Reticular Formation, Brain Stem

Abstract

The reticular formation of the brain stem is the most ancient part of the brain and the one part that is absolutely necessary to the life of the organism. It consists of large numbers of neurons and fibers, and exclusive of the adjacent cranial nerve nuclei, long ascending and descending tracts, and a few large nuclear masses such as the olives, nucleus ruber, and substantia nigra, it constitutes the core of the brain stem. It is generally thought of as extending from the caudal medulla to the interface between mesencephalon (midbrain) and diencephalon (thalamus-hypothalamus). However, a series of cell masses clustered in the medial portions of the thalamus continue forward, forming the thalamic nonspecific system and, as such, can be thought of as the reticular formation of the thalamus.