscle. Two types of fibers, a thick fiber, known as myosin and a thin fiber, known as actin, alternate within a voluntary muscle. These alternating bands of fibers give the muscles a striped appearance, which is why they are sometimes known as striped or striated muscles.
