Three muscle fibers are shown in cross-section. The nuclei of the cells are seen to be small, dark, pyknotic and lying just beneath the plasma membrane. The centers of the myofibers are occupied by eosinophilic cytoplasm. Skeletal muscle is deep brown in color due to the presence of a pigmented protein called myoglobin.
Skeletal muscle is in reality a syncytium.
The longest muscle fibers in the human body are in the sartorius muscle of the thigh. In longitudinal sections, skeletal muscle fibres characteristically demonstrate alternating dark and light-staining bands, giving them a striated appearance. In cross section, skeletal muscle cells of the adult are polygonal, while those of children and certain muscles of face, even in adults, are roughly circular. Numerous nuclei are seen in the periphery closely applied to the plasma membrane also called the sarcolemma. The presence of nuclei in the center of the cell is abnormal and usually indicative of pathology.