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The patient with acute neurological problems
Published in Peate Ian, Dutton Helen, Acute Nursing Care, 2020
Oligodendrocytes generate myelin within the CNS (see Figure 9.3). Schwann cells, also a type of glial cell, generate myelin in the PNS. Schwann cells wrap around axons, forming a myelin sheath. The outer layer includes the Schwann cell’s cytoplasm and nucleus and is called the neurolemma. The neurolemma is thought to promote axon regeneration in the PNS. When a myelinated axon is examined microscopically, there appear to be gaps in the myelin called nodes of Ranvier. One Schwann cell myelinates the segment of axon between two nodes of Ranvier; myelinated nerves will therefore have several Schwann cells (see Figures 9.3 and 9.4).
The Nervous System and Its Disorders
Published in Walter F. Stanaszek, Mary J. Stanaszek, Robert J. Holt, Steven Strauss, Understanding Medical Terms, 2020
Walter F. Stanaszek, Mary J. Stanaszek, Robert J. Holt, Steven Strauss
Some axons are surrounded by a myelin sheath (neurilemma or neurolemma) consisting of the lipid substance myelin. The myelin sheath is discontinuous approximately every millimeter at the neurofibril nodes, also called the nodes of Ranvier. The myelin serves as an electrical insulator, forcing the impulse to jump from one node to another, which functions to increase the speed of conduction in a myelinated nerve and decrease the energy required for transmission. Further, the larger a nerve is, the more quickly it can conduct impulses. Because of their speed of conduction, large myelinated nerves are the primary conductors of impulses to skeletal muscles, allowing the rapid responses
Nervous System
Published in George W. Casarett, 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.
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).
The osmotic demyelination syndrome: the resilience of thalamic neurons is verified with transmission electron microscopy
Published in Ultrastructural Pathology, 2020
Jacques Gilloteaux, Joanna Bouchat, Jean-Pierre Brion, Charles Nicaise
NN neuron cell bodies were typically oblong to round-shaped according to randomness of sectioning. They contained a large euchromatic nucleus with minor to deep indentations that gave them with LM semi-thin sections a sort of wrinkled coffee bean-like aspects. Their heterochromatin content was faintly dispersed throughout the nucleoplasm as discrete clusters while a few rare packets decorated the inner nuclear envelope membrane with a part that constituted the chromatin-associated portion of the nucleolus. The nucleolus often reached 1.5 to 3.5 µm wide and displayed characteristics of a very active cell. There, the chromatin-associated (CA) with the nucleolus component was noticed as the most heavily contrasted component of the active nucleolus forming wavy, dense-entwined swirls (dense fibrillar region or DF) delimitating circular zones containing the fine fibrillar regions (or FF), altogether named nucleolar organizer centers or NORs. Thus, a NOR usually appeared as a round hole perforation-like of the netting aspect whose content usually is a fine fibrillar region or body where the ongoing transcriptions occurred (Figures 5a–d and 6), as recognized and identified by previous studies. An enormous nucleolus with numerous NORs is depicted in Figure 5c–d where the resulting transcripts can be recognized as innumerable ribonucleoproteins and appeared as accumulated granular component. According to activity of the cell, these accumulations, within the meshwork of DF can create an overflow granular ‘cloud’ that constituted the other nucleolus component or granular center (GC) of the nucleolus within the nucleoplasm (Figure 5d). Again, any random sectioning plane sometime did not allow to view the entire complexity of the nucleolus. In any favorable case of plane of ultrathin sectioning, the neuron nucleolus was most often detected in a subcentral core position of the nucleoplasm associated with a zone where one deep indentation of the nuclear envelope existed as seen with LM views (Figures 3, 4 and 5 a–d). The perikaryal areas of the neuron cell bodies seemed narrow but crowded by typical cell’s organelles such as small stacks of Nissl bodies where RER-SER and free polysomes accompanied concentrically-located saccular packets of Golgi apparatus, small but numerous mitochondria and a few lysosomal bodies among which some displayed pale inner fatty droplets, making them typical lipofuscin residual deposits. It necessitated some scrutiny to detect some of the axo-somatic synaptic zones along the perikaryal neurolemma as marked with arrows (Figure 6).