The reticular formation is a system of grey longitudinal nuclei made up of nerve cells, lying in the central portions of the brainstem. It extends from the lower end of the medulla oblongata to the upper end of midbrain and a small part of thalamus. At all levels, it occupies the central areas of the brainstem as it fills the territories not occupied by the cranial nerve nuclei and by the large white nerve fiber tracts. The raphe nuclei (with serotonin neurotransmitter) and the locus coeruleus (norepinephrine) are also parts of this network of grey structures. Blood supply: collateral branches of basilar artery, which is the union of the two vertebral arteries.
The reticular formation is the central core of the tegmentum. It is an intricate neural network, which is composed of reticular nuclei, with ascending and descending reticular pathways (tracts). The neurons that make up the grey nuclei of the reticular formation have wide dendritic arborizations, with their long axons giving off numerous collateral projections. Approximately, the medial two-thirds of this network of grey nuclei consist of many large nerve cells, the so-called giant cells, while the remainder is composed of small neurons located in the lateral areas. The afferent and efferent connections show only a rough topographic order. In general, we can say that the lateral parts of the reticular formation receive afferent nerve impulses, while the medial portions sends out many long ascending and descending fibers, carrying efferent executive impulses.
Function
The reticular formation exerts cardiovascular control as it contains the cardiac and vasomotor centers in the medulla oblongata. It also functions as a relay station for eye and ear nerve impulses from the brain to the cerebellum, coordinating visual, auditory, and vestibular sensory information with motor coordination. Different areas of the reticular formation also inhibit or promote the motor reaction of the spinal cord, with all the inhibitory effects being bilateral. Other regions of this complex structure of the brainstem exert generalized excitatory influences of the cerebral cortex.
The reticular formation acts on the alpha motor neurons of the spinal cord, which innervate the main fibers of the muscles involved in voluntary movement. To summarize, it is functionally and morphologically related to the spinal cord, cerebellum, limbic system, and cerebral cortex. The term ¨reticular formation¨ was introduced by the German neuroanatomist Otto Friedrich Deiters in the 19th century. It reflects only the formation morphological characteristics.
Below, schematic picture of neurons of the reticular formation, with long descending and ascending axons.
