Light micrograph showing the cross striation of skeletal muscle fibres. An alternation of dark bands (A band) and light bands (I band) is observed. In turn, in the centre of the I band there is a darker line that is the Z line. The space between two Z lines corresponds to the sarcomere, the structural and functional unit of the myofibril. The myofibrils occupy a large part of the cytoplasm of the muscle fibre, displacing the nuclei to the periphery of the cell.