What is the function of cholinesterase at the neuromuscular junction?

• A. Breaks down Acetylcholine to stop the signal
• B. Enhances acetylcholine release
• C. Stores calcium in sarcoplasmic reticulum
• D. Forms cross-bridges between actin and myosin

Answer: (A)

At the neuromuscular junction, the signal is delivered by acetylcholine and must be quickly terminated to stop the muscle from staying contracted. Cholinesterase, specifically acetylcholinesterase, rapidly breaks down acetylcholine in the synaptic cleft after it has activated the receptors on the muscle membrane. This enzymatic breakdown ends the chemical signal, allowing the ion channels to close and the muscle fiber to repolarize, which leads to relaxation. The rapid termination also frees the space for the next nerve impulse to be properly timed. The breakdown products, choline and acetate, can be recycled so new acetylcholine can be synthesized for future signaling. If acetylcholine were not broken down, the receptor would remain stimulated, causing prolonged contraction.