Muscle fibres. Computer-enhanced confocal light micrograph of skeletal (striated) muscle fibres. Skeletal muscle is under the conscious control of the brain. The fibres have dark bands running across them. Each fibre comprises several parallel strands (myofibrils) of the contractile proteins actin and myosin. These are arranged alternately along the length of the fibre, giving it a banded appearance. When the muscle contracts, the actin and myosin filaments slide over one another. Magnification unknown.