Muscle Contraction Report

During muscle contraction, groups of muscle fibres trigger a nerve to change the tension in the muscle. The first step in muscle contraction is the brain sending a message to the central nervous system, which in turn sends it to the peripheral nervous system then to the neuromuscular junction. The neurotransmitter, ACh is released into a space between the neuron and the muscle membrane. The action potential is generated altering the sarcolemma. This causes a change in the muscle membrane. As calcium ions are released during the resting phase, the binding sites of the tropomyosin located on the thin actin filaments are covered with troponins. ATP surrounds the thick myosin filament. When contraction happens, calcium ions bind to the troponin,
which exposes the binding sites of tropomyosin causing the formation of cross bridges. The cross bridges are responsible for the sliding mechanism between the thick and thin filaments. The cross bridge phase repeats from movement to release. The last phase of muscle contraction, the muscle returns to resting. ACh release is stopped and the remaining ACh is inactivated. ATPase forces calcium ions back to the sarcoplasmic reticulum and the binding sites on the thin actin filaments are covered back up with tropomyosin. Because of the calcium ions being absence, troponin returns to cover the binding sites on tropomyosin. Then the cross bridges breakaway and the contraction stops.