Final answer:
When a stimulus travels toward a synapse, calcium channels open at the presynaptic end, leading to fusion of synaptic vesicles with the presynaptic membrane and release of neurotransmitters.
Step-by-step explanation:
When a stimulus, in the form of an action potential, travels toward a synapse, several events occur. Firstly, the action potential depolarizes the presynaptic membrane, leading to the opening of voltage-gated calcium channels at the presynaptic end. As a result, Ca2+ ions enter the nerve ending, increasing the concentration of calcium inside the presynaptic neuron.
Following this, the influx of calcium ions triggers a cascade of events that promotes the fusion of synaptic vesicles with the presynaptic membrane. These vesicles contain neurotransmitter molecules, which are then released into the synaptic cleft through a process known as exocytosis. Once in the synaptic cleft, neurotransmitters can bind to receptors on the postsynaptic neuron, which may trigger a response in that neuron, such as depolarization or hyperpolarization, depending on the nature of the neurotransmitter.
It is important to note that the prompt fusion of synaptic vesicles with the axonal membrane following calcium influx is an essential part of neurotransmitter release and synaptic transmission, and not an inhibition or inactivation of the synapse.