Striated muscle. Coloured scanning electron micrograph (SEM) of human striated muscle. Striated muscle occurs in all skeletal muscles and its movement is under voluntary control. It is composed of long muscle fibres made up of cylindrical myofibrils (green) containing contractile proteins. The parallel arrangement of the myo- fibrils is seen here. The regular pattern of the contractile proteins in the myofibrils produces characteristic stripes or striations (not seen). Infiltrating the myofibrils at these regular intervals is sarcoplasmic reticulum (globose, orange), the muscle's specialized membrane system. Magnification: unknown.