What is a neurotransmitter?

Brain cells are connected in large networks. There are places where two cells come into very close contact and messages can be passed from one cell to the other (these places are called synapses). This happens by one of the cells releasing a chemical messenger (called a neurotransmitter) that can cross the short gap to the next brain cell and activate or inhibit it. There are lots of different neurotransmitters in the brain, though each neurone generally only contains one. How well they work plays an important role in a number of mental illnesses.

There are at least 5 neurotransmitters that may play a role in mood, anxiety and depression. While the distinction between neurotransmitters and hormones is generally clear-cut, a substance can act as a neurotransmitter in one region of the brain while serving as a hormone elsewhere.