Voluntary muscles are under the animal's conscious control e.g. The skeletal muscles that move the bones. The ends of skeletal muscle are attached to bones by means of tough inelastic tissue called tendons. When the muscle contacts it becomes shorter and thicker, and pulls the bones together via the inelastic tendon. The end of a muscle which is attached to an immovable bone is said to be the origin of the muscle. The opposite end which is attached to a movable bone (i.e. Bone that moves when the muscle contacts) is called insertion of the muscle. A skeletal muscle is composed of numerous cells known as muscle fibres. When examined under the microscope each skeletal muscle fiber appears as a long, roughly cylindrical thread with many nuclei embedded in its cytoplasm (called sarcoplasm). The fiber contains numerous transverse light and dark bands forming cross striations or stripes. Therefore skeletal muscle is also called striated or striped muscle. Each fiber is enclosed by a thin membrane, the sacrolemma. All the fibers in a single muscle are held together by tough connective tissue which emerge at the ends of the muscle as tendons. A skeletal muscle is capable of quick contractions but is easily fatigued.
