Mechanical response characteristics of the hearing organ in the low-frequency regions of the cochlea

Ulfendahl, Mats; Khanna, Shyam M.; Fridberger, Anders; Flock, Åke; Flock, Britta; Jäger, Wanje

doi:10.1152/jn.1996.76.6.3850

Cited by 51 publications

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“…Frequency tuning may, therefore, be less sharp and response amplitudes lower than is the case in vivo. Previous studies, and data obtained with the current technique, showed that mechanical frequency-tuning curves obtained in this preparation (20) are similar to inner hair cell receptor-potential tuning curves measured from the same cochlear region in vivo at 50-70 dB SPL (21). At these stimulus levels, the response of the hearing organ begins to be dominated by passive mechanics.…”

Section: Discussionsupporting

confidence: 79%

Imaging hair cell transduction at the speed of sound: Dynamic behavior of mammalian stereocilia

Fridberger

Tomo

Ulfendahl

et al. 2006

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

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The cochlea contains two types of sensory cells, the inner and outer hair cells. Sound-evoked deflection of outer hair cell stereocilia leads to fast force production that will enhance auditory sensitivity up to 1,000-fold. In contrast, inner hair cells are thought to have a purely receptive function. Deflection of their stereocilia produces receptor potentials, transmitter release, and action potentials in the auditory nerve. Here, we describe a method for rapid confocal imaging. The method was used to image stereocilia during simultaneous sound stimulation in an in vitro preparation of the guinea pig cochlea. We show that inner hair cell stereocilia move because they interact with the fluid surrounding the hair bundles, but stereocilia deflection occurs at a different phase of the stimulus than is generally expected. In outer hair cells, stereocilia deflections were Ϸ1͞3 of the reticular lamina displacement. Smaller deflections were found in inner hair cells. The ratio between stereocilia deflection and reticular lamina displacement is important for auditory function, because it determines the stimulus applied to transduction channels. The low ratio measured here suggests that amplification of hair-bundle movements may be necessary in vivo to preserve transduction fidelity at low stimulus levels. In the case of the inner hair cells, this finding would represent a departure from traditional views on their function. functional imaging ͉ optical flow ͉ cochlear mechanics T he sense of hearing, so critical for communication, depends on a small population of sensory hair cells inside the inner ear. These hair cells come in two versions, the outer and inner hair cells, which have very different functions. Outer hair cells are capable of rapid force generation that serves to amplify the vibration of the hearing organ (1-3). This motor activity leads to a large increase of auditory sensitivity. In contrast, inner hair cells are thought to have a purely sensory role. More than 90% of the afferent fibers of the auditory nerve connect to inner hair cells (4); these are, therefore, absolutely necessary for sound perception. Both cell types have the astounding ability to convert nanometer displacements into electric current. This feat is accomplished by mechanically sensitive ion channels that probably belong to the transient receptor potential family (5). These channels are located along actin-filled protrusions called stereocilia.Deflection of stereocilia causes channel-gating. The relation between deflection and receptor current has been characterized in vitro by pushing stereocilia with glass probes or water jets (e.g., 6-8). However, little information is available from more intact systems. In the cochlea, the stimulus applied to the transduction channels depends on the ratio between stereocilia deflection and sound-evoked vibration of the reticular lamina. The ratio is determined by complicated mechanical processes. In the case of outer hair cells, stereocilia interact with an accessory structure, the tectorial membr...

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Section: Discussionsupporting

confidence: 79%

Imaging hair cell transduction at the speed of sound: Dynamic behavior of mammalian stereocilia

Fridberger

Tomo

Ulfendahl

et al. 2006

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

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“…The increase was approximately 25% and is similar to reported values [20]. Current injections revealed fundamental differences between the individual OHC rows.…”

Section: Current Affects Sound-evoked Rl Vibrationssupporting

confidence: 89%

Active Outer Hair Cells Affect the Sound-Evoked Vibration of the Reticular Lamina

Jacob

Fridberger

Shera³

et al. 2011

AIP Conference Proceedings

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Abstract. It is well established that the organ of Corti uses active mechanisms to enhance its sensitivity and frequency selectivity. Two possible mechanisms have been identified, both capable of producing mechanical forces, which can alter the sound-evoked vibration of the hearing organ. However, little is known about the effect of these forces on the sound-evoked vibration pattern of the reticular lamina. Current injections into scala media were used to alter the amplitude of the active mechanisms in the apex of the guinea pig temporal bone. We used time-resolved confocal imaging to access the vibration pattern of individual outer hair cells. During positive current injection the the sound-evoked vibration of outer hair cell row three increased while row one showed a small decrease. Negative currents reversed the observed effect. We conclude that the outer hair cell mediated modification of reticular lamina vibration patterns could contribute to the inner hair cell stimulation.

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“…Previous studies on this in vitro preparation showed that the opening in the bone, which is necessary to gain optical access to the sensory cells, leads to frequency tuning curves that are sharper than those frequency tuning curves likely to be observed in vivo (27). This effect occurs because the opening creates a pressure release pathway, which reduces the effective stimulus level at frequencies below 300 Hz (the opening is expected to influence current-evoked motion relatively less than stapes-evoked motion).…”

Section: Significancementioning

confidence: 89%

Minimal basilar membrane motion in low-frequency hearing

Warren

Ramamoorthy

Ciganović

et al. 2016

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

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Low-frequency hearing is critically important for speech and music perception, but no mechanical measurements have previously been available from inner ears with intact low-frequency parts. These regions of the cochlea may function in ways different from the extensively studied high-frequency regions, where the sensory outer hair cells produce force that greatly increases the soundevoked vibrations of the basilar membrane. We used laser interferometry in vitro and optical coherence tomography in vivo to study the low-frequency part of the guinea pig cochlea, and found that sound stimulation caused motion of a minimal portion of the basilar membrane. Outside the region of peak movement, an exponential decline in motion amplitude occurred across the basilar membrane. The moving region had different dependence on stimulus frequency than the vibrations measured near the mechanosensitive stereocilia. This behavior differs substantially from the behavior found in the extensively studied high-frequency regions of the cochlea.hearing | basilar membrane | optical coherence tomography | hair cells S ound causes traveling waves to propagate within the fluids of the inner ear and along the basilar membrane, from the base of the cochlea toward its apex (1-4). These waves move the sensory hair cells, deflect their stereocilia, and lead to receptor potential generation and modulation of spike rates in the auditory nerve. Because of systematic variations in basilar membrane properties, high-frequency sound stimulates sensory cells near the base of the cochlear spiral, whereas the low sound frequencies that are most important for speech and music perception cause maximal stimulation of hair cells near the apex of the spiral.Importantly, the sensory outer hair cells of the organ of Corti are mechanically active: Their soma changes length upon electrical stimulation (5, 6), and their hair bundles can provide force (7-9). Recent theoretical and experimental work showed that forces produced by the outer hair cells feed back into the sound-evoked motion of the basilar membrane and amplify the fluid motion associated with the traveling wave (10-12). The amplitude of the traveling wave therefore grows successively as it moves forward, causing a 1,000-fold increase of sound-evoked basilar membrane motion at the place of maximum vibration (13)-at least in the high-frequency regions of the cochlea. The functionally important low-frequency parts of the inner ear appear to behave in a different manner, however.Specifically, a recent mathematical model suggested a "ratchet" behavior, where the sensory outer hair cells amplify sound-evoked motion close to stereocilia, but not at the basilar membrane (14). If the theory has merit, basilar membrane movements are expected to be quite small, to be uninfluenced by hair-cell force generation, and to peak at a frequency that is unrelated to the frequency at which the hair bundles vibrate with their largest amplitude, a behavior distinct from the behavior found in the high-frequency regions.Some expe...

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Mechanical response characteristics of the hearing organ in the low-frequency regions of the cochlea

Cited by 51 publications

References 0 publications

Imaging hair cell transduction at the speed of sound: Dynamic behavior of mammalian stereocilia

Imaging hair cell transduction at the speed of sound: Dynamic behavior of mammalian stereocilia

Active Outer Hair Cells Affect the Sound-Evoked Vibration of the Reticular Lamina

Minimal basilar membrane motion in low-frequency hearing

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