gaines2016_v3.hoc

Myelinated axon model for afferent and efferent axons, adapted from Gaines 2016

Visceral myelinated axons can have smaller diameters than somatic myelinated axons, outside the range for the ultrastructural relationships presented in (McIntyre et al., 2002). The published interpolations (McIntyre et al., 2002) fail to extrapolate to these small myelinated axon diameters. To model the distribution of fiber diameters and g-ratios measured for myelinated axons in the pelvic nerve, we related the axon diameter and compartment length at each of the node of Ranvier (NODE), paranode (MYSA), juxtaparanode (FLUT) and stereotypical internode (STIN).

This figure shows the relationships between fiber diameter and the other ultrastructural parameters. Inner (axon) diameters at each of the MYSA, FLUT, and STIN were scaled to match the observed distribution of myelinated pelvic nerve axon g-ratios. The fit procedure produced negative estimates for STIN length and number of myelin lamellae at small axon diameters, and so saturating hyperbolic equations were fit for these variables. Equations were fit to the relevant data in (McIntyre et al., 2002). With the exception of the relative length of the FLUT within the internode, these equations closely matched the extrapolated small-diameter fibers presented in (Pelot et al., 2019).