Neurotransmitters are the chemicals which account for the transmission of signals from one neuron to the next across synapses. They are also found at the axon endings of motor neurons, where they stimulate the muscle fibers to contract. They and their close relatives are produced by some glands such as the pituitary and the adrenal glands.

Serotonin: Changes in the serotonin levels in the brain can alter the mood. For example, medications that affect the action of serotonin are used to treat depression.

Dopamine: A precursor (forerunner) of adrenaline and a closely related molecule, noradrenaline. Dopamine is formed by the decarboxylation (removal of a carboxyl group) from dopa. Dopa is used in the treatment of Parkinson disease. Parkinson disease is believed to be related to low levels of dopamine in certain parts of the brain.

Acetylcholine: plays a role in skeletal muscle movement, as well as in the regulation of smooth muscle and cardiac muscle. In the central nervous system acetylcholine is believed to be involved in learning, memory, and mood.

Endorphins: Any of a group of peptide hormones that bind to opiate receptors and are found mainly in the brain. Endorphins reduce the sensation of pain and affect emotions. //-->

Agonist: A drug that binds to a receptor of a cell and triggers a response by the cell. An agonist often mimics the action of a naturally occurring substance.

Antagonist: is the opposite of an agonist which stimulates an action. Antagonists and agonists are key players in pharmacology and in the chemistry of the human body.

Neuroscience for kids: Neurotransmitters