Propagation on a central fiber surrounded by inactive fibers in a multifibered bundle model

• Published in: Annals of biomedical engineering 1996-11, Vol.24 (6), p.647-661
• Main Authors: ROBERGE, F. A, WANG, S, HOGUES, H, LEON, L. J
• Format: Article
• Language: English
• Subjects: Action Potentials - physiology; Animals; Biological and medical sciences; Biothermics. Biomagnetism. Bioelectricity; Electric Conductivity; Electric Impedance; Fundamental and applied biological sciences. Psychology; Heart Conduction System - physiology; In Vitro Techniques; Models, Biological; Neural Conduction - physiology; Tissues, organs and organisms biophysics
• ISSN: 0090-6964; 1573-9686
• DOI: 10.1007/BF02684178

We studied uniform propagation on a central active fiber surrounded by inactive fibers in a multifibered bundle model lying in a large volume conductor. The behavior of a fully active bundle is considered in a companion paper. The bundle is formed by concentric layers of small cylindrical fibers (radius 5 microns), with a uniform minimum distance (d) between any two adjacent fibers, to yield a bundle radius of about 72 microns. Individual fibers are identical continuous cables of excitable membrane based on a modified Beeler-Reuter model. The intracellular volume fraction (fi) increases to a maximum of about 90% as d is reduced and remains unchanged for d < 0.01 micron. In the range of d < 0.01 micron, the central fiber is effectively shielded from external effects by the first concentric layer of inactive fibers, and a large capacitive load current flows across the surrounding inactive membranes. In addition, the fiber proximity produces a circumferentially nonuniform current density (proximity effect) that is equivalent to an increased average longitudinal interstitial resistance. The conduction velocity is reduced as d becomes smaller in the range of d < 0.1 micron, the interstitial potential becomes larger, and both the maximum rate of rise and time constant of the foot of the upstroke are increased. On the other hand, for d > 0.1 micron, there are negligible changes in the shape of the upstroke, and the behavior of the central fiber is close to that of a uniform cable in a restricted volume conductor. For d larger than about 1.2 microns, the active fiber environment is close to an unbounded isotropic volume conductor.