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Spinal Cord and Reflexes
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
The sensory fibers that enter the spinal cord through the dorsal roots are part of what are referred to as the first-order neurons in the pathway from the periphery to the cerebral cortex. As mentioned before, the cell bodies of these first-order neurons are in the dorsal root ganglia. The dorsal column–medial lemniscus pathway (DCML), also known as the posterior column-medial lemniscus pathway (PCML), contains first-order afferents that convey sensations of fine touch, vibration, and proprioception. The pathway is divided into two components: (i) the gracile fasciculus that carries information from the lower limb, below T6, and terminates in the gracile nuclei in the medulla (Figure 12.17), and (ii) the cuneate fasciculus that carries information from the upper limb, above T6, and terminates in the cuneate nuclei in the medulla. The neurons of the gracile and cuneate nuclei are second-order neurons in the pathway from the periphery to the cerebral cortex. Their axons decussate at the level of the medulla, travel up the brainstem as the medial lemniscus on the contralateral side, and terminate in the thalamus, which relays the signals to the cerebral cortex.
The Somatosensory System
Published in Golara Honari, Rosa M. Andersen, Howard Maibach, Sensitive Skin Syndrome, 2017
Tactile primary afferents, or first-order neurons, immediately turn up the spinal cord toward the brain, ascending in the dorsal white matter and forming the dorsal columns. In a cross section of the spinal cord at cervical levels, two separate tracts can be seen—the midline tracts comprise the gracile fasciculus conveying information from the lower half of the body (legs and trunk) and the outer tracts comprise the cuneate fasciculus conveying information from the upper half of the body (arms and trunk). At the medulla, situated at the top of the spinal cord, the primary tactile afferents make their first synapse with second-order neurons, where fibers from each tract synapse in a nucleus of the same name—the gracile fasciculus axons synapse in the gracile nucleus and the cuneate axons synapse in the cuneate nucleus. The neurons receiving the synapse provide the secondary afferents and immediately cross to form a new tract on the contralateral side of the brainstem—the medial lemniscus—which ascends through the brainstem to the next relay station in the midbrain, the thalamus.
Cervical myelopathy causing numbness and paresthesias in lower extremities: A case report identifying the cause of a false positive Sharp–Purser test
Published in Physiotherapy Theory and Practice, 2019
The author also hypothesized that at the hair salon, the pressure of the sink in combination with cervical extension, decreased the central canal space even more so than active cervical flexion, and increased pressure was placed both on the aforementioned gracile fasciculus (medial aspect of dorsal column of spinal cord), and the cuneate fasciculus (the lateral aspect of the dorsal column of the spinal cord). The cuneate fasciculus provides the brain with ascending sensory information from the arms (Purves et al., 2014). The patient did not experience symptoms with active cervical extension during the physical therapy examination because there was no pressure applied posteriorly to the cervical spine and/or she did not go to end range cervical extension. It is probable that the severely narrow central canal from C4 thru C7 discovered on imaging would cause various compromise to the dorsal and/or the anterolateral columns of the spinal cord, where the spinothalamic tract is located, depending on the position of the head and neck (Purves et al., 2014).
Lipofibromatosis: Central Nervous System Involvement by a Benign Neoplasm
Published in Fetal and Pediatric Pathology, 2023
Alejandra Rebolledo, Laura J. Guerra, Ander EO. Dubón, Mauricio Brindis
At four months of life, the first resection of the mass was attempted through suboccipital craniotomy and C1-C2 laminectomy. The unencapsulated mass infiltrated beyond the cervical canal and occupied the entire fourth ventricle, leading to a partial resection and the requirement of a ventriculoperitoneal shunt. Severe bilateral alterations in the gracile and cuneate fasciculus were confirmed. There was no clinical improvement. He required mechanical ventilation by tracheostomy and feeding by an orogastric tube. He developed chronic pulmonary disease, inappropriate antidiuretic hormone secretion syndrome and had a neurogenic bladder.