Skeletal muscle fibre. Coloured scanning electron micrograph (SEM) of skeletal muscle fibre. This type of muscle is striated. Muscle cells contain cylindrical organelles in the form of bundles of filaments (orange, myofibrils). Each filament can be thick (made up of myosin) or thin (made up of actin). In the case of skeletal (and cardiac) muscle, the filaments have a specific length, less than the length of the muscle cell. They are organised into repeating subunits (sarcomeres) along the length of the muscle cell. The resulting myofibrils run parallel to each other, causing the cell to appear striped (striated). The muscle is surrounded by connective tissue (loose strands).