Raphe nuclei
Encyclopedia
The raphe nuclei are a moderate-size cluster of nuclei
found in the brain stem
. Their main function is to release serotonin
to the rest of the brain
. Selective serotonin reuptake inhibitor
(SSRI) antidepressant
s are believed to act in these nuclei, as well as at their targets.
, 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:
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
Many of the neurons in the nuclei (but not the majority) are serotonergic; i.e., contain serotonin
, a type of monoamine neurotransmitter. 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.
Projections from the raphe nuclei also terminate in the dorsal horn of spinal gray matter where they regulate the release of enkephalins, which inhibit pain sensation.
The raphe nuclei provides feedback to the suprachiasmatic nuclei (SCN), thus contributing in circadian rhythms in animals. The SCN transmits to the raphe nuclei via the dorsomedial hypothalamus nucleus altering serotonin levels for sleep/wake states. The raphe nuclei will then transmit feedback to the SCN about the animal's vigilance and levels of alertness. This reciprocal feedback between the two structures provides an adaptable yet stable basis of circadian rhythms.
Nucleus (neuroanatomy)
In neuroanatomy, a nucleus is a brain structure consisting of a relatively compact cluster of neurons. It is one of the two most common forms of nerve cell organization, the other being layered structures such as the cerebral cortex or cerebellar cortex. In anatomical sections, a nucleus shows up...
found in the brain stem
Brain stem
In vertebrate anatomy the brainstem is the posterior part of the brain, adjoining and structurally continuous with the spinal cord. The brain stem provides the main motor and sensory innervation to the face and neck via the cranial nerves...
. Their main function is to release serotonin
Serotonin
Serotonin or 5-hydroxytryptamine is a monoamine neurotransmitter. Biochemically derived from tryptophan, serotonin is primarily found in the gastrointestinal tract, platelets, and in the central nervous system of animals including humans...
to the rest of the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
. Selective serotonin reuptake inhibitor
Selective serotonin reuptake inhibitor
Selective serotonin re-uptake inhibitors or serotonin-specific reuptake inhibitor are a class of compounds typically used as antidepressants in the treatment of depression, anxiety disorders, and some personality disorders. The efficacy of SSRIs is disputed...
(SSRI) antidepressant
Antidepressant
An antidepressant is a psychiatric medication used to alleviate mood disorders, such as major depression and dysthymia and anxiety disorders such as social anxiety disorder. According to Gelder, Mayou &*Geddes people with a depressive illness will experience a therapeutic effect to their mood;...
s are believed to act in these nuclei, as well as at their targets.
Anatomy
The raphe nuclei are traditionally considered to be the medial portion of the reticular formationReticular formation
The reticular formation is a part of the brain that is involved in actions such as awaking/sleeping cycle, and filtering incoming stimuli to discriminate irrelevant background stimuli...
, and they
appear as a ridge of cells in the center and most medial portion of the brain stem
Brain stem
In vertebrate anatomy the brainstem is the posterior part of the brain, adjoining and structurally continuous with the spinal cord. The brain stem provides the main motor and sensory innervation to the face and neck via the cranial nerves...
.
In order from caudal to rostral, the raphe nuclei are known as the nucleus raphe obscurus
Nucleus raphe obscurus
The nucleus raphes obscurus, despite the implications of its name, has some very specific functions and connections of afferent and efferent nature. The nucleus raphes obscurus projects to the cerebellar lobes VI and VII and to crus II along with the nucleus raphes pontis .This so called nucleus...
, the raphe magnus, the raphe pontis, the raphe pallidus, the nucleus centralis superior
Nucleus centralis superior
The median raphe nucleus is composed of polygonal, fusiform and pyriform neurons and exists rostral to the nucleus raphe pontis....
, nucleus raphe dorsalis
Nucleus raphe dorsalis
The dorsal raphe nucleus is located on the midline of the brainstem and is part of the raphe nucleus, consisting of the rostral and caudal subdivisions....
, 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
NeuroNames
NeuroNames is an integrated nomenclature for structures in the brain and spinal cord of the four species most studied by neuroscientists: human, macaque, rat and mouse. It offers a standard, controlled vocabulary of common names for structures, which is suitable for unambiguous neuroanatomical...
makes the following ordering:
- Raphe nuclei of medullaMedulla oblongataThe medulla oblongata is the lower half of the brainstem. In discussions of neurology and similar contexts where no ambiguity will result, it is often referred to as simply the medulla...
- Nucleus raphe obscurusNucleus raphe obscurusThe nucleus raphes obscurus, despite the implications of its name, has some very specific functions and connections of afferent and efferent nature. The nucleus raphes obscurus projects to the cerebellar lobes VI and VII and to crus II along with the nucleus raphes pontis .This so called nucleus...
(nucleus raphe obscurus) - Nucleus raphe magnusNucleus raphe magnusThe nucleus raphes magnus, located directly rostral to the nucleus raphes obscurus, is afferently stimulated from axons in the spinal cord and cerebellum....
(raphe magnus) - Nucleus pallidus (raphe pallidus)
- Nucleus raphe obscurus
- Raphe nuclei of the pontinePontinePontine may refer to:* Having to do with the pons, a structure located in the brain stem * Pontine Marshes, a region of Italy near Rome* Pontine Islands, islands of Italy near Circeo...
reticular formation- Pontine raphe nucleusPontine raphe nucleusThe Pontine raphe nucleus is one of the raphe nuclei. It is located in the pontine tegmentum....
(raphe pontis) - Inferior central nucleus
- Pontine raphe nucleus
- Raphe nuclei of the midbrain reticular formation
- Superior central nucleus (nucleus centralis superior)
- Dorsal raphe nucleus (nucleus raphe dorsalis)
Projections
These nuclei interact with almost every pertinent portion of the brain, but only a few of them have specifically independent interaction. 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
Function
The raphe nuclei have a vast impact upon the central nervous system.Many of the neurons in the nuclei (but not the majority) are serotonergic; i.e., contain serotonin
Serotonin
Serotonin or 5-hydroxytryptamine is a monoamine neurotransmitter. Biochemically derived from tryptophan, serotonin is primarily found in the gastrointestinal tract, platelets, and in the central nervous system of animals including humans...
, a type of monoamine neurotransmitter. 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.
Projections from the raphe nuclei also terminate in the dorsal horn of spinal gray matter where they regulate the release of enkephalins, which inhibit pain sensation.
The raphe nuclei provides feedback to the suprachiasmatic nuclei (SCN), thus contributing in circadian rhythms in animals. The SCN transmits to the raphe nuclei via the dorsomedial hypothalamus nucleus altering serotonin levels for sleep/wake states. The raphe nuclei will then transmit feedback to the SCN about the animal's vigilance and levels of alertness. This reciprocal feedback between the two structures provides an adaptable yet stable basis of circadian rhythms.
See also
- Locus ceruleusLocus ceruleusThe locus coeruleus , is a nucleus in the brainstem involved with physiological responses to stress and panic. It was discovered in the 18th century by Félix Vicq-d'Azyr....
- Substantia nigraSubstantia nigraThe substantia nigra is a brain structure located in the mesencephalon that plays an important role in reward, addiction, and movement. Substantia nigra is Latin for "black substance", as parts of the substantia nigra appear darker than neighboring areas due to high levels of melanin in...
- Pedunculopontine nucleusPedunculopontine nucleusThe pedunculopontine nucleus is located in the brainstem, caudal to the substantia nigra and adjacent to the superior cerebellar peduncle. It has two divisions, one containing cholinergic neurons, the pars compacta, and one containing mostly glutamatergic neurons, the pars dissipata...
- List of regions in the human brain