Light micrograph of a section through skeletal muscle. A muscle is composed of groups of bundles, or fascicles, of single nerve fibres (pink). A nerve fibre contains contractile proteins arranged in smaller structures called myofibrils. Skeletal muscle is responsible for voluntary muscle movement in the body. A blood vessel runs from top right to lower left. Cell nuclei are blue. Magnification: x200 when printed at 15cm wide.