Everyone feels, react and act. So, what triggers this feelings and actions in human? Serotonin does. Serotonin is a chemical that acts in the brain and other parts of the body to influence many feelings, actions and processes.
Some of the important functions regulated by serotonin include appetite, sleep, aggression, and moods. In the brain and the rest of the nervous system, serotonin acts as a neurotransmitter, a chemical that carries signals from one nerve cell to another.