The arrangement of the actin and myosin myofilaments in sarcomeres gives the myofibril a bandedA light I band which consists only of actin myofilaments spans each z disk and ends at the myosin myofilaments a darker central region in each sarcomere called an a band extends the length of the myosin myofilamenths overlap for some distance at both ends of the a band in the center of each sarcomere is a second light zone called the h zone which consists only of myosin myofilaments the myosin myofilaments are anchored in the center of the sarcomere at a darkstaining band called the m line the alternating i bands and a bands of the sarcomeres are responsible for the striations seen in skeletal muscle fibers observed through the microscope