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Muscle and Nerve Histology
Published in Maher Kurdi, Neuromuscular Pathology Made Easy, 2021
Peripheral nerves develop in the fetus during the 15th week of gestation. Each nerve trunk is divided into multiple fascicles. Each individual fascicle consists of three layers (Figure 1.6): Epineurium, the outer layer, is a dense collagenous connective tissue containing thick elastic fibers.Perineurium, the middle layer, is a cylindrical fibrocollagenous layer containing epithelial membrane antigen (EMA) positively stained perineurial cells. Renault bodies are normal structures with ellipsoid shapes located in the sub-perineurial space. They contain fibroblasts and mast cells and lack of axons. Of 600 sural nerve biopsies, 2% have Renault bodies. Unfamiliarity with these bodies' appearance may result in diagnostic errors. They could be misinterpreted as endoneurial edema or an infarct.Endoneurium, the inner layer, is a loose connective tissue that surrounds individual nerve fiber (axons), fibroblasts, mast cells, fixed macrophages, and capillaries. The endoneurium is completely isolated from the perineurium and Schwann cells.
Spinal Cord and Reflexes
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
In a manner exactly analogous to skeletal muscle (Figure 9.1), the individual nerve fibers of a peripheral nerve are surrounded by a thin layer of connective tissue, the endoneurium. Groups of nerve fibers are bundled together into fascicles that are surrounded in turn by another layer of connective tissue, the perineurium. The whole nerve is ensheathed by a layer of connective tissue, the epineurium. Blood vessels run between the fascicles.
The nervous system and the eye
Published in C. Simon Herrington, Muir's Textbook of Pathology, 2020
James A.R. Nicoll, William Stewart, Fiona Roberts
Histologically, a peripheral nerve consists of longitudinally orientated nerve fibres running in a fascicle. Each fibre is surrounded by collagenous tissue called the endoneurium, each fascicle by perineurium, and all the fascicles in a given nerve by the epineurium. Within the endoneurium the myelinated axons are supported by Schwann cells which manufacture and maintain the myelin sheaths between the nodes of Ranvier. Unlike the oligodendrocyte of the CNS, which supports the internodal myelin of many axons, the Schwann cell supports the internodal myelin of only one segment of an axon. The thickness of the myelin sheath is proportional to the diameter of the axon.
Therapeutic issues in Guillain–Barré syndrome
Published in Expert Review of Neurotherapeutics, 2023
The effectiveness of corticosteroids in chronic inflammatory demyelinating polyneuropathy (CIDP) has long been reported [65]. Although no high-powered randomized control trial is available [66], clinicians’ experience [67,68] and non-randomized studies suggest that corticosteroids are beneficial in CIDP. Despite promising results of high-dose methylprednisolone in a rat model of acute neuritis [69], corticosteroids did not show the anticipated efficacy in human GBS. A Cochrane review of six trials including 587 participants showed no significant effect [70]. However, it is possible that the benefits of suppressing the inflammatory response in GBS may be offset by unintended effects on the repair process, such as the loss of skeletal muscle electrical excitability [71]. If this hypothesis is correct, a very early course of corticosteroids may be beneficial in a subset of patients with conduction block but not denervation [70]. Thus, it cannot be completely excluded that a very early corticosteroid treatment could be beneficial before the destructive impact of endoneurial edema in the proximal nerve trunks. Indeed, some authors tend to demonstrate some favorable outcomes of high doses glucocorticoids in AIDP patients [72].
Potential Effects of Stem Cells Derived from the Peripheral Nerve and Adipose Tissue after the Nerve Crush Injury in Control and Obese Rats
Published in Journal of Investigative Surgery, 2022
Elif Kayhan Kustepe, Berrin Zuhal Altunkaynak, Işınsu Alkan, Elfide Gizem Kivrak, Alişan Yildiran, Stefano Geuna
The general view of the peripheral nerve, connective tissue and axonal structures was healthy in the NOC group, and the vessels in the endoneurium were noteworthy (Figures 5 and 6). Myelinated nerve fibers, myelin sheath and unmyelinated axons with mitochondria had a normal appearance (Figure 7). In the NOH group, the peripheral nerve content was seen to be damaged, consisting of axons with scattered boundaries. Also in the endoneurium, macrophages were observed (Figures 5 and 6). Myelinated axons and myelin sheaths had an irregular appearance and scattered myelin sheath fragments were observed. In addition, there were some smaller nerve fibers and thinner myelin sheath in this group when comparing with those of the NOC group. Unmyelinated axons showed less clustering and their number was less than that of myelinated fibers. In Schwann cells, irregular bordered, pycnotic or heterochromatic nuclei were remarkable (Figure 6). Peripheral nerve structures in the NOPS group had a healthy appearance. In this group, small size but thick myelin sheathed axons were observed (Figures 5 and 6). In this group, there was a healthy appearance of Schwann cells (Figure 6). In the histopathological analysis of the NOY group, the density of healthy and small size myelinated and unmyelinated axons observed high (Figures 5 and 6). In addition, degenerate axons, macrophages as well as mast cells have been seen (Figure 5). The endoneurium was healthy and the Schwann cells enveloped more than one unmyelinated axon (Figures 5–7).
GDNF enhances human blood-nerve barrier function in vitro via MAPK signaling pathways
Published in Tissue Barriers, 2018
Chaoling Dong, Eroboghene E. Ubogu
Tight regulation of water, ion, nutrient, metabolite and xenobiotic concentrations within peripheral nerves is critical to maintaining the internal microenvironment needed for physiologic axonal signal transmission.1-3 The blood supply to human nerves is derived from extrinsic arteries known as the vasa nervosum. These vessels subsequently branch to form a macrovascular anastomosis within the external epineurium and smaller diameter vessels within the concentric multilayered perineurium. The latter vessels penetrate the innermost perineurium to form endoneurial microvessels. In contrast to the highly permeable fenestrated epineurial blood vessels that lack tight junctions, the endoneurial microvasculature lack fenestrations and consist of tight junction-forming endothelial cells. These cells share a basement membrane with pericytes which form a non-continuous surrounding layer along the endothelial cell abluminal border.4,5 As a consequence, endoneurial microvessels form the BNB, as these endothelial cells are in direct contact with circulating blood. Current knowledge of the molecular and biophysical characteristics of the human BNB in vitro, including measures of transendothelial electrical resistance (TEER), solute permeability to small and large molecules, and response to cytokine and mitogen stimulus has been recently summarized.6 Comprehensive data on the molecular composition of the human BNB based on RNA sequencing has also been recently published.7