The raphespinal tract is a descending spinal cord tract located in the

medulla oblongata The medulla oblongata or simply medulla is a long stem-like structure which makes up the lower part of the brainstem. It is anterior and partially inferior to the cerebellum. It is a cone-shaped neuronal mass responsible for autonomic (involun ...

. It consists of two tracts an anterior raphespinal tract, and a lateral raphespinal tract that mainly descend in the

lateral funiculus The most lateral of the bundles of the anterior nerve roots is generally taken as a dividing line that separates the anterolateral system into two parts. These are the anterior funiculus, between the anterior median fissure and the most lateral ...

Fibers Fiber (spelled fibre in British English; from ) is a natural or artificial substance that is significantly longer than it is wide. Fibers are often used in the manufacture of other materials. The strongest engineering materials often inco ...

descend in the ventral portion of the lateral funiculus, mainly bilaterally to terminate in laminae I, II, and IV. The tract emerges from three of the

raphe nuclei The raphe nuclei (, "seam") are a moderate-size cluster of nuclei found in the brain stem. They have 5-HT1 receptors which are coupled with Gi/Go-protein-inhibiting adenyl cyclase. They function as autoreceptors in the brain and decrease the ...

, the

magnus Magnus, meaning "Great" in Latin, was used as cognomen of Gnaeus Pompeius Magnus in the first century BC. The best-known use of the name during the Roman Empire is for the fourth-century Western Roman Emperor Magnus Maximus. The name gained wid ...

, obscurus, and pallidus. The fibers of the raphespinal tract are mainly serotonergic. When raphe nuclei are stimulated they release

serotonin Serotonin (), also known as 5-hydroxytryptamine (5-HT), is a monoamine neurotransmitter with a wide range of functions in both the central nervous system (CNS) and also peripheral tissues. It is involved in mood, cognition, reward, learning, ...

which modulates the transmission of

pain Pain is a distressing feeling often caused by intense or damaging Stimulus (physiology), stimuli. The International Association for the Study of Pain defines pain as "an unpleasant sense, sensory and emotional experience associated with, or res ...

Pathways

Pain pathways converging upon the raphe nuclei to modulate pain via the raphespinal tract include: ** Laminae I and V of spinal cord→ spinomesencephalic tract →

periaqueductal gray The periaqueductal gray (PAG), also known as the central gray, is a brain region that plays a critical role in autonomic function, motivated behavior and behavioural responses to threatening stimuli. PAG is also the primary control center for ...

→

nucleus raphe magnus The nucleus raphe magnus (NRM) is one of the seven raphe nuclei. It is situated in the pons in the brainstem, just rostral to the nucleus raphe obscurus. The NRM receives afferent stimuli from the enkephalinergic neurons of the periaqueductal ...

→ ** Laminae I and V of spinal cord → spinomesencephalic tract →

mesencephalon The midbrain or mesencephalon is the uppermost portion of the brainstem connecting the diencephalon and cerebrum with the pons. It consists of the cerebral peduncles, tegmentum, and tectum. It is functionally associated with vision, hearing, mo ...

→ **

Nociceptive In physiology, nociception , also nocioception; ) is the sensory nervous system's process of encoding noxious stimuli. It deals with a series of events and processes required for an organism to receive a painful stimulus, convert it to a molecular ...

group C Group C was a category of sports car racing introduced by the FIA in 1982 and continuing until 1993, with ''Group A'' for Touring car racing, touring cars and ''Group B'' for Grand tourer, GTs. It was designed to replace both Group 5 (motorspor ...

first-order

nerve fiber An axon (from Greek ἄξων ''áxōn'', axis) or nerve fiber (or nerve fibre: see spelling differences) is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action pot ...

→

interneurons Interneurons (also called internuncial neurons, association neurons, connector neurons, or intermediate neurons) are neurons that are not specifically motor neurons or sensory neurons. Interneurons are the central nodes of neural circuits, ena ...

of lamina II (substantia gelatinosa) and lamina III of the

posterior grey column The grey columns are three regions of the somewhat ridge-shaped mass of grey matter in the spinal cord. These regions present as three columns: the anterior grey column, the posterior grey column, and the lateral grey column, all of which are ...

of the spinal cord → second-order neurons of laminae V-VIII of spinal cord →

spinoreticular tract The spinoreticular tract (also paleospinothalamic pathway, or indirect pathway of the anterolateral system) is a partially decussating (crossed-over) four-neuron sensory pathway of the central nervous system. The tract transmits slow nociceptive/ ...

→

and gigantocellular raphe nucleus → * Raphespinal tract →

spinal trigeminal nucleus The spinal trigeminal nucleus is a nucleus in the medulla that receives information about deep/crude touch, pain, and temperature from the ipsilateral face. In addition to the trigeminal nerve (CN V), the facial (CN VII), glossopharyngeal (CN ...

and

of the spinal cord → activating serotonergic synapses with inhibitory enkephalinergic interneurons → inhibitory enkephalinergic synapses with nociceptive first-order nerve fibers.

Function

Electrical stimulation of either the periaqueductal gray or (its downstream target) nucleus raphe magnus induces profund

analgesia Pain management is an aspect of medicine and health care involving relief of pain (pain relief, analgesia, pain control) in various dimensions, from acute and simple to chronic and challenging. Most physicians and other health professionals ...

; this effect can be abolished both by transection of the raphespinal tract as well as by opioid receptor antagonists (evidencing one of the mechanisms by which

opioid Opioids are a class of Drug, drugs that derive from, or mimic, natural substances found in the Papaver somniferum, opium poppy plant. Opioids work on opioid receptors in the brain and other organs to produce a variety of morphine-like effects, ...

bring about pain relief). An electrical stimulator implant of the periaqueductal gray can be used clinically for pain management, evoking instantaneous pain relief upon activation. The raphespinal tract appears to also be involved in modulating motor activity as serotonin increases the excitability of motor neurons - serotonin-blocking medications can alleviate

spasticity Spasticity () is a feature of altered skeletal muscle performance with a combination of paralysis, increased tendon reflex activity, and hypertonia. It is also colloquially referred to as an unusual "tightness", stiffness, or "pull" of muscles. ...

caused by damage to the motor pathways.

References

{{Reflist Spinal cord tracts Motor system

Pathways

Function

See also

References