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Modeling axon-myelin relationships: insights on signal propagation and modulation

Claire Guerrier,听Universit茅 C么te d'Azur
Tuesday February 18, 12-1pm
Montreal Neurological Institute, deGrandpre Communications Centre

Abstract: The profound functional significance of myelin is revealed by the severe neurological deficits that are consequent upon multiple inherited or acquired demyelinating conditions. Recent observations demonstrate that the dimensions of myelin sheaths relative to axon calibres can be modulated in response to adult experience with significant functional consequences. Despite the widely accepted demonstration that adult myelin is adaptive and the rapidly growing evidence that such plasticity plays a key role in both normal and abnormal nervous system function, the effects of such myelin and axonal organization changes on signal propagation are not clearly understood.
In this project, using data on myelin sheath thickness in relation to axonal diameter coming from gene edited mice, we investigate the effects of myelination on the propagation of electrical signals along these axons and vice versa. We consider an electrical model based on cable theory and on Holdgkin-Huxley type formalism to represent voltage gated channels at the nodes of Ranvier (NoR).
Using this model, we investigate the effects of parameter sets corresponding to pathological myelin-axon-NoR organisation, on signal propagation. Using mathematical analysis and simulations, we show that the different frequencies constituting a signal travel at their own speed, that depends on the fibre properties. Although in normal axons and for a typical signal, the difference of speed for different frequencies is negligible, in abnormal demyelinated axons, there are drastic differences, which perturbs signal propagation and modifies the shape of the outcoming signal.

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