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The raphe nuclei (Latin for 'the bit in a fold or seam') is a moderate-size cluster of nuclei found in the brain stem, and releases serotonin to the rest of the brain. Selective serotonin reuptake inhibitor (SSRI) antidepressants are believed to act at these nuclei.
Anatomy
The raphe nuclei are traditionally considered to be the medial portion of the reticular formation, and they appear as a ridge of cells in the center and most medial portion of the brain stem.
In order from caudal to rostral, the raphe nuclei are known as the nucleus raphe obscurus, the raphe magnus, the raphe pontis, the raphe pallidus, the nucleus centralis superior, nucleus raphe dorsalis, nuclei linearis intermedius and linearis rostralis. Some scientists chose to group the linearis nuclei into one nucleus, shrinking the number of raphe to seven, e.g., NeuroNames makes the following ordering:
- Raphe nuclei of medulla
- Raphe nuclei of the pontine reticular formation
- Raphe nuclei of the midbrain reticular formation
Projections
All of these nuclei have fascinating interactions with almost every pertinent portion of the brain, but only a few of them have specifically independent interaction worth exploring in their own right. These select nuclei are discussed as follows.Overall, the caudal raphe nuclei, including the raphe magnus, pallidus and raphe obscurus, all project towards the spinal cord and brain stem. The more-rostral nuclei, including the raphe pontis, centralis (also called median), dorsal, tend to project towards the brain areas of higher function.
The 8 raphe nuclei receive afferent connections from some of the most fascinating spots in the brain, only to project back to them and alter their processes.
Function
The raphe nuclei have a vast impact upon the central nervous system. The raphe nuclei can be of particular interest to neurologists and psychologists since many of the neurons in the nuclei (but not the majority) are serotonergic, i.e., contain serotonin - a type of monoamine neurotransmitter. Serotonin, also called 5-HT, seems to be the culprit in many of our modern psycho-pharmaceutical problems, such as anorexia, depression, and sleep disorders. It is not the sole culprit in the aforementioned disorders, but it is the area that the pharmacologists know how to affect in the best manner. It is important to note that pharmacology traditionally affects global serotonin levels, while the actions of the raphe nuclei are dependent on the complex interplay between nuclei.
References
See also
"Raphe nuclei"