Nucleus raphe magnus
Encyclopedia
The nucleus raphes magnus, located directly rostral to the nucleus raphes obscurus, is afferently stimulated from axons in the spinal cord
and cerebellum
.
This makes the nucleus raphes magnus a likely candidate for part of the motor system
; however, it seems to participate in the endogenous analgesia system. Mounting evidence suggests that the nucleus raphes magnus plays an important role in homeostatic regulation .
The nucleus raphes magnus receives descending afferents from the periaqueductal gray
, the paraventricular hypothalamic nucleus, central nucleus of the amygdala
, lateral hypothalamic area, parvocellular reticular nucleus
and the prelimbic, infralimbic, medial and lateral precentral cortices .
All of these brain areas influence the main function of the nucleus raphes magnus.
The main function of the nucleus raphes magnus is mostly pain mediation; in fact it sends projections to the dorsal horn of the spinal cord to directly inhibit pain. The nucleus raphes magnus releases enkephalin when stimulated.
The periaqueductal gray
, the epicenter of analgesia, sends efferent connections to the nucleus raphes magnus in when it is stimulated by opiates (endogenous or otherwise).
Electrical stimulation of the PAG produces analgesia, as well as administration of morphine to the PAG or nucleus raphes magnus.
The antinociceptic effects of electrical stimulation of the PAG can be blocked by administering naloxone
, an opiate antagonist
, to the nucleus raphes magnus.
All of this seems to indicate that the nucleus raphes magnus is part of the endogenous opiate system, and acts to inhibit pain in the spinal cord.
Spinal cord
The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...
and cerebellum
Cerebellum
The cerebellum is a region of the brain that plays an important role in motor control. It may also be involved in some cognitive functions such as attention and language, and in regulating fear and pleasure responses, but its movement-related functions are the most solidly established...
.
This makes the nucleus raphes magnus a likely candidate for part of the motor system
Motor system
The motor system is the part of the central nervous system that is involved with movement. It consists of the pyramidal and extrapyramidal system....
; however, it seems to participate in the endogenous analgesia system. Mounting evidence suggests that the nucleus raphes magnus plays an important role in homeostatic regulation .
The nucleus raphes magnus receives descending afferents from the periaqueductal gray
Periaqueductal gray
Periaqueductal gray is the gray matter located around the cerebral aqueduct within the tegmentum of the midbrain. It plays a role in the descending modulation of pain and in defensive behaviour...
, the paraventricular hypothalamic nucleus, central nucleus of the amygdala
Amygdala
The ' are almond-shaped groups of nuclei located deep within the medial temporal lobes of the brain in complex vertebrates, including humans. Shown in research to perform a primary role in the processing and memory of emotional reactions, the amygdalae are considered part of the limbic system.-...
, lateral hypothalamic area, parvocellular reticular nucleus
Parvocellular reticular nucleus
The parvocellular reticular nucleus is part of the brain located dorsolateral to the nucleus reticularis pontis caudalis.The dorsal portion of the reticular nucleus has been shown to innervate the mesencephalic trigeminal nucleus and its surrounding area....
and the prelimbic, infralimbic, medial and lateral precentral cortices .
All of these brain areas influence the main function of the nucleus raphes magnus.
The main function of the nucleus raphes magnus is mostly pain mediation; in fact it sends projections to the dorsal horn of the spinal cord to directly inhibit pain. The nucleus raphes magnus releases enkephalin when stimulated.
The periaqueductal gray
Periaqueductal gray
Periaqueductal gray is the gray matter located around the cerebral aqueduct within the tegmentum of the midbrain. It plays a role in the descending modulation of pain and in defensive behaviour...
, the epicenter of analgesia, sends efferent connections to the nucleus raphes magnus in when it is stimulated by opiates (endogenous or otherwise).
Electrical stimulation of the PAG produces analgesia, as well as administration of morphine to the PAG or nucleus raphes magnus.
The antinociceptic effects of electrical stimulation of the PAG can be blocked by administering naloxone
Naloxone
Naloxone is an opioid antagonist drug developed by Sankyo in the 1960s. Naloxone is a drug used to counter the effects of opiate overdose, for example heroin or morphine overdose. Naloxone is specifically used to counteract life-threatening depression of the central nervous system and respiratory...
, an opiate antagonist
Receptor antagonist
A receptor antagonist is a type of receptor ligand or drug that does not provoke a biological response itself upon binding to a receptor, but blocks or dampens agonist-mediated responses...
, to the nucleus raphes magnus.
All of this seems to indicate that the nucleus raphes magnus is part of the endogenous opiate system, and acts to inhibit pain in the spinal cord.