This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
The action of acetylcholine at the neuromuscular junction is terminated primarily by: 
Select and explain. 
A. Diffusion into the surrounding extracellular fluid, B. Uptake into the nerve ending, C. Uptake into the muscle, D. Enzymatic breakdown by acetylcholinesterase
D: Enzymatic breakdown by acetylcholinesterase
Answer: D: Enzymatic breakdown by acetylcholinesterase 
Explanation: The action of acetylcholine at the neuromuscular junction is terminated primarily by enzymatic breakdown by acetylcholinesterase. The acetylcholinesterase is attached to the basal lamina that fills the synaptic trough. There is no uptake of acetylcholine at the neuromuscular junction. A small amount of the acetylcholine will diffuse into the surrounding extracellular fluid but this is not the primary method by which its action is terminated.