The ends of the axons are clusters of terminal buttons. Terminal buttons are small knobs that secrete chemicals called the neurotransmitters. These chemicals serve as that messengers that may activate neighboring neurons.hare to: 1  Inside the Brain: What is a Neurotransmitter? 2  Reuptake Inhibitor: A Psychological Definition Reuptake inhibitors increase the amount of available chemicals in the brain, called neurotransmitters. 3  What Chemical Causes Depression? 4  What Does Marijuana Do to the Brain? 5  What Is a Neurotransmitter? 6  Why Is Nicotine Addictive?