Which one of the following statements about neurotransmission is correct?

Question

BlackTom AI · Accepted Answer

Neurotransmitters usually bind receptors with relatively low affinity and transiently activate them, enabling rapid on–off signaling at synapses.

1) Relevant knowledge points and concepts
- Fast synaptic transmission relies on rapid ligand–receptor kinetics: neurotransmitters are released in a pulse, bind receptors quickly, and unbind quickly so signaling can be brief and time-locked.
- Termination mechanisms (reuptake transporters, enzymatic degradation such as acetylcholinesterase, and diffusion) rapidly clear neurotransmitters; low-to-moderate affinity supports rapid clearance.
- Receptor classes: ionotropic (ligand-gated ion channels) mediate very rapid, transient currents; metabotropic (G-protein coupled) can produce slower, longer-lasting effects. Neuropeptides and neuromodulators are exceptions with higher affinity and longer actions.
- Calcium’s role: influx of Ca2+ into the presynaptic terminal triggers vesicle fusion and neurotransmitter release — calcium is a trigger, not “secreted” as a transmitter.

2) Step-by-step reasoning
- Typical small-molecule neurotransmitters (glutamate, GABA, acetylcholine, monoamines) are released, bind receptors briefly, and are removed rapidly. This physiology implies relatively low/transient receptor binding is the norm for fast neurotransmission.
- Exceptions: peptide transmitters and some neuromodulators bind with higher affinity and act longer, but these do not overturn the general pattern.
- Compare options: the first option correctly states the typical low-affinity, transient activation (with allowance for exceptions). The others contain clear inaccuracies.

3) No numeric calculations are needed.

4) Why the correct answer is correct
- Low affinity and transient receptor activation explain how synapses convey temporally precise signals and how termination mechanisms are effective. Empirical examples include nicotinic acetylcholine receptors producing brief postsynaptic currents rapidly terminated by acetylcholinesterase and reuptake.

5) Why the other options are incorrect
- Option 2: A neuron’s transmitter identity is intrinsic (it doesn’t switch between excitatory/inhibitory release depending on inputs); some neurons co-release transmitters but release is not simply determined by excitation vs inhibition.
- Option 3: Chemical neurotransmission requires Ca2+ influx to trigger release, but calcium is not “secreted” as a transmitter.
- Option 4: While receptors are proteins, neurotransmitters are chemically diverse (amino acids, amines, peptides, gases), so it is false that all are amino acids.

Conclusion: The correct answer is the first option — neurotransmitters typically have relatively low affinity for, and only transiently activate, their receptors — which matches the provided answer.

Which one of the following statements about neurotransmission is correct?单项选择题

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