| Nucleus raphe magnus | |
|---|---|
 Section of the medulla oblongata at about the middle of the olive. (Raphe nuclei not labeled, but 'raphe' labeled at left.) | |
| Details | |
| Identifiers | |
| Latin | nucleus raphes magnus |
| MeSH | D065846 |
| NeuroNames | 739 |
| NeuroLex ID | birnlex_1363 |
| TA98 | A14.1.04.321 |
| TA2 | 6038 |
| FMA | 72584 |
| Anatomical terms of neuroanatomy | |
Thenucleus raphe magnus (NRM) is one of the sevenraphe nuclei. It is situated in thepons in thebrainstem,[1]: 306 just rostral to thenucleus raphe obscurus.[citation needed]
The NRM receives afferent stimuli from theenkephalinergic neurons of theperiaqueductal gray; theserotonergic neurons of the NRM then bilaterally project efferents to the enkephalinergic and dynorphin-containing interneurons of thesubstantia gelatinosa of theposterior grey column of the spinal cord. This neural path thus mediates pain perception through pre-synaptic inhibition of first-order afferent (sensory) neurons.[1]: 225
It receives afferents from thespinal cord andcerebellum.[citation needed]
It receives descending afferents from theperiaqueductal grey matter (PAG), theparaventricular hypothalamic nucleus, central nucleus of theamygdala, lateralhypothalamic area,parvocellular reticular nucleus and the prelimbic, infralimbic, medial and lateral precentral cortices.[2][non-primary source needed] It is one of the afferent targets of theascending reticular activating system.[1]: 311
It projects efferents to theposterior grey column (to modulate pain).[3]
The nucleus raphe magnus seems to participate in the endogenous analgesia system. Mounting evidence suggests that the nucleus raphe magnus plays an important role in homeostatic regulation. Its afferents from thespinal cord andcerebellum suggest it may be a part of themotor system.[4][non-primary source needed][5][non-primary source needed]
The main function of the nucleus raphe magnus is pain mediation. The nucleus raphe magnus releasesserotonin when stimulated. It sends projections to theenkephalin-releasing interneurons of theposterior grey column to directly inhibit pain.[3]
Theperiaqueductal gray (PAG), an area of the brain involved in mediatinganalgesia, sends efferent stimuli to the nucleus raphe magnus when stimulated by opioids (endogenous or otherwise); electrical stimulation of the PAG as well as administration of opioid agonists to the PAG or nucleus raphe magnus producesanalgesia; theantinociceptic effects of electrical stimulation of the PAG can be blocked by administeringnaloxone (an opiateantagonist) to the nucleus raphe magnus. Similarly, afferent fibres from thespinothalamic tract synapse at the periaqueductal grey matter which in turn projects to the nucleus raphe magnus, which when stimulated directly inhibits pain fibers in the posterior grey column, alleviating pain. All of this seems to indicate that the nucleus raphe magnus is part of the endogenous opiate system, and acts to inhibit pain in the spinal cord.[citation needed]
