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Nervous System: Neuron, Synapse, Reflexes · Zoology

At a chemical synapse, what triggers the fusion of neurotransmitter-filled vesicles with the presynaptic membrane?

  1. The influx of $Na^{+}$ ions
  2. The efflux of $K^{+}$ ions
  3. The influx of $Ca^{2+}$ ions
  4. The binding of ATP to the vesicle surface
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Correct answer: The influx of $Ca^{2+}$ ions

When an action potential reaches the axon terminal, it opens voltage-gated $Ca^{2+}$ channels. The resulting rise in intracellular calcium concentrations signals the synaptic vesicles to undergo exocytosis.

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