Hubbry Logo
Posterolateral tractPosterolateral tractMain
Open search
Posterolateral tract
Community hub
Posterolateral tract
logo
8 pages, 0 posts
0 subscribers
Be the first to start a discussion here.
Be the first to start a discussion here.
Posterolateral tract
Posterolateral tract
Posterolateral tract
View on Wikipedia
from Wikipedia
Posterolateral tract
Diagram showing a few of the connections of afferent (sensory) fibers of the posterior root with the efferent fibers from the ventral column and with the various long ascending fasciculi. (Lissauer's fasciculus visible in upper left.)
Diagram of the principal fasciculi of the spinal cord. (Lissauer's fasciculus visible in upper right.)
Details
Identifiers
Latintractus posterolateralis
NeuroNames782
NeuroLex IDnlx_143969
TA98A14.1.02.228
TA26092
FMA72616
Anatomical terms of neuroanatomy

The posterolateral tract (fasciculus of Lissauer, Lissauer's tract, tract of Lissauer, dorsolateral fasciculus, dorsolateral tract, zone of Lissauer) is a small strand situated in relation to the tip of the posterior column close to the entrance of the posterior nerve roots. It is present throughout the spinal cord, and is most developed in the upper cervical regions.

Structure

[edit]

The posterolateral tract contains centrally projecting axons from dorsal root ganglion cells carrying peripheral pain and temperature information (location, intensity and quality). These axons enter the spinal column and penetrate the grey matter of the dorsal horn, where they synapse on second-order neurons in either the substantia gelatinosa of Rolando or the nucleus proprius. Those neurons project their axon to the anterolateral quadrant of the contralateral half of the spinal cord, where they give the spinothalamic tract. The axons of second-order neurons ultimately synapse on neurons in the ventral posterior lateral nucleus (VPL) of the thalamus after coursing in the spinal lemniscus. After this, the 3rd order neuron fibers traverse the internal capsule and the corona radiata, ultimately synapsing in the post central gyrus (somatosensory cortex). The location of this synapse is dependent upon the somatotopic organisation of the somatosensory cortex, it can be estimated according to the position on the 'somatosensory homunculus'

The posterolateral tract consists of fine fibers which do not receive their myelin sheaths until toward the close of fetal life. In addition it contains great numbers of fine non-myelinated fibers derived mostly from the dorsal roots but partly endogenous in origin.

These fibers are intimately related to the substantia gelatinosa[1] which is probably their terminal nucleus.

The non-myelinated fibers ascend or descend for short distances not exceeding one or two segments, but most of them enter the substantia gelatinosa at or near the level of their origin.

Clinical significance

[edit]

During a complete occlusion of the ventral artery of the spinal cord, it is the only tract spared along with the dorsal columns. The posterolateral spinal tracts are involved with neurological deficits seen in pernicious anemia.

Eponym

[edit]

The tract of Lissauer was named after German neurologist Heinrich Lissauer (1861-1891).

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Posterolateral tract

View on Grokipedia
from Grokipedia
The posterolateral tract, also known as Lissauer's tract or the dorsolateral tract, is a narrow bundle of unmyelinated and thinly myelinated axons situated in the posterolateral of the , immediately adjacent to the apex of the dorsal (posterior) horn. It primarily comprises the intraspinal branches of primary afferent fibers from dorsal root ganglia that transmit nociceptive () and thermoreceptive () signals, allowing these fibers to ascend or descend for one to two spinal segments before penetrating the dorsal horn to synapse with second-order neurons. This tract plays a crucial role in the initial processing of somatosensory information within the anterolateral system, particularly for sharp pain, crude touch, and temperature discrimination from the contralateral side of the body. Upon synapsing in laminae I and II (substantia gelatinosa) of the dorsal horn, the second-order neurons decussate (cross) via the anterior white commissure to join the lateral and anterior spinothalamic tracts, which then ascend contralaterally through the to thalamic nuclei and ultimately the somatosensory cortex. The tract's fibers originate from small-diameter Aδ and C nociceptors in peripheral nerves, ensuring rapid or prolonged transmission of aversive stimuli to facilitate protective reflexes and conscious perception. Named after German neurologist Heinrich Lissauer, who described it in 1885, the posterolateral tract is evolutionarily conserved across vertebrates and is essential for gating pain signals in the , with disruptions linked to conditions like central pain syndromes or . Its superficial position makes it vulnerable to certain pathologies, such as in , where degeneration can impair pain and temperature sensation below the lesion level. In clinical , the tract is visualized via in MRI studies, aiding in the diagnosis of injuries affecting sensory pathways.

Anatomy

Location and gross structure

The posterolateral tract, also known as Lissauer's tract or the dorsolateral fasciculus, is a longitudinal bundle of fibers situated in the posterolateral aspect of the , immediately lateral to the dorsal horn. It occupies the dorsolateral region within the lateral funiculus, wedged between the dorsal horn and the surface of the cord. This tract extends the full length of the , from cervical to levels, running parallel to the posterolateral sulcus near the dorsal root entry zone. Individual fibers within the tract typically ascend or descend only 1–2 spinal segments before synapsing, forming a continuous pathway along the cord's axis. In gross anatomical cross-sections, the posterolateral tract appears as a thin, ribbon-like structure of small, fine myelinated axons, bordered medially by the dorsal horn and laterally by the broader lateral funiculus. It is visible as a distinct, narrow band at the tips of the dorsal horns, though its subtle size makes it more prominent in histological preparations than in macroscopic views.

Microscopic composition

The posterolateral tract, also known as Lissauer's tract, is composed primarily of unmyelinated and thinly myelinated axons originating from sensory neurons in the dorsal root ganglia. These axons represent the peripheral processes of small-diameter primary afferents that enter the via the dorsal roots. The tract itself is a narrow bundle of fibers located along the posterolateral aspect of the dorsal horn, containing a mix of ascending and descending segments that allow for short rostrocaudal travel before synaptic termination. The population within the tract predominantly includes A-delta (Aδ) fibers, which are thinly myelinated with diameters of 1-5 μm and conduction velocities of 5-30 m/s, and C-type fibers, which are unmyelinated with diameters less than 1 μm and slower conduction velocities of 0.5-2 m/s. These fiber types specifically convey nociceptive signals for and thermoreceptive signals for temperature, with Aδ fibers mediating sharp, localized sensations and C fibers handling dull, diffuse ones. Upon entering the , these axons course for 1-3 segments in the posterolateral tract before branching to primarily in Rexed lamina I (marginal zone) and lamina II (substantia gelatinosa) of the ipsilateral dorsal horn. Histologically, the tract's composition is characterized by its predominance of small-diameter fibers exhibiting variable myelination, appearing as a distinct band of lightly stained or unstained elements in myelin-specific preparations due to the scarcity of thick sheaths. Confirmation of this fine axonal makeup has been achieved through classical histological techniques such as silver impregnation, which selectively highlights the unmyelinated and thinly myelinated components, rendering the tract more darkly stained compared to adjacent myelinated pathways. This method, pioneered in early neuroanatomical studies, underscores the tract's role as a conduit for thinly insulated sensory afferents rather than heavily myelinated proprioceptive or touch fibers.

Relations to adjacent structures

The posterolateral tract occupies the dorsolateral portion of the lateral funiculus in the . Its medial boundary abuts the apex of the dorsal horn ( I-II), where primary afferents synapse with second-order neurons; these axons then decussate obliquely through the anterior white commissure, typically 1-2 segments rostral to their entry level, before ascending contralaterally in the spinothalamic tracts. Laterally, the tract lies superficial (peripheral) to the dorsal spinocerebellar tract within the lateral funiculus and deep (central) to the dorsal root entry zone at the posterolateral sulcus, positioning it ventral to incoming sensory rootlets. Inter-segmentally, its ascending fibers remain segregated in the lateral , distinct from the ipsilateral gracile and cuneate tracts confined to the posterior (dorsal) columns, though both pathways process somatosensory inputs from shared peripheral origins before diverging. The tract's vascular supply derives primarily from branches of the posterior spinal arteries, which perfuse the posterolateral .

Function

Role in ascending sensory pathways

The posterolateral tract, also known as the tract of Lissauer, serves as the initial entry point and a short-distance relay within the anterolateral system, facilitating the transmission of crude touch, , and sensations from peripheral afferents to second-order neurons in the dorsal horn. Primary sensory afferents from dorsal roots, primarily Aδ and C fibers, enter the and immediately bifurcate into ascending and descending branches that travel 1-2 segments within the tract before penetrating the gray matter. These fibers then synapse onto second-order neurons predominantly in I (marginal zone) and II (substantia gelatinosa) of the ipsilateral dorsal horn. The tract specifically conveys non-discriminative sensory modalities, including fast, sharp mediated by thinly myelinated Aδ fibers and slow, dull along with crude touch via unmyelinated C fibers, as well as warm and cold temperature sensations. Aδ fibers transmit localized, acute pricking at conduction velocities of 5-40 m/s, while C fibers carry diffuse, burning and thermal information more slowly. This segregation allows for the initial processing of noxious and thermal stimuli before integration in higher centers. Following synaptic relay in the dorsal horn, second-order neurons decussate through the anterior white commissure and join the contralateral anterolateral spinothalamic tracts—the lateral tract for and , and the anterior tract for crude touch—before ascending through the to terminate in the ventral posterolateral (VPL) nucleus of the . From the VPL nucleus, third-order thalamic neurons project to the (S1) in the , enabling conscious perception of these sensations. This pathway sequence ensures efficient relay of essential survival-related sensory information while bypassing fine discriminative processing handled by other tracts.

Signal modulation and integration

The posterolateral tract, also known as Lissauer's tract, facilitates gating mechanisms for sensory signals through interactions with in the substantia gelatinosa (Rexed lamina II) of the dorsal horn, where primary afferent fibers synapse and undergo modulation. These provide presynaptic and postsynaptic inhibition to fine-tune nociceptive and thermal inputs, as outlined in the of , which posits that non-nociceptive afferents can activate inhibitory circuits to suppress transmission at this level. Descending inhibitory pathways from the (PAG) in the further engage these gating processes by releasing endogenous opioids that hyperpolarize dorsal horn neurons, reducing the excitability of fibers within the posterolateral tract. Integration with adjacent neural elements occurs through propriospinal neurons, which are local intersegmental circuits that influence dorsal horn processing to adjust sensory signals for segmental reflexes prior to their relay to higher centers like the . This allows for dynamic processing of somatosensory information, where propriospinal projections from nearby laminae influence the tract's output, enabling coordinated responses to stimuli across spinal levels without immediate supraspinal involvement. Neurotransmitter dynamics in the posterolateral tract's synaptic zones primarily involve glutamate as the excitatory mediator released by primary afferents to activate postsynaptic neurons in the dorsal horn. Local inhibition is mediated by enkephalins from opioid-containing and GABA from neurons in the substantia gelatinosa, which dampen excessive signaling and contribute to the tract's role in balanced sensory integration. In adaptive contexts, the posterolateral tract supports central sensitization, where repeated nociceptive firing patterns enhance synaptic efficacy in the dorsal horn, amplifying pain perception through mechanisms like activation and . This process underscores the tract's involvement in activity-dependent plasticity, allowing the to adapt to persistent stimuli while maintaining overall sensory .

Clinical significance

Pathological conditions

Syringomyelia involves the formation of a fluid-filled , or , within the , which expands and compresses surrounding neural structures, including the posterolateral tract of Lissauer and the decussating fibers of the spinothalamic pathway. This compression disrupts the transmission of and sensations while sparing the dorsal columns responsible for touch and , resulting in a characteristic often described as a "cape-like" distribution across the shoulders and arms. Patients typically experience bilateral loss of and sensation below the level of the , with preserved fine touch, leading to injuries from unnoticed burns or cuts in affected areas. Tabes dorsalis, a late manifestation of , causes demyelination primarily in the dorsal roots and posterior columns, impairing nociceptive relay through degeneration of incoming sensory fibers. This leads to severe, paroxysmal "lightning pains" in the lower extremities due to aberrant firing in damaged nociceptive pathways, alongside from proprioceptive deficits. The manifests as a wide-based, staggering worsened in the dark, as patients rely on visual cues to compensate for lost position sense, and is often accompanied by Argyll Robertson pupils. Spinal cord trauma resulting in lateral hemisection, as seen in Brown-Séquard syndrome, damages the posterolateral tract on the ipsilateral side, contributing to loss of and sensation at the level of the lesion, while interruption of the produces contralateral loss beginning one or two segments below. Ipsilateral and motor function are also affected due to involvement of adjacent tracts. The syndrome often arises from penetrating injuries like stab wounds and highlights the tract's role in lateralized sensory processing, with recovery varying based on the extent of axonal sparing. Inflammatory conditions such as feature demyelinating plaques that disrupt spinothalamic conduction, leading to dysesthesias like burning or tingling sensations in the limbs. These plaques induce central hyperexcitability and partial deafferentation, contributing to chronic central pain syndromes characterized by spontaneous, non-evoked that persists despite treatment. Symptoms often correlate with lesion location in the cervical or thoracic cord, exacerbating and mobility issues in affected individuals.

Diagnostic and therapeutic implications

Diagnosis of posterolateral tract involvement relies on advanced imaging techniques and targeted clinical assessments to evaluate fiber integrity and sensory function. (MRI) is particularly useful for detecting hyperintensities in the posterolateral regions of the associated with demyelinating conditions, such as , where lesions disrupt the tract's sheaths and lead to . tensor imaging (DTI), a specialized MRI method, quantifies tract integrity by measuring water along axons, enabling visualization of fiber damage or disruption in neuropathic conditions affecting the posterolateral tract. These imaging modalities provide non-invasive insights into tract , guiding from other disorders. Clinical testing complements imaging by directly probing sensory deficits mediated by the posterolateral tract. Thermal quantitative sensory testing (QST) assesses thresholds for warm and cold sensations, identifying abnormalities in temperature perception that indicate tract dysfunction, as it evaluates small-fiber pathways involved in thermosensation. Pinprick testing, a bedside method using a sharp stimulus to evoke , detects deficits in and serves as a reliable surrogate for posterolateral tract integrity, with loss of sharp-dull discrimination signaling anterolateral system impairment. Therapeutic interventions target the posterolateral tract to alleviate pain transmission, focusing on modulation at spinal synapses and neuronal activity. Intrathecal opioids, delivered directly to the , bind to receptors on tract neurons and primary afferents, inhibiting nociceptive signal propagation and providing targeted relief for severe, syndromes involving the tract. Spinal cord stimulation (SCS) involves implanting electrodes to deliver electrical impulses that alter tract excitability, effectively reducing by gating pain signals at the dorsal horn level and improving in refractory cases. Prognostic outcomes for posterolateral tract injuries, particularly from spinal trauma, emphasize the importance of timely interventions to preserve function and promote recovery mechanisms. Early surgical or pharmacological management following trauma minimizes secondary damage, enhancing the potential for tract preservation and functional restoration. Recovery is often linked to axonal , where spared neurons form new collaterals to compensate for lost connections, contributing to partial sensory regain in incomplete injuries.

History and eponymy

Historical discovery

The posterolateral tract, also known as Lissauer's tract or the dorsolateral fasciculus, was first described in 1885 by German neurologist Heinrich Lissauer (1861–1891) during his medical studies at the University of Leipzig under pathologist Karl Weigert. Working with sections from human subjects, Lissauer utilized Weigert's stain to identify a distinct bundle of fine fibers positioned between the posterior roots and the lateral edge of the dorsal horn, noting its longitudinal course and potential relation to dorsal root entry. This initial observation was detailed in a brief abstract published in Neurologisches Centralblatt, marking the tract's recognition as a specialized pathway in the 's . Key advancements in 19th-century neurohistology further illuminated the tract's structure and function. Camillo Golgi's impregnation technique, introduced in 1873 and known as the "black reaction," enabled selective staining of entire neurons and their processes, revealing intricate fiber trajectories in the and substantiating the tract's role as an entry zone for primary sensory afferents from dorsal roots. This method, applied in subsequent examinations, highlighted the tract's proximity to the substantia gelatinosa and its segregation of small-diameter sensory fibers, building on Lissauer's findings to differentiate it from adjacent pathways like the posterior columns. In the early , experimental confirmation advanced through and lesion studies. Stephen Walter Ranson's 1913–1914 investigations in cats employed the pyridine silver method after dorsal rhizotomy, demonstrating that the tract contains ascending and descending collaterals from primary afferents, with fibers distributing to the marginal zone of the dorsal horn over one to three segments. These cat-based experiments clarified the tract's continuity and somatotopic organization, linking it explicitly to nociceptive and thermal . The understanding of the tract evolved significantly by the mid-20th century, particularly through physiological and studies associating it with transmission. In 1952, K.M. Earle examined the tract's possible relation to the pathway through targeted lesions in animal models, showing that interrupting the tract disrupts localization and intensity without affecting touch or , thus establishing its selective role in nociceptive pathways. By the , electron microscopy studies uncovered axoaxonic synapses and interneuronal contacts within the tract, transforming its conceptualization from a mere conduit to a dynamic site for presynaptic modulation of sensory signals.

Eponymous naming and key contributors

The posterolateral tract is primarily known eponymously as Lissauer's tract, named after the German neurologist Heinrich Lissauer (1861–1891), who provided the first detailed description of this dorsolateral bundle of fibers in an 1885 abstract using Weigert's staining method to highlight its position between the posterior roots and the lateral pyramidal tract. Lissauer's work emphasized the tract's marginal zone in the , distinguishing it as a distinct pathway for ascending and descending fine fibers. Alternative designations include dorsolateral fasciculus, a term introduced by early neuroanatomists such as Joseph Jules Dejerine in his seminal 1895 treatise Anatomie des centres nerveux, where he cataloged pathways based on degeneration studies. In contemporary anatomical literature, the descriptive name posterolateral tract is favored for its clarity, reflecting the structure's location adjacent to the dorsal horn without reliance on historical eponyms. Key contributors to understanding the tract extend beyond its namer. In the 1890s, Spanish neurohistologist advanced visualization of its synaptic terminations through meticulous Golgi-stained illustrations of dorsal horn neurons, revealing fine axonal arborizations in his comprehensive histological atlas. Later, in the 1960s, British neurophysiologist Patrick D. Wall contributed significantly by co-developing the of pain modulation, which posits the tract's role in integrating nociceptive signals within the substantia gelatinosa, as evidenced in his experimental studies on dorsal horn excitability. Naming controversies have arisen over attribution, with some historians arguing that credit should partially extend to earlier observers like Austrian physician Ludwig Türck (1810–1868), who in the 1850s described longitudinal spinal fiber bundles via anterograde degeneration experiments, predating Lissauer's focused delineation by decades. These debates underscore the incremental nature of 19th-century spinal anatomy, where Türck's broader tract mappings laid groundwork but lacked the specificity that solidified Lissauer's eponym.

References

  1. https://nba.uth.tmc.edu/neuroscience/m/s2/chapter03.html
  2. https://www.ncbi.nlm.nih.gov/books/NBK10967/
  3. https://nba.uth.tmc.edu/neuroscience/m/s2/chapter06.html
  4. https://www.ncbi.nlm.nih.gov/books/NBK507824/
  5. https://www.ncbi.nlm.nih.gov/books/NBK545206/
  6. https://www.amboss.com/us/knowledge/spinal-cord-tracts-and-reflexes/
  7. https://www.kenhub.com/en/library/anatomy/the-spinal-cord
  8. https://www.researchgate.net/publication/229507491_The_tract_of_lissauer_and_the_Substantia_Gelatinosa_Rolandi
  9. https://www.ncbi.nlm.nih.gov/books/NBK6229/
  10. https://onlinelibrary.wiley.com/doi/10.1002/cne.901720308
  11. https://www.kenhub.com/en/library/anatomy/ascending-and-descending-tracts-of-the-spinal-cord
  12. https://www.bellarmine.edu/faculty/mwiegand/atlas/df.html
  13. https://journals.physiology.org/doi/10.1152/jn.1998.80.2.667
  14. https://www.ncbi.nlm.nih.gov/books/NBK556013/
  15. https://nba.uth.tmc.edu/neuroanatomy/L3/Lab03p01_index.html
  16. http://anat403.class.uic.edu/Lectures/lecture7_09.htm
  17. https://www.ncbi.nlm.nih.gov/books/NBK551522/
  18. https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.25079
  19. https://www.ncbi.nlm.nih.gov/books/NBK537110/
  20. https://emedicine.medscape.com/article/1151685-clinical
  21. https://www.ncbi.nlm.nih.gov/books/NBK557891/
  22. https://www.ncbi.nlm.nih.gov/books/NBK538135/
  23. https://pmc.ncbi.nlm.nih.gov/articles/PMC11221503/
  24. https://www.frontiersin.org/journals/neurology/articles/10.3389/fneur.2021.799698/full
  25. https://pmc.ncbi.nlm.nih.gov/articles/PMC7277673/
  26. https://pmc.ncbi.nlm.nih.gov/articles/PMC8032899/
  27. https://pmc.ncbi.nlm.nih.gov/articles/PMC11368601/
  28. https://pmc.ncbi.nlm.nih.gov/articles/PMC8280296/
  29. https://pmc.ncbi.nlm.nih.gov/articles/PMC2964993/
  30. https://pmc.ncbi.nlm.nih.gov/articles/PMC6703564/
  31. https://pmc.ncbi.nlm.nih.gov/articles/PMC3250295/
  32. https://pmc.ncbi.nlm.nih.gov/articles/PMC2897707/
  33. https://www.researchgate.net/publication/342318635_Tribute_to_Heinrich_Lissauer_Breakthroughs_made_in_a_Short_Life
  34. https://pubmed.ncbi.nlm.nih.gov/15036445/
  35. https://pmc.ncbi.nlm.nih.gov/articles/PMC6388087/
  36. https://pubmed.ncbi.nlm.nih.gov/15264793/
  37. https://onlinelibrary.wiley.com/doi/10.1002/cne.900240408
  38. https://onlinelibrary.wiley.com/doi/10.1002/cne.900960104
  39. https://radiopaedia.org/articles/dorsolateral-fasciculus?lang=us
  40. https://pcpr.pitt.edu/wp-content/uploads/2018/01/Melzack-Wall.pdf
  41. https://thejns.org/focus/view/journals/neurosurg-focus/16/1/foc.2004.16.1.16.pdf
Add your contribution
Related Hubs
User Avatar
No comments yet.