The reticular formation gives rise to three functionally different fiber systems. One component of this system mediates motor functions, a second component mediates autonomic functions, and a third component modulates pain impulses.
Fibers arising from the medulla emerge from a group of large cells located medially called the nucleus reticularis gigantocellularis. These cells project bilaterally to all levels of the spinal cord, and this pathway is referred to as the medullary (lateral) reticulospinal tract (Fig. 9-15). A key function of this pathway is that it powerfully suppresses extensor spinal reflex activity. In contrast, a separate retic-ulospinal pathway arises from two distinct nuclear groups in the medial aspect of the pontine reticular formation; these two nuclear groups are called the nucleus reticularis pontis caudalis and nucleus reticularis pontis oralis. These neurons project ipsilaterally to the entire extent of the spinal cord, and their principal function is to facilitate extensor spinal reflexes. This fiber bundle is called the pontine (medial) reticulospinal tract (Fig. 9-15).