Outline the process of muscle contraction.

The sliding filament mechanism allows for muscle contraction. When an action potential arrives it travels through the sarcoplasmic reticulum and spreads down the transverse tubules into the muscle belly causing calcium ions to be released. These calcium ions then bind to troponin which is situated on tropomyosin which makes up the double helical strand of actin (the thin filament of the sarcoplasm). This binding changes the structure of troponin moving tropomyosin away from the myosin binding site on actin. This allows the globular head of myosin to bind forming a cross bridge, a molecule of ATP is then used to perform a power stroke and move the actin filament closer to the Z line (shortening the sarcomere). In order to repeat this process another molecule of ATP is needed to break the cross bridge as long as calcium ions are still present. The simultaneous shortening of sarcomeres will contract a muscle with the force and strength of contraction influenced by the recruitment of sarcomeres.