Eccles Institute of Neuroscience Seminar Series: How do middle ear muscles protect the cochlea? Revisiting the old intralabyrinthine pressure theory

The middle ear muscles are part of a control system for regulating the acoustic input to a supersensitive detector, the cochlea, preventing overload and damage. Yet there is a long-standing paradox. When Békésy measured sound transmission through the middle ear of cadavers, he found that acoustic transmission was not affected when the annular ligament was stretched by pressure. Similarly, reflex activation experiments often show only a few decibels of attenuation, assumed to be due to stiffening of middle ear joints and ligaments. In contrast, psychophysical experiments reveal attenuations of 30 dB or more when the middle ear muscles are voluntarily contracted. How can the difference be explained? This presentation shows how the paradox can be resolved by reconsidering a theory put forward by Gellé in the 19th century. According to Gellé’s intralabyrinthine pressure theory, which has long been dismissed, the purpose of the middle ear muscles is to press the stapes inwards and raise the hydraulic pressure in the labyrinthine fluids, thereby regulating cochlear sensitivity. Here I revisit the theory and show how it can explain a range of recent audiological findings. The theory is updated and the hypothesis made that static pressure in the cochlear fluids is sensed by the outer hair cells, which are in continuous hydraulic connection with the stapes. It is this factor which reduces the gain of the cochlear amplifier and provides rapid and effective overload protection. The case is made that the intralabyrinthine pressure theory deserves renewed attention and some implications are considered.

Date & time

3.30–4.30pm 10 August 2012

Location

The Finkel Lecture Theatre, The John Curtin School of Medical Research, Building 131, Garran Road, ANU

Contacts

 Danielle Khalidi
 +61 2 61253926

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