Final answer:
Nerve impulses trigger the release of neurotransmitters via voltage-gated Ca²⁺ channels, leading to exocytosis from the presynaptic neuron into the synaptic cleft, thereby allowing signals to be transmitted to the postsynaptic neuron.
Step-by-step explanation:
Impulses arriving at the synaptic nerve promote the release of neurotransmitters, which are chemical messengers that allow neurons to communicate with each other or with other types of cells, like muscle cells. The release process entails the arrival of an action potential at the axon terminal, which then triggers the opening of voltage-gated Ca²⁺ channels. The influx of Ca²⁺ into the presynaptic neuron causes synaptic vesicles containing neurotransmitters to merge with the presynaptic membrane and release their contents into the synaptic cleft through a process known as exocytosis.
The neurotransmitters then travel across the synaptic cleft and bind to specific receptors on the postsynaptic neuron's membrane. This binding alters the electrochemical potential of the postsynaptic cell, thereby propagating the electrical impulse and continuing the transmission of the nerve signal. Neurotransmitters are swiftly broken down or reabsorbed by the presynaptic cell after they have fulfilled their role to ensure the synapse is ready for the next signal.