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Effect of geometrical irregularities on propagation delay in axonal trees

Manor, Yair and Koch, Christof and Segev, Idan (1991) Effect of geometrical irregularities on propagation delay in axonal trees. Biophysical Journal, 60 (6). pp. 1424-1437. ISSN 0006-3495. http://resolver.caltech.edu/CaltechAUTHORS:20130816-103214095

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Abstract

Multiple successive geometrical inhomogeneities, such as extensive arborization and terminal varicosities, are usual characteristics of axons. Near such regions the velocity of the action potential (AP) changes. This study uses AXONTREE, a modeling tool developed in the companion paper for two purposes: (a) to gain insights into the consequence of these irregularities for the propagation delay along axons, and (b) to simulate the propagation of APs along a reconstructed axon from a cortical cell, taking into account information concerning the distribution of boutons (release sites) along such axons to estimate the distribution of arrival times of APs to the axons release sites. We used Hodgkin and Huxley (1952) like membrane properties at 20 degrees C. Focusing on the propagation delay which results from geometrical changes along the axon (and not from the actual diameters or length of the axon), the main results are: (a) the propagation delay at a region of a single geometrical change (a step change in axon diameter or a branch point) is in the order of a few tenths of a millisecond. This delay critically depends on the kinetics and the density of the excitable channels; (b) as a general rule, the lag imposed on the AP propagation at a region with a geometrical ratio GR greater than 1 is larger than the lead obtained at a region with a reciprocal of that GR value; (c) when the electronic distance between two successive geometrical changes (Xdis) is small, the delay is not the sum of the individual delays at each geometrical change, when isolated. When both geometrical changes are with GR greater than 1 or both with GR less than 1, this delay is supralinear (larger than the sum of individual delays). The two other combinations yield a sublinear delay; and (d) in a varicose axon, where the diameter changes frequently from thin to thick and back to thin, the propagation velocity may be slower than the velocity along a uniform axon with the thin diameter. Finally, we computed propagation delays along a morphologically characterized axon from layer V of the somatosensory cortex of the cat. This axon projects mainly to area 4 but also sends collaterals to areas 3b and 3a. The model predicts that, for this axon, areas 3a, 3b, and the proximal part of area 4 are activated approximately 2 ms before the activation of the distal part of area 4.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1016/S0006-3495(91)82179-8DOIArticle
http://www.sciencedirect.com/science/article/pii/S0006349591821798PublisherArticle
Additional Information:Copyright © 1991 The Biophysical Society. Published by Elsevier Inc. We are grateful to Dr. Y. Yarom for his fruitful critics. We also thank the referees for their insightful comments which helped to improve the quality of this paper. This work was supported by grants from the National Institutes of Health and the Office of Naval Research to Dr. Segev, and by a Presidential Young Investigator Award (NSF) and funds from the James S. McDonnell foundation to Dr. Koch.
Group:Koch Laboratory, KLAB
Funders:
Funding AgencyGrant Number
National Institutes of HealthUNSPECIFIED
U.S. Office of Naval Research UNSPECIFIED
NSF Presidential Young Investigator AwardUNSPECIFIED
James S. McDonnell FoundationUNSPECIFIED
Record Number:CaltechAUTHORS:20130816-103214095
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20130816-103214095
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:40470
Collection:CaltechAUTHORS
Deposited By: KLAB Import
Deposited On:26 Jan 2008 04:18
Last Modified:02 Oct 2013 19:24

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