Final answer:
Acetylcholinesterase (AChE) is crucial for ending ACh signaling by breaking down acetylcholine into acetyl and choline at neuromuscular junctions, preventing unwanted prolonged muscle contractions.
Step-by-step explanation:
ACh-esterase, also known as acetylcholinesterase (AChE), is responsible for terminating ACh signaling at neuromuscular junctions. The enzyme breaks down acetylcholine (ACh) into acetyl and choline, ensuring that ACh does not continuously bind to ACh receptors, which would lead to unwanted prolonged muscle contractions. AChE is found in the synaptic cleft, where it plays a crucial role in the cholinergic system by quickly hydrolyzing ACh after signal transmission to prevent excessive excitation at neuromuscular junctions.