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Key human anatomy and physiology principles as they relate to rehabilitation engineering
Published in Alex Mihailidis, Roger Smith, Rehabilitation Engineering, 2023
Qussai Obiedat, Bhagwant S. Sindhu, Ying-Chih Wang
If electrical impulses travel along the neural membrane without any insulation, the axonal conduction velocity may travel at merely 2–10 m/s, the speed at which an electrochemical impulse propagates down a neural pathway. Amazingly, some neurons conduct at speed of 80–120 m/s. Such a high conduct velocity cannot be achieved by a passive flow of ions alone. To increase the conduction velocity of action potentials, the nerve fibers are further insulated with the fat-like substance forming a sheath around the nerve fibers, a process called myelination. The presence of myelin prevents the local current from leaking across the internodal membrane. The result is a greatly enhanced velocity of action potential conduction. The propagation of action potentials along myelinated axons from one node of Ranvier to the next node is called the saltatory conduction. As such, damage to the myelin has a significant impact on the nerve conduction velocity and the results could be devastating. For example, individuals may suffer from immune system attacks and damage to the protective myelin sheath causing communication problems between the brain and the rest of the body. Multiple sclerosis (MS) damages the myelination of the CNS, resulting in widely varying central nerve symptoms. Guillain-Barre syndrome (GBS) damages the myelination of the PNS, causing muscle weakness, reflex loss, and numbness or tingling in parts of the body. GBS can lead to temporary total body paralysis for weeks, which makes the follow-up rehabilitation a lengthy process to recondition the muscles (Lundy-Ekman 2013).
Chapter 16 Electrophysiology
Published in B H Brown, R H Smallwood, D C Barber, P V Lawford, D R Hose, Medical Physics and Biomedical Engineering, 2017
External current flow around a nerve fibre is also responsible for the transmission of an action potential along the nerve. The external current flow at the point of depolarization disturbs the transmembrane potential further along the fibre and this causes depolarization to spread. An action potential is transmitted along a fibre with a speed of a few metres per second. It can be shown experimentally that external current flow is essential to the transmission of action potentials, by removing a single nerve fibre from the surrounding extracellular fluid; under these conditions an action potential is not transmitted. In figure 16.2 the nerve axon on the left is shown surrounded by bands of myelin. Myelin is an electrical insulator which prevents current flowing from the nerve axon into the extracellular fluid, and if it were continuous along the nerve then no action potentials would be possible. However, the myelin is actually in bands with areas called the nodes of Ranvier between the bands. External current can flow from the nodes of Ranvier and the effect of the myelin is to speed up the transmission of nerve action potentials which jump from one node to the next. This process is called saltatory conduction and it allows action potentials to be transmitted at about ten times the speed which fibres without myelin conduct impulses. The fast nerve fibres which supply our muscles are myelinated fibres, whereas the slow fibres used to transmit pain sensation are slow non-myelinated fibres.
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
Alongside an idealized neuron, Figure 5 depicts an oligodendrocyte cell whose branches enclose the axon of a cerebral neuron in a myelin sheath. While myelin is not essential for neural function, it is used in many classes of neurons within and outside the central nervous system to enhance electrical conduction. In the brain, unmyelinated neurons constitute ‘gray matter’ while myelinated neurons are called ‘white matter’ because a mass of fatty myelin has a white appearance [35,36]. Myelin sheaths are punctuated by breaks called Nodes of Ranvier that enable an action potential to propagate efficiently through the length of the axon through a process known as saltatory conduction [37].
Modulation of myelin formation by combined high affinity with extracellular matrix structure of electrospun silk fibroin nanoscaffolds
Published in Journal of Biomaterials Science, Polymer Edition, 2019
Sha Liu, Changmei Niu, Ziqi Xu, Yingyu Wang, Yunyun Liang, Ying Zhao, Yahong Zhao, Yumin Yang
Myelin is formed by glial cells that wrapping around axons. The myelination of axon is a necessary process for the proper physiological function of the nervous system, as myelin allow rapid propagation of nerve impulses by saltatory conduction in axons [15]. Co-culture of DRG neurons and Schwann cells is usually used to study the myelin sheath of PNS. In this study, we established a co-culture model of DRG neurons and Schwann cells to observe myelination in vitro.