The Common Vein Copyright 2010
‘The reticular activating system (aka RAS, ascending reticular activating system) is an ill defined part of the nervous system that structurally represents the upper part of the reticular formation which is a loosely arranged network of neurons distributed throughout the brainstem wherever there are no specific neural tracts or nuclei. It lies between the medulla oblongata and midbrain and is connected to the thalamus.
Functionally it is a part of the brain considered to be the center of arousal and motivation. It indirectly relates to our state of conciousness, and is involved with the control of the circadian rhythm, respiration, cardiac rhythms, and sexual function. Since it is connected to the thalamus it becomes by definition connected to many parts of the cerbral cortex, in addition to the basal regions and the medulla.
In the instance of pain, the RAS is activated by the C fibers and hence enables a painful stimulus to arouse us from sleep, create a sense of urgency, and can cause changes in heart rate or respiration rate. The proposed mechanisms are initially mediated through the release of chemical transmitters that create a change in the electrical mileu and the induction of a new electrical impulse in the RAS.
It appears that the opiate derivatives may block the action of the RAS and thus reduce and help treat and manage pain.
Courtesy Ashley Davidoff MD copyright 2008 77059c01b01.8s