Final answer:
Neurotransmitters are chemicals released by neurons at the axon terminals into the synaptic cleft, leading to communication between neurons.
Step-by-step explanation:
Molecules that are synthesized by a neuron and released when a nerve signal reaches an axon terminal are called neurotransmitters. These chemical signals are stored in synaptic vesicles and upon reaching the axon terminal, they are released into the synaptic cleft, the gap between neurons, through a process known as exocytosis. The neurotransmitters then bind to receptors on the postsynaptic neuron's membrane, which can initiate a new electrical signal in the receiving neuron or modulate its activity.
Examples of neurotransmitters include acetylcholine, dopamine, serotonin, and GABA, each playing different roles in neural communication and having potential excitatory or inhibitory effects on the postsynaptic neuron.