By Chandan Sekhon - Medicine Student @ Peterhouse, Cambridge
Skeletal muscle makes up every voluntary muscle in the body, however it can also have involuntary roles. For example, running, jumping and other voluntary movements are made possible by skeletal muscle contraction. The involuntary functions of skeletal muscle include those actions in reflex arcs, for example in response to sharp pain. This involuntary function of skeletal muscle plays a protective role to ensure the body does not become injured. Skeletal muscle is often attached to bones via tendons across joints which conduct these movements across the joints by moving bones closer together. Skeletal muscle can also have a stabilising role, for example the rotator cuff muscles in the shoulder stabilise the head of the humerus. Contraction results following the propagation of action potentials to neuromuscular junctions in muscle fibres.
Skeletal muscle is arranged in a series of long multinucleated cells called myocytes which lie parallel to each other in fascicles. The entire muscle is supported in a sheath of epimysium. Myofibrils comprise of multiple repeat contractile units called sarcomeres giving skeletal muscle a striated appearance, as shown below: