Nervous System
George W. Casarett in Radiation Histopathology: Volume II, 2019
Nerve fibers are axons with coverings of ectodermal origin. In the peripheral nervous system, all axons are surrounded by a neurolemma composed of Schwann cells. There are no Schwann cells around axons in the central nervous system, but homologous neuroglial cells are distributed along the fiber tracts. By light microscopy, all but the smallest axons are surrounded by a myelin sheath. The myelin sheath is regarded as having been laid down and maintained by the cells of the sheath of Schwann in the case of peripheral nerves, or by homologous neuroglial cells in the central nervous system. Since even the smallest visible fibers may show some birefringent material around them under the polarizing microscope, it is possible that all fibers have some myelin around them. The refractility of myelin gives the white color to the fiber masses in the central nervous system and many peripheral nerves.
Inflammatory diseases affecting the spinal cord
Milosh Perovitch in Radiological Evaluation of the Spinal Cord, 2019
Progressive hypertrophic polyneuritis is a rare disease, often familial, characterized by considerable enlargement of peripheral nerves and slowly progressive symptoms of polyneuritis. The disease is linked to the names of Dejerine and Sottas (Dejerine-Sottas disease) who gave its first description in 1893.128 The volume of the peripheral nerves can be considerably increased, sometimes in an asymmetric fashion. The cranial nerves may also be involved. This thickening of the nerves is mainly due to the hypertrophy and proliferation of the neurilemma that can form masses or layers resembling an onion around the nerve fibers.77, 126 Myelographic changes produced by the thickened nerves of the cauda equina are usually evident. They can provoke a partial obstruction of the subarachnoid space and give an irregular appearance to the column of the contrast medium. Occasionally, a tumorous thickening around the nerve root may be confused with neurofibroma, especially if the intervertebral foramina are enlarged. The myelographie appearance of progressive hypertrophic polyneuritis is similar to the widening of the nerve roots seen in a herniated disk or redundant nerve roots, in chronic diabetic neuritis, in the recurrent postinfective polyneuropathy, and in Refsum’s syndrome.128
The control systems: nervous and endocrine
Nick Draper, Helen Marshall in Exercise Physiology, 2014
The structure of an unmyelinated nerve also includes Schwann cells that wrap around the fibres, but unlike myelinated nerves, many fibres are encapsulated by one Schwann cell, but are not individually myelinated (see Figure 4.3). The majority of nerves, however, are myelinated which increases the speed of nervous transmission. Within the PNS, the presence of Schwann cells, and the neurilemma surrounding each axon, provide a protective tube in the event of injury (providing the nerve fibres remain aligned). In this situation, the protective tube created by the Schwann cell and neurilemma enables neurogenesis (new tissue growth). However, if the damaged neuron is misaligned during injury the tissue may not be able to repair itself. In the CNS there is currently little or no chance of nervous tissue regeneration, although research into medical stimuli for neurogenesis is progressing.
Effects of Theranekron and alpha-lipoic acid combined treatment on GAP-43 and Krox-20 gene expressions and inflammation markers in peripheral nerve injury
Published in Ultrastructural Pathology, 2021
Leman Sencar, Gülfidan Coşkun, Dilek Şaker, Tuğçe Sapmaz, Samet Kara, Alper Çelenk, Sema Polat, Derviş Mansuri Yılmaz, Y. Kenan Dağlıoğlu, Sait Polat
Following injury, serious histological changes are observed in the distal and proximal part of the peripheral nerve. It is known that during the first 6 hours, the nucleus migrates to the periphery and the Nissl bodies undergo chromatolysis in the neuron cell body. Distal occurs to the damaged area in the axonal cytoskeleton and myelin sheath, and Wallerian degeneration occurs as a result of fragmentation and degeneration.5,9 As a result, in the first 48–96 hours it was determined that the axon continuity disrupted and impulse transmission was impaired. The regeneration process begins after phagocytosis of myelin sheath and axon debris by Schwann cells and macrophages.4,7 As Schwann cells form the Büngner bands that guide the formed axon sprouts, the axon starts growing at a rate of 1–3 mm per day in the neurilemma tube.6 Furthermore, significant structural changes are also observed in the proximal segment of the nerve close to the damaged area.4
The leptin receptor mutation of the obese Zucker rat causes sciatic nerve demyelination with a centripetal pattern defect
Published in Ultrastructural Pathology, 2018
Jacques Gilloteaux, Kritika Subramanian, Nadia Solomon, Charles Nicaise
Altogether, these defects do not usually include the adaxonal membrane (Figures 5(c), 10(d), 11, and 12(a–f)). These micrographs with important tearing of the myelin show inward vacuole-like spaces lined by the adaxonal membrane, leaving separated the intact neuroplasm and the axonal content. These myelin tearings feature all sorts of membranous debris, including some waxy, electron dense remnants (Figures 4(b), 11, 12(a–f), 13(a–e), and 14(a)). Further, the complex degradation of the same myelin leaves large adaxonal spaces and an axonal content compressed to totally unwrapped myelin in the same area where typical, undulating tight myelin occurs and identifies the juxta- and paranodal zones (Figures 4(b), 13(a–e), 14(a–c), and 15). In the same paranodal zones, myelin keeps some of its interconnected membranes leaving remaining ones attached across the annulus with clear intermembranous, somewhat punctate junctions. These encompass SC’s outer membrane leaflet contacts albeit most of it is fissured by small intraperiod elongated vacuoles, (Figures 9 and 14(b,c)). There, even though the myelin ravages tear apart the entire width of its annulus morphology, it remains form a distorted, multicurved outline where displaced layers of membranes are still retained together. Cross-sections of those teased membranes, amassed with defects, appear as if they were bales of wires (Figure 14(b)). Following the most ultimate disengagement of the myelin ring in the near internode and paranode regions, the adaxonal membrane that has maintained the neurolemma out of the insulating defects can show breaches without that of the neuroplasm (Figures 13(b) and 14(a–c)).
Development of polypyrrole/collagen/nano-strontium substituted bioactive glass composite for boost sciatic nerve rejuvenation in vivo
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2019
Bo Lin, Guoqing Dun, Dongzhu Jin, Yaowu Du
TEM was utilized to watch the ultra-structural morphology of recovered nerves. Fascicles with various sizes, each comprises of a few layers of axons, fibroblasts and enclosed SCs in the majority of the gatherings (Figure 5(d–f)). Myelin sheath thickness was fundamentally more noteworthy in the fibroblasts and enclosed SCs bunch than in the PPY/Coll/n-Sr@BG gathering. While the thicknesses of the control and PPY/Coll gatherings were comparative, they were unmistakably not exactly those seen in the other two gatherings [39]. To more readily assess the recuperation of harmed nerves, the centre fragment of recovered nerves was coloured with H&E re-coloring 24 weeks after the careful activity. All rodents were healthy and no passings were accounted for; wound disease and extreme tissue responses occurred amid the recuperation. Veins existed in the composite course gatherings (Figure 5(d–f)), which demonstrated that the veins produce and give supplements to harmed nerves amid the procedure of recuperation. Neurilemma cell existed in the three gatherings and advanced the development of harmed nerves. The myelinated fibre in 5 g and 5 h were appropriated in course of action with slender myelin cover in a manner and most unpredictable connective tissues in development. The fibre of recovered nerves in Figure 5(i) is increasingly roundabout fit as a fiddle, better-proportioned in size and orchestrated more thickly than in Figure 5(g,h). There are an expansive number of fascicular structures dispersed all through nerves in Figure 5(i). In light of the structural perception, the myelinated fibres in Figure 5(i) is more prominent in number and more concentrated than those in Figure 5(g,h) 24 weeks after implantation. Nerves were in more prominent extent in Figure 5(g–i), and this extent was near what was available in Figure 5(g–i).