View source for Nucleus raphe magnus

{{Short description|Cluster of nuclei in the brain stem}}
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| Name            = Nucleus raphe magnus
| Latin           = nucleus raphes magnus
| Image           = Gray694.png
| Caption         = Section of the medulla oblongata at about the middle of the olive. (Raphe nuclei not labeled, but 'raphe' labeled at left.)
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The '''nucleus raphe magnus''' ('''NRM''')  is one of the seven [[raphe nuclei]]. It is situated in the [[pons]] in the [[brainstem]],<ref name="Patestas-2016">{{Cite book |last=Patestas |first=Maria A. |title=A Textbook of Neuroanatomy |last2=Gartner |first2=Leslie P. |date= |publisher=Wiley-Blackwell |year=2016 |isbn=978-1-118-67746-9 |edition=2nd |location=Hoboken, New Jersey}}</ref>{{Rp|page=306}} just rostral to the [[nucleus raphe obscurus]].{{Citation needed|date=August 2023}}

The NRM receives afferent stimuli from the [[Enkephalin|enkephalinergic]] neurons of the [[periaqueductal gray]]; the [[Serotonin|serotonergic]] neurons of the NRM then bilaterally project efferents to the enkephalinergic and dynorphin-containing interneurons of the [[Substantia gelatinosa of Rolando|substantia gelatinosa]] of the [[Posterior horn of spinal cord|posterior grey column of the spinal cord]]. This neural path thus mediates pain perception through pre-synaptic inhibition of first-order afferent (sensory) neurons.<ref name="Patestas-2016" />{{Rp|page=225}}

== Anatomy ==

=== Afferents ===
It receives afferents from the [[spinal cord]] and [[cerebellum]].{{Citation needed|date=August 2023}}

It receives descending afferents from the [[periaqueductal grey matter]] (PAG), the [[paraventricular hypothalamic nucleus]], central nucleus of the [[amygdala]], lateral [[hypothalamic]] area, [[parvocellular reticular nucleus]] and the prelimbic, infralimbic, medial and lateral precentral cortices.<ref>Hermann, Dirk M. et al.  Afferent projections to the rat nuclei raphe magnus, raphe pallidus and reticularis gigantocellularis pars demonstrated by iontophoretic application of choleratoxin (subunit b). Journal of Chemical Neuroanatomy Volume 13, Issue 1, June 1997, Pages 1-21</ref>{{Non-primary source needed|date=August 2023}} It is one of the afferent targets of the [[ascending reticular activating system]].<ref name="Patestas-2016" />{{Rp|page=311}}

=== Efferents ===
It projects efferents to the [[Posterior horn of spinal cord|posterior grey column]] (to modulate pain).<ref name="Haines" />

== Neurophysiology and function ==
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 the [[spinal cord]] and [[cerebellum]] suggest it may be a part of the [[motor system]].<ref>Hellman, Kevin et al. Activity of murine magnus raphe cells predicts tachypnea and on-going nociceptive responsiveness. Journal of Neurophysiology Volume 98, Issue 6, December 2007, Pages 3121-33.</ref>{{Non-primary source needed|date=August 2023}}<ref>Hellman, Kevin et al., Opioid microinjection into raphe magnus modulates cardiorespiratory function in mice and rats. American Journal of Physiology Regulator Integratory Comp Physiology. Volume 297, Issue 5, November 2009, Pages R1400-8.</ref>{{Non-primary source needed|date=August 2023}}

=== Pain modulation ===
The main function of the nucleus raphe magnus is pain mediation. The nucleus raphe magnus releases [[serotonin]] when stimulated. It sends projections to the [[enkephalin]]-releasing interneurons of the [[Posterior horn of spinal cord|posterior grey column]] to directly inhibit pain.<ref name="Haines">Haines, Duane E., and M. D. Ard. Fundamental Neuroscience for Basic and Clinical Applications. Philadelphia, PA: Elsevier/Saunders, 2013.</ref>

The [[Periaqueductal gray|periaqueductal gray (PAG)]], an area of the brain involved in mediating [[analgesia]], 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 produces [[analgesia]]; the [[antinociceptic]] effects of electrical stimulation of the PAG can be blocked by administering [[naloxone]] (an opiate [[Receptor antagonist|antagonist]]) to the nucleus raphe magnus. Similarly, afferent fibres from the [[spinothalamic 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|date=August 2023}}

==References==
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{{Rhombencephalon}}
{{Authority control}}

[[Category:Medulla oblongata]]
[[Category:Serotonin]]