Final answer:
Voltage-gated calcium channels are opened as a result of electrical signals reaching the axon terminal. This initiates a cascade leading to neurotransmitter release, which can then activate ligand-gated channels in the postsynaptic membrane.
Step-by-step explanation:
When electrical signals, in the form of action potentials, reach the axon terminal of a neuron, they trigger the opening of voltage-gated calcium channels. This is because the depolarization of the presynaptic membrane leads to an influx of Na+ ions through voltage-gated sodium channels, which further depolarizes the membrane and subsequently causes the opening of voltage-gated calcium channels. The entry of calcium ions (Ca2+) into the cell is crucial, as it initiates a signaling cascade that results in synaptic vesicles fusing with the presynaptic membrane and releasing neurotransmitters into the synaptic cleft.
Upon reaching the postsynaptic membrane, these neurotransmitters can then bind to receptors which are often ligand-gated channels, such as those for acetylcholine, allowing ions like sodium, calcium, and potassium to flow through and generate an action potential in the target cell, if conditions permit. This process occurs at the neuromuscular junction and other types of synapses in the nervous system.