Neurotransmitters - special chemicals in the brain, far more common among vertebrates. These chemicals diffuse across the synapse separating two neurons. After attaching to the receptor molecule, the neurotransmitter is quickly removed, either by enzymes or by diffusion into the cell. There are over 30 known neurotransmitters. Acetylcholine is broken down by acetyl cholinesterase.
Dopamine is found in the brain and plays a role in maintaining a sense of awareness and well-being.
Dopamine is also involved in the integration of signals for muscle control in a part of the midbrain. Serotonin is also found in the brain. Low levels are associated with severe depression . New drugs for treating depression, anxiety and related disorders inhibit the resorption of serotonin Endorphins are the natural analgesics that attach to the opiate receptor sites.