Neurotransmitter

Neurotransmitters are chemicals in the brain which allow the transmission of nerve impulses. The brain is made up of billions of neurons (brain cells) and these cells do not directly touch each other. Instead they release electrical impulses which are carried to other neurons by neurotransmitters. Researchers have identified about 50 different neurotransmitters including well known examples such as dopamine and serotonin

Relation to mental disorders
Changes in the amounts of certain neurotransmitters is linked to various mental disorders including but not limited to depression, anxiety and attention deficit/hyperactivity disorder (ADHD).