The release of neurotransmitter molecules from a neuron is primarily caused by an action potential arriving at the axon terminal, which opens voltage‑gated calcium (Ca²⁺) channels and triggers Ca²⁺‑dependent exocytosis of synaptic vesicles.

Key mechanism

  • An electrical signal called an action potential travels down the axon to the presynaptic terminal.
  • This depolarization opens voltage‑gated Ca²⁺ channels , allowing Ca²⁺ ions to rush into the terminal.
  • The rise in intracellular Ca²⁺ binds to specialized proteins such as synaptotagmin and activates SNARE proteins , causing synaptic vesicles to fuse with the presynaptic membrane and release neurotransmitter by exocytosis.

If this was a multiple‑choice question

On typical exam questions that ask, “Which of these causes the release of neurotransmitter molecules?” the correct option is usually something like:

  • “An action potential reaching the axon terminal”
  • or “Influx of Ca²⁺ ions into the presynaptic terminal”

Both phrases describe the same core trigger: action potential–induced Ca²⁺ influx leading to vesicle exocytosis and neurotransmitter release.

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