Within the CNS, the release of neurotransmitter from a terminal bouton at a chemical synapse is dependent upon which of the following?

Question

BlackTom AI · Accepted Answer

Neurotransmitter release is triggered by calcium entry through voltage-gated calcium channels at the presynaptic terminal. Key concepts: action potentials depolarize the presynaptic bouton, voltage-gated Ca2+ channels (primarily P/Q- and N-type in the CNS) open, Ca2+ influx creates a local high-[Ca2+] microdomain, Ca2+ binds the vesicular Ca2+ sensor (e.g., synaptotagmin), and SNARE-mediated membrane fusion causes exocytosis of neurotransmitter.

Step-by-step reasoning:
1) An action potential arrives at the terminal bouton and depolarizes the membrane.
2) Depolarization opens voltage-gated Ca2+ channels clustered at active zones.
3) Ca2+ flows down its electrochemical gradient into the cytosol; intracellular [Ca2+] near release sites rises transiently from ~100 nM to several μM (microdomain).
4) Ca2+ binds to synaptotagmin and other Ca2+-sensing proteins, inducing conformational changes that drive the SNARE complex to fuse synaptic vesicles with the plasma membrane.
5) Neurotransmitter is released into the synaptic cleft and diffuses to postsynaptic receptors.

Why the correct answer is correct:
Opening of voltage-gated calcium channels is the immediate, necessary trigger for vesicle fusion and transmitter release in chemical synapses in the CNS. Blocking these channels prevents release; opening them (via depolarization) is sufficient to cause release.

Why the other options are incorrect:
- Opening of ligand-gated calcium channels: Some ligand-gated receptors (e.g., NMDA receptors) are Ca2+-permeable, but they are typically postsynaptic and mediate postsynaptic signaling, not the primary mechanism that triggers presynaptic vesicle fusion. Presynaptic release depends on voltage-gated Ca2+ channels.
- Hyperpolarization of the synaptic terminal: Hyperpolarization reduces the likelihood of opening voltage-gated Ca2+ channels and thus inhibits release, the opposite of what is required.
- Synthesis of acetylcholinesterase: Acetylcholinesterase breaks down acetylcholine in the cleft; its synthesis is unrelated to the acute Ca2+-dependent step that causes release.

Conclusion: Therefore, the correct answer is Opening of voltage-gated calcium channels, matching the provided answer.

Within the CNS, the release of neurotransmitter from a terminal bouton at a chemical synapse is dependent upon which of the following?单项选择题

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