For our purposes the reticular formation consists of regions of the brainstem that I have not covered thus far in my lectures. In other words, after you eliminate all of the sensory and motor nuclei, the ascending and descending tracts, you have the reticular formation. This region consists of an intermingling of fibers amongst clusters of cell bodies. Classically, the reticular formation extends from the lower medulla to the upper midbrain. The cells of the reticular formation are often described as columns, and categorized into medial "effector" and lateral "affector" groups, but this nomenclature is plagued with exceptions. More important than this antiquated description is the recent identification of numerous cell groups with highly specific functions. The three schematic diagrams through medullary, pontine, and midbrain levels of the brainstem demonstrate the location of the reticular formation. Only specific monoamine cell groups have been labeled in these drawings. I want you to know the transmitters (see following page) used by these various regions of the reticular formation. You should especially know the LOCUS COERULEUS ("the blue spot" since the cells contain melanin) ==NOREPINEPHRINE and the RAPHE (seam or zipper) == SEROTONIN relationships. You will hear more about the role of the brainstem reticular formation in the second one-half of the course. In particular, certain regions of the reticular formation are involved in the regulation of the sleep-waking cycle.

TABLE I-- MONOAMINE CELL GROUPS
Transmitter	Locations of cell bodies	Termination sites
Dopamine	In addition to the nigrostriatal system, most dopamine neurons with long axons are in the ventral tegmental area of the midbrain retic. formation.	Primarily in limbic system and olfactory areas.
Norepinephrine	Primarily in the locus coeruleus but also in small clusters in other parts of the reticular formation.	All parts of the brain: cerebral cortex, cerebellum,thalamus, limbic system, brainstem, and spinal cord.
Serotonin	Raphe nuclei of the mid-brain, pontine, and medullary parts of the reticular formation.	Heavy ascending projections to limbic system and olfactory areas; lighter descending projections to cerebellum and spinal cord.