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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.
Prospects of Nanotechnology in Brain Targeting Drug Delivery
Published in Bhaskar Mazumder, Subhabrata Ray, Paulami Pal, Yashwant Pathak, Nanotechnology, 2019
Srijita Chakrabarti, Probin Kr Roy, Pronobesh Chattopadhyay, Bhaskar Mazumder
Oligodendrocytes are responsible for the formation and maintenance of the myelin sheath, which surrounds the axons and is essential for the fast transmission of action potentials by salutatory conduction. The BBB is additionally protected by a high concentration of P-glycoprotein (P-gp), which is an active drug-efflux-transporter protein residing in the luminal membranes of the cerebral capillary endothelium. Drug molecules are removed by P-gp from the endothelial cell cytoplasm before they pass through the brain parenchyma. ApoE is a glycoprotein which interacts with the low-density lipoprotein receptors (LDLR), and thus significantly modulates plasma lipoprotein and cholesterol levels (Hauser et al., 2011). ApoE is synthesized primarily by astrocytes in adult brain tissue, however sometimes it is synthesized by microglia and neurons under certain physiological and pathological conditions. During nerve regeneration, ApoE acts as a scavenger of lipophilic molecules. In the peripheral circulation in the brain, the role of ApoE involves cholesterol transport and intercellular exchange of metabolites between neurons and glial cells (Nagpal et al., 2013).
Tissue Structure and Function
Published in Joseph W. Freeman, Debabrata Banerjee, Building Tissues, 2018
Joseph W. Freeman, Debabrata Banerjee
Neuroglia support and nourish neurons, there are far more neuroglia than neurons. Among the neuroglia are Schwann cells. These neuroglia cells increase the speed of the impulse down the length of the axon by myelinating it, producing a medullary sheath (Figure 4.24). This sheath is not continuous because it is interrupted by spaces called the nodes of Ranvier (Figure 4.24). The myelin sheaths increase electrical resistance across the cell membrane by a factor of 5,000 and decreases capacitance by a factor of 50. Myelin is a mixture of lipids (70%–80%) and proteins (20%–80%) that form around the nerve fibers, giving them a white appearance. Oligodendrocytes also myelinate axons (Figure 4.25). Oligodendrocytes interact with neurons in the central nervous system (CNS), whereas Schwann cells myelinate neurons in the peripheral nervous system (PNS).
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].
A Functional BCI Model by the P2731 working group: Physiology
Published in Brain-Computer Interfaces, 2021
Ali Hossaini, Davide Valeriani, Chang S. Nam, Raffaele Ferrante, Mufti Mahmud
The brain also contains a range of cells that support its electrical, biochemical and metabolic functions. Collectively known as glia, these cells support, protect, nourish and insulate neurons, and they are essential for proper cognition as well as health. The primary categories of glial cells are microglia, astrocytes, oligodendrocytes and NG2-glia progenitor cells. Oligodendrocytes are essential to the operation of the brain as an electrical organ because they act as insulators when signals are propagating through axons [34].