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Refractive index and its effect upon conduction/insulation

  1. Jun 21, 2012 #1
    Dear All,
    thank you for taking the time to view my post. I am a Biologist and I have come across a curious characteristic of proteins that are structural constituents of Nerve cell sheaths (These proteins in addition to lipids surround nerve axons). In general, they seem to have a high refractive index, not far off that found in crystallins that form the lens of the eye.

    I was just wondering if there is any reason physical reason why such a property may provide functional significance to the propagation of nerve impulses, which essentially result from the movement of charged ions separated by a membrane through a channel (simplified version). The proteins in question are found in the sheath on the external side of the membrane.

    I realise that this is a biology question but I have posted it here as it concerns the physics of any relations between refractive index, electrical conduction and insulation.

    I found some information about semiconductors that have a layer of material with a high refractive index surrounding them but I am unclear whether this is relevant and in what capacity this layer is acting, specifically the role of high refractive index.

    I am curious because for some reason these proteins have evolved this characteristic, and whilst it may possibly be incidental, the data is intriguing.

    Any opinions would be greatly appreciated. I thank you all in advance.
  2. jcsd
  3. Jun 21, 2012 #2


    User Avatar

    That's a really good question.........That's a really interesting question......Unfortunately, I do not have the answer.

    It may effect temperature. btw I'm completely guessing here. Because of the high refractive index, certain thermal energy will be reflected back - which then will be made available to the ions.

    And the action of the high refractive index of the insulating sheath may be to regulate the temperature (and the speed) of the ions.

    Again, completely guessing, the high refractive index, could be a means of regulating temperature. It might be the proteins way of releasing energy when it has too much to function, and holding it in when it needs it.
  4. Jun 21, 2012 #3
    Probably not.

    The index of refraction of the eye lens is not that high, about 1.4. This is lower than glass and only slightly higher than water.

    A nerve sheath like this surrounded in fluid and other tissue would have no guiding properties for nerve impulses.
  5. Jun 22, 2012 #4
    Dear All,
    thank you for your replies. Firstly I want to apologise for an error in
    my first post. When I stated refractive index, I meant to say
    refractive index increment:

    http://www.polyanalytik.com/determination-of-refractive-index-increment.php [Broken]

    Some extra infor: The proteins that form the gradient lens of the eye in humans, called crystallins, existing various types with different structures and amino acid sequences. They form an interacting superstructure at very high concentrations that minimizes the scattering of light, chromatic aberrations and aggregation (These proteins are not replaced like other
    proteins, they last from development in the womb, until death).

    So krd, what you are eluting to is that through the refraction of IR energy, ions are kept in
    a high energy state, and this enhances the efficiency of conduction of ions through the membrane channel and thus nerve conduction? This is very interesting if this is the case.

    Antiphon, you have a valid point. But, lens serves its function well, and moreover, the proteins have evolved to be different in terms of refractive index increment. The refractive index increment of crystallins has been studied to an extent:

    Human αA-crystallin 0.1938
    Human αB-crystallin 0.1922
    Human βA1/A3-crystallin 0.1979
    Human βA2-crystallin 0.1956
    Human γA-crystallin 0.2000
    Human γB-crystallin 0.1988


    The Molecular Refractive Function of Lens γ-Crystallins
    Huaying Zhao 1 , Patrick H. Brown 2 , M. Teresa Magone 1
    and Peter Schuck 1 ⁎
    Dynamics of Macromolecular Assembly Section, Laboratory of Cellular Imaging and Macromolecular Biophysics,
    National Institutes of Health, Bethesda, MD, USA
    Biomedical Engineering and Physical Sciences Shared Resource, National Institute of Biomedical Imaging
    and Bioengineering, National Institutes of Health, Bethesda, MD, USA

    When you say guiding properties, I assume you mean playing a direct role in channelling the nerve impulse? If so, I am inclined to agree, however, what I was trying to find out was whether there was any reason why the refraction of energy would somehow aid conduction in some way. The sheath also contains lipids which are know to insulate nerve axons thus preventing the cross propagation of signals. The question is, is there any significance of these proteins and their high Rii values.

    Thank you both for your time and expertise, and please let me know what you think. I once again apologise for the error in my first post.
    Last edited by a moderator: May 6, 2017
  6. Jun 22, 2012 #5


    User Avatar

    Yes, but it's a wild guess.

    Refractive index is an optical characteristic. To explain precisely what is happening is more complicated. Down at the molecular scale it would get even a little more complicated - but that is where the Ri is coming from, and the other optical characteristics.

    But what I'm thinking, is the proteins, lipids etc are using their optical characteristics to regulate temperature into an optimal range. And why I'm thinking this, is the nano-tech engineers can make very small things - but they generally only hold together at incredibly low temperatures - temperature is a big problem. Whereas the biological molecules and cells, they can operate at room temperature. Certainly for organisms on a larger scale temperature regulation is absolutely essential. I wonder at the scale of nerve axons is similar temperature regulation also absolutely essential - if that's true then the optical characteristics of the material at that scale would be crucial - sine qua non.

    It's interesting. Maybe there's a field of study in nano-engineering that covers it. Temperature is very serious problem for getting these little tiny things to work.
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