WMZ: Z191701361450 WMR: R209318204033 |
Pathology of hair cells and neurones | ||
Overview / Aminoglycosides / Noise Trauma / Excitotoxicity / Presbycusis / Tinnitus | ||
Pictures : M. Lenoir, M. Lavigne-Rebillard |
Патология волосковых клеток |
Три основных негенетических фактора вызываю потерю волосковых клеток и ведут к потере слуха: ототоксические лекарства, шумовые травмы и старение. |
Loss of OHCs: incomplete deafness and hearing aids | |
M. Lenoir | |
When the lesion affects OHCs only, as in these pictures showing intact IHCs, deafness is characterized by a 50 to 60 dB loss and a dramatic impairment of frequency discrimination. See below a corresponding speech audiogram. | |
This test is based upon the ability of the subject to correctly repeat words presented to him at different loudnesses. A normally-hearing subject (blue curve) is able to repeat correctly 100% of words heard at 20 dB. A subject whose OHCs have been damaged (red curve) needs a 50 dB amplification to begin understanding the list of words, and he never gets 100% of correct responses no matter what the sound intensity (i.e. his speech discrimination is altered). |
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Loss of IHCs and OHCs: complete deafness | |
M. Lavigne-Rebillard |
When both IHCs and OHCs have disappeared, the organ of Corti is no longer recognisable and deafness is total. However, as in this pictures, nerve endings (asterisk) often remain. This is how cochlear implants are able to function. |
M. Lenoir |
In this scanning electron micrograph, a surface view of the organ of Corti (soon after hair cells have disappeared) shows no stereocilia, but there are remnants (red arrow). The head of pillar (p) and Deiters' cells (d) are still recognizable. scale bar: 10 µm |
N.B. In these situations, an hearing aid will have no effect. Only direct electrical stimulation of these fibres may help (i.e. a cochlear implant). | |
M. Lavigne-Rebillard |
Another example of organ of Corti degeneration. But in this case, due to the very low number of remaining fibres (asterisk) a cochlear implant would not work very well. |
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