scholarly journals On the Molecular Filters in Cochlea Transduction

2018 ◽  
Vol 10 (4) ◽  
pp. 48
Author(s):  
Valeri Goussev
Keyword(s):  
Hair Cells ◽  
Feedback Loop ◽  
Basilar Membrane ◽  
Automatic Gain Control ◽  
Gain Control ◽  
Outer Hair Cells ◽  
Tectorial Membrane ◽  
Inner Hair Cell ◽  
Perception Threshold ◽  
Spatially Distributed

The article is devoted to the specific consideration of the cochlear transduction for the low level sound intensities, which correspond to the regions near the perception threshold. The basic cochlea mechanics is extended by the new concept of the molecular filters, which allows discussing the transduction mechanism on the molecular level in the space-time domain. The molecular filters are supposed to be built on the set of the stereocilia of every inner hair cell. It is hypothesized that the molecular filters are the sensors in the feedback loop, which includes also outer hair cells along with the tectorial membrane and uses the zero compensation method to evaluate the traveling wave shape on the basilar membrane. Besides the compensation, the feedback loop, being spatially distributed along the cochlea, takes control over the tectorial membrane strain field generated by the outer hair cells, and implements it as the mechanism for the automatic gain control in the sound transduction.

scholarly journals On the molecular filters in cochlea transduction

2018 ◽  
Author(s):  
Valeri Goussev
Keyword(s):  
Hair Cells ◽  
Feedback Loop ◽  
Basilar Membrane ◽  
Automatic Gain Control ◽  
Gain Control ◽  
Outer Hair Cells ◽  
Tectorial Membrane ◽  
Inner Hair Cell ◽  
Perception Threshold ◽  
Spatially Distributed

AbstractThe article is devoted to the specific consideration of the cochlear transduction for the low level sound intensities, which correspond to the regions near the perception threshold. The basic cochlea mechanics is extended by the new concept of the molecular filters, which allows us to discuss the transduction mechanism on the molecular level in the space-time domain. The molecular filters are supposed to be built on the set of the stereocilia of every inner hair cell. It is hypothesized that the molecular filters are the sensors in the feedback loop, which includes also outer hair cells along with the tectorial membrane and uses the zero compensation method to evaluate the traveling wave shape on the basilar membrane. Besides the compensation, the feedback loop, being spatially distributed along the cochlea, takes control over the tectorial membrane strain field generated by the outer hair cells, and implements it as the mechanism for the automatic gain control in the sound transduction.

scholarly journals Direct Visualization of Organ of Corti Kinematics in a Hemicochlea

1999 ◽  
Vol 82 (5) ◽  
pp. 2798-2807 ◽  
Author(s):  
Xintian Hu ◽  
Burt N. Evans ◽  
Peter Dallos
Keyword(s):  
Hair Cell ◽  
Hair Cells ◽  
Basilar Membrane ◽  
Mechanical Vibration ◽  
Cell Receptor ◽  
Outer Hair Cells ◽  
Tectorial Membrane ◽  
Low Frequencies ◽  
Geometric Models ◽  
Membrane Vibration

The basilar membrane in the mammalian cochlea vibrates when the cochlea receives a sound stimulus. This mechanical vibration is transduced into hair cell receptor potentials and thereafter encoded by action potentials in the auditory nerve. Knowledge of the mechanical transformation that converts basilar membrane vibration into hair cell stimulation has been limited, until recently, to hypothetical geometric models. Experimental observations are largely lacking to prove or disprove the validity of these models. We have developed a hemicochlea preparation to visualize the kinematics of the cochlear micromechanism. Direct mechanical drive of 1–2 Hz sinusoidal command was applied to the basilar membrane. Vibration patterns of the basilar membrane, inner and outer hair cells, supporting cells, and tectorial membrane have been recorded concurrently by means of a video optical flow technique. Basilar membrane vibration was driven in a direction transversal to its plane. However, the direction of the resulting vibration was found to be essentially radial at the level of the reticular lamina and cuticular plates of inner and outer hair cells. The tectorial membrane vibration was mainly transversal. The transmission ratio between cilia displacement of inner and outer hair cells and basilar membrane vibration is in the range of 0.7–1.1. These observations support, in part, the classical geometric models at low frequencies. However, there appears to be less tectorial membrane motion than predicted, and it is largely in the transversal direction.

New Insights in the Evaluation of Cochlear Impairment

1984 ◽  
Vol 93 (4_suppl) ◽  
pp. 74-75
Author(s):  
Hallowell Davis
Keyword(s):  
Hair Cells ◽  
Basilar Membrane ◽  
Sensory System ◽  
Cell System ◽  
Great Sensitivity ◽  
Outer Hair Cells ◽  
Passive Component ◽  
Inner Hair Cell ◽  
Tuning Curves ◽  
Severe Impairment

A major new insight into cochlear mechanisms is the recognition of an active process, the cochlear amplifier, that contributes energy to the mechanical movement of the basilar membrane at low sound intensities. The extra energy makes possible the great sensitivity of hearing and also the very sharp tuning of individual neural units, ie, the tips of their tuning curves. The inner hair cells are the final receptor cells, but the outer hair cells are essential for the amplifier action. The amplifier is much more sensitive to anoxia, ototoxic drugs, noise, etc, than the inner hair cell system alone. Severe impairment of the amplifier causes a sensorineural hearing loss with recruitment. Only the tails of tuning curves remain. Thus the cochlea is a dual sensory system, a robust but insensitive broadly tuned passive component sided by a vulnerable, sensitive sharply tuned active component.

scholarly journals A role for tectorial membrane mechanics in activating the cochlear amplifier

2020 ◽  
Author(s):  
A. Nankali ◽  
Y. Wang ◽  
C. E. Strimbu ◽  
E. S. Olson ◽  
K. Grosh
Keyword(s):  
Experimental Data ◽  
Mathematical Model ◽  
Phase Shift ◽  
Hair Cells ◽  
Basilar Membrane ◽  
Outer Hair Cells ◽  
Tectorial Membrane ◽  
Cochlear Amplifier ◽  
Active Process ◽  
Electrical Responses

ABSTRACTThe mechanical and electrical responses of the mammalian cochlea to acoustic stimuli are nonlinear and highly tuned in frequency. This is due to the electromechanical properties of cochlear outer hair cells (OHCs). At each location along the cochlear spiral, the OHCs mediate an active process in which the sensory tissue motion is enhanced at frequencies close to the most sensitive frequency (called the characteristic frequency CF). Previous experimental results showing an approximate 0.3 cycle phase shift in the OHC-generated extracellular voltage relative the basilar membrane displacement that is initiated at a frequency approximately one-half octave lower than the CF are repeated in the present paper with similar findings. This shift is significant because it brings the phase of the OHC-derived electromotile force near to that of the basilar membrane velocity at frequencies above the shift, thereby enabling the transfer of electrical to mechanical power at the basilar membrane. In order to seek a candidate physical mechanism for this phenomenon, we used a comprehensive electromechanical mathematical model of the cochlear response to sound. The model predicts the phase shift in the extracellular voltage referenced to the basilar membrane at a frequency approximately one-half octave below CF, in accordance with the experimental data. In the model, this feature arises from a minimum in the radial impedance of the tectorial membrane and its limbal attachment. These experimental and theoretical results are consistent with the hypothesis that a tectorial membrane resonance introduces the correct phasing between mechanical and electrical responses for power generation, effectively turning on the cochlear amplifier.SIGNIFICANCEThe mechanical and electrical responses of the mammalian cochlea are nonlinear exhibiting up to a thousand-fold difference in gain depending on the frequency and level of sound stimulus. Cochlear outer hair cells (OHC) are broadband electro-mechanical energy converters that mediate this nonlinear active process. However, the mechanism by which the OHC electromotile force acquires the appropriate phase to power this nonlinearity remains unknown. By analyzing new and existing experimental data and using a mathematical model, we address this open issue. We present evidence which suggests that a relatively simple feature, the frequency dependence of the radial impedance of the tectorial membrane, provides requisite mechanics to turn on the frequency-specific nonlinear process essential for healthy hearing.

scholarly journals Activity-dependent regulation of prestin expression in mouse outer hair cells

2015 ◽  
Vol 113 (10) ◽  
pp. 3531-3542 ◽  
Author(s):  
Yohan Song ◽  
Anping Xia ◽  
Hee Yoon Lee ◽  
Rosalie Wang ◽  
Anthony J. Ricci ◽  
...  
Keyword(s):  
Hearing Loss ◽  
Hair Cell ◽  
Hair Cells ◽  
Information Transfer ◽  
Outer Hair Cell ◽  
Endocochlear Potential ◽  
Outer Hair Cells ◽  
Tectorial Membrane ◽  
Inner Hair Cell ◽  
Activity Dependent

Prestin is a membrane protein necessary for outer hair cell (OHC) electromotility and normal hearing. Its regulatory mechanisms are unknown. Several mouse models of hearing loss demonstrate increased prestin, inspiring us to investigate how hearing loss might feedback onto OHCs. To test whether centrally mediated feedback regulates prestin, we developed a novel model of inner hair cell loss. Injection of diphtheria toxin (DT) into adult CBA mice produced significant loss of inner hair cells without affecting OHCs. Thus, DT-injected mice were deaf because they had no afferent auditory input despite OHCs continuing to receive normal auditory mechanical stimulation and having normal function. Patch-clamp experiments demonstrated no change in OHC prestin, indicating that loss of information transfer centrally did not alter prestin expression. To test whether local mechanical feedback regulates prestin, we used TectaC1509G mice, where the tectorial membrane is malformed and only some OHCs are stimulated. OHCs connected to the tectorial membrane had normal prestin levels, whereas OHCs not connected to the tectorial membrane had elevated prestin levels, supporting an activity-dependent model. To test whether the endocochlear potential was necessary for prestin regulation, we studied TectaC1509G mice at different developmental ages. OHCs not connected to the tectorial membrane had lower than normal prestin levels before the onset of the endocochlear potential and higher than normal prestin levels after the onset of the endocochlear potential. Taken together, these data indicate that OHC prestin levels are regulated through local feedback that requires mechanoelectrical transduction currents. This adaptation may serve to compensate for variations in the local mechanical environment.

scholarly journals Inner hair cell stereocilia are embedded in the tectorial membrane

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Pierre Hakizimana ◽  
Anders Fridberger
Keyword(s):  
Electron Microscopy ◽  
Hair Cell ◽  
Mechanical Stimulation ◽  
Hair Cells ◽  
Viscous Drag ◽  
Tectorial Membrane ◽  
Inner Hair Cell ◽  
Inner Hair Cells ◽  
Inward Currents

AbstractMammalian hearing depends on sound-evoked displacements of the stereocilia of inner hair cells (IHCs), which cause the endogenous mechanoelectrical transducer channels to conduct inward currents of cations including Ca2+. Due to their presumed lack of contacts with the overlaying tectorial membrane (TM), the putative stimulation mechanism for these stereocilia is by means of the viscous drag of the surrounding endolymph. However, despite numerous efforts to characterize the TM by electron microscopy and other techniques, the exact IHC stereocilia-TM relationship remains elusive. Here we show that Ca2+-rich filamentous structures, that we call Ca2+ ducts, connect the TM to the IHC stereocilia to enable mechanical stimulation by the TM while also ensuring the stereocilia access to TM Ca2+. Our results call for a reassessment of the stimulation mechanism for the IHC stereocilia and the TM role in hearing.

scholarly journals Hearing at threshold intensities: by slow mechanical traveling waves or by fast cochlear fluid pressure waves

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Haim Sohmer
Keyword(s):  
Soft Tissue ◽  
Hair Cells ◽  
Traveling Wave ◽  
Basilar Membrane ◽  
Fluid Pressure ◽  
Low Frequency ◽  
Frequency Discrimination ◽  
Outer Hair Cells ◽  
Common Mechanism ◽  
Frequency Stimulation

The three modes of auditory stimulation (air, bone and soft tissue conduction) at threshold intensities are thought to share a common excitation mechanism: the stimuli induce passive displacements of the basilar membrane propagating from the base to the apex (slow mechanical traveling wave), which activate the outer hair cells, producing active displacements, which sum with the passive displacements. However, theoretical analyses and modeling of cochlear mechanics provide indications that the slow mechanical basilar membrane traveling wave may not be able to excite the cochlea at threshold intensities with the frequency discrimination observed. These analyses are complemented by several independent lines of research results supporting the notion that cochlear excitation at threshold may not involve a passive traveling wave, and the fast cochlear fluid pressures may directly activate the outer hair cells: opening of the sealed inner ear in patients undergoing cochlear implantation is not accompanied by threshold elevations to low frequency stimulation which would be expected to result from opening the cochlea, reducing cochlear impedance, altering hydrodynamics. The magnitude of the passive displacements at threshold is negligible. Isolated outer hair cells in fluid display tuned mechanical motility to fluid pressures which likely act on stretch sensitive ion channels in the walls of the cells. Vibrations delivered to soft tissue body sites elicit hearing. Thus, based on theoretical and experimental evidence, the common mechanism eliciting hearing during threshold stimulation by air, bone and soft tissue conduction may involve the fast-cochlear fluid pressures which directly activate the outer hair cells.

High-Voltage Electron Microscopic Study of the Inner Ear: Technique and Preliminary Results

1983 ◽  
Vol 92 (1_suppl) ◽  
pp. 3-12 ◽  
Author(s):  
Tomonori Takasaka ◽  
Hideich Shinkawa ◽  
Kozo Watanuki ◽  
Sho Hashimoto ◽  
Kazutomo Kawamoto
Keyword(s):  
Electron Microscopy ◽  
Hair Cell ◽  
Inner Ear ◽  
High Voltage ◽  
Hair Cells ◽  
Outer Hair Cells ◽  
Tectorial Membrane ◽  
Preliminary Results ◽  
Voltage Electron ◽  
Cuticular Plate

The technique and some preliminary results of the application of high-voltage electron microscopy (HVEM) to the study of inner ear morphology in the guinea pig are reported in this paper. The main advantage of HVEM is that sharp images of thicker specimens can be obtained because of the greater penetrating power of high energy electrons. The optimum thickness of the sections examined with an accelerating voltage of 1,000 kV was found to be between 500 to 800 nm. The sections below 500 nm in thickness often had insufficient contrast, while those above 800 nm were rather difficult to interpret due to overlap of images of the organelles. The whole structure of the sensory hairs from the tip to the rootlet was more frequently observed in the 800-nm thick sections. Thus the fine details of the hair attachment to the tectorial membrane as well as the hair rootlet extension into the cuticular plate could be thoroughly studied in the HVEM. In specimens fixed in aldehyde containing 2% tannic acid, the attachment of the tips of the outer hair cell stereocilia to the tectorial membrane was observed. For the inner hair cells, however, the tips of the hairs were separated from the undersurface of the tectorial membrane. The majority of the rootlets of the outer hair cells terminated at the midportion of the cuticular plate, while most of the inner hair cell rootlets traversed the entire width of the cuticular plate and extended into the apical cytoplasm. These differences in ultrastructural appearance may indicate that the two kinds of hair cells play different roles in the acoustic transduction process. The three-dimensional arrangement of the nerve endings on the hair cells was also studied by the serial thick-sectioning technique in the HVEM. In general, an entire arrangement of the nerve endings was almost completely cut in less than ten 800-nm thick sections instead of the 50- to 100-ultrathin (ie, less than 100 nm) conventional sections for transmission electron microscopy. The present study confirms an earlier report that the first row outer hair cells in the third cochlear turn are innervated by nearly equal numbers of efferent and afferent endings, the average number being nine.

scholarly journals The Role of Prestin in the Generation of Electrically Evoked Otoacoustic Emissions in Mice

2008 ◽  
Vol 99 (4) ◽  
pp. 1607-1615 ◽  
Author(s):  
Markus Drexl ◽  
Marcia M. Mellado Lagarde ◽  
Jian Zuo ◽  
Andrei N. Lukashkin ◽  
Ian J. Russell
Keyword(s):  
Hair Cells ◽  
Otoacoustic Emissions ◽  
Temporal Structure ◽  
Organ Of Corti ◽  
Outer Hair Cells ◽  
Tectorial Membrane ◽  
Wild Type ◽  
Short Delay ◽  
Delay Component

Electrically evoked otoacoustic emissions are sounds emitted from the inner ear when alternating current is injected into the cochlea. Their temporal structure consists of short- and long-delay components and they have been attributed to the motile responses of the sensory-motor outer hair cells of the cochlea. The nature of these motile responses is unresolved and may depend on either somatic motility, hair bundle motility, or both. The short-delay component persists after almost complete elimination of outer hair cells. Outer hair cells are thus not the sole generators of electrically evoked otoacoustic emissions. We used prestin knockout mice, in which the motor protein prestin is absent from the lateral walls of outer hair cells, and Tecta ΔENT/ΔENT mice, in which the tectorial membrane, a structure with which the hair bundles of outer hair cells normally interact, is vestigial and completely detached from the organ of Corti. The amplitudes and delay spectra of electrically evoked otoacoustic emissions from Tecta ΔENT/ΔENT and Tecta +/+ mice are very similar. In comparison with prestin +/+ mice, however, the short-delay component of the emission in prestin −/− mice is dramatically reduced and the long-delay component is completely absent. Emissions are completely suppressed in wild-type and Tecta ΔENT/ΔENT mice at low stimulus levels, when prestin-based motility is blocked by salicylate. We conclude that near threshold, the emissions are generated by prestin-based somatic motility.

scholarly journals Amplification lags nonlinearity in the recovery from reduced endocochlear potential

2020 ◽  
Author(s):  
C. Elliott Strimbu ◽  
Yi Wang ◽  
Elizabeth S. Olson
Keyword(s):  
Hair Cells ◽  
Otoacoustic Emissions ◽  
Basilar Membrane ◽  
Frequency Tuning ◽  
Organ Of Corti ◽  
Endocochlear Potential ◽  
Outer Hair Cells ◽  
Frequency Resolution ◽  
Operating Condition ◽  
Distortion Product

ABSTRACTThe mammalian hearing organ, the cochlea, contains an active amplifier to boost the vibrational response to low level sounds. Hallmarks of this active process are sharp location-dependent frequency tuning and compressive nonlinearity over a wide stimulus range. The amplifier relies on outer hair cell (OHC) generated forces driven in part by the endocochlear potential (EP), the ~ +80 mV potential maintained in scala media, generated by the stria vascularis. We transiently eliminated the EP in vivo by an intravenous injection of furosemide and measured the vibrations of different layers in the cochlea’s organ of Corti using optical coherence tomography. Distortion product otoacoustic emissions (DPOAE) were monitored at the same times. Following the injection, the vibrations of the basilar membrane lost the best frequency (BF) peak and showed broad tuning similar to a passive cochlea. The intra-organ of Corti vibrations measured in the region of the OHCs lost their BF peak and showed low-pass responses, but retained nonlinearity, indicating that OHC electromotility was still operational. Thus, while electromotility is presumably necessary for amplification, its presence is not sufficient for amplification. The BF peak recovered nearly fully within 2 hours, along with a non-monotonic DPOAE recovery that suggests that physical shifts in operating condition are a final step in the recovery process.SIGNIFICANCEThe endocochlear potential, the +80 mV potential difference across the fluid filled compartments of the cochlea, is essential for normal mechanoelectrical transduction, which leads to receptor potentials in the sensory hair cells when they vibrate in response to sound. Intracochlear vibrations are boosted tremendously by an active nonlinear feedback process that endows the cochlea with its healthy sensitivity and frequency resolution. When the endocochlear potential was reduced by an injection of furosemide, the basilar membrane vibrations resembled those of a passive cochlea, with broad tuning and linear scaling. The vibrations in the region of the outer hair cells also lost the tuned peak, but retained nonlinearity at frequencies below the peak, and these sub-BF responses recovered fairly rapidly. Vibration responses at the peak recovered nearly fully over 2 hours. The staged vibration recovery and a similarly staged DPOAE recovery suggests that physical shifts in operating condition are a final step in the process of cochlear recovery.

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