Which ONE of the following statements about chemical neurotransmission is CORRECT?

Question

BlackTom AI · Accepted Answer

Neurotransmitter release is triggered by Ca2+ influx through presynaptic voltage-gated calcium channels, which initiates vesicle fusion with the presynaptic membrane.

1. Relevant knowledge points and concepts
- Action potential arrival at the presynaptic terminal depolarizes the membrane and opens voltage-gated calcium channels (VGCCs; e.g., P/Q and N types).
- Ca2+ entry raises local intracellular [Ca2+], Ca2+ binds synaptotagmin and triggers SNARE-mediated fusion of synaptic vesicles with the presynaptic membrane (exocytosis).
- Classical small-molecule transmitters are packaged in small clear vesicles and often synthesized locally in the terminal; neuropeptides are synthesized in the soma, packed into large dense-core vesicles, and transported down the axon.
- Vesicular loading uses proton gradients generated by a vesicular H+-ATPase (indirect ATP use), but vesicle release itself is Ca2+-dependent exocytosis.

2. Step-by-step reasoning
- Step 1: AP depolarizes presynaptic terminal.
- Step 2: VGCCs open—Ca2+ flows into the terminal.
- Step 3: Increased Ca2+ binds release machinery (synaptotagmin), promoting SNARE complex-driven fusion of synaptic vesicles with the presynaptic membrane.
- Step 4: Neurotransmitter is released into the synaptic cleft and acts on postsynaptic receptors.

3. Intermediate/quantitative steps
- No numerical calculations are required; the causal chain is electrophysiological: depolarization → VGCC opening → Ca2+ influx → synaptotagmin activation → vesicle fusion.

4. Why the correct answer is correct
- The statement that chemical neurotransmission is reliant upon Ca2+ influx via presynaptic voltage-gated calcium channels accurately describes the essential trigger for synchronous neurotransmitter release. Without this Ca2+ entry, exocytosis of synaptic vesicles does not occur efficiently.

5. Why the other options are incorrect
- Option A is wrong: vesicles fuse with the presynaptic membrane, not the postsynaptic membrane.
- Option C is misleading: peptide transmitters are released by Ca2+-dependent exocytosis of dense-core vesicles; ATP-driven transporters (as the primary release mechanism) is incorrect. (ATP is used by vesicular H+-ATPases to load transmitters, but not as the direct release trigger.)
- Option D is incorrect: small clear vesicles (not "small dense core") contain classical transmitters that are often synthesized in the terminal; peptide transmitters in large dense-core vesicles are synthesized in the soma and transported, typically by slow axonal transport, not necessarily by "fast transporters" as stated.

6. Conclusion
The correct choice is the statement about reliance on Ca2+ influx through presynaptic voltage-gated calcium channels, which matches the provided answer.

Which ONE of the following statements about chemical neurotransmission is CORRECT?Single choice

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