When an action potential reaches the axon terminal of a motor neuron at the neuromuscular junction, the exocytosis of synaptic vesicles is directly triggered by the influx of which of the following ions into the synaptic knob?

Step-by-step solution

The transmission of a nerve impulse across a chemical synapse involves the release of neurotransmitters. When an action potential (impulse) arrives at the axon terminal, it causes voltage-gated calcium channels to open. The resulting influx of calcium ions ( Ca²⁺ ) into the synaptic knob stimulates the movement of synaptic vesicles towards the pre-synaptic membrane. These vesicles fuse with the plasma membrane and release their neurotransmitter (such as acetylcholine at the neuromuscular junction) into the synaptic