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 smaller fibres called myofibrils. These are around 1-2 micrometres (millionths of a metre) in diameter. The fibre has a sheath of connective tissue (endomysium) that is seen as the strands scattered around the image. Skeletal muscle, named because skeletal bones are moved with this muscle, is under voluntary control. Magnification: x800 when printed 10 centimetres wide.