There are three main types of neurons: 1) sensory neurons; 2) motor neurons; and 3) interneurons (also called association neurons). Sensory neurons conduct impulses from sensory organs (eyes, ears, and the surface of the skin) into the central nervous system. Motor neurons conduct impulses from the central nervous system to muscles or glands. Interneurons are neither sensory neurons nor motor neurons. They permit elaborate processing of information to generate complex behaviors. Interneurons comprise the majority of neurons in the central nervous system.
The structure of a basic nerve cell. (From Bear, Mark F., Connors, Barry W., and Paradiso, Michael A. Neuroscience: Exploring the Brain. 2nd Ed. Philadelphia: Lippincott, Williams & Wilkins, 2001.)