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Homo Sapiens (“Us”): Strengths and Weaknesses
Published in Michael Hehenberger, Zhi Xia, Huanming Yang, Our Animal Connection, 2020
Michael Hehenberger, Zhi Xia, Huanming Yang
A nerve is defined as a cable-like, enclosed, bundle of axons (nerve fibers, projections of neurons) in the peripheral nervous system. It typically conducts electrical impulses known as action potentials, away from the nerve cell body. Axons transmit information to different neurons, muscles, and glands by having electrochemical impulses travel from peripheral organs to the cell body. This information is then propagated from the cell body to the spinal cord. In addition to neurons, nerves also include non-neuronal cells that coat the axons in myelin. There are two types of axons in the nervous system, namely myelinated and unmyelinated axons. Myelin is a layer of a fatty insulating substance and plays an important role in brain health.
Propagation of the Action Potential
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
The solution, in the form of myelinated axons, is ingeniously simple and highly effective. The axon is surrounded by a myelin sheath consisting of up to 200 layers or so of passive cell membrane interrupted at regular intervals in what are referred to as the nodes of Ranvier (Figure 4.7). The region between adjacent nodes is the internode, whose length is roughly 100–150 times the axon diameter and ranges in length between about 200 µm and 2.5 mm, depending on axon diameter. The sheath is wrapped around the axon during embryonic development by specialized satellite cells of the nervous system – the glial cells (Section 1.2.3). In the central nervous system, the glial cells that form the myelin sheath are referred to as oligodendrocytes, with each oligodendrocyte forming one internode of myelin for up to about 50 adjacent axons. In the peripheral nervous system, a glial cell referred to as a Schwann cell forms one internode of only a single axon.
Neural Stem Cells and Oligodendrocyte Progenitors in the Central Nervous System
Published in Richard K. Burt, Alberto M. Marmont, Stem Cell Therapy for Autoimmune Disease, 2019
Jennifer A. Jackson, Diana L. Clarke
Recently, mouse oligodendroglial progenitors derived from totipotent embryonic stem cells were transplanted into a myelin-deficient rat model.37 These cells were able to interact with the host neurons and efficiently myelinate axons in the brain and spinal cord. Similarly, oligodendrocyte progenitors have been isolated from the adult brain. These cells have been propagated extensively in vitro as neurospheres—clonal spheroid cell aggregates that detach from the tissue culture dish and grow in suspension21—to generate a large number of multipotent stem cell progeny that maintain their myelinating potential.38 Phenotypic characterization of these cells has indicated that these oligodendrocyte progenitors resemble neonatal rather than adult progenitors. The ability to generate such cells from both embryonic stem cells and the adult brain opens many possibilities to explore the potential of these cells for repairing myelin disorders. Moreover, the ability of the adult-derived oligodendrocyte progenitors to apparently dedifferentiate to a more primative state, suggests that these cells may also represent a unique progenitor cell population that may be permissive to manipulation both in vitro and in vivo.
The therapeutic effect of nano-zinc on the optic nerve of offspring rats and their mothers treated with lipopolysaccharides
Published in Egyptian Journal of Basic and Applied Sciences, 2023
Eman Mohammed Emara, Hassan Ih El-Sayyad, Amr M Mowafy, Heba a El-Ghaweet
The optic nerve (cranial nerve II) is a central nervous system (CNS) tract that passes through the optic canal to leave the orbit. It is made up of the retinal ganglion cells (RGCs) axons. It allows vision by transmitting neural impulses from the retina to the brain. It is divided into four sections: the intraocular nerve head, the intraorbital, the intracanalicular and the intracranial [6]. The types of glial cells in the optic nerve are oligodendrocytes, astrocytes and microglia. Oligodendrocytes are responsible for producing the myelin sheaths that protect the CNS axons and contact nodes of Ranvier as well as they are the locations where action potentials are propagated and axonal integrity. Astrocytes are responsible for numerous physiological and pathological activities such as potassium homeostasis and metabolism as well as reactive astrogliosis in response to CNS trauma. Microglia are immune cells in CNS and have a significant impact on inflammation and infections [7].
Centella asiatica L. Urban protects against morphological aberrations induced by chronic unpredictable mild stress in rat’s hippocampus via attenuation of oxidative stress
Published in Egyptian Journal of Basic and Applied Sciences, 2022
Saravanan Jagadeesan, Samaila Musa Chiroma, Mohamad Aris Mohd Moklas, Mohamad Taufik Hidayat Baharuldin, Che Norma Mat Taib, Zulkhairi Amom, Thirupathirao Vishnumukkala, Warren Thomas, Onesimus Mahdi
The myelin sheath plays a vital role in the central nervous system because of its role in the trophic support of axons and rapid signal conduction [52]. The myelin sheath also has a role in the protection and insulation of axons. Hence, damage to the myelin sheaths could result in severe neurological deficits affecting the normal signaling, and leading therefore to neurological dysfunction. An increase in the number of demyelinated axons and destruction of the myelin sheath around axons were reported in rats exposed to either physiological or physical stressors [53]. It has been reviewed that demyelination is associated with anxiety- and depression-related behaviors in rodents [54]. In this study, CUMS rats also exhibited defects of the myelin sheaths which include detachment from the axons, discontinuous, and bulging of myelin sheath. These structural anomalies of the myelin sheath could be attributed to the depression-like behaviors and cognitive deficits observed in the CUMS rats [6]. Prevention of the structural alterations was seen in fluoxetine and CA (400 and 800 mg/kg) treated groups of rats in the current study. Rao and his team have also reported that CA extract significantly increased the dendritic arborization of hippocampal CA3 neurons in vivo studies on rats [55]. In another study on chronic mild stress-induced rat models of depression, it was observed that fluoxetine delayed the development of white matter demyelination [56].
Deep Brain Stimulation Coding in Parkinson’s: An Evolving Approach
Published in IETE Journal of Research, 2021
Dabbeta Anji Reddy, Venkateshwarla Rama Raju, G. Narsimha
An axon is a nerve-fiber which is a stretched lean protuberance of a neuron (i.e. nerve-cell) which conducts electrical impulses (electrical signals). The myelin is a lipid-rich and greasy substance which sets the nerve-cell axons (the nervous system’s wires) to lag them and augment the pace at which electrical impulses are conceded running down the axon. The huge thickness myelinated axons (belong to Group A and Group B Nerve fibers) usually have slightest threshold for activating and transmitting the impulses to and receive impulses from other axons that retort to neurons and also retort to tiny pulse widths comparing soma with dendrites. With bipolar configuration, the intensity of field decreases to one-quarter when the distance from electrode doubles. The intensity of electrical field increases as the distance between negative (−Ve-cathode) and positive (+Ve-anode) increases by ample and thick bi-polar-specification yielding high strength of field contrasting to slender specification. Albeit, the open-loop DB stimulus device has a narrow capacity to modulate the silhouette of electrical field and counter the strength of stimuli to maximally induce the neural pathways (the neuronal pathways) of significance and diminish the involuntary stretch to anatomical structures directing dyskinesias. With the advancement of powerful computers and computing machines, the neuroscientists learnt to code and encode (programming) the DBS in a way similar to flowchart and algorithmic manner of pseudo code of computer programming.