Reticular system

Formatio reticularis

RAS, Reticular substance,

Formatio reticularis is developmentally a very old and original part of the brain.
The area can be divided into a large number of core groups, including pattern generators, each with its own special functions:
1/ control of the degree of alertness of the CNS; the reticular activation system2/ control of the basic tone (basic tension) of skeletal muscle,
3/ Locomotion Control
4/ Posture control
5/ control of breathing,
6/ control of blood circulation (heart and blood vessels),
7/ control of eye movements (gaze direction centers),
8/ control of chewing, swallowing, coughing, sneezing, vomiting, bowel and bladder emptying,
9/ control/modification of pain sensations.

Formatio reticularis is structured as a diffuse mesh-like system (reticulum = mesh) of larger and smaller neurons with longitudinal axons and with dendrite trees that branch primarily in the transversal plane.
The system extends centrally in the brainstem and extends from the lower part of the medulla to the upper part of the midbrain. Most of the upward and downward pathway systems of the brainstem pass through the meshes of the reticular system and make synaptic connections with this. These parts together can be considered the classical reticular system; see below with regard to the extended concept.

Very roughly, the "classical" reticular system is divided into:
a longitudinal central central part of the Raphe;
an upper mesencephalon part,
an external and
an inner part
of which the latter two are each in turn divided into a pons part and a medulla oblongatadel.

Formatio reticularis is unique in its content of neuronal accumulations with production and, in the case of the CNS, an almost global proliferation of nerve fibers with special transmitter and modulator substances, all of which are very important for certain cognitive abilities, visceral functions and emotional states. These include:
1/ adrenaline-producing cell groups 2/ noradrenaline-producing cell groups 3/ dopamine-producing cell groups 4/ serotonin-producing cell groups 5/ acetylcholine-producing cell groups

The special mesh-like/reticular structure of the nerve tissue continues "upwards" in the midbrain and here forms a thin layer - the reticular thalamus nucleus - on the outside of the thalamus itself. The nucleus is sometimes counted as a special part, an offshoot, from the reticular system proper.
A further attempt to extend the concept of formatio reticularis means that parts of the basal forebrain with its acetylcholine-producing cell groups, especially the nucleus basalis Meynert, should be counted as a telencephal extension of the reticular system.
Note: references in Mesulam, M-M. (2000) Structure and Function of Cholinergic Pathways in the Cerebral Cortex, Limbic System, Basal Ganglia, and Thalamus of the Human Brain, in Back to Psychopharmacology - The Fourth Generation of Progress. ACNP..