Neurophysiology and Synapses · USMLE Step 1

At a typical chemical synapse, what triggers the release of neurotransmitter from presynaptic vesicles into the synaptic cleft?

  1. Influx of chloride ions into the presynaptic terminal
  2. Depolarization-triggered opening of voltage-gated sodium channels
  3. Depolarization-triggered opening of voltage-gated calcium channels
  4. Activation of postsynaptic G-protein receptors
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Correct answer: Depolarization-triggered opening of voltage-gated calcium channels

When an action potential reaches the presynaptic terminal, it depolarizes the membrane and opens voltage-gated calcium channels; the resulting calcium influx triggers fusion of vesicles and release of neurotransmitter.

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