Final answer:
Tiny saclike structures called synaptic knobs release chemicals known as neurotransmitters when an electrical impulse reaches the end of an axon. These neurotransmitters cross the synaptic cleft to relay the signal to the next cell.
Step-by-step explanation:
When an electrical impulse reaches the end of an axon, tiny saclike structures known as synaptic knobs manufacture chemicals called neurotransmitters. These neurotransmitters are contained within structures at the axon terminal called synaptic vesicles. Once the action potential arrives, it causes the influx of calcium ions, which in turn leads to the fusion of these vesicles with the presynaptic membrane, releasing the neurotransmitters into the synaptic cleft that separates the presynaptic and postsynaptic neurons.
Neurotransmitters then travel across this cleft and bind to receptors on the membrane of the postsynaptic cell, which could be another neuron or a different type of cell such as a muscle cell. If it's a neuron, the binding of neurotransmitters will initiate a new action potential in that cell, continuing the nerve impulse. The entire process is crucial for the transmission of signals throughout the nervous system.