Skeletal muscle. Coloured transmission electron micrograph (TEM) of a cross section through human skeletal (striated) muscle. Blocks of muscle (lighter orange) are surrounded by connective tissue. Filaments of the proteins actin and myosin (tiny dots) form the muscle myofibrils, which are enclosed by sarcoplasmic reticulum. The actin and myosin filaments can slide over one another, allowing the muscle to contract. Mitochondria (darker orange ovals) provide the large amounts of energy required by skeletal muscle. Skeletal muscle is under the conscious control of the brain.