What ion tiggers the release of actycholine into the synaptic cleft?

The release of acetylcholine into the synaptic cleft is triggered by an influx of calcium ions (Ca²⁺) into the presynaptic neuron. When an action potential reaches the axon terminal, voltage-gated calcium channels open, allowing Ca²⁺ to flow into the cell. This increase in intracellular calcium concentration prompts synaptic vesicles containing acetylcholine to fuse with the presynaptic membrane, leading to the release of the neurotransmitter into the synaptic cleft.