Neurotransmitter
Neurotransmitter, chemical made by neurons, or nerve cells . Neurons send out neurotransmitters as chemical signals to activate or inhibit the function of neighboring cells. Within the central nervous system, which consists of the brain and the spinal cord, neurotransmitters pass from neuron to neuron. In the peripheral nervous system, which is made up of the nerves that run from the central nervous system to the rest of the body, the chemical signals pass between a neuron and an adjacent muscle or gland cell. Nine chemical compounds—belonging to three chemical families—are widely recognized as neurotransmitters. In addition, certain other body chemicals, including adenosine, histamine , enkephalins, endorphins, and epinephrine , have neurotransmitterlike properties. Experts believe that there are many more neurotransmitters as yet undiscovered. The first of the three families is composed of amines, a group of compounds containing molecules of carbon, hydrogen, and nitrogen. Among the