Dissection of the Mechanical Impedance Components of the Outer Hair Cell Using a Chloride-Channel Blocker

Harasztosi, Csaba; Gummer, Anthony W.; Shera, Christopher A.; Olson, Elizabeth S.

doi:10.1063/1.3658120

Cited by 1 publication

(1 citation statement)

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“…The impedance Z ohc of an OHC from the 14-kHz place in response to sinusoidal forcing at frequencies up to 10 kHz has been measured after the application of anthracene-9-carboxylic acid (9AC) (29), which apparently reduces the stiffness of OHCs without affecting their damping (30). To explain the impedance measurements, we propose a simple mechanical model of the basolateral surface ( Fig.…”

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confidence: 99%

Effects of cochlear loading on the motility of active outer hair cells

Maoiléidigh

Hudspeth

2013

Proc. Natl. Acad. Sci. U.S.A.

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Outer hair cells (OHCs) power the amplification of sound-induced vibrations in the mammalian inner ear through an active process that involves hair-bundle motility and somatic motility. It is unclear, though, how either mechanism can be effective at high frequencies, especially when OHCs are mechanically loaded by other structures in the cochlea. We address this issue by developing a model of an active OHC on the basis of observations from isolated cells, then we use the model to predict the response of an active OHC in the intact cochlea. We find that active hair-bundle motility amplifies the receptor potential that drives somatic motility. Inertial loading of a hair bundle by the tectorial membrane reduces the bundle's reactive load, allowing the OHC's active motility to influence the motion of the cochlear partition. The system exhibits enhanced sensitivity and tuning only when it operates near a dynamical instability, a Hopf bifurcation. This analysis clarifies the roles of cochlear structures and shows how the two mechanisms of motility function synergistically to create the cochlear amplifier. The results suggest that somatic motility evolved to enhance a preexisting amplifier based on active hair-bundle motility, thus allowing mammals to hear high-frequency sounds.adaptation | electromotility | hearing | nonlinear dynamics O ur ears are amazing signal detectors that reconcile great sensitivity with an enormous dynamic range. The faintest sounds that we can hear vibrate our eardrums by less than 1 pm and are a trillion times less intense than the loudest sounds that we can tolerate (1, 2). We can distinguish pure tones that differ in frequency by less than 0.2%, yet the frequency range of our ears exceeds a thousandfold (2). These features are all the more remarkable given that the mechanoreceptive organ of Corti operates in liquid and is therefore highly damped (3).An active process enhances the performance of the mammalian ear by augmenting sound-induced vibrations in the cochlea (2-6). This process results from the action of specialized outer hair cells (OHCs) whose motility boosts the motion of the cochlea in response to sounds, thus amplifying the signal transmitted to the brain. These cells counteract the damping that would otherwise limit the cochlea's sensitivity and frequency discrimination (3, 7). OHCs exhibit two forms of mechanical activity, hair-bundle motility and somatic motility, which may both contribute to the cochlear amplifier.Named for the mechanosensitive hair bundles protruding from their apices, hair cells transduce vibrations of their bundles into an electrical response. Cochlear hair cells are housed in the cochlear partition, which includes the organ of Corti sandwiched between the tectorial and basilar membranes (Fig. 1A). The hair bundle of each OHC is connected at its tip to the acellular tectorial membrane, and the soma of each OHC is linked to the basilar membrane through a rigid Deiters' cell (8). These membranes mechanically load each OHC with mass, damping, and stiffness....

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confidence: 99%