What are the changes in hair cell density and length along the cochlea?

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In summary, the conversation discusses the research on the cochlea and its hair cells, specifically their role in receiving and amplifying sound. The main topic is the density profile of hair cells as a spatial filter and how the spacing between cells affects the ability to discriminate frequency. The participants also mention the difficulty in finding photographs of the entire length of the cochlea and share new information about the length and density changes of hair cells along the cochlea.
  • #1
andrewr
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Hi,

I've been studying the cochlea, and how the hair cells (IHCs) receive sound, and some amplify it (OHCs) ; and am trying to get an idea of the density profile of hair cells acting as a spatial filter.

The smallest discrimination in frequency that is positional (not temporal) coded, would be the frequency difference of the position of one hair cell ; so I want to know the profile (density) change of cells along the whole cochlea.

After looking at photomicrographs/sem online, I was only able to measure the spacing between cells in one (arbitrary/unknown) place in the cochlea; and it was about 10microns -- center to center -- axially along a single row of OHC's.

That good enough for a crude estimate test (assuming it was constant everywhere); for a human can discriminate a pitch change of about 5 "cents" near middle "C"; which works out to ~.77Hz ;

I used human cadaver data from ( Greenwood // or // Zwisloski ) to make a curve fit of resonance distance along the cochlea (passive resonance) vs. frequency -- and I get a result that .77Hz is roughly 15microns of distance near middle "C". -- So, about 1.5 hair cells... ( which is what I would expect 1 to 2 cells... )

Now, I just want to improve on that:
Does anyone know of a source that shows cell spacings from one end of the cochlea (basal/oval window) to the other (helicotrema) ?

I know it doesn't vary a lot, eg: it's less than 2:1 ratio ; but I can't seem to find any photographs of more than just one end of the cochlea at a time...

Thanks!

P.S. Here's my estimate of passive resonance frequency as a function of distance along the cochlea.
f( x[cm] ) [Hz] ~= 10**( -0.069*x**3 + 0.3293*x**2 - 1.115*x + 4.522 )

:)
 
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  • #2
:zzz:

Well, I still haven't found any pictures... esp. human ones...
but I stumbled across something I didn't know that is suggestive:

Researcher "Barbara A. Bohne" notes in her "morphological analysis of hair cells in the Chinchila cochlea", that across several mammals, the outer hair cell has a systematic length change across the length of the cochlea; eg: longer at the apical end (low frequencies) and shorter at the basal end.

The length of the cells (not the width/spacing), I would estimate, changes by a factor of ~2.25:1 to ~3:1 ; so, if you see that number show up -- it's probably about length and not width spacing.
Larger cells = suggests more energy capability / larger mass / longer power stroke for amplification at low frequency ; eg: the cell size/length change is suggestive of tuning.

Secondly:
She also notes that hair density is supposedly lower in longer cochleas...
But, she notes that the width does not change significantly in her study -- so that it must be cell "spacing" which causes the density change... hmmm...

Cell sizes in her table, on average, show only a trend of around a 4% change in width from basal to apical measurements in her cochleas... (less than 1 std deviation in size chg, though, so not significant).

...
So, I am definitely looking for spacing changes between hair cells, as the cells themselves aren't expected to become wider or narrower.
 
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1. What is the function of cochlear hair cells?

Cochlear hair cells are responsible for converting sound waves into electrical signals that can be interpreted by the brain. They are an essential part of the auditory system and play a crucial role in our ability to hear.

2. How do cochlear hair cells work?

Cochlear hair cells are arranged in rows within the cochlea, a spiral-shaped organ in the inner ear. When sound waves enter the ear, they cause the hair cells to vibrate, which triggers the release of neurotransmitters. These electrical signals are then sent to the brain via the auditory nerve to be processed and interpreted as sound.

3. Can cochlear hair cells be damaged?

Yes, cochlear hair cells can be damaged by loud noises, certain medications, and aging. When this happens, it can result in hearing loss or impairment. Unlike other cells in the body, cochlear hair cells do not regenerate, so any damage is permanent.

4. How does hearing loss occur in relation to cochlear hair cells?

Hearing loss can occur when the cochlear hair cells are damaged or destroyed, making it difficult for the brain to receive and interpret sound signals. This can happen gradually over time due to aging or can be caused by sudden exposure to loud noises, resulting in permanent hearing loss.

5. Can cochlear hair cells be repaired or replaced?

Currently, there is no way to repair or replace damaged or lost cochlear hair cells. However, there are technologies such as hearing aids and cochlear implants that can help individuals with hearing loss by amplifying or directly stimulating the auditory nerve. Researchers are also exploring potential treatments and therapies to regenerate cochlear hair cells in the future.

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