Final answer:
The statement that Acetylcholinesterase (AChE) degrades ACh in the motor end-plate membrane is true, with the enzymatic action primarily occurring in the synaptic cleft to prevent extended muscle contraction.
Step-by-step explanation:
The statement is true: most of the Acetylcholine (ACh) is degraded by the enzyme acetylcholinesterase (AChE) which is found in the synaptic cleft, not specifically in the motor end-plate membrane as mentioned in the question. However, since AChE is closely associated with the area surrounding the motor end plates, the enzyme plays a crucial role in breaking down ACh to prevent ongoing stimulation of muscle fibers which could lead to extended muscle contraction.
ACh is synthesized in the motor neuron and, upon release, it crosses the synaptic cleft and binds to receptors on the motor end-plate. This binding triggers depolarization, which is essential for muscle contraction. Once its action is complete, ACh needs to be rapidly broken down by AChE into acetyl and choline, to halt the signal and allow the muscle to relax. This process is vital for the proper functioning of muscle contractions and to prevent unwanted extended muscle excitation and contraction.