Skeletal muscle fibre. Coloured transmission electron micrograph (TEM) of a longitudinal section through a skeletal (or striated) muscle fibre. The banding pattern on the fibre arises from the regular arrangement of its microscopic fibres, or myofibrils. The fibre is surrounded by a membrane (sarcolemma, pink line bordering brown region, upper left to top right). Beyond this lies a sheath of connective tissue (endomysium, beige). Many mitochondria (small black dots), which produce the energy for contraction of the fibre, are also seen. Skeletal muscle is used to move the long bones. It is under voluntary control.