Skeletal muscle fibre. Coloured scanning electron micrograph (SEM) of a freeze-fractured skeletal (or striated) muscle fibre. The fracturing of the fibre has revealed that it consists of a bundle of myofibrils (red). The fibre has a sheath of connective tissue (endomysium) that is seen as the strands (yellow) scattered around the image. Skeletal muscle is under voluntary control. Magnification unknown.