Final answer:
Choline acetyltransferase catalyzes the formation of ACh from acetyl CoA and choline in the motor nerve ending axoplasm, while acetylcholinesterase breaks down ACh in the synaptic cleft to prevent continuous stimulation of muscle contraction.
Step-by-step explanation:
The enzyme that catalyzes the reaction of acetyl coenzyme A (acetyl CoA) and choline to form acetylcholine (ACh) in the motor nerve ending axoplasm is known as choline acetyltransferase. This is a distinct process from the action of acetylcholinesterase (AChE), which is responsible for breaking down ACh in the synaptic cleft. Acetylcholinesterase's role is crucial as it ensures that ACh does not continually stimulate muscle contraction by hydrolyzing ACh to choline and acetate, keeping the synaptic cleft free of ACh post neural signal transmission.