Final answer:
Muscle contraction is driven by the sliding filament model, where actin and myosin proteins slide past each other. The process is initiated by the neurotransmitter ACh, which triggers depolarization and calcium release, leading to the exposure of actin sites and the docking of myosin heads. ATP provides the energy for the power stroke, causing the thin filaments to slide by the thick filaments and resulting in muscle fibre shortening.
Step-by-step explanation:
Muscle contraction is described by the sliding filament model of contraction. ACh is the neurotransmitter that binds at the neuromuscular junction (NMJ) to trigger depolarization, and an action potential travels along the sarcolemma to trigger calcium release from SR. The actin sites are exposed after Ca2+ enters the sarcoplasm from its SR storage to activate the troponin-tropomyosin complex so that the tropomyosin shifts away from the sites. The cross-bridging of myosin heads docking into actin-binding sites is followed by the 'power stroke'-the sliding of the thin filaments by thick filaments. The power strokes are powered by ATP. Ultimately, the sarcomeres, myofibrils, and muscle fibres shorten to produce movement.