A theoretical and experimental study of the mechanism of axoplasmic convection in nerve fibers driven by peristaltic surface waves
Department of Mechanical Engineering
Doctor of Engineering Science
Levy, Martin J.
Progelhof, Richard C.
Droughton, John Vincent
In the study of cell biology, investigators have found that substances which are produced within the cell nucleus are sometimes found throughout the cell at points distant from the site of production. In the case of nerve cells (neurons), this is particularly dramatic because of the unusual elongated geometry of these cells.
A neuron possesses a cylindrical tubular extension called an "axon" or "axis cylinder" which is characterized by a large length-to-diameter ratio (103-106). The existence of a continuous proximo-distal flow of axoplasm within these cylindrical axons has now been demonstrated by numerous investigators. In this study, engineering techniques are employed to explore the role of microperistalsis as a possible driving mechanism for this axoplasmic flow.
An experimental technique for injecting axons (5-10 microns-diameter) with micropipettes under visual microscopic control has been perfected. A new technique for microcapillary tube viscometric measurements applicable to micro samples of biological materials is presented. Using these techniques, a flow curve has been obtained for the axoplasmic substance. The results of these experiments indicate that axoplasin behaves as a highly viscous, pseudo-plastic material. No evidence of significant time-dependent thixotropic or viscoelastic effects was apparent.
A theoretical analysis of the peristaltic pumping of pseudoplastic fluids at low Reynolds numbers by means of an infinite train of sinusoidal peristaltic waves is. presented. Results are shown as a series of pump characteristic curves involving the geometrical properties of tlie wave and the flow properties of the pseudo-plastic fluid as parameters. Data obtained from experiments performed on a plane, two-dimensional model are used to confirm the theoretical results.
Cinemicrographic evidence reported in the literature describing waves traveling over the surface of axons in culture is discussed. A study of the geometrical properties of the peristaltic waves taken from these motion picture data is presented.
The viscometric data obtained from axoplasm are used to establish system resistance curves for axons idealized as uniform cylindrical tubes. These data are correlated with the theoretical pump characteristic curves to determine an expected flow rate. A comparison between the theoretical flow rates and the observed axonal flow rates gives quantitative support to the hypothesis that peristalsis is the mechanism for axoplasmic flow. In addition, it is shown that the peristaltic pumping of a pseudoplastic fluid depends only on the geometrical properties of the peristaltic waves and the flow behavior index of the fluid. For this case of axoplasm, this indicates that the theoretical flow speed of axoplasm is independent both of the consistency of the axoplasmic material and the diameter of the axon.
njit-etd1971-004 (166 pages ~ 7,023 KB pdf)
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Created June 24, 2008