when stimulated by subsequent nerve impulses causing the two sets of filaments to slide past each other. As a result, the actin filaments, anchored at their midpoints to the Z lines, exert a pulling force against the Z lines. The Z lines are pulled closer together shortening the length of each sarcomere. As each sarcomere is shortened, the length of each myofibril and fiber is shortened and, thus, the length of the muscle itself is shortened as well.
