Effect of the myelin sheath aqueous layers on the action potentials in simulated hereditary and chronic demyelinating neuropathies

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The action potentials reflect the conduction properties in nerve excitable structures. In order to expand our studies of the conduction properties, the effect of the myelin sheath aqueous layers on propagated action potentials is compared in previously simulated by us demyelinating neuropathies such as Charcot-Marie-Tooth disease type 1A (CMT1A), chronic inflammatory demyelinating polyneuropathy (CIDP) and CIDP subtypes. Using our multi-layered model of human motor nerve fibre, the calculated action potentials are presented in a simulated normal case and in three cases of progressively greater demyelinations (i. e. internodal systematic demyelinations (ISDs) as specific indicators of CMT1A; paranodal systematic demyelinations (PSDs) as specific indicators of CIDP; and paranodal internodal systematic demyelinations (PISDs) as specific indicators of CIDP subtypes for s=1, 2, 3) without/with aqueous layers within the myelin sheath. Two cases of each demyelinated subtype are mild and one is severe. The loss of the myelin lamellae and their corresponding aqueous layers in the ISD1 and ISD2 cases additionally slows the conduction velocity. The uniform reduction of the paranodal seal resistance in the PSD1 and PSD2 cases with aqueous layers additionally increases the conduction velocity of the action potentials in comparison with the cases when the aqueous layers are not taken into account. However, the effect of the aqueous layers on the conduction properties is neutralized when the demyelinations are heterogeneous such as in the PISDs. The present study shows that the conduction velocity of the action potentials in the simulated CMT1A and CIDP depends on the aqueous layers. Scripta Scientifica Medica 2012; 44(2): 53-57.