Watch this video, which explains the types of neurotransmitters and how they excite or inhibit neurons (nerve cells). Each neurotransmitter can directly or indirectly influence neurons in a specific portion of the brain, thereby affecting behavior. There are billions of nerve cells located in the brain, which do not directly touch each other. Nerve cells communicate messages by secreting neurotransmitters. Some common neurotransmitters are acetylcholine, norepinephrine, dopamine, serotonin and gamma aminobutyric acid (GABA). Acetylcholine and norepinephrine are excitatory neurotransmitters while dopamine, serotonin, and GABA are inhibitory.