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Spinal Cord and Reflexes
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
Positioned closely to the lateral spinothalamic tract, and similarly having its neurons of origin in the dorsal horn of the spinal cord, is the spinoreticular tract. The axons of this tract decussate to the other side of the spinal cord and ascend the spinal cord to terminate on third-order neurons in the medullary-pontine reticular formation. The third-order neurons project to intralaminar nuclei of the thalamus, which in turn project diffusely to many parts of the cerebral cortex. In this way, pain reaches consciousness and results in behavioral arousal and a memory of the pain. In fact, this pathway through the reticular formation is considered part of the ascending reticular arousal system (ARAS), which is responsible for regulating states of consciousness, alertness, and sleep-wake transitions.
Central Modulation of Pain
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
A second tract that conveys nociceptive information is the spinoreticular tract (SRT), which terminates in the reticular formation of the medulla. The cells of origin of the spinoreticular tract are located in the deep layers of the dorsal horn and in laminae VII and VIII of the ventral horn. These cells send projections to several nuclei in the reticular formation such as the lateral reticular nucleus, nucleus gigantocellularis, nucleus paragigantocellularis lateralis in the medulla, the pontine nuclei oralis and caudalis and the parabrachial region. Many spinoreticular neurons are activated preferentially by noxious input, but there is no clear somatotopic organization of the SRTs. These projections terminate in close apposition to regions that are involved in blood pressure and motor control and the descending inhibition of pain. Therefore, it appears that this pathway is involved in the basic autonomic, motor and endogenous analgesic responses to nociceptive input. Central processing of this information may contribute to emotional responses associated with anxiety or threat.
The Physiology of Pain
Published in Bernard J. Dalens, Jean-Pierre Monnet, Yves Harmand, Pediatric Regional Anesthesia, 2019
Bernard Jacques Dalens, Brigitte Storme
Schematically, three supraspinal axes are involved in the feeling of pain: The spinothalamic tracts, the posterolateral thalamus, and the sensory cortex are involved in sensory-discriminative pain.The spinoreticular tracts, the medullary and mesencephalic reticular formation, the reticulothalamic pain pathways, the posteromedial thalamic, and the hypothalamic projections to cortical and limbic system structures are all involved in motivational-directive pain.The corticothalamic (periventricular) pathways, the raphe nuclei, and the descending tracts of the dorsal spinal fasciculi are involved in the suppression of pain mechanisms.
Emerging targets and uses of neuromodulation for pain
Published in Expert Review of Neurotherapeutics, 2019
Beatriz Costa, Isadora Ferreira, Alisson Trevizol, Aurore Thibaut, Felipe Fregni
The afferent fibers of the vagus nerve project to the spinal nucleus of the trigeminal nerve and the nucleus of the solitary tract (NST) [67]. The spinal nucleus of the trigeminal nerve receives sensitive fibers not only from the vagus nerve, but also from the trigeminal, facial, and glossopharyngeal nerves. The axons cross the midline in the brainstem and project, through the anterior trigeminothalamic tract, to the contralateral ventral posteromedial nucleus (VPM) of the thalamus. The NTS is at the center of the nuclei that form the gray matter of the medulla oblongata and receives information from multiple visceral organs, enteroceptive information and afferent signals from the spinal cord, the brainstem (area postrema, gray periaqueductal gray substance, and the parabrachial nucleus), brain (hypothalamus, thalamus and amygdala), and the cerebellum [67]. The NTS has projections to the locus coeruleus, raphe nuclei, amygdala, hippocampus, and the VPM. The locus coeruleus sends noradrenergic input to the raphe nuclei, the thalamus, the hippocampus, and the neocortex [58,67]. The raphe nuclei are mostly formed by serotonergic neurons, which project to the midline and intralaminar nuclei of the thalamus, the hippocampus, and the neocortex. Moreover, there are reciprocal connections between the LC and the raphe nuclei [58,67]. The VPM receives information from the amygdala, the postrema area, the hypothalamus, the reticular formation, the raphe nuclei, and the NST [58,67]. Most of the neurons located in the VPM are modulated through glutamatergic, cholinergic and GABAergic tonus, especially from the NST. The structures here described, especially the NST and its relation to the LC and the raphe nuclei, are part of the pain inhibitory system, which involves the inhibition of nociceptive transmission at the spinal cord [68]. This hypothesis is corroborated by studies that showed a decreased activity of second-order nociceptive neurons in the spinothalamic and spinoreticular tract of the spinal cord as well as in the trigeminal nuclear complex following the activation of afferent vagal fibers [58].
Assessment of spinal cord relative vulnerability in C4–C5 compressive cervical myelopathy using multi-modal spinal cord evoked potentials and neurological findings
Published in The Journal of Spinal Cord Medicine, 2021
Yasuaki Imajo, Tsukasa Kanchiku, Hidenori Suzuki, Norihiro Nishida, Masahiro Funaba, Toshihiko Taguchi, Takashi Sakai
Kameyama et al. reported the relationship between the morphology and pathology in nine patients with OPLL in the cervical spine.20 When there was mild compression upon spinal cords with a boomerang shape (central type), only flattening of the anterior horn and loss of the anterior horn cells were observed, without white matter lesions in three patients. Even in severe compression cases, major pathological changes were limited to the gray matter together with the ventrolateral part of the posterior column (Burdach tract) in two patients. There was no descending degeneration in the lateral corticospinal tract or the Goll tract; there were no clinical findings in one patient with mild compression and one with severe compression. Two of three patients with clinical findings showed sensory loss in the lower extremity; one patient showed spastic tetraparesis and urinary disturbance. Urinary disturbance is caused by the involvement of the anterior funiculus (reticulospinal tract and spinoreticular tract).21,22 Generally, the anterior funiculus is finally disturbed in patients with CSM.23 Therefore, we considered that this patient with urinary disturbance already had sensory disturbance in the lower extremities. The Goll tract was involved in all these patients, although there was only mild compression on the spinal cord. Therefore, the clinical findings were not consistent with the pathological findings. Cord damage is considered to be mediated by ischemia as a result of the mechanical disturbance of the microcirculation.20 It is difficult to assess how spinal tract lesions involving the posterior horn progress from mild to severe using pathological findings. Conversely, in four patients with severe compression on the spinal cord with a triangular shape (diffuse type), both gray and white matters showed severe damage, including necrosis. Only the anterior columns were free of pathological changes. Ascending degeneration of the posterior column, including the Goll tract, as well as descending degeneration of the lateral corticospinal tract were present above and below the compression level.20 According to the pathological findings, the involvement of spinal cords with a triangular shape (diffuse type) was more severe than boomerang shape (central type).