Monday, April 12, 2010

Flexoelectric Motors of the Inner Ear

One of the many fascinating designs in biology is the workings of our senses. Here, for example, is a description of recent findings on the actions of hair cells in the inner ear. It is yet another example of incredible biology at work:

Microvilli (stereocilia) projecting from the apex of hair cells in the inner ear are actively motile structures that feed energy into the vibration of the inner ear and enhance sensitivity to sound. The biophysical mechanism underlying the hair bundle motor is unknown. In this study, we examined a membrane flexoelectric origin for active movements in stereocilia and conclude that it is likely to be an important contributor to mechanical power output by hair bundles. We formulated a realistic biophysical model of stereocilia incorporating stereocilia dimensions, the known flexoelectric coefficient of lipid membranes, mechanical compliance, and fluid drag. Electrical power enters the stereocilia through displacement sensitive ion channels and, due to the small diameter of stereocilia, is converted to useful mechanical power output by flexoelectricity. This motor augments molecular motors associated with the mechanosensitive apparatus itself that have been described previously. The model reveals stereocilia to be highly efficient and fast flexoelectric motors that capture the energy in the extracellular electro-chemical potential of the inner ear to generate mechanical power output. The power analysis provides an explanation for the correlation between stereocilia height and the tonotopic organization of hearing organs. Further, results suggest that flexoelectricity may be essential to the exquisite sensitivity and frequency selectivity of non-mammalian hearing organs at high auditory frequencies, and may contribute to the “cochlear amplifier” in mammals.

9 comments:

  1. Marvelous design indeed! And let us not forget that millions upon millions of concurrent auditory signals generated by the hair cells must be properly processed by the auditory cortex before we can even begin to interpret complex sounds into meaningful speech, music and whatnot. Thanks for the post.

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  2. Interesting stuff. But Cornelius offers absolutely zero evidence of design at work - other than his own argument from credulity. Sorry, but taking an article and bolding the passages that seem "incredible" is not doing science. What is needed is some analysis of how this example fits into the ID paradigm - e.g., is there evidence of CSI, evidence of IC? etc.

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  3. @Timcol62,
    Your comment is not "doing science" either. So?

    Hunter did not claim that he had demonstrated CSI or IC in regard to flexoelectric motors of the inner ear. That is not the same as offering "absolutely zero evidence of design at work."

    For most people, hearing an explanation of how a complex machine works counts as quite a bit of evidence that it was designed. If I saw a stealth bomber's innards, and especially if I heard a description of how they worked, it would take a great deal of counter-evidence to convince me that it was *not* designed. Even Dawkins admits that the biological world "seems designed" (i.e. shows evidence of design). Thus the burden of proof is on the one who claims such systems are *not* designed.

    Dawkins et al. say they have provided evidence that such systems can be produced by undirected processes, and would not be produced by (their conception of) a designer. Hunter argues that the former claim has failed miserably, and that the latter is a theological rather than scientific argument. This post informally supports the argument that evolutionists' proposed mechanisms do not plausibly account for the complexity of biological mechanisms. The more rigorous formulation has been made elsewhere; must it be repeated with every new example?

    "other than his own argument from credulity"
    (I think you mean *in*credulity...)
    This is a pitiable tactic of proponents of a failing theory... to criticize their proponents for being insufficiently imaginative to bridge the gap between the evidence, and the theory.

    Sure, incredulity is not proof that a theory is wrong. But again, the rigorous arguments like CSI and IC have been made elsewhere. If someone wants to demonstrate CSI/IC or lack thereof for this particular mechanism, that would be a positive contribution. That does not detract from the value of making the fascinating design of stereocilia more widely known.

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  4. Lars - yes, you're correct I meant to say incredulity.

    "the rigorous arguments like CSI and IC have been made elsewhere. If someone wants to demonstrate CSI/IC or lack thereof for this particular mechanism, that would be a positive contribution."

    I was hoping that Cornelius, as a fellow of the DI would make this contribution.

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  5. Very interesting topic.

    Of course the predictions of ID in this situation
    are that these structures are genetically unique
    and genetically isolated so that there can be no
    possible pathway of mutation and natural selection.

    But wait, Dr. Hunter merely picks a cherry here,
    and marvels at it. Where is the genetic study
    Dr. Hunter? Where is the *science* of ID?

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  6. But wait, Dr. Hunter merely picks a cherry here, and marvels at it.

    So I would assume that you're against all the bad design arguments typical to Darwinists? If they can argue that something is poorly designed then why can't someone else point to good design?

    At any rate, there's nothing wrong with marveling at it. And to all the Darwinists who consistently make arguments of this sort: "I would design things better. Any competent designer would do things my way..." that they would need to design the ear and the whole body to unfold from an embryo about the size of the period at the end of this sentence. They would also have to take into account design constraints in the real world, as opposed to the imaginary worlds that they usually work in. It is not as if they have designed a machine that runs for days on plants and animal products, evolves/unfolds from an embryo and sometimes sings and dances, writes Mozart and so on. So it is unlikely that they have enough knowledge to judge design the way that they typically do.

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  7. @John Stockwell, "Of course the predictions of ID in this situation are that these structures are genetically unique and genetically isolated so that there can be no possible pathway of mutation and natural selection."

    It sounds like you're talking about Behe's prediction that some systems are irreducibly complex, i.e. there can be no gradual pathway of random mutation and natural selection.

    "Where's the *science* of ID?"

    Gathering data is part of science. Looking for examples that confirm or disconfirm a hypothesis is part of science.

    Tim and John seem to be complaining that Dr Hunter ("as a Fellow of the DI") does not perform experiments in regard to the interesting tidbits he posts on this blog.

    My impression of Hunter's role at the DI is that of a writer in philosophy of science, and of high-level analysis of claims regarding evolution. This is a valuable role, it's just not primary research.

    But if you think not doing experimental research is a fault, you must be very dissatisfied with Einstein's a-priori principles and thought experiments. You must also be making the same public complaints about Richard Dawkins or PZ Myers or Sean Carroll whenever they write about someone else's results and don't perform their own experiments. Am I misunderstanding your complaint?

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  8. Dr Hunter writes:

    So I would assume that you're against all the bad design arguments typical to Darwinists? If they can argue that something is poorly designed then why can't someone else point to good design?



    Because all structures seem to be both evidence of good and bad
    "design", the concept of design really only tells us about the people
    making the call and not about the phenomenon.

    Science is about finding processes. Simply claiming arbitrarily that
    one item is an example of "design" does not tell us about the process
    of origin of the object.

    Approaching biology from an evolutionary perspective gives us a place
    to start in understanding structures. Common descent allows us to
    examine related organisms for clues into the origin. The design
    assertion tells us absolutely nothing.


    Lars wrote:
    Gathering data is part of science. Looking for examples that confirm or disconfirm a hypothesis is part of science.


    What hypothesis? Dr. Hunter is not "collecting data" he is cherrypicking
    the data. If there is a prediction he is testing, it isn't obvious what it
    is.


    Lars wrote further:

    But if you think not doing experimental research is a fault, you must be very dissatisfied with Einstein's a-priori principles and thought experiments.



    It is not apparent to me that Dr. Hunter is doing science of *any* variety.
    Einstein had a well developed mathematical theory with which to
    generate gedanken experiments. Dr. Hunter has only his denial
    of evolution.

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  9. John Stockwell:

    ===
    Dr Hunter writes:

    So I would assume that you're against all the bad design arguments typical to Darwinists? If they can argue that something is poorly designed then why can't someone else point to good design?
    ===

    Except that I didn't write that.

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