Biomedical subjects

H G Hentschel

Publications and source records attributed to H G Hentschel.

5 recordsLinked to original sources

PubMed2000

Excitable calcium wave propagation in the presence of localized stores.

We study the propagation of calcium waves in the presence of a discrete distribution of calcium stores. Calcium-induced calcium release coupled to diffusion can be used to produce a criterion for wave propagation across connected clusters of stores. The velocity of the resulting wave and its relationship to the frequency of the excitatory stimulus can then be described using percolation theory. Simulations show a homogeneous and a fractal regime and are in agreement with both experiments and theory.

Animals↗

PubMed1999

Models of axon guidance and bundling during development.

Diffusible chemoattractants and chemorepellants, together with contact attraction and repulsion, have been implicated in the establishment of connections between neurons and their targets. Here we study how such diffusible and contact signals can be involved in the whole sequence of events from bundling of axons, guidance of axon bundles towards their targets, to debundling and the final innervation of individual targets. By means of computer simulations, we investigate the strengths and weaknesses of a number of particular mechanisms that have been proposed for these processes.

Animals↗

PubMed1999

Tuning friction with noise and disorder.

We present numerical and experimental evidence which demonstrates that under certain conditions friction can be reduced by spatial disorder and/or thermal noise. We discuss possible mechanisms for this behavior.

Journal Article↗

PubMed1996

The origin of neuronal polarization: a model of axon formation.

During development, most neurons become polarized when one neurite, generally the longest, becomes the axon and the other neurites become dendrites. The physical mechanism responsible for such length-related differentiation has not been established. Here, we present a model of neuronal polarization based upon the existence of a "determinant chemical' whose concentration at the neurite tips influences the growth rate of the neurite. Over an extended parameter range the equations describing the formation, transport, and consumption of this chemical and the resulting neurite growth undergo a winner-take-all instability, yielding rapid growth of one neurite (the axon) and diminished growth of all others. The behaviour of this model agrees well with the results of axotomy experiments and experiments in which growth-modulating substances are applied to individual growth cones. Possible candidates for the determinant chemical are discussed, and further experiments are proposed to test the model.

Animals↗

PubMed1996

Diffusion-regulated control of cellular dendritic morphogenesis.

Highly branched dendritic shapes are distinguishing characteristics of neurons and certain other cell types, but the physical mechanisms responsible for their formation are not well understood. Here, we model the growth of cells under the control of diffusible growth-regulating factors (morphogens such as calcium ion) whose local internal concentration results from influx and active extrusion across the cell membrane. Nonlinearities in voltage-dependent ionic permeabilities enhance unstable growth, so that branching dendritic outgrowths results from self-sustaining internal morphogen gradients. Simulations display complex patterns of branching growth, influenced by membrane conductance, galvanotropism and chemotropism. This self-organizing pattern formation is in agreement with the development of real neurons under corresponding conditions.

Animals↗