Final answer:
Muscle contraction is a complex process involving the binding of acetylcholine (ACh) at the neuromuscular junction (NMJ) and the sliding of filaments to produce movement. The enzyme acetylcholinesterase (AChE) removes ACh from the synaptic cleft to prevent extended muscle contraction.
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 the sarcoplasmic reticulum (SR). The actin sites are exposed after Ca²+ enters the sarcoplasm from its SR storage to activate the troponin-tropomyosin complex, causing the tropomyosin to shift and revealing myosin binding sites. The cross-bridging of myosin heads docking into actin-binding sites is followed by the power stroke, which results in the sliding of the thin filaments by thick filaments. The power strokes are powered by ATP. Ultimately, the sarcomeres, myofibrils, and muscle fibers shorten to produce movement.
The enzyme acetylcholinesterase (AChE) removes lingering acetylcholine (ACh) from the synaptic cleft, preventing extended muscle contraction by breaking down ACh into acetyl and choline so it does not remain bound to ACh receptors.