Info wanted on biomechanics and neural processes

Edwin R. Yeh ery2 at po.CWRU.Edu
Sat Feb 5 14:43:32 EST 1994


In a previous article, A D Brazelton () says:

>In article <2ifjeo$d04 at news.u.washington.edu> meir at zoology.washington.edu (Eli Meir) writes:
>>    Does anyone out there know of references for experimental or
>>theoretical work done on the effects of stress and strain on neuronal
>>processes.  I mean stress and strain in the biomechanical sense (ie -
>>getting pulled and pushed around), and I'm not interested in stress
>>activated channels, unless all channels are stress-activated - I'm
>>interested in normal, everyday axons and dendrites, and what happens to
>>their electrical properties when they get stretched or twisted.  Any
>>info would be appreciated.

I have not heard of a particular references in the original questions;
however, I think it is worthy of investigation. Can you also name
a few situations (perhaps, certain injury or disease) that will
actually cause mechanical stress on neurons?

Since you are not interested in stress activated channels, I suggest
that you redrive the cable equations with your assumptions on stretch.
By that I mean starting from R = (ro * l)/A and proceeds with your
assumption of delta l. You should be able to derive the passive model
with Rl, Rm, and Cm with Ohm's Law, Kirchoff's Law and Conservation
of Energy. This will tell you how the current will be conducting
passively. 

Another consideration you might want to take into account is the
changes in concentration releveant to the neural membrane in study.
Since we know that the resting membrane potential is dictacted by
the extracellular and intraceullar [K+],[Na+],[Cl-],[Anions] 
concentrations by their Nersnst Potential, the effect of stretching 
may have influence on the effective concentration since the volume is 
changed. Intuitively then, this will have an effect on the generation 
of action potential since the level of resting membrane potential
will determine how likely this neuron will be perturbed to be deplorized
-- in a sense then, the stretching may change its threshold of firing.

>How is it possible to study the effects of mechanical stress on the
>electrical properties of neuronal processes without considering 
>stretch-sensitive ion channels?  Is there another stretch-sensitive 
>mechanism which does not involve ionic currents?
>
>Tony Brazelton
>Neuronal Pattern Analysis Group, Beckman Institute
>University of Illinois at Urbana-Champaign

Usually in the theoretical modeling approach to the study, we divide
things up and model it accrodingly to the phenomena we wish to observe.
One of the way, we do that is by looking at the passive membrane properties 
(i.e. Cable Equations by Rall) and active membrane properties (such as 
Hudgkin-Huxley, Frankenhauser, or Sweeney.) Thus, what I wrote above 
can describe the effects of mechanical stress in the passive model. 
However, you are right in that, in order to get a better picture, we 
should look into the strech-sensitive ion channels. (BTW, aren't all 
ion channels potentially strech-sensitive? That is, by stetching, they 
may allow ions or even molecules that are normally too large to pass in 
or out thereby increase or decrease their concentration.)

Below are a few references that may be of interest:

Koch and Segev (eds.) _Methods in Neuronal Modeling_, MIT PRESS, 1989.
  -- Rall's Cable Equation is in one of the chapters, or you can
     directly look into the _Handbook of Physiology_.

Plonsey and Barr. _Bioelectricity_, QP341.P734 1988

Let me know how your research turned out. Good luck.

Edwin


-- 
Edwin R. Yeh < ery2 at po.cwru.edu > | Research Interests      
Dept. of Biomedical Engineering   | + Direct Neural Control & Perception 
Case Western Reserve University   | + Non-invasive Neuronal Data Acquistion
Cleveland, OH 44106               | + Brain-Computer Interface  



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