A computer model for action potential propagation through branch point in myelinated
nerves.
Zhou, Lei, and Shing-Yan Chiu.
Department of Physiology, University of Wisconsin School of Medicine, Madison, WI
53706
APStracts 7:0476J, 2000.
A mathematical model is developed for simulation of action potential propagation through a
single branch point of a myelinated nerve fiber with a parent branch bifurcating into two
identical daughter branches. This model is based on a previously published multi-layer
compartmental model for single unbranched myelinated nerve fibers (Halter and Clark 1991).
Essential modifications were made to couple both daughter branches to the parent branch. There
are two major features in this model. First, the model could incorporate detailed geometrical
parameters for the myelin sheath and the axon, accomplished by dividing both structures into
many segments. Second, each segment has two layers, the myelin sheath and the axonal
membrane, allowing voltages of intra-axonal space and periaxonal space to be calculated
separately. In this model, K ion concentration in the periaxonal space is dynamically linked to
the activity of axonal fast K channels underneath the myelin in the paranodal region. Our model
demonstrates that the branch point acts like a low-pass filter, blocking high frequency
transmission from the parent to the daughter branches. Theoretical analysis showed that the cut-
off frequency for transmission through the branch point is determined by temperature, local K
ion accumulation, width of the periaxonal space, and internodal lengths at the vicinity of the
branch point. Our result is consistent with empirical findings of irregular spacing of nodes of
Ranvier at axon abors, suggesting that branch points of myelinated axons play important roles in
signal integration in an axonal tree.
Received 7 June 2000; accepted in final form 20 September 2000
APS Manuscript Number J437-0.
Article publication pending Am J Physiol
ISSN 1080-4757 Copyright 2000 The American Physiological Society.
Published in APStracts on 20 October 2000