Sliding Filament Model of Muscle Contraction
Two adjacent sarcomeres are shown going through cycles of contraction and relaxation. If the thin filaments are attached to something such that a load can be developed, tension will develop on the sarcomeres as they shorten. Click here to see the key for this animation. Note that as the sarcomere contracts, the Z lines move closer together. The myosin thick filaments "walk" their way along nearby actin thin filaments. Since the structure of the thick filament allows the myosin to "walk" in both directions and since the myosin fibers do not stretch, the thin filaments of opposite polarity are pulled together.