Impact of Extracellular Current Flow on Action Potential Propagation in Myelinated Axons.

Autor:	Abdollahi N; Neurosciences and Mental Health, The Hospital for Sick Children, Toronto, Ontario M5G 0A4, Canada.; Institute of Biomedical Engineering, University of Toronto, Toronto, Ontario M5S 3G9, Canada., Prescott SA; Neurosciences and Mental Health, The Hospital for Sick Children, Toronto, Ontario M5G 0A4, Canada steve.prescott@sickkids.ca.; Institute of Biomedical Engineering, University of Toronto, Toronto, Ontario M5S 3G9, Canada.; Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
Jazyk:	angličtina
Zdroj:	The Journal of neuroscience : the official journal of the Society for Neuroscience [J Neurosci] 2024 Jun 26; Vol. 44 (26). Date of Electronic Publication: 2024 Jun 26.
DOI:	10.1523/JNEUROSCI.0569-24.2024
Abstrakt:	Myelinated axons conduct action potentials, or spikes, in a saltatory manner. Inward current caused by a spike occurring at one node of Ranvier spreads axially to the next node, which regenerates the spike when depolarized enough for voltage-gated sodium channels to activate, and so on. The rate at which this process progresses dictates the velocity at which the spike is conducted and depends on several factors including axial resistivity and axon diameter that directly affect axial current. Here we show through computational simulations in modified double-cable axon models that conduction velocity also depends on extracellular factors whose effects can be explained by their indirect influence on axial current. Specifically, we show that a conventional double-cable model, with its outside layer connected to ground, transmits less axial current than a model whose outside layer is less absorptive. A more resistive barrier exists when an axon is packed tightly between other myelinated fibers, for example. We show that realistically resistive boundary conditions can significantly increase the velocity and energy efficiency of spike propagation, while also protecting against propagation failure. Certain factors like myelin thickness may be less important than typically thought if extracellular conditions are more resistive than normally considered. We also show how realistically resistive boundary conditions affect ephaptic interactions. Overall, these results highlight the unappreciated importance of extracellular conditions for axon function. Competing Interests: The authors declare no competing financial interests. (Copyright © 2024 the authors.)
Databáze:	MEDLINE
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