Muscle anatomy. Cutaway artwork showing the anatomy and internal structure of a muscle, from the macroscopic (left) to the microscopic (right) level. At upper left, a muscle is shown with nerves (blue). The cutaway section shows the muscle consisting of muscle bundles (fascicles). Each fascicle consists of muscle fibres (the third stage shown here, also with nerves, blue). The fibres consist of myofibrils, shown here with green and yellow sheaths, the cell membrane or sarcolemma. The smallest element are the myofilaments (right) consisting of the proteins actin (blue) and myosin (red).