Which one of the following statements about neurotransmission is correct?
关于神经传递，下列哪一项陈述是正确的？

Question

BlackTom AI · Accepted Answer

Neurotransmitter–receptor binding is typically brief and of relatively low affinity, so synaptic signaling is fast and easily terminated.

Relevant concepts:
- Neurotransmitters bind postsynaptic receptors with kinetics (on/off rates) suited for rapid synaptic communication; many ionotropic receptors have micromolar-range affinities and large transient cleft concentrations during release.
- Rapid termination mechanisms (enzymatic degradation, reuptake, diffusion) and receptor unbinding ensure brief activation.
- Exceptions: neuromodulators and neuropeptides often act at metabotropic receptors with higher affinity (nanomolar) and longer-lasting effects.

Step-by-step reasoning:
1. At an active synapse, a vesicle releases transmitter into the cleft producing a transient, high local concentration (often hundreds of micromolar to millimolar for a few hundred microseconds–milliseconds).
2. Receptors (especially ionotropic types) have relatively low affinity (Kd typically in the micromolar range), so they bind and then rapidly unbind as cleft concentration falls. This produces a short postsynaptic current.
3. Termination is achieved by acetylcholinesterase (for ACh), monoamine transporters or glutamate transporters, and diffusion — not by permanently tight binding of transmitter to receptor.
4. Because some transmitters (peptides, monoamines acting on GPCRs) produce slower, longer-lasting responses, the first statement’s caveat “although there are exceptions” is important.

Why the correct answer is correct:
- It captures the typical low-affinity, transient receptor activation underlying fast synaptic transmission while acknowledging exceptions (neuromodulators).

Why the other options are incorrect:
- Option 2: A given neuron generally releases its characteristic transmitter(s) regardless of being excited or inhibited; neurons do not switch release based on each input’s sign (though co-release and modulation occur).
- Option 3: Calcium influx into the presynaptic terminal triggers vesicle fusion; neurotransmission does not require “secretion of calcium.”
- Option 4: While receptors are proteins, neurotransmitters are chemically diverse (amino acids, amines, peptides, gases like NO), so “all neurotransmitters are amino acids” is false.

Final confirmation: The correct choice is the first option (neurotransmitters typically have relatively low affinity and only transiently activate their receptors), which matches the provided answer.

Which one of the following statements about neurotransmission is correct? 关于神经传递，下列哪一项陈述是正确的？单项选择题

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