How are neurotransmitters cleared from the synaptic cleft?

• A. Diffusion only.
• B. Reuptake, enzymatic degradation, or diffusion; acetylcholine degraded by acetylcholinesterase.
• C. Enzymatic degradation only without reuptake.
• D. Active transport into postsynaptic neuron.

Answer: (B)

Neurotransmitter clearance from the synaptic cleft relies on three main processes: diffusion away from the cleft, reuptake into the presynaptic neuron, and enzymatic degradation in the synaptic space. For acetylcholine, acetylcholinesterase rapidly breaks it down, quickly terminating the signal. Including all three mechanisms—diffusion, reuptake, and enzymatic degradation—best captures how signals are stopped and neurotransmitters are cleared. If you focus only on diffusion, you miss the efficient recycling and breakdown that speed up termination. If you rely only on enzymatic degradation, you ignore the crucial reuptake process. Active transport into the postsynaptic neuron isn’t the standard clearance route for most transmitters, so it doesn’t fit as the main mechanism.