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| Spinothalamic tract | |
|---|---|
 Diagram showing the anterior and lateral spinothalamic tracts within thespinal cord - | |
| Details | |
| Part of | Spinal cord |
| System | Somatosensory system |
| Decussation | Anterior white commissure |
| Parts | Anterior and lateral tracts |
| From | Skin |
| To | Thalamus |
| Artery | Anterior spinal artery |
| Function | Gross touch and temperature |
| Identifiers | |
| Latin | tractus spinothalamicus |
| MeSH | D013133 |
| NeuroNames | 2058,810 |
| TA98 | A14.1.04.138 |
| TA2 | 6102 |
| FMA | 72644 |
| Anatomical terms of neuroanatomy | |
Thespinothalamic tract is anerve tract in theanterolateral system in thespinal cord.[1] This tract is an ascending sensory pathway to thethalamus. From theventral posterolateral nucleus in the thalamus, sensory information is relayed upward to thesomatosensory cortex of thepostcentral gyrus.
The spinothalamic tract consists of two adjacent pathways: anterior and lateral. The anterior spinothalamic tract carries information aboutcrude touch. The lateral spinothalamic tract conveyspain andtemperature.[2]
In thespinal cord, the spinothalamic tract hassomatotopic organization. This is the segmental organization of itscervical,thoracic,lumbar, andsacral components, which is arranged from most medial to most lateral respectively.
The pathway crosses over (decussates) at the level of the spinal cord, rather than in thebrainstem like thedorsal column-medial lemniscus pathway andlateral corticospinal tract. It is one of the three tracts which make up theanterolateral system: anterior and lateral spinothalamic tract,spinotectal tract,spinoreticular tract.
There are two main parts of the spinothalamic tract:
The spinothalamic tract, like thedorsal column-medial lemniscus pathway, uses three neurons to convey sensory information from the periphery to conscious level at the cerebral cortex.
Pseudounipolarneurons in thedorsal root ganglion have axons that lead from theskin into the dorsalspinal cord where they ascend or descend one or two vertebral levels viaLissauer's tract and thensynapse with secondary neurons in either thesubstantia gelatinosa of Rolando or thenucleus proprius. These secondary neurons are calledtract cells.
The axons of the tract cells cross over (decussate) to the other side of the spinal cord via theanterior white commissure, and to the anterolateral corner of the spinal cord (hence the spinothalamic tract being part of theanterolateral system). Decussation usually occurs 1-2 spinal nerve segments above the point of entry. The axons travel up the length of the spinal cord into thebrainstem, specifically therostral ventromedial medulla.
Traveling up the brainstem, the tract moves dorsally. The neurons ultimately synapse with third-order neurons in several nuclei of the thalamus—including the medial dorsal, ventral posterior lateral, and ventral posterior medial nuclei. From there, signals go to thecingulate cortex, theprimary somatosensory cortex, andinsular cortex respectively.
Theanterior spinothalamic tract (Latin:tractus spinothalamicus anterior) orventral spinothalamic fasciculus situated in the marginal part of theanterior funiculus and intermingled more or less with thevestibulospinal tract, is derived from cells in theposterior column or intermediategray matter of the opposite side.Aβ fibres carry sensory information pertaining to crude touch from the skin. After entering the spinal cord the first order neurons synapse (in the nucleus proprius), and the second order neurons decussate via theanterior white commissure. These second order neurons ascend synapsing in the VPL of the thalamus. Incoming first order neurons can ascend or descend via the Lissauer tract.
Its fibers convey crude touch information to the VPL (ventral posterolateral nucleus) of thethalamus.
The fibers of the anterior spinothalamic tract conduct information about pressure and crude touch (protopathic). The fine touch (epicritic) is conducted by fibers of the medial lemniscus. The medial lemniscus is formed by the axons of the neurons of the gracilis and cuneatus nuclei of the medulla oblongata which receive information about light touch, vibration and conscient proprioception from the gracilis and cuneatus fasciculus of the spinal cord. This fasciculus receive the axons of the first order neuron which is located in the dorsal root ganglion that receivesafferent fibers from receptors in the skin, muscles and joints.
High-resolution RNA sequencing finds the anterior spinothalamic tract has five distinct types of neurons. Three clusters of which are located mainly in laminae I–III of the dorsal horn and two clusters in deeper laminae.[3]
Thelateral spinothalamic tract (orlateral spinothalamic fasciculus), is a bundle ofafferent nerve fibers ascending through the white matter of thespinal cord, in the spinothalamic tract, carrying sensory information to thebrain. It carries pain, and temperature sensory information (protopathic sensation) to thethalamus. It is composed primarily of fast-conducting, sparselymyelinatedA delta fibers and slow-conducting, unmyelinatedC fibers. These are secondary sensory neurons which have alreadysynapsed with the primarysensory neurons of theperipheral nervous system in theposterior horn of the spinal cord (one of the threegrey columns).
There is evidence to suggest the existence of a projection from lamina I and deeper layers of the dorsal horn to the ventrobasal complex and other thalamic nuclei, eventually passing pain and temperature information to the SI and SII somatosensory cortices.[4] In macaque monkeys, neurons from the posterior part of the ventral medial nucleus terminate at the posterior half of the superior limiting sulcus that bounds the dorsal insular cortext.[5]
Together with the anterior spinothalamic tract, the lateral spinothalamic tract is sometimes termed thesecondary sensory fasciculus orspinal lemniscus.
The neurons of the lateral spinothalamic tract originate in thespinaldorsal root ganglia. They project peripheral processes to the tissues in the form of free nerve endings which are sensitive to molecules indicative of cell damage. The central processes enter the spinal cord in an area at the back of the posterior horn known as theposterolateral tract. Here, the processes ascend approximately two levels before synapsing on second-order neurons. These secondary neurons are situated in the posterior horn, specifically in theRexed laminae regions I, IV, V and VI. Region II is primarily composed ofGolgi IIinterneurons, which are primarily for the modulation of pain, and largely project to secondary neurons in regions I and V. Secondary neurons from regions I and V decussate across theanterior white commissure and ascend in the (now contralateral) lateral spinothalamic tract. These fibers will ascend through thebrainstem, including themedulla oblongata,pons andmidbrain, as the spinal lemniscus until synapsing in the ventroposteriorlateral (VPL) nucleus of thethalamus. The third order neurons in the thalamus will then project through theinternal capsule andcorona radiata to various regions of thecortex, primarily theprimary somatosensory cortex (Brodmann areas 3, 1, and 2).
The types of sensory information means that the sensation is accompanied by areflex.[citation needed]
There are two sub-systems identified:
Theanterolateral system (ALS) is an ascending bundle of fibers in the spinal cord, carried in three main pathways ortracts.[1] The tracts conveypain,[6]temperature (protopathic sensation), andcrude touch from the periphery to thebrain. The most important of these is the spinothalamic tract.[2]
| Name | Destination | Function |
|---|---|---|
| spinothalamic tract (lateral andanterior) | thalamus | important in the localization of painful or thermal stimuli |
| spinoreticular tract | reticular formation | causes alertness and arousal in response to painful stimuli |
| spinotectal tract | tectum | orients the eyes and head towards the stimuli |
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In contrast to the axons of second-order neurons indorsal column-medial lemniscus pathway, the axons of second-order neurons in the spinothalamic tracts cross at every segmental level in the spinal cord. This fact aids in determining whether a lesion is in the brain or the spinal cord. With lesions in the brain stem or higher, deficits of pain perception, touch sensation, and proprioception are all contralateral to the lesion. With spinal cord lesions, however, the deficit in pain perception is contralateral to the lesion, whereas the other deficits are ipsilateral. SeeBrown-Séquard syndrome.
Unilateral lesions usually cause contralateralanaesthesia (loss of pain and temperature). Anaesthesia will normally begin 1-2 segments below the level of lesion, due to the sensory fibers being carried by dorsal-lateral tract of Lissauer up several levels upon entry into the spinal cord, and will affect all caudal body areas. This is clinically tested by using pin pricks.
This article incorporates text in thepublic domain frompage 760 of the 20th edition ofGray's Anatomy(1918)
