View source for Spinothalamic tract

{{short description|Sensory pathway from the skin to the thalamus}}
{{More references needed|date=July 2024}}
{{Infobox tract
| Name            = Spinothalamic tract
| Latin           = tractus spinothalamicus
| Image           = 
| Image2          = Spinal Cord Sensory Pathways.png| 
| Caption2        = Diagram showing the anterior and lateral spinothalamic tracts within the [[spinal cord]] - 
|PartOf=[[Spinal cord]]| Components      =Anterior and lateral tracts
| Artery          =[[Anterior spinal artery]]
| Vein            =
|System=[[Somatosensory system]]|Function=Gross touch and temperature|From=[[Skin]]|To=[[Thalamus]]|Decussation=[[Anterior white commissure]]}}

The '''spinothalamic tract'''  is a [[nerve tract]] in  the [[anterolateral system]] in the [[spinal cord]].<ref name="Haines">{{cite book |last1=Haines |first1=Duane |title=Fundamental neuroscience for basic and clinical applications |date=2018 |publisher=Elsevier |location=Philadelphia, PA |isbn=9780323396325 |page=259 |edition=Fifth}}</ref> This tract is an ascending sensory pathway to the [[thalamus]]. From the [[ventral posterolateral nucleus]] in the thalamus, sensory information is relayed upward to the [[somatosensory cortex]] of the [[postcentral gyrus]].

The spinothalamic tract consists of two adjacent pathways: anterior and lateral. The anterior spinothalamic tract carries information about [[crude touch]]. The lateral spinothalamic tract conveys [[pain]] and [[temperature]].<ref name="Al-Chalabi">{{cite journal |last1=Al-Chalabi |first1=Mustafa |last2=Reddy |first2=Vamsi |last3=Gupta |first3=Sonu |title=Neuroanatomy, Spinothalamic Tract |url=https://www.ncbi.nlm.nih.gov/books/NBK507824/ |website=StatPearls |publisher=StatPearls Publishing |access-date=19 July 2024 |date=2024|pmid=29939601 }}</ref>

In the [[spinal cord]], the spinothalamic tract has [[somatotopic arrangement|somatotopic organization]]. This is the segmental organization of its [[Neck|cervical]], [[thoracic]], [[lumbar]], and [[Sacrum|sacral]] 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 the [[brainstem]] like the [[dorsal column-medial lemniscus pathway]] and [[lateral corticospinal tract]]. It is one of the three tracts which make up the [[Spinothalamic tract#Anterolateral system|anterolateral system]]: anterior and lateral spinothalamic tract, [[spinotectal tract]], [[spinoreticular tract]].

==Structure==
[[File:Spinal cord tracts - English.svg|thumb|upright= 1.8|The anterior and lateral spinothalamic tracts labelled at lower right as tracts of the anterolateral system.]] 
There are two main parts of the spinothalamic tract: 
* The [[lateral spinothalamic tract]] transmits [[pain]] and [[temperature]].
* The [[anterior spinothalamic tract]] (or ''ventral'' spinothalamic tract) transmits crude touch and firm pressure.

The spinothalamic tract, like the [[dorsal column-medial lemniscus pathway]], uses three neurons to convey sensory information from the periphery to conscious level at the cerebral cortex.

[[Pseudounipolar]] [[neuron]]s in the [[dorsal root ganglion]] have axons that lead from the [[skin]] into the dorsal [[spinal cord]] where they ascend or descend one or two vertebral levels via [[Lissauer's tract]] and then [[synapse]] with secondary neurons in either the [[substantia gelatinosa of Rolando]] or the [[nucleus proprius]]. These secondary neurons are called ''tract cells''.

The axons of the tract cells cross over (decussate) to the other side of the spinal cord via the [[anterior white commissure]], and to the anterolateral corner of the spinal cord (hence the spinothalamic tract being part of the [[anterolateral 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 the [[brainstem]], specifically the [[rostral 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 the [[cingulate cortex]], the [[primary somatosensory cortex]], and [[insular cortex]] respectively.

===Anterior spinothalamic tract===
The  '''anterior spinothalamic tract''' (Latin: ''tractus spinothalamicus anterior'') or '''ventral spinothalamic fasciculus''' situated in the marginal part of the [[anterior funiculus]] and intermingled more or less with the [[vestibulospinal tract]], is derived from cells in the [[posterior column]] or intermediate [[gray matter]] of the opposite side.  [[Type II sensory fiber|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 the [[anterior 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 the [[thalamus]].

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 receives [[afferent nerve fiber|afferent 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.<ref name="k847">{{cite journal |last1=Bell |first1=Andrew M. |last2=Utting |first2=Charlotte |last3=Dickie |first3=Allen C. |last4=Kucharczyk |first4=Mateusz W. |last5=Quillet |first5=Raphaëlle |last6=Gutierrez-Mecinas |first6=Maria |last7=Razlan |first7=Aimi N. B. |last8=Cooper |first8=Andrew H. |last9=Lan |first9=Yuxuan |last10=Hachisuka |first10=Junichi |last11=Weir |first11=Greg A. |last12=Bannister |first12=Kirsty |last13=Watanabe |first13=Masahiko |last14=Kania |first14=Artur |last15=Hoon |first15=Mark A. |date=2024 |title=Deep sequencing of Phox2a nuclei reveals five classes of anterolateral system neurons |journal=Proceedings of the National Academy of Sciences |volume=121 |issue=23 |doi=10.1073/pnas.2314213121 |issn=0027-8424 |last16=Macaulay |first16=Iain C. |last17=Denk |first17=Franziska |last18=Todd |first18=Andrew J.|pages=e2314213121 |doi-access=free |pmid=38805282 |pmc=11161781 |bibcode=2024PNAS..12114213B }}</ref>

===Lateral spinothalamic tract===
The '''lateral spinothalamic tract''' (or '''lateral spinothalamic fasciculus'''), is a bundle of [[afferent nerve fiber]]s ascending through the white matter of the [[spinal cord]], in the spinothalamic tract, carrying sensory information to the [[human brain|brain]]. It carries pain, and temperature sensory information ([[protopathic sensation]]) to the [[thalamus]]. It is composed primarily of fast-conducting, sparsely [[myelinated]] [[A delta fiber]]s and slow-conducting, unmyelinated [[Group C nerve fiber|C fibers]]. These are secondary sensory neurons which have already [[synapse]]d with the primary [[sensory neuron]]s of the [[peripheral nervous system]] in the [[posterior horn of spinal cord|posterior horn of the spinal cord]] (one of the three [[grey column]]s).

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.<ref>{{cite journal |last1=Willis |first1=William D. |last2=Zhang |first2=Xijing |last3=Honda |first3=Christopher N. |last4=Giesler |first4=Glenn J. |title=A critical review of the role of the proposed VMpo nucleus in pain |journal=The Journal of Pain |date=1 April 2002 |volume=3 |issue=2 |pages=79–94 |doi=10.1054/jpai.2002.122949 |pmid=14622792 |url=https://www.sciencedirect.com/science/article/pii/S1526590002798428 |issn=1526-5900|url-access=subscription }}</ref> 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.<ref>{{cite journal |last1=Craig |first1=A.D. (Bud) |title=Topographically Organized Projection to Posterior Insular Cortex from the Posterior Portion of the Ventral Medial Nucleus (VMpo) in the Long-tailed Macaque Monkey |journal=The Journal of Comparative Neurology |date=1 January 2014 |volume=522 |issue=1 |pages=36–63 |doi=10.1002/cne.23425 |pmid=23853108 |pmc=4145874 |issn=0021-9967}}</ref>

Together with the anterior spinothalamic tract, the lateral spinothalamic tract is sometimes termed the ''secondary sensory fasciculus'' or ''spinal lemniscus''.

====Anatomy====
The neurons of the lateral spinothalamic tract originate in the [[spinal column|spinal]] [[dorsal root ganglion|dorsal 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 the [[posterolateral 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 the [[Rexed laminae]] regions I, IV, V and VI.  Region II is primarily composed of [[Golgi II]] [[interneuron]]s, 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 the [[anterior white commissure]] and ascend in the (now contralateral) lateral spinothalamic tract. These fibers will ascend through the [[brainstem]], including the [[medulla oblongata]], [[pons]] and [[midbrain]], as the spinal lemniscus until synapsing in the ventroposteriorlateral (VPL) nucleus of the [[thalamus]].  The third order neurons in the thalamus will then project through the [[internal capsule]] and [[corona radiata]] to various regions of the [[cerebral cortex|cortex]], primarily the [[primary somatosensory cortex]] ([[Brodmann area]]s 3, 1, and 2).

==Function==
The types of sensory information means that the sensation is accompanied by a [[reflex]].{{citation needed|date=November 2016}}

There are two sub-systems identified: 
* Direct (for direct conscious appreciation of pain) 
* Indirect (for affective and arousal impact of pain). Indirect projections include 
** Spino-Reticulo-Thalamo-Cortical (part of the [[ascending reticular activating system]] (ARAS)
** Spino-Mesencephalic-Limbic (for affective impact of pain).

===Anterolateral system===
The [[anterolateral system]] (ALS) is an ascending bundle of fibers in the spinal cord, carried in three main pathways or [[nerve tract|tracts]].<ref name="Haines"/> The tracts  convey [[pain]],<ref name="urlChapter 25:Neural Mechanisms of Cardiac Pain: The Anterolateral System">{{cite web |url=http://symptomresearch.nih.gov/chapter_25/sec3/crfs3pg1.htm |title=Chapter 25:Neural Mechanisms of Cardiac Pain: The Anterolateral System |access-date=2009-11-26 |url-status=dead |archive-url=https://web.archive.org/web/20100811084717/http://symptomresearch.nih.gov/chapter_25/sec3/crfs3pg1.htm |archive-date=2010-08-11 }}</ref> [[temperature]] ([[protopathic sensation]]), and [[crude touch]] from the periphery to the [[brain]]. The most important of these is the spinothalamic tract.<ref name="Al-Chalabi"/>

{| class="wikitable"
! Name !! Destination !! Function
|-
| spinothalamic tract ([[Lateral spinothalamic tract|lateral]] and [[Anterior spinothalamic tract|anterior]]) || [[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
|}

==Clinical significance==
{{Unreferenced section|date=July 2024}}
In contrast to the axons of second-order neurons in [[dorsal 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. See [[Brown-Séquard syndrome]].

Unilateral lesions usually cause contralateral [[anaesthesia]] (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.

==See also==
{{Anatomy-terms}}
* [[Periaqueductal gray]]
* [[Neothalamus]]

==References==
{{Gray's}}
{{Reflist}}

==External links==
* {{BrainInfo|ancil|964}}
* [https://web.archive.org/web/20060828114210/http://www.mfi.ku.dk/ppaulev/chapter3/images/fp3-9.jpg Diagram at mfi.ku.dk]
* [https://web.archive.org/web/20050910003921/http://www.uwm.edu/~tking/king3_6.htm Overview at uwm.edu]

{{Somatosensory system}}
{{Spinal cord}}
{{Medulla}}
{{Pons}}
{{Mesencephalon}}
{{Diencephalon}}
{{Neural tracts}}
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[[Category:Spinal cord tracts]]
[[Category:Sensory systems]]
[[Category:Thalamic connections]]