The mechanical properties of ciliary bundles of turtle cochlear hair cells.

Crawford, A. C.; Fettiplace, Robert

doi:10.1113/jphysiol.1985.sp015750

Cited by 458 publications

(334 citation statements)

References 32 publications

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“…This bundle does not behave as a merely passive transducer. Evoked hair-bundle oscillations instead demonstrate that the hair bundle is capable of producing active transient motions and of amplifying mechanical inputs [17][18][19][20]. Moreover, hair bundles can produce limit-cycle oscillations, a phenomenon that may underly otoacoustic emissions [21].…”

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confidence: 99%

Essential Nonlinearities in Hearing

et al. 2000

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Our hearing organ, the cochlea, evidently poises itself at a Hopf bifurcation to maximize tuning and amplification. We show that in this condition several effects are expected to be generic: compression of the dynamic range, infinitely sharp tuning at zero input, and generation of combination tones. These effects are "essentially" nonlinear in that they become more marked the smaller the forcing: there is no audible sound soft enough not to evoke them. All the well-documented nonlinear aspects of hearing therefore appear to be consequences of the same underlying mechanism. PACS numbers: 87.19.Dd, 43.66. + y, 87.17.Nn The classic Helmholtz theory [1] posits that our hearing organ, the cochlea, is arranged like a harp or the back plane of a piano, with a number of highly tuned elements arrayed along a frequency scale, performing Fourier analysis of the incoming sound. Although the notion that the inner ear works like a musical instrument offers a beautiful esthetic symmetry, it has serious flaws. In the 1940s, Gold [2] pointed out that the cochlea's narrow passageways are filled with fluid, which dampens any hope of simple mechanical tuning. He argued that the ear cannot operate as a passive sensor, but that additional energy must be put into the system. As in the operation of a regenerative receiver [3], active amplification of the signal can compensate for damping in order to provide highly tuned responses. von Békésy's classic measurements in the cochlea [4] demonstrated the mapping of sound frequencies to positions along the cochlea. He observed the tuning to be quite shallow and found cochlear responses to behave linearly over the range of physiologically relevant sound intensities. Gold's notions were largely set aside in favor of the hypothesis of coarse mechanical tuning followed by a "second filter," whose nature was surmised to be electrical.von Békésy conducted his measurements on cadavers, whose dead cochleas lacked power sources or amplifiers that might have provided positive feedback. Only fairly recently, laser-interferometric velocimetry performed on live and reasonably intact cochleas has led to a very different picture [5,6]. There is, in fact, sharp mechanical tuning, but it is essentially nonlinear: there is no audible sound soft enough that the cochlear response is linear. Although the response far from the resonance's center is linear, at the resonance's peak the response rises sublinearly, compressing almost 80 dB into about 20 dB (Fig. 1). The width of the resonance increases with increasing amplitude, being least for sounds near the threshold of hearing. Observation of the response's essential nonlinearity at the level of cochlear mechanics contradicts von Békésy's finding. Furthermore, this nonlinearity does not originate in the rigidity of membranes or in fluid-mechanical effects. Because it reversibly disappears if the cochlea's ionic gradient is temporarily disturbed, the nonlinearity depends on a biological power supply [7].Gold conjectured that a regenerative mechanism for hearing...

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confidence: 99%

Essential Nonlinearities in Hearing

et al. 2000

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“…Visual and video observations of hair bundle motion during slow (∼1 Hz) deflections suggested that bundles of bullfrog saccular hair cells and turtle cochlear hair cells move as a unit without splay [1,5,6,11]. Optical measurements confirmed that the bundle moves as a unit even up to high frequencies [12,14], at least for small deflections (<50 nm).…”

Section: Introductionmentioning

confidence: 66%

Horizontal Top Connectors Mediate a Sliding Adhesion to Hair Cell Stereocilia

Karavitaki

Corey

Shera³

et al. 2011

AIP Conference Proceedings

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Abstract. When the tip of a hair bundle is deflected , the stereocilia pivot as a unit, producing a shearing displacement between adjacent tips. It is not clear how stereocilia can stick together laterally but still shear. We used dissociated hair cells from the bullfrog saccule and high-speed video imaging to characterize this sliding adhesion. Movement of individual stereocilia was proportional to height, indicating that stereocilia pivot at their basal insertion points. All stereocilia moved by approximately the same angular deflection, and the same motion was observed at 1, 20 and 700 Hz stimulus frequency. Motions were consistent with a geometric model that assumes the stiffness of lateral links holding stereocilia together is >1000 times the pivot stiffness of stereocilia and that these links can slide in the membrane-in essence, that stereocilia shear without separation. The same motion was observed when bundles were moved perpendicular to the tip links, or when tip links, ankle links and shaft connectors were cut, ruling out these links as the basis for sliding adhesion. Stereocilia rootlet angles tend to push stereocilia tips together. However, stereocilia remained cohesive for large deflections, ruling out rootlet prestressing as the basis for sliding adhesion. The horizontal top connectors apparently mediate a sliding adhesion. Consequently, all transduction channels of a hair cell are mechanically in parallel, an arrangement that may enhance amplification in the inner ear.

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“…Therefore, it is possible that long-term adaptation is mediated by a suppression of active amplification. To further support this hypothesis we studied the spontaneous emission of electrical noise (Crawford and Fettiplace, 1985;Martin et al, 2003) which is proposed to be a manifestation of active amplification (Martin et al, 2003). A link between active amplification and long-term adaptation predicts that activation would have the same depressing effect on test responses and on the spontaneous noise.…”

Section: Long-term Adaptation Results From Suppression Of Active Amplmentioning

confidence: 99%

“…Single mechanoreceptor cells are thought to underlie active mechanical amplification since hair cells exhibit all of the manifestations of the process, including enhanced gain of minute inputs and the production of spontaneous mechanical emissions (Jaramillo et al, 1993;Hudspeth, 1999, 2001;Martin et al, 2003). These spontaneous mechanical emissions are accompanied by an electrical component (Crawford and Fettiplace, 1985;Martin et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

Dissection of Gain Control Mechanisms inDrosophilaMechanotransduction

Chadha

Cook

2012

J. Neurosci.

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Mechanoreceptor cells respond to a vast span of stimulus intensities, which they transduce into a limited response-range using a dynamic regulation of transduction gain. Weak stimuli are detected by enhancing the gain of responses through the process of active mechanical amplification. To preserve responsiveness, the gain of responses to prolonged activation is rapidly reduced through the process of adaptation. We investigated long-term processes of mechanotransduction gain control by studying responses from single mechanoreceptor neurons in Drosophila. We found that mechanical stimuli elicited a sustained reduction of gain that we termed long-term adaptation. Long-term adaptation and the adaptive decay of responses during stimuli had distinct kinetics and they were independently affected by manipulations of mechanotransduction. Therefore, long-term adaptation is not associated with the reduction of response gain during stimulation. Instead, the long-term adaptation suppressed canonical features of active amplification which were the high gain of weak stimuli and the spontaneous emission of noise. In addition, depressing amplification using energy deprivation recapitulated the effects of long-term adaptation. These data suggest that long-term adaptation is mediated by suppression of active amplification. Finally, the extent of long-term adaptation matched with cytoplasmic Ca 2ϩ levels and dTrpA1-induced Ca 2ϩ elevation elicited the effects of long-term adaptation. Our data suggest that mechanotransduction employs parallel adaptive mechanisms: while a rapid process exerts immediate gain reduction, long-term adjustments are achieved by attenuating active amplification. The slow adjustment of gain, manifest as diminished sensitivity, is associated with the accumulation of Ca 2ϩ .

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The mechanical properties of ciliary bundles of turtle cochlear hair cells.

Cited by 458 publications

References 32 publications

Essential Nonlinearities in Hearing

Essential Nonlinearities in Hearing

Horizontal Top Connectors Mediate a Sliding Adhesion to Hair Cell Stereocilia

Dissection of Gain Control Mechanisms inDrosophilaMechanotransduction

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