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PubMed1981

Organization of spinothalamic tract axons within the rat spinal cord.

Two techniques have been used to examine the organization of spinothalamic tract axons within the spinal cord of the rat. In the initial experiments, the thalamus was filled on one side with horseradish peroxidase (HRP) using a series of small injections. The injections were preceded by lesions of various areas of the ventral quadrant. These studies indicated that the cells of origin of STT axons ascending within the ventral funiculus (VF) are located primarily in the ventral-most areas of the dorsal horn and the intermediate gray zone. The cells of origin of STT axons projecting within the ventrolateral funiculus (VLF) are located not only deep within the gray matter but in addition within the dorsal-most two thirds of the dorsal horn, the area of the spinal cord gray matter shown in previous studies to contain the vast majority of cells with cutaneous tactile and nociceptive input. To examine these projections directly, rats received either a series of HRP injections that filled the thalamus on one side or a small injection into either medial or lateral thalamus. Examination of the labeled axons in horizontal sections through the cervical cord indicated that STT axons ascending to lateral thalamus do so in the VLF. In contrast, axons terminating in medial thalamus ascend in the VF. Additional experiments have shown that axons ascending to the lateral thalamus are distributed throughout the VLF at lumbar levels. Within the thoracic cord, lateral projecting SST axons are distributed throughout much of the VLF but are not found in close proximity to the ventral horn. At cervical levels all lateral-projecting STT axons have assumed a position on the lateral rim of the VLF. These and previously published data have demonstrated that the rat spinothalamic tract is composed of two components that differ in the distribution of their cells of origin, the area of the cord in which they ascend, and the thalamic nuclei in which they terminate.

Animals↗

PubMed1983

The terminations of the spinothalamic tract in the cat.

The termination sites of the spinothalamic tract (STT) in the cat have been examined using the anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). Cats which received an injection of WGA-HRP at the spinal cervical level (C7-C8) displayed anterograde labelling in the ventral posterior lateral (VPL), ventrolateral, lateral posterior, limitans, suprageniculate, medial geniculate pars magnocellularis, central lateral, paracentral, centrum medianum, submedius, central medial, reuniens, rhomboid and periventricular thalamic nuclei. Lumbar injection (L2-L3) produced a similar although less intense pattern of labelling, with only the VPL displaying an obvious topological organization. Although the STT terminations in the cat appear to be less dense than those observed in the rat or monkey the present results demonstrate that in the cat a wide variety of thalamic nuclei receive a direct STT projection and that the cat VPL, like rat, monkey and man, receives a direct STT input.

Animals↗

PubMed2000

Intrapericardiac injections of algogenic chemicals excite primate C1-C2 spinothalamic tract neurons.

Extracellular potentials of 38 C1-C2 spinothalamic tract (STT) neurons in anesthetized monkeys (Macaca fascicularis) were examined for responses to intrapericardiac injections of an algogenic chemical mixture (adenosine, 10(-3) M; bradykinin, prostaglandin E(2), serotonin, histamine, each 10(-5) M). Chemical stimulation of cardiac/pericardiac receptors increased activity of 21 cells, decreased activity of 5 cells, and did not change activity of 12 cells. Cells excited by chemical stimuli received input from noxious mechanical stimulation of somatic fields; most receptive fields included the neck, inferior jaw, or head areas. Nerve ablations in 11 cells excited by intrapericardiac chemicals showed that cardiac input activated by algogenic chemicals traveled primarily in vagal afferent fibers to C1-C2 segments; phrenic or cardiopulmonary sympathetic inputs were predominant in 2 of 11 cells. These results supported the concept that activation of cardiac vagal afferents might lead to the production of referred pain sensation in somatic fields innervated from high cervical segments.

Afferent Pathways↗

PubMed1998

Distribution and morphology of spinothalamic tract neurons in the rat.

Previous studies showed that spinothalamic tract (STT) neurons in the dorsal horn head have a distinct laminar organization that corresponds to the cytoarchitectonic divisions. However, groupings of STT neurons in the deeper part of the spinal gray matter have not yet been established, since, in these regions, the distribution of STT neurons with similar morphology does not follow the cytoarchitectonic subdivisions. To classify STT neurons in the deep part of the rat spinal gray matter, not only the distribution but also the size and shape of STT neurons were investigated in the present study by the method of retrograde axonal transport of wheat germ agglutinin-horseradish peroxidase. In addition to the confirmation of the previously described groups of STT neurons in the dorsal horn head, this study showed novel groupings of STT neurons in the deeper part of the spinal gray matter. First, the interomedio-ventral group of STT neurons, which spreads over laminae VII through IX, were classified into four subgroups in the cervical cord according to their side of projection and medio-lateral location: ipsilateral-medial, ipsilateral-lateral, contralateral-medial and contralateral-lateral. These subgroups were different not only in distribution of neurons but also in mean size of their cell bodies. On the ipsilateral side, neurons in the lateral subgroup were smaller than those in the medial subgroup, while on the contralateral side, the lateral subgroup had larger neurons than the medial subgroup. Second, STT neurons in laminae IV-VI were classified into the dorsal horn neck and base groups based on the orientation of their somata and their rostrocaudal distribution. Neurons in the dorsal horn neck group were more densely distributed and more horizontally aligned than those in the dorsal horn base group. The dorsal horn base group contained more STT neurons projecting to the medial thalamus than the dorsal horn neck group.

Anatomy, Artistic↗

PubMed1989

Urinary bladder and hindlimb afferent input inhibits activity of primate T2-T5 spinothalamic tract neurons.

1. Extracellular recordings were made from 41 spinothalamic tract (STT) neurons on the left side of the T2-T5 spinal segments of 20 monkeys (Macaca fascicularis) anesthetized with alpha-chloralose. Manipulation of the left triceps-chest region and electrical stimulation of cardiopulmonary sympathetic afferent fibers excited these cells. 2. Isotonic urinary bladder distensions (UBD) to pressures between 20 and 80 cmH2O reduced the spontaneous activity in 33 of 41 cells. Cell activity was significantly reduced by UBD at 20 cmH2O. Distensions to 40, 60, and 80 cmH2O produced progressively greater reductions in spontaneous discharge. Activity was decreased throughout distension in 29 cells (tonic inhibition) and at the onset of distension in 3 neurons (phasic inhibition). In one cell, inhibition followed a brief excitation at the onset of distension (phasic excitation-tonic inhibition). Spontaneous bladder contractions also inhibited STT cell activity. 3. Inhibition by UBD was observed in STT cells characterized as wide dynamic range, high threshold, and high threshold inhibitory. No correlation existed between cell type or laminar location and inhibition by urinary bladder distension. Cells excited by cardiopulmonary sympathetic afferent A delta- and C-fibers had a significantly greater tendency to be inhibited by UBD (17 of 18) than cells activated by A delta- but not C-fibers (13 of 20). 4. Urinary bladder distension and pinch of the hindlimbs also reduced activity of STT cells excited by input from cardiopulmonary sympathetic afferents and from the proximal forelimb. 5. Urinary bladder distension to 40, 60, or 80 cmH2O produced a greater absolute but smaller relative reduction in the firing frequency of STT cells as spontaneous activity increased. Thus the magnitude of this inhibitory effect may depend on whether the inhibitory effect is measured as an absolute or relative change in cell activity. 6. Convergent inhibitory input from somatic regions also was observed. Noxious pinch of the hamstring region of the right hindlimb decreased activity in 32 of 39 cells. Left hindlimb pinch inhibited 21 of 38 cells, and 15 of 29 cells were inhibited by right triceps pinch. 7. Convergent inhibitory input from the hamstring region of the hindlimbs and from the urinary bladder to upper thoracic STT cells may be important for coding the intensity and location of noxious visceral and somatic stimuli and for organizing the appropriate sequence of motor responses when multiple noxious stimuli are present.

Action Potentials↗

PubMed1981

Responses of spinothalamic tract cells in the thoracic spinal cord of the monkey to cutaneous and visceral inputs.

Somatovisceral convergence was demonstrated in recordings from 15 of 16 spinothalamic tract cells in the lower thoracic spinal cords of anesthetized monkeys. Inputs were produced by mechanical (or sometimes electrical) stimulation of the skin over the lower trunk and by electrical stimulation of the greater splanchnic nerve through a buried electrode. The volley in the greater splanchnic nerve was monitored using a buried electrode on the sympathetic chain. Spinothalamic tract cells could be excited by activity in A delta and C fibers, but no effects produced by A beta fibers were noted. In some cases inhibitory effects were observed due to movement of hair on the trunk, and inhibitory interactions could be demonstrated between cutaneous and visceral afferent volleys.

Animals↗

PubMed1994

Effects of systemic morphine on lamina I spinothalamic tract neurons in the cat.

Lamina I spinothalamic tract (STT) neurons are an integral component of the central representation of pain and temperature and thus their sensitivity to various analgesics needs to be examined. In the present study, the effects of successive, cumulative doses (0.125-2.0 mg/kg) of intravenous morphine sulfate on the quantitative stimulus-response properties of nociceptive lamina I STT cells have been tested in the intact, barbiturate-anesthetized cat. Both nociceptive-specific (n = 7) and multireceptive (heat, pinch and cold sensitive; n = 7) lamina I STT cells were inhibited in a dose-dependent manner. Parallel dose-dependent effects on responses to noxious heat and pinch were generally observed that reduced ongoing discharge levels and the slopes of the stimulus-response functions. However, non-STT lamina I cells (n = 5) differed significantly; the responses of one multireceptive (heat, pinch and cold-sensitive) cell and the responses to pinch of 3 of 4 wide dynamic range cells were not inhibited. In addition, two-thirds of the nociceptive lamina I STT cells showed enhanced responses at the lowest dose of morphine (0.125 mg/kg). These results contrast with the varied effects of morphine reported for superficial dorsal horn cells with uncharacterized projections and they support the role of lamina I STT cells in pain. Furthermore, these observations are consistent with previous findings indicating that lamina I STT neurons are a distinct subpopulation of lamina I cells. These results support previous evidence that opiatergic modulation of sensory activity in lamina I is functionally organized.

Animals↗

PubMed1984

Factors influencing peripheral nerve stimulation produced inhibition of primate spinothalamic tract cells.

Several factors that influence the inhibition of primate spinothalamic tract (STT) cells produced by repetitive peripheral conditioning stimulation have been studied. Identified STT cells were recorded from the lumbosacral spinal cord in intact, anesthetized monkeys. In addition, presumed STT cells were recorded from unanesthetized, decerebrate or decerebrate, spinalized monkeys; these cells were identified by antidromic activation from the contralateral ventral lateral funiculus of the upper cervical spinal cord. Activity of the STT cells was evoked by electrically stimulating the sural nerve with pulses having an intensity strong enough to activate C fibers. The C fiber evoked STT cell activity was compared before, during and after repetitive conditioning stimuli applied to the tibial nerve for 5 min. By applying repetitive strengths of conditioning stimuli, it was found that the A delta fiber group is the most important for producing inhibition of STT cells, although significant additional effects were also produced by the A alpha beta and C fiber groups. Conditioning stimuli with fixed intensity at different frequencies showed that the higher the frequency the more powerful the inhibition within the range we tested (0.5-20 Hz). The inhibition produced by peripheral nerve stimulation was segmentally organized, so the most effective nerve in producing inhibition amongst those tested was the ipsilateral tibial nerve. The contralateral sciatic nerve, the ipsilateral median nerve and the contralateral median nerve were less effective in that order. The results of the present experiments suggest that the most effective way to produce analgesia by peripheral nerve stimulation would be by high frequency stimulation of a nerve innervating the area from which pain originates with an intensity at least strong enough to activate A delta fibers.

Animals↗

PubMed2004

How many spinothalamic tract cells are there? A retrograde tracing study in cat.

The spinothalamic tract, well known for its role in nociception, is the most frequently studied ascending pathway originating from the spinal cord. It is known that spinothalamic neurons are located in all segments of the spinal cord, but in most mammals the total number of spinothalamic neurons is not known. In three cats, after large wheat germ agglutinin-conjugated horseradish peroxidase injections involving all parts (one case) or almost all parts of the thalamus (two cases), the number of retrogradely labeled profiles was counted in a 1:4 series of sections of all spinal segments from C1 to Coc2. After applying the correction factor of Abercrombie (Anat. Rec. 94 (1946) 239), it appears that a total of 12,000 cells in the spinal cord project to the thalamus.

Animals↗

PubMed1975

The ventral spinothalamic tract and other ascending systems of the ventral funiculus of the spinal cord.

The ascending degeneration resulting from experimental lesions of the ventral funiculus of the spinal cord of Macaca mulatta has been studied using the Nauta technique and its variants. The ventral spinothalamic tract is shown to be an independent entity with respect to the lateral spinothalamic tract; its fibers are widely distributed in the ventral funiculus and it establishes connections with the brain stem and thalamus which are analogous but not identical to those of the latter. Its role in the relay of nociceptive input is discussed in view of the similarity in hodology of the two systems and it is proposed that it may be responsible for the failure of anterolateral cordotomy to control pain on a long term basis. Other ascending systems in the ventral funiculus include the spino-olivary and spino-reticular tracts, as well as minor connections to the N. of Edinger-Westphal, the red nucleus and the superior colliculus. The projections from the ventral quadrant of the spinal cord to the brain stem are almost entirely ipsilateral until the rostral mesencephalon is reached, at which level the N. of Darkschewitz receives both ipsilateral and crossed input; the magnocellular nucleus of the medial geniculate body receives a small contribution which is mainly ipsilateral. In the thalamus the VPL receives predominantly ipsilateral projections while the input to the paralaminar nuclei is only slightly less pronounced contralaterally than ipsilaterally.

Animals↗

PubMed1997

Inhibitors of G-proteins and protein kinases reduce the sensitization to mechanical stimulation and the desensitization to heat of spinothalamic tract neurons induced by intradermal injection of capsaicin in the primate.

Intradermal injection of capsaicin results in sensitization of spinothalamic tract cells to brushing and pressure applied to the cutaneous receptive field in anesthetized monkeys. A significant increase in background activity also occurs immediately after capsaicin injection that lasts for at least 2 h. A 40-50% decrease in the response to noxious heat stimuli is also observed following capsaicin injection. This study investigated the spinal role of second messengers by extracellularly recording from spinothalamic tract cells and delivering inhibitors of second messenger pathways to the spinal cord by microdialysis. Blockade of protein kinases with the general protein kinase inhibitor, H7 (5.0 mM, n = 6), reduced the sensitization of the cells to brush and pressure. Blockade of protein kinase C with NPC15437 (10.0 mM, n = 10) reduced the increased background activity and the increased responses to brush. Blockade of protein kinase A with H89 (0.01 mM, n = 9) was most effective. H89 reduced the background activity, the increased responses to brush and press, and reversed the decreased response to noxious heat stimuli. Blockade of G-proteins with the general G-protein inhibitor, GDP-beta-S (1.0 mM, n = 9), reduced the background activity and the responses to brush and pressure without affecting the decreased response to heat. Thus, multiple intracellular messengers appear to be involved in the processing of central sensitization induced by activation of C-fibers following intradermal injection of capsaicin.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1978

Neural representation of cutaneous aftersensations by spinothalamic tract neurons.

Temporal summation of second pain and long-lasting tactile-evoked aftersensations are examples of sensory phenomenons that cannot be explained on the basis of responses of primary afferents. Two distinct classes of monkey spinothalamic tract neurons have responses to controlled natural stimuli that parallel and thus could account for the above phenomenons. One class, termed wide-dynamic-range, receives excitatory effects from sensitive mechanoreceptive afferents and from various nociceptive afferents including Adelta and C mechanothermal nociceptive afferents. Another class, termed nociceptive-specific, receives excitatory effects exclusively from primary nociceptive afferents. Both classes respond with an early and late response to a single noxious heat pulse (peak temperature = 51 C). The late response, unlike C nociceptive afferents but like second pain, summates in magnitude with each successive heat pulse. Gentle moving tactile stimuli evoke long-lasting (20-56 sec) after-discharges only in wide dynamic range neurons, and are similar in duration to the tactile after-sensation evoked by similar stimuli. Both the after-discharges and after-sensations can be abruptly terminated by rubbing the affected region. Temporal summation of second pain and cutaneous after-sensations are at least partly subserved by spinal cord mechanisms within the dorsal horn and are manifested in the output of spinothalamic tract neurons.

Animals↗

PubMed1989

A dorsolateral spinothalamic tract in macaque monkey.

Prior work has indicated the existence of a major spinal cord pathway made up of lamina I cell axons ascending in the dorsolateral funiculus in both rat and cat. In cat, a portion of this lamina I dorsolateral funiculus pathway terminates in the thalamus. The purpose of this report is to demonstrate that a similar dorsolateral spinothalamic tract exists in macaque monkey. Retrograde transport of horseradish peroxidase, injected into the somatosensory thalamus of monkeys, was used to identify the cells of origin of the spinothalamic tract in the cervical and lumbar enlargements. In order to determine the funicular courses of the axons contributing to the spinothalamic pathway, thalamic injections of horseradish peroxidase were combined with ipsilateral ventral or dorsolateral thoracic spinal cord lesions. The results indicate that in macaque monkey many lamina I cell axons ascend to the thalamus in the dorsolateral funiculus, contralateral to their parent cells. Some lamina I cell axons as well as the majority of axons of spinothalamic cells located in deeper laminae ascend in the contralateral ventral quadrant to terminate in the thalamus. The existence in macaque of a dorsolateral spinothalamic pathway comprised of lamina I cell axons strongly implies the presence of a similar pathway in humans and has important implications regarding the mechanisms underlying both clinical and experimental nociception.

Animals↗

PubMed1998

Cardiopulmonary sympathetic input excites primate cuneothalamic neurons: comparison with spinothalamic tract neurons.

Stimulation of cardiopulmonary sympathetic afferent fibers excites thoracic and cervical spinothalamic tract (STT) cells that respond primarily to noxious somatic stimuli. Neurons in dorsal column nuclei respond primarily to innocuous somatic inputs, but noxious stimulation of pelvic viscera activates gracile neurons. The purpose of this study was to compare effects of thoracic visceral input on cuneothalamic and STT neurons. Stellate ganglia of 17 anesthetized monkeys (Macaca fascicularis) were stimulated electrically to activate cardiopulmonary sympathetic afferent fibers. Somatic receptive fields were manipulated with brush, tap, and pinch stimuli. Extracellular discharge rate was recorded for neurons antidromically activated from ventroposterolateral (VPL) thalamus. Stimulation of the ipsilateral stellate ganglion increased activity of 17 of 38 cuneothalamic neurons and of 1 gracilothalamic neuron with an upper body somatic field. Spinal cord transections showed that cardiopulmonary input to cuneothalamic neurons traveled in ipsilateral dorsal column and probably in dorsolateral funiculus. One of eight gracilothalamic neurons with lower body fields was inhibited by cardiopulmonary input, and none were excited. Stimulation of the ipsilateral stellate ganglion increased activity in 10 of 10 T3-T4 STT neurons. Evoked discharge rates, latencies to activation and durations of peristimulus histogram peaks were significantly less for cuneothalamic neurons compared with STT neurons. Furthermore, additional long latency peaks of activity developed in histograms for 6 of 10 STT neurons but never for cuneothalamic neurons. Contralateral cardiopulmonary sympathetic input did not excite cuneothalamic neurons but increased activity of 7 of 10 T3-T4 STT neurons. Most cuneothalamic neurons (24 of 31 cells tested) responded primarily to innocuous somatic stimuli, whereas STT neurons responded primarily or solely to noxious pinch of somatic fields. Neurons that responded to cardiopulmonary input most often had somatic fields located on proximal arm and chest. Results of this study showed that cardiopulmonary input was transmitted in dorsal pathways to cuneate nucleus and then to VPL thalamus and confirmed that STT neurons transmit nociceptive cardiopulmonary input to VPL thalamus. Differences in neuronal responses to noxious stimulation of cardiopulmonary sympathetic afferent fibers suggest that dorsal and ventrolateral pathways to VPL thalamus play different roles in the transmission and integration of nociceptive cardiac information.

Animals↗

PubMed1983

A hypothesis on the functional significance of the dendritic projections of spinothalamic tract cells to the white matter of the cat spinal cord.

Deep, lumbar, spinothalamic tract cells have fine distal dendrites which project to, and receive synaptic connections within, the ventral (VF) and/or lateral funiculi (LF). The projection to the LF is inversely related (P less than 0.05) to the projection of the VF. It is proposed that the white matter dendrites receive a particular level of tonic, excitatory drive from a wide variety of axons in the VF and/or LF and that this drive is responsible for the spontaneous activity seen in these cells; activity which provides a baseline against which particular forms of natural stimulation may be registered either by causing an increase or a decrease in the firing frequency.

Animals↗

PubMed2004

Comparison of responses of primate spinothalamic tract neurons to pruritic and algogenic stimuli.

We investigated the role of mechanosensitive spinothalamic tract (STT) neurons in mediating 1) the itch evoked by intradermal injection of histamine, 2) the enhanced sense of itch evoked by innocuous stroking (alloknesis), and 3) the enhanced pain evoked by punctate stimulation (hyperalgesia) of the skin surrounding the injection site. Responses to intradermal injections of histamine and capsaicin were compared in STT neurons recorded in either the superficial or the deep dorsal horn of the anesthetized monkey. Each neuron was identified by antidromic activation from the ventral posterior lateral nucleus of thalamus and classified by its initial responses to mechanical stimuli as wide dynamic range (WDR) or high-threshold (HT). Approximately half of the WDRs and one of the HTs responded weakly to histamine, some with a duration > 5 min, the maximal time allotted. WDRs but not HTs exhibited a significant increase in response to punctate stimulation after histamine consistent with their possible role in mediating histamine-induced hyperalgesia. Neither type of neuron exhibited significant changes in response to stroking, consistent with their unlikely role in mediating alloknesis. Furthermore, nearly all STT neurons exhibited vigorous and persistent responses to capsaicin, after which they became sensitized to stroking and to punctate stimulation. We conclude that the STT neurons in our sample are more likely to contribute to pain, allodynia, and hyperalgesia than to itch and alloknesis.

Action Potentials↗

PubMed2000

Locations of spinothalamic tract axons in cervical and thoracic spinal cord white matter in monkeys.

The spinothalamic tract (STT) is the primary pathway carrying nociceptive information from the spinal cord to the brain in humans. The aim of this study was to understand better the organization of STT axons within the spinal cord white matter of monkeys. The location of STT axons was determined using method of antidromic activation. Twenty-six lumbar STT cells were isolated. Nineteen were classified as wide dynamic range neurons and seven as high-threshold cells. Fifteen STT neurons were recorded in the deep dorsal horn (DDH) and 11 in superficial dorsal horn (SDH). The axons of 26 STT neurons were located at 73 low-threshold points (<30 microA) within the lateral funiculus from T(9) to C(6). STT neurons in the SDH were activated from 33 low-threshold points, neurons in the DDH from 40 low-threshold points. In lower thoracic segments, SDH neurons were antidromically activated from low-threshold points at the dorsal-ventral level of the denticulate ligament. Neurons in the DDH were activated from points located slightly ventral, within the ventral lateral funiculus. At higher segmental levels, axons from SDH neurons continued in a position dorsal to those of neurons in the DDH. However, axons from neurons in both areas of the gray matter were activated from points located in more ventral positions within the lateral funiculus. Unlike the suggestions in several previous reports, the present findings indicate that STT axons originating in the lumbar cord shift into increasingly ventral positions as they ascend the length of the spinal cord.

Action Potentials↗

PubMed2001

The crossing of the spinothalamic tract.

The question whether the spinothalamic and spinoreticular fibres cross the cord transversely or diagonally was investigated in cases of anterolateral cordotomy and in a case of thrombosis of the anterior spinal artery. The pattern of sensory loss following transection of the anterolateral quadrant of the cord consists of a narrow area of decreased nociception and thermanalgesia at the level of the incision; it extends for 1-2 segments cranial and cordal to the incision. This area is immediately cranial to the area of total loss of these modalities. This pattern of sensory loss is explained as follows. The cordotomy incision transects two groups of fibres: those that are already within the anterior and anterolateral funiculi and those that are crossing the cord. The area of total thermanaesthesia and analgesia is due to transection of fibres that are already within this region. The area of partial sensory loss is due to transection of the fibres that are crossing the cord at that level. Owing to the craniocaudal extent of the branches of the dorsal roots, there is an overlap of their collaterals that results in every spinothalamic neurone receiving an input from several dorsal roots. The narrow cordotomy incision thus divides the few fibres crossing at that level, causing diminished noxious and thermal sensibility over a few segments above and below the incision. These facts can be accounted for only on the assumption that these spinothalamic fibres are crossing the cord transversely. This evidence of transverse crossing was found in the cervical, thoracic and lumbar segments. There were three of 63 cordotomies for which this explanation of the partial sensory loss could not be maintained. Although no explanation has been suggested, this is unlikely to be due to the fibres crossing the cord diagonally.

Afferent Pathways↗