scholarly journals Effects of coiling on the micromechanics of the mammalian cochlea

2005 ◽  
Vol 2 (4) ◽  
pp. 341-348 ◽  
Author(s):  
Hongxue Cai ◽  
Daphne Manoussaki ◽  
Richard Chadwick
Keyword(s):  
Outer Hair Cell ◽  
Basilar Membrane ◽  
Travelling Waves ◽  
Organ Of Corti ◽  
Tectorial Membrane ◽  
Governing Equations ◽  
Element Analysis ◽  
Curvature Effects ◽  
Curvilinear Coordinate ◽  
Cochlear Partition

The cochlea transduces sound-induced vibrations in the inner ear into electrical signals in the auditory nerve via complex fluid–structure interactions. The mammalian cochlea is a spiral-shaped organ, which is often uncoiled for cochlear modelling. In those few studies where coiling has been considered, the cochlear partition was often reduced to the basilar membrane only. Here, we extend our recently developed hybrid analytical/numerical micromechanics model to include curvature effects, which were previously ignored. We also use a realistic cross-section geometry, including the tectorial membrane and cellular structures of the organ of Corti, to model the apical and basal regions of a guinea-pig cochlea. We formulate the governing equations of the fluid and solid domains in a curvilinear coordinate system. The WKB perturbation method is used to treat the propagation of travelling waves along the coiled cochlear duct, and the O (1) system of the governing equations is solved in the transverse plane using finite-element analysis. We find that the curvature of the cochlear geometry has an important functional significance; at the apex, it greatly increases the shear gain of the cochlear partition, which is a measure of the bending efficiency of the outer hair cell stereocilia.

scholarly journals Cochlear partition anatomy and motion in humans differ from the classic view of mammals

2019 ◽  
Vol 116 (28) ◽  
pp. 13977-13982 ◽  
Author(s):  
Stefan Raufer ◽  
John J. Guinan ◽  
Hideko Heidi Nakajima
Keyword(s):  
Basilar Membrane ◽  
Organ Of Corti ◽  
Tissue Structure ◽  
Cochlear Mechanics ◽  
Laboratory Animals ◽  
Transverse Motion ◽  
Tectorial Membrane ◽  
Peak Displacement ◽  
Cochlear Partition ◽  
Fixed Structure

Mammals detect sound through mechanosensitive cells of the cochlear organ of Corti that rest on the basilar membrane (BM). Motions of the BM and organ of Corti have been studied at the cochlear base in various laboratory animals, and the assumption has been that the cochleas of all mammals work similarly. In the classic view, the BM attaches to a stationary osseous spiral lamina (OSL), the tectorial membrane (TM) attaches to the limbus above the stationary OSL, and the BM is the major moving element, with a peak displacement near its center. Here, we measured the motion and studied the anatomy of the human cochlear partition (CP) at the cochlear base of fresh human cadaveric specimens. Unlike the classic view, we identified a soft-tissue structure between the BM and OSL in humans, which we name the CP “bridge.” We measured CP transverse motion in humans and found that the OSL moved like a plate hinged near the modiolus, with motion increasing from the modiolus to the bridge. The bridge moved almost as much as the BM, with the maximum CP motion near the bridge–BM connection. BM motion accounts for 100% of CP volume displacement in the classic view, but accounts for only 27 to 43% in the base of humans. In humans, the TM–limbus attachment is above the moving bridge, not above a fixed structure. These results challenge long-held assumptions about cochlear mechanics in humans. In addition, animal apical anatomy (inSI Appendix) doesn’t always fit the classic view.

Chlorpromazine Alters Cochlear Mechanics and Amplification: In Vivo Evidence for a Role of Stiffness Modulation in the Organ of Corti

2007 ◽  
Vol 97 (2) ◽  
pp. 994-1004 ◽  
Author(s):  
Jiefu Zheng ◽  
Niranjan Deo ◽  
Yuan Zou ◽  
Karl Grosh ◽  
Alfred L. Nuttall
Keyword(s):  
Outer Hair Cell ◽  
Basilar Membrane ◽  
Organ Of Corti ◽  
Lateral Wall ◽  
Mechanical Force ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Cochlear Amplification

Although prestin-mediated outer hair cell (OHC) electromotility provides mechanical force for sound amplification in the mammalian cochlea, proper OHC stiffness is required to maintain normal electromotility and to transmit mechanical force to the basilar membrane (BM). To investigate the in vivo role of OHC stiffness in cochlear amplification, chlorpromazine (CPZ), an antipsychotic drug that alters OHC lateral wall biophysics, was infused into the cochleae in living guinea pigs. The effects of CPZ on cochlear amplification and OHC electromotility were observed by measuring the acoustically and electrically evoked BM motions. CPZ significantly reduced cochlear amplification as measured by a decline of the acoustically evoked BM motion near the best frequency (BF) accompanied by a loss of nonlinearity and broadened tuning. It also substantially reduced electrically evoked BM vibration near the BF and at frequencies above BF (≤80 kHz). The high-frequency notch (near 50 kHz) in the electrically evoked BM response shifted toward higher frequency in a CPZ concentration-dependent manner with a corresponding phase change. In contrast, salicylate resulted in a shift in this notch toward lower frequency. These results indicate that CPZ reduces OHC-mediated cochlear amplification probably via its effects on the mechanics of the OHC plasma membrane rather than via a direct effect on the OHC motor, prestin. Through modeling, we propose that with a combined OHC somatic and hair bundle forcing, the upward-shift of the ∼50-kHz notch in the electrically-evoked BM motion may indicate stiffness increase of the OHCs that is responsible for the reduced cochlear amplification.

scholarly journals An Analytical Mechanical Model of Corti in the Cochlea

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Jiangtao Su ◽  
Wenjuan Yao ◽  
Zhengshan Zhao
Keyword(s):  
Mechanical Model ◽  
Basilar Membrane ◽  
Low Frequency ◽  
Organ Of Corti ◽  
Negative Influence ◽  
Outer Hair Cells ◽  
Tectorial Membrane ◽  
Response Patterns ◽  
Motion Patterns ◽  
Loss Of Hearing

The organ of Corti (OC) in the cochlea is a significant structure for feeling sound. The components of OC and the interaction of the part with the surroundings contribute to the fact that the passive tuning of the cochlear macrostructure is unclear. Based on the interaction between the basilar membrane (BM), tectorial membrane (TM), reticular lamina (RL), and various parts of OC, a mechanical model of the cochlea is established to study the motion patterns of each part under the action of a certain pressure. The variational principle is applied to the calculation of the analytical expression of the displacement of the BM. The results of the analytical solution differ little from the experimental value, and the variation trend is consistent, which presents the correctness of the model. The parameter sensitivity analysis is carried out for obtaining the interaction principle and the primary and secondary roles of each component in the process of the sense of sound. The results show that the absence of the TM and the decrease in the stiffness of the outer hair cells (OHCs) and OHC bundles will shift vibratory response patterns to lower frequencies, in which the lack of TM will result in the greatest reduction of CF. The absence of RL exerts a negative influence on the CF as well as the amplitude of BM and thereby loss of hearing. Therefore, both TM and RL are essential structures during the process of the sense of sound. At the same time, the resonance frequency at the base of the BM is concentrated on the high-frequency segment, while the apex of the BM is mainly in the low frequency. Different points of BM correspond to different CF, which demonstrates the frequency selectivity of the BM.

scholarly journals The origin of mechanical harmonic distortion within the organ of Corti in living gerbil cochleae

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Wenxuan He ◽  
Tianying Ren
Keyword(s):  
Hair Cells ◽  
Outer Hair Cell ◽  
Basilar Membrane ◽  
Second Harmonic ◽  
Harmonic Distortion ◽  
Organ Of Corti ◽  
Outer Hair Cells ◽  
Experimental Animals ◽  
Cellular Origin ◽  
Low Coherence

AbstractAlthough auditory harmonic distortion has been demonstrated psychophysically in humans and electrophysiologically in experimental animals, the cellular origin of the mechanical harmonic distortion remains unclear. To demonstrate the outer hair cell-generated harmonics within the organ of Corti, we measured sub-nanometer vibrations of the reticular lamina from the apical ends of the outer hair cells in living gerbil cochleae using a custom-built heterodyne low-coherence interferometer. The harmonics in the reticular lamina vibration are significantly larger and have broader spectra and shorter latencies than those in the basilar membrane vibration. The latency of the second harmonic is significantly greater than that of the fundamental at low stimulus frequencies. These data indicate that the mechanical harmonics are generated by the outer hair cells over a broad cochlear region and propagate from the generation sites to their own best-frequency locations.

scholarly journals Watching Death in the Gerbil Cochlea Using Optical Coherence Tomography (OCT)

2021 ◽  
Author(s):  
Nam Hyun Cho ◽  
Haobing Wang ◽  
Sunil Puria
Keyword(s):  
Optical Coherence Tomography ◽  
Hair Cell ◽  
Outer Hair Cell ◽  
Round Window ◽  
Fluid Pressure ◽  
Organ Of Corti ◽  
Round Window Membrane ◽  
Tectorial Membrane ◽  
Optical Coherence

Because it is difficult to directly observe the morphology of the living cochlea, our ability to infer the mechanical functioning of the living ear has been limited. Nearly all of our knowledge about cochlear morphology comes from postmortem tissue that was fixed and processed using procedures that possibly distort the structures and fluid spaces of the organ of Corti. In this study, optical coherence tomography was employed to obtain in vivo and postmortem micron-scale volumetric images of the high-frequency hook region of the gerbil cochlea through the round-window membrane. The anatomical structures and fluid spaces of the organ of Corti were segmented and quantified in vivo and over a 90-minute postmortem period. The results show that some aspects of the organ of Corti are significantly altered over the course of death, such as the volumes of the fluid spaces, whereas the dimensions of other features change very little. We postulate that the fluid space of the outer tunnel and its surrounding tectal cells form a resonant structure that can affect the motion of the reticular lamina and thereby have a profound effect on outer-hair-cell transduction and thus cochlear amplification. In addition, the in vivo fluid pressure of the inner spiral sulcus is postulated to effectively inflate the connected sub-tectorial gap between the tectorial membrane and the reticular lamina. This gap height decreases after death, which is hypothesized to reduce and disrupt hair-cell transduction.

scholarly journals A flexible anatomical set of mechanical models for the organ of Corti

2021 ◽  
Vol 8 (9) ◽  
pp. 210016
Author(s):  
Jorge Berger ◽  
Jacob Rubinstein
Keyword(s):  
Hair Cell ◽  
Mechanical Response ◽  
Outer Hair Cell ◽  
Basilar Membrane ◽  
Signal To Noise Ratio ◽  
Equations Of Motion ◽  
Fluid Motion ◽  
Organ Of Corti ◽  
Outer Hair Cells ◽  
Inner Hair Cell

We build a flexible platform to study the mechanical operation of the organ of Corti (OoC) in the transduction of basilar membrane (BM) vibrations to oscillations of an inner hair cell bundle (IHB). The anatomical components that we consider are the outer hair cells (OHCs), the outer hair cell bundles, Deiters cells, Hensen cells, the IHB and various sections of the reticular lamina. In each of the components we apply Newton’s equations of motion. The components are coupled to each other and are further coupled to the endolymph fluid motion in the subtectorial gap. This allows us to obtain the forces acting on the IHB, and thus study its motion as a function of the parameters of the different components. Some of the components include a nonlinear mechanical response. We find that slight bending of the apical ends of the OHCs can have a significant impact on the passage of motion from the BM to the IHB, including critical oscillator behaviour. In particular, our model implies that the components of the OoC could cooperate to enhance frequency selectivity, amplitude compression and signal to noise ratio in the passage from the BM to the IHB. Since the model is modular, it is easy to modify the assumptions and parameters for each component.

scholarly journals Cochlear amplification and tuning depend on the cellular arrangement within the organ of Corti

2018 ◽  
Vol 115 (22) ◽  
pp. 5762-5767 ◽  
Author(s):  
Hamid Motallebzadeh ◽  
Joris A. M. Soons ◽  
Sunil Puria
Keyword(s):  
Hair Cells ◽  
Outer Hair Cell ◽  
Basilar Membrane ◽  
Measurement Techniques ◽  
Organ Of Corti ◽  
Sensory Epithelium ◽  
Sound Levels ◽  
Cochlear Amplification ◽  
Sound Transduction ◽  
Deiters Cell

The field of cochlear mechanics has been undergoing a revolution due to recent findings made possible by advancements in measurement techniques. While it has long been assumed that basilar-membrane (BM) motion is the most important determinant of sound transduction by the inner hair cells (IHCs), it turns out that other parts of the sensory epithelium closer to the IHCs, such as the reticular lamina (RL), move with significantly greater amplitude for weaker sounds. It has not been established how these findings are related to the complex cytoarchitecture of the organ of Corti between the BM and RL, which is composed of a lattice of asymmetric Y-shaped elements, each consisting of a basally slanted outer hair cell (OHC), an apically slanted phalangeal process (PhP), and a supporting Deiters’ cell (DC). Here, a computational model of the mouse cochlea supports the hypothesis that the OHC micromotors require this Y-shaped geometry for their contribution to the exquisite sensitivity and frequency selectivity of the mammalian cochlea. By varying only the OHC gain parameter, the model can reproduce measurements of BM and RL gain and tuning for a variety of input sound levels. Malformations such as reversing the orientations of the OHCs and PhPs or removing the PhPs altogether greatly reduce the effectiveness of the OHC motors. These results imply that the DCs and PhPs must be properly accounted for in emerging OHC regeneration therapies.

Acoustic Boundary Layer Attenuation in Ducts With Rigid and Elastic Walls Applied to Cochlear Mechanics

2017 ◽  
Vol 139 (10) ◽  
Author(s):  
Frank Böhnke ◽  
Sebastian Semmelbauer
Keyword(s):  
Boundary Layer ◽  
Otoacoustic Emissions ◽  
Basilar Membrane ◽  
Organ Of Corti ◽  
Sensory Cells ◽  
The Finite Element Method ◽  
Hearing Sensitivity ◽  
Cochlear Partition ◽  
Temporal Bones ◽  
Hearing System

The cochlea is the most important part of the hearing system, due to the fact that it transforms sound guided through air, bone, and lymphatic fluid to vibrations of the cochlear partition which includes the organ of Corti with its sensory cells. These send nerve impulses to the brain leading to hearing perception. The work presents the wave propagation in rigid ducts filled with air or water including viscous-thermal boundary layer damping. In extension, a mechanical box model of the human cochlea represented by a rectangular duct limited by the tapered basilar membrane at one side is developed and evaluated numerically by the finite element method. The results match with rare experiments on human temporal bones without using the physically unfounded assumption of Rayleigh damping. A forecast on the concept of the traveling wave parametric amplification is given to potentially explain the high hearing sensitivity and otoacoustic emissions.

scholarly journals A flexible anatomic set of mechanical models for the organ of Corti

2019 ◽  
Author(s):  
Jorge Berger ◽  
Jacob Rubinstein
Keyword(s):  
Hair Cell ◽  
Outer Hair Cell ◽  
Basilar Membrane ◽  
Mechanical Performance ◽  
Signal To Noise Ratio ◽  
Fluid Motion ◽  
Organ Of Corti ◽  
Outer Hair Cells ◽  
Inner Hair Cell ◽  
Mechanical Models

We build a flexible platform for the study of the mechanical performance of the organ of Corti (OoC) in the transduction of basilar membrane (BM) vibrations to motion of an inner hair cell bundle (IHB). In this platform, each anatomic component of the OoC is described by an equation of motion that can be followed in time. We propose an initial set of models that attempt to capture the nonlinearities of somatic and bundle motility, but can nevertheless be easily handled. The anatomic components that we consider are the outer hair cells (OHCs), the outer hair cell bundles, Deiters cells, Hensen cells, the IHB and various sections of the reticular lamina. We study endolymph fluid motion in the subtectorial gap and then the mutual interactions among the components of the OoC, including the pressure exerted by endolymph. Minute bending of the apical ends of the OHCs can have a significant impact on the passage of motion from the BM to the IHB, including possible critical oscillator behaviour, even without the assistance of tectorial motion, shearing, or bundle motility. Thus, the components of the OoC could cooperate to enhance frequency selectivity, amplitude compression and signal to noise ratio in the passage from the BM to the IHB. Our models also provide a mechanism that could contribute to appropriate amplification of the wave travelling along the cochlea.

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