Talk:Basilar membrane

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I think that the image showing the "sinusoidal drive through the oval window" is rather misleading. Anyone looking at it casually would assume that it means that low frequency sound localizes at the base of the cochlea and high frequency at the apex, which, as I understand it, is the wrong way round. I'm not an expert on fluid mechanics and I'm not sure what the "travelling wave" and "fluid streamlines" mean - they may well be correct. But the diagram is not explained in the article and the legend really does not help. To the non-expert observer who is likely to come to Wikipedia for a quick explanation, the diagram seems to imply just the opposite to what is actually happening. I put forward the suggestion that the diagram should be replaced by one showing the actual sound frequency localization. The "travelling wave" stuff is not a headline issue regarding cochlea function, while I would think that neural line-labelling of sound frequency resulting (at least in part) from vibration-localization on the basilar membrane is. Wjheitler (talk) 10:50, 29 March 2015 (UTC)

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Please check this section:

Frequency dispersion A third, evolutionarily younger, function of the basilar membrane is strongly developed in the cochlea of most mammalian species and weakly developed in some bird species. It is the function of frequency dispersion of incoming sound waves. In brief, the membrane is tapered and it is stiffer at one end than at the other. The dispersion of fluid waves causes sound input of a certain frequency to vibrate some locations of the membrane more than other locations. As shown in experiments by Nobel Prize laureate Georg von Békésy, high frequencies lead to maximum vibrations at the basal end of the cochlear coil (narrow, stiff membrane), and low frequencies lead to maximum vibrations at the apical end of the cochlear coil (wide, more compliant membrane). This "place-frequency map" can be described quantitatively by the Greenwood function and its variants.

I believe the morphology of the basilar membrane is the other way around: narrow and stiff at the base (near the oval window) and wide and flexible at the apex. —Preceding unsigned comment added by Sfoleor (talk • contribs) 09:56, 2 February 2009 (UTC)

I removed this section:

The benefit that animals have from this third function is still a matter of research. The hypothesis of von Békésy that it would provide frequency selectivity for the hair cells turned out to be in error. Research results of recent decades showed that frequency selectivity in hearing remains intact even with an immobilized basilar membrane [1]. Therefore one had to conclude that also mammals, as all other land vertebrates, hear frequency-selectively due to intrinsically tuned hair cells. This conclusion was later confirmed by an extensive study where a large-scale pharmacological knockout of one type of hair cells resulted in a complete loss of frequency-selective hearing, even though the basilar membrane had remained fully functional [2].

because the cited articles do not support the gist of the paragraph. The results of article two and the role of outer hair cells in general (which was the true mystery of von Bekesy's results) do need to be incorporated into this article. But it is the role of outer hair cells to augment the resonance of the basilar membrane that probably leads to hearing loss in bats without outer hair cells, not special frequency tuning of the outer hair cells. The first article doesn't speak to the issues of the removed paragraph. --Chinasaur 01:55, 22 March 2006 (UTC)

Dear Chinasaur, the report by Nageris et al. (1996) clearly presents data in the text and in the figures that demand the above stated conclusion. You also misunderstood the report by Kössl et al. (2000). It is not true that the basilar membrane (BM) must move, before the stereocilia can move. Nilsen and Russell (1999) showed in highly sophisticated experiments that the BM on its own (post mortem) starts moving above noise (displacement of 0.5 nm) at levels > 65 dB SPL (their Fig.5). This clearly shows that the BM on its own cannot carry any sound signal at low sound levels. The cochlear fluids, however, can. It is therefore necessary to assume that they provide the adequate stimulus for the stereocilia in all vertebrates. See also the replication of these results in Nilsen and Russell (2000). I will therefore re-install the section that you deleted, and then extend the reference list. DiMare 14:34, 30 June 2006 (UTC)

As to the irrelevance of the basilar membrane for frequency selectivity in hearing, please also note the following typical summary. I has been on the best website concerning the functional anatomy of the inner ear for many years:

"Current concept: Because of the discovery of the outer hair cell (OHC) active mechanism which explains the exquisite properties of sensitivity and tuning of the cochlea, the travelling wave versus resonance theory is not a hot debate any longer. Most acousticians and physiologists now think that the physical model of damping resonance, based upon OHC properties, is close to reality; the travelling wave tends now to be considered an epiphenomenon."[3] -- DiMare 18:02, 10 February 2007 (UTC)

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Where did the value for 30,000 stereocilia come from? I looked through each image and could not find it. This site: http://hyperphysics.phy-astr.gsu.edu/hbase/sound/corti.html states that there are between 16 and 20 thousand stereocilia on an average basilar membrane. 93.97.34.206 (talk) 00:11, 3 April 2012 (UTC) Simon Edwards, MEng Acoustical Engineering student, ISVR

Indeed, I see 15000 in sources such as this one and 16000 here. Hair cells, not stereocilia. Dicklyon (talk) 17:15, 11 April 2013 (UTC)

When I partially inverted this revert, I didn't notice it was a revert. So I partially agreed and partially disagreed with these two involved editors. Others should take a look. Please state reasons in edit summary if you make changes to data or whatever. Dicklyon (talk) 17:12, 11 April 2013 (UTC)

@Yintan²: My edits from today were based on the sources that were already referenced. Please read these anatomical data first before you blindly revert necessary corrections. Thank you. DiMare (talk) 21:20, 11 April 2013 (UTC)

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Figure removed

Sinusoidal drive through the oval window (top) causes a traveling wave of fluid–membrane motion. A modeled snapshot of fluid streamlines is shown. The wavelength is long compared to the duct height near the base, in what is called the long-wave region, and short (0.5 to 1.0 mm in typical observations) near the place where the displacement and velocity are maximized, just before cutoff, in the short-wave region.

References

In this edit, an IP removed a sketch that I made years ago, with edit summary "The image removed is incorrect - the waves which resonate with the base of the cochlea are the highest-frequency ones, with low-frequency waves residing near the apex." While I can't argue with what that says about how high and low frequencies are localized, the conclusion that the image is incorrect is wrong. The image only shows one frequency, and shows how the wavenumber (spatial frequency) changes from base (top, longwave region) toward the place of resonance (bottom, shortwave region).

Since it's my own sketch, I won't put it back, and ask other editors to consider it. Dicklyon (talk) 01:22, 19 January 2017 (UTC)

Changed my mind. Since the removal was a section blanking by an unknown, I undid it. Any objections? Dicklyon (talk) 08:17, 12 September 2017 (UTC)

Wikipedia articles have failed to explain the basic workings of the human auditory system.

My frustration isn't just with Wikipedia articles. I have read dozens of Internet articles and watched numerous videos attempting to explain the human auditory system, and every one of them skips over a simple explanation of the path that sound waves take after they enter through the oval window of the cochlea. This "path," as I'm describing it, gets even more fuzzy once a tutorial starts talking about bending stereocilia, potassium ions, spiral ganglions, and neurotransmitters. The sequence of those particular events is easy enough to follow, but the big question of the path that the original sound information has taken is left out.

The first and most elementary question is: what path do the sound waves take to reach the basilar membrane? Nobody answers that question. I have searched the various online encyclopedias, medical websites, university publications, scientific papers, etc., and they all skip over the question and only offer a vague, generic explanation, such as "sound waves entering the cochlea cause the basilar membrane to vibrate." It should be obvious that isn't an adequate explanation. The only source I have found that attempts to answer the question is a YouTube video titled Auditory Transduction (2002). According to that video, sound waves traveling on an upward course through the scala vestibuli cause Reissner's membrane to vibrate, and that causes vibrations in the endolymph fluid of the cochlear duct (scala media), and that, in turn, causes the basilar membrane to vibrate. In that description, the sound vibrations are coming from "above," relatively speaking. But if you look up Reissner's membrane as a separate subject on Wikipedia or anywhere else, it says nothing about sound waves passing through Reissner's membrane into the cochlear duct and impacting the basilar membrane. The articles just say that Reissner's membrane serves to separate the fluids of the cochlear duct from fluid in the scala vestibuli. Even so, that explanation seems more reasonable than the alternative, which would be for sound waves to ascend upward through the scala vestibuli to the apex, then descend down though the scala tympani before impacting the underside of the basilar membrane. There are a couple of difficulties with that possibility. For one thing, there is a membrane at the apex of the cochlea called the helicotrema. It's not clear the degree that the helicotrema is porous. Does it allow the free flow of fluid? The other thing is, I have read that fluids in the scala vestibuli and scala tympani are somewhat different (not to be confused with the endolymph of the cochlear duct, which is potassium-rich). If the fluids are at all different, that would seem to indicate that there is not a continuous, unimpeded flow between the scala vestibuli and the scala tympany and that the helicoteama is something of a barrier. In the scenario described in the video I mentioned, sound waves entering at Reissner's membrane pass through the cochlear duct and end up in the scala tympany, where they continue their journey to the round window.

In addition to questions about the "mechanical path" that sound waves take to reach the basilar membrane, there are questions about the "transduction path" -- i.e., how mechanical energy gets transformed, or transduced, into nerve impulses. This gets skipped over in most of the articles I have read on the Internet. What the articles do explain is this: Movement in the basilar membrane causes stereocilia hairs to rub against the underside of the tectorial membrane, which bend the stereocilia and open up channels that allow an influx of positively charged potassium ions to enter hair cells. What is confusing about that, first of all, is that there seem to be two sensory devices: the basilar membrane, and also the stereocilia. Are they tuned to the same frequency?

What puzzles me is how mechanical information about a particular sound, once it is received by a stereocilia hair, makes its way to the auditory nerve. Do potassium ions carry the sound waves deeper into the hair cell? From what I understand, a depolarization effect opens up channels in the hair cell wall, which allows sodium ions to enter. And that triggers the release of neurotransmitters. Do the neurotransmitters take up information about the sound waves? There has to be a message carrier somewhere in the chain of events, otherwise where does the spiral ganglion and auditory nerve get its information from?

The path that mechanical ("sound") information takes becomes an electrical path and finally becomes a neurological path. But it's certainly one, continuous path. What seems to be missing in all the explanations is a precise map of the course that the sound information takes with no segments of the trip left to the imagination. If there is an explanation in the Wikipedia articles that I have missed, I would be appreciative if someone would guide me in that direction. Otherwise, I would hope that someone who has the answers (and isn't just guessing) would update the Wikipedia articles in question and provide some references to materials that I can study to further my knowledge.

James725496 (talk) 20:23, 9 February 2021 (UTC)Thanks, James. 

Reference 1. YouTube video titled Auditory Transduction (2002).

References

Apparently erroneous description of cochlear mechanics

After reading the following page in a book, it seems to me that the description of the anatomy, physiology and mechanics in the section Basilar membrane#Structure must be wrong.

Hall, Michael E.; Hall, John E. (2021). Guyton and Hall textbook of medical physiology (14th ed.). Philadelphia, PA: Elsevier. p. 665. ISBN 978-0-323-59712-8.

And in that case, I ask myself why no one else has noticed this and fixed it. According to the Guyton/Hall book, the variable widths and stiffness in this sentence actually apply to the "basilar fibers" (which are probably the same as hair cells), not to the basilar membrane.

"The basilar membrane is widest (0.42–0.65 mm) and least stiff at the apex of the cochlea, and narrowest (0.08–0.16 mm) and stiffest at the base (near the round and oval windows)."

According to the Guyton/Hall book, the fibers vary in two dimensions, their length and their diameter. It is the fiber length which varies from "0.42–0.65mm" to "0.08–0.16mm", not the membrane width, although they might both vary by similar amounts. But the fiber diameter varies also, which gives a factor of 100 difference in "stiffness" according to Guyton/Hall. They say that fiber length varies from 0.04 to 0.5 millimetres. Many diagrams that I have seen also suggest that the membrane width does not vary by a factor of 12.

The cited article does say that the basilar membrane changes in width and stiffness, but without giving numbers.

Oghalai JS (October 2004). "The cochlear amplifier: augmentation of the traveling wave within the inner ear". Current Opinion in Otolaryngology & Head and Neck Surgery. 12 (5): 431–8. doi:10.1097/01.moo.0000134449.05454.82. PMC 1315292. PMID 15377957.

So now I wonder which one is correct. My hunch is that the 2004 article is an informal rough description, whereas the 2021 book is a more precise statement of the mechanics. Basic physics makes me think the 2021 book is correct.

Can anyone give a definitive answer about this question? Is it the mechanical properties and geometry of the basilar hairs/fibers which determine frequency response? Or is it principally the properties of the basilar membrane? Alan U. Kennington (talk) 06:18, 25 October 2024 (UTC)