The chemicals released from axonal terminals are called neurotransmitters. They transmit signals from one neuron to another across a small gap called the synapse. When a neuron is activated, synaptic vesicles present in the axon release the neurotransmitters, which cross the gap to be absorbed by the receptor neuron.
Discovered by Austrian scientist Otto Loewi in 1921, neurotransmitters are synthesized from amino acids in the cell body of the neuron and play an important role in regular body functions. Over a hundred neurotransmitters have been identified by scientists, and they can be classified into two types by function. Excitatory neurotransmitters such as epinephrine and norepinephrine stimulate neurons. Inhibitory neurotransmitters such as serotonin and GABA stabilize and calm the brain. When neurotransmitter levels are not in the optimal range, there can be adverse effects on the body.