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1
Giese, Arnaud. "Régulation de la protéine centrale de la polarité planaire cellulaire Vangl2 dans l’organe de Corti". Thesis, Bordeaux 2, 2010. http://www.theses.fr/2010BOR21761/document.
Testo completoAbstract (sommario):
Outre leur polarité apico-basale, certaines cellules épithéliales développent une seconde polarité, appelée Polarité Planaire Cellulaire (PCP). L'axe de la PCP est orienté perpendiculairement à l'axe de polarité apico-basale et régit l'orientation uniforme de certaines structures, comme les poils ou cils, non seulement à l'échelle de la cellule mais également au sein du tissu. L'épithélium cochléaire est l'un des meilleurs modèles d'étude de PCP chez les mammifères. En effet, les cellules neuro-épitheliales qui le composent, soutenues par des cellules de soutien, présentent à leur apex, des touffes ciliaires dont l'orientation est parfaitement coordonnée par la voie de la polarité planaire. Les deux premiers gènes impliqués dans la PCP chez les mammifères, Vangl2 et Scrib1, ont été identifiés sur la base du phénotype de la cochlée chez les mutants. L'analyse de la localisation de Vangl2 dans l'organe de Corti a également révélé une localisation asymétrique proximo-distale et transitoire de la protéine, perpendiculaire à l'axe apico-basal classique. Cette asymétrie apparaît à la jonction entre deux types cellulaires : une cellule sensorielle ciliée et une cellule de soutien. J'ai pu montrer au cours de mes travaux de thèse que cette asymétrie était majoritairement due à une accumulation de Vangl2 du côté distal des cellules de soutien, et que dans une moindre mesure, Vangl2 pouvait ségréger du côté distal des cellules ciliées. Cette localisation subcellulaire très précise et limitée dans l'espace semble être indépendante de l'expression du gène Scrib1 dans les cellules ciliées. La délétion du gène Scrib1 dans les cellules ciliées m'a toutefois permis de mettre en évidence que ce gène avait un rôle autonome dans la régulation de la PCP, et que les cellules de soutien de l'organe de Corti pouvaient jouer un rôle prépondérant dans le contrôle de la PCP. Mes travaux ont également permis de mettre en évidence que GIPC1 avait un rôle dans la régulation de la PCP et le maintien de l'intégrité des touffes ciliaires des cellules sensorielles, et que le complexe GIPC1/Myosine VI pouvait réguler l'établissement de l'asymétrie de Vangl2 dans l'organe de CortiSeveral epithelia exhibit a second polarity perpendicular to the apico-basal axis, called planar polarity and that governs the orientation of structures such as stereocilia and hear. Our laboratory studies planar polarity, using mammalian cochlear sensory epithelium and we focus our studies on Vangl2, that we identified as the first mammalian planar polarity gene. Vangl2 encodes a four-transmembrane protein that contains a PDZ binding domain in its C-terminus tail. Vangl2 is asymmetrically located at the junction between mechanosensory hair cells and supporting cells, and this asymmetry appears important for planar cell polarity. I have shown in my thesis, using STED microscopy, that Vangl2 asymmetry is mainly due to an accumulation of Vangl2 to the distal side of supporting cells. I sought to dissect the molecular role of Vangl2 by analysing its trafficking within the cochlear epithelium. Deletion analysis shows that the last 12 amino acids, unlike its N-terminus tail are essential for Vangl2 endoplasmic reticulum sorting, its plasma membrane targeting and its function. Conditional mutant mice analysis show that Scrib1, which we have previously shown, interacts with Vangl2 through the PDZ binding domain of its C-terminal tail, is not the protein mediating this asymmetry. My work also highlight that GIPC1 had a role in the regulation of PCP and maintaining the integrity of hair bundles of sensory cells, and that the complex GIPC1/Myosin VI could regulate Vangl2 asymmetry in the organ of Corti
2
Ku, Emery Mayon. "Modelling the human cochlea". Thesis, University of Southampton, 2008. https://eprints.soton.ac.uk/64535/.
Testo completoAbstract (sommario):
One of the salient features of the human cochlea is the incredible dynamic range it possesses—the loudest bearable sound is 10,000,000 times greater than the softest detectable sound; this is in part due to an active process. More than twelve thousand hairlike cells known as outer hair cells are believed to expand and contract in time to amplify cochlear motions. However, the cochlea’s response is more than just the sum of its parts: the local properties of outer hair cells can have unexpected consequences for the global behaviour of the system. One such consequence is the existence of otoacoustic emissions (OAEs), sounds that (sometimes spontaneously!) propagate out of the cochlea to be detected in the ear canal. In this doctoral thesis, a classical, lumped-element model is used to study the cochlea and to simulate click-evoked and spontaneous OAEs. The original parameter values describing the microscopic structures of the cochlea are re-tuned to match several key features of the cochlear response in humans. The frequency domain model is also recast in a formulation known as state space; this permits the calculation of linear instabilities given random perturbations in the cochlea which are predicted to produce spontaneous OAEs. The averaged stability results of an ensemble of randomly perturbed models have been published in [(2008) ‘Statistics of instabilities in a state space model of the human cochlea,’ J. Acoust. Soc. Am. 124(2), 1068-1079]. These findings support one of the prevailing theories of SOAE generation. Nonlinear simulations of OAEs and the model’s response to various stimuli are performed in the time domain. Features observed in the model include the saturation of the forces generated by the OHCs, compression of amplitude growth with increasing stimulus level, harmonic and intermodulation distortion, limit cycle oscillations that travel along the cochlear membranes, and the mutual suppression of nearby linear instabilities.
3
van, der Vyver Johannes Petrus. "A biomorphic electronic Hopf cochlea /". Zürich : ETH, 2006. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=16941.
Testo completo
4
Morell, Ybarz Maria. "Ultrastructural analysis of odontocete cochlea". Doctoral thesis, Universitat Politècnica de Catalunya, 2012. http://hdl.handle.net/10803/125113.
Testo completoAbstract (sommario):
The morphological study of the Odontocete organ of Corti including possible pathological features resulting from sound over-exposure, represent a key conservation issue to assess the effects of acoustic pollution on marine ecosystems. Through the collaboration with stranding networks belonging to 26 countries, 150 ears from 13 species of Odontocetes were processed. In this dissertation, we present a standard protocol to 1) compare the ultrastructure of the cochlea in several Odontocete species and 2) investigate possible damage as a consequence of sound exposure, using scanning (SEM) and transmission (TEM) electron microscopy, and immunohistochemistry.
In a preliminary study, computerized tomography scans were performed before decalcification with ears of 15 odontocete species, proposing a set of standard measurements which classified very well the species. In addition, the constant ratio between measurements of inner and middle ear structures contributed to confirm the active role of the odontocete middle ear in sound reception mechanism.
We established a decalcification protocol using the fast commercial decalcifier RDO® and EDTA (Ethylendiaminetetraacetic acid). Although further experiments should be conducted to assess the suitability of using one or the other method (because the number of samples treated with EDTA was comparatively small), RDO® at specific dilutions decreased the decalcification time of cetacean ear bones with control of the decalcification endpoint, helping a faster access to inner structures.
The complementary use of electron microscopy and immunofluorescence allowed the description in odontocetes of new morphological features of tectorial membrane, spiral limbus, spiral ligament, stria vascularis, hair cells and their innervation. Furthermore, this study revealed qualitative and quantitative morphological characteristics of the organ of Corti in high-frequency hearing species, including 1) an outer hair cell (OHC) small length, 2) a thick cuticular plate in OHC, and a thick reticular lamina, 3) robust cup formation of the Deiters cell body, 4) the high development of cytoskeleton in Deiters and pillar cells and 5) the basilar membrane high stiffness. Interestingly, all these features, including a common molecular design of prestin, are also shared by echolocating bats, suggesting a convergent evolution in echolocating species.
The presence of scars among hair cell rows, the pattern of stereocilia imprints in the tectorial membrane and the condition of fibrocytes II and IV were criteria suitable to determine or discard possible acoustic trauma, despite the numerous artefacts that rapidly develop as a consequence of tissue autolysis.
Consequently, matching the preliminary approximation of the cochlear frequency map with the damaged region would bring information on the sound source that would have triggered a possible lesion.
5
Jia, Huan. "Stratégies pharmacologiques pour la prévention de la fibrose intra-cochléaire". Thesis, Montpellier 1, 2012. http://www.theses.fr/2012MON1T001.
Testo completoAbstract (sommario):
L'implantation cochléaire reste à ce jour le seul moyen capable de restaurer la perception auditive chez les personnes présentant une surdité sévère ou profonde en échec d'appareillage conventionnel. Son principe repose sur la stimulation électrique directe des neurones auditifs de la cochlée par un faisceau d'électrode inséré dans l'oreille interne. Malgré les progrès réalisés dans le manufacturage des électrodes et dans la technique chirurgicale, le geste d'insertion du faisceau d'électrode demeure traumatique. Ce traumatisme est souvent responsable de la perte de l'audition résiduelle sur les fréquences graves et d'une réaction inflammatoire conduisant à une cicatrisation fibreuse. Cette réaction fibreuse est délétère à la fois pour le fonctionnement de l'implant, car augmentant l'impédance des électrodes, mais aussi pour l'audition résiduelle lorsqu'elle est préservée, limitant ainsi les possibilités de stimulation hybride électro-acoustique. Aussi les recherches actuelles tendent à réduire cette fibrose par des moyens pharmacologiques limités, utilisant un corticoïde (dexaméthasone), sans pour autant que son efficacité n'ait été démontrée de manière formelle in vitro ou in vivo. En outre, les cibles moléculaires visées lors de la réaction inflammatoire et fibrotique dans la cochlée n'étant pas clairement identifiées, il est difficile de savoir si cette approche thérapeutique est la plus adaptée. Dans ce travail nous avons donc mis au point des modèles in vitro de culture de tranche de cochlée et d'explant cochléaire de rat pour tester l'efficacité antifibrotique et la toxicité de plusieurs drogues, dont la dexaméthasone, mais aussi l'aracytine, antimitotique non ototoxique et d'utilisation sûre au contact du système nerveux central. Entre nos mains, il apparaît que la stratégie antimitotique par application d'aracytine était plus efficace contre la fibrose et moins toxique pour les cellules sensorielles que la dexamethasone. Dans une seconde partie de ce travail, nous avons utilisé deux modèles in vivo de fibrose cochléaire, à savoir : l'induction d'une labyrinthite immune à Keyhole Limpet Hemocyanin et l'implantation chronique d'un corps étranger intra-cochléaire. A nouveau, l'aracytine délivrée par pompe osmotique intracochléaire permettait de réduire significativement la fibrose dans le modèle de labyrinthite alors que l'effet de la dexamethasone n'était pas significatif. De même la préservation de l'audition était statistiquement meilleure dans le groupe des animaux traités par antimitotiques. Aussi seule l'aracytine a été testée dans l'autre modèle de corps étranger intracochléaire. Elle permettait également de réduire la fibrose observée dans la cochlée, sans effet toxique sur les neurones auditifs. Si la préservation de l'audition était impossible dans le groupe contrôle, l'audition sur les basses fréquences était conservée chez les animaux traités par aracytine. Enfin, les seuils de stimulation électrique capables de provoquer une réponse électrophysiologique par le potentiel évoqué auditif étaient significativement inférieurs dans le groupe traité par aracytine. Ainsi, nous avons pu montrer qu'une stratégie antimitotique était capable d'inhiber efficacement la fibrose dans la cochlée in vitro et in vivo, et ce avec une efficacité supérieure à la dexaméthasone. Nous recommandons donc d'envisager en pratique clinique l'utilisation de l'aracytine pour prévenir la fibrose cochléaire. De plus, ce travail souligne l'intérêt de mieux décortiquer les voies cellulaires conduisant à l'inflammation et à la fibrose cochléaire, de sorte à déterminer les meilleures cibles et molécules candidates. Ces mêmes molécules pourront être testées sur les modèles que nous avons mis au point afin de proposer de nouvelles alternatives thérapeutiques à la prévention de la fibrose cochléaireCochlear implantation is the only treatment capable of restoring the auditory pathways in patient suffering from severe to profound hearing loss with poor benefit from hearing aids. Its functioning relies on direct electric stimulation of primary auditory neurons through an electrode array inserted into the cochlea.Despite the advances in electrode design and surgical technique, the act of inserting the electrode array is still traumatic. These traumas result in the loss of residual hearing in low frequencies and provoke an inflammatory reaction leading to fibrous scarring. This fibrous reaction is deleterious to not only the implant performance by increasing the impedance of the electrodes, but also the preserved residual hearing which limit the possibilities of hybrid electro-acoustic stimulation.Current researches aim at limiting this fibrosis by drug application, such as corticosteroids. Therefore dexamethasone is frequently used, but its effectiveness has been only demonstrated formally in vitro or in vivo. Furthermore, the molecular targets set in the fibrotic and inflammatory reaction in the cochlea are not clearly identified, and it is unclear whether this therapeutic approach is best suited.In this study we have developed in vitro models of rat cochlear slice and cochlear explants culture to test the antifibrotic efficacy and toxicity of various drugs, including dexamethasone, but also aracytine, an antimitotic drug with very low ototoxicity which is safely used in contact with the central nervous system. In our hands, it appears that antimitotic aracytine is more effective against fibrosis and less toxic to the sensory cells than the anti-inflammatory drug dexamethasone.In the second part of this study, we used two in vivo models of cochlear fibrosis namely the KLH(keyhole limpet hemocyanin)-induced sterile labyrinthitis and the foreign-body-induced chronic labyrinthitis. Again, the intracochlear fibrosis in the model of KLH-induced labyrinthitis was signticantly reduced by the osmotic pump with aracytine, while the effect of dexamethasone was not significant. Also the preservation of the hearing was statistically better in the group of animals treated with this antimitotic drug. Consequently, aracytine was the only drug tested in the other model of foreign-body-induced labyrinthitis. Again, aracytine reduced fibrosis in the cochlea, without any toxic effects on auditory neurons. While the preservation of the hearing was not achieved in the control group, the low frequencies hearing was preserved in animals treated with aracytine. Finally, the thresholds of electrical stimulation eliciting auditory brainstem response recordings were significantly lower in the treated group by aracytine.Thus, we have shown that an antimitotic strategy was able to inhibit fibrosis effectively in the cochlea in vitro and in vivo, and this with a greater efficiency than dexamethasone. We therefore recommend considering in clinical practice the use of aracytine to prevent cochlear fibrosis. In addition, this study stresses the importance of analyzing the cellular pathways of cochlear inflammation and fibrosis, in order to determine the best targets and candidate molecules. These molecules could be tested on the models that we have developed in order to offer new therapeutic options to prevent cochlear fibrosis
6
Edelmann, Karola. "Richtungshören bei Kindern mit bilateralen Cochlea-Implantaten im Vergleich zu Kindern mit unilateralem Cochlea-Implantat". [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=976294052.
Testo completo
7
Fragnière, Eric. "Analogue VLSI emulation of the cochlea /". Lausanne, 1998. http://library.epfl.ch/theses/?nr=1796.
Testo completo
8
Blomkvist, Anna, e Anna Fritz-Sundström. "Språkutveckling hos barn med cochlea implantat". Thesis, Örebro University, School of Humanities, Education and Social Sciences, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:oru:diva-9919.
Testo completo
9
Shiraishi, Hisako. "Design of an Analog VLSI Cochlea". University of Sydney. Electrical and Information Engineering, 2003. http://hdl.handle.net/2123/556.
Testo completoAbstract (sommario):
The cochlea is an organ which extracts frequency information from the input sound wave. It also produces nerve signals, which are further analysed by the brain and ultimately lead to perception of the sound. An existing model of the cochlea by Fragni`ere is first analysed by simulation. This passive model is found to have the properties that the living cochlea does in terms of the frequency response. An analog VLSI circuit implementation of this cochlear model in CMOS weak inversion is proposed, using log-domain filters in current domain. It is fabricated on a chip and a measurement of a basilar membrane section is performed. The measurement shows a reasonable agreement to the model. However, the circuit is found to have a problem related to transistor mismatch, causing different behaviour in identical circuit blocks. An active cochlear model is proposed to overcome this problem. The model incorporates the effect of the outer hair cells in the living cochlea, which controls the quality factor of the basilar membrane filters. The outer hair cells are incorporated as an extra voltage source in series with the basilar membrane resonator. Its value saturates as the input signal becomes larger, making the behaviour rather closer to that of a passive model. The simulation results show this nonlinear phenomenon, which is also seen in the living cochlea. The contribution of this thesis is summarised as follows: a) the first CMOS weak inversion current domain basilar membrane resonator is designed and fabricated, and b) the first active two-dimensional cochlear model for analog VLSI implementation is developed.
10
Kallweit, Nicole [Verfasser]. "Laserinduzierte Stimulation der Cochlea / Nicole Kallweit". Garbsen : TEWISS - Technik und Wissen GmbH, 2019. http://d-nb.info/1176156241/34.
Testo completo
11
Evans, Jared. "Piezoelectric-Based, Self-Sustaining Artificial Cochlea". Wright State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=wright1389196704.
Testo completo
12
Vignali, Dario. "Modelling nonlinear interactions within the cochlea". Thesis, University of Southampton, 2017. https://eprints.soton.ac.uk/412704/.
Testo completoAbstract (sommario):
The auditory system has a wide dynamic range and remarkable selectivity, due partly to the nonlinear processing within the cochlea. Modelling the performance of the cochlea is a way to gain insight into how it operates and to better understand its mechanical structure, whose arrangement generates nonlinear phenomena. A box model with nonlinear micromechanics was simulated using the state space method and the quasi-linear method to understand nonlinear dynamic interactions within the cochlea. The results from the quasi-linear model were essential for obtaining cochlear compression curves, which were used to tune the saturation parameters of the nonlinear function incorporated into the state space model. The nonlinear state space model allows time domain simulations to be performed that can replicate spontaneous otoacoustic emissions (SOAEs); sounds that can be measured in the ear canal, which are generated inside the cochlea and are by-products of the nonlinear process of the cochlear amplifier. The time domain model was mathematically formulated to reduce the computational load, which has previously limited the number of results that could be obtained. A novel method of incorporating initial conditions into the state space model has also been developed. Time domain simulations illustrate how SOAEs are due to limit cycle oscillations, whose amplitude is controlled by the saturation of the cochlea's amplification process. The results support the standing wave theory, whereby the emissions are produced by the reflection from random perturbations along the length of the cochlear partition at one end and the stapes at the other. Simulations of the interaction between a SOAE and low frequency bias tones give results that are comparable with those produced experimentally, but allow a greater physical interpretation. Simulations are also performed of the interaction between a SOAE and other stimuli, such as a swept tone that sweeps through the frequency of the emission and a high-level, low-frequency tone.
13
Fasquelle, Lydie. "TMPRSS3 dont les mutations sont responsables des surdités humaines DFNB8/10, joue un rôle crucial dans la survie des cellules sensorielles lors de l'entrée en fonction cochléaire : caractérisation du modèle animal et identification des voies de signalisation impliquées". Thesis, Montpellier 1, 2011. http://www.theses.fr/2011MON1T026.
Testo completoAbstract (sommario):
TMPRSS3 est une sérine protéase mutée dans les surdités humaines DFNB8/10. Pour déterminer le rôle de cette protéine dans la physiologie cochléaire, nous avons généré puis caractérisé le phénotype auditif d'un modèle murin mimant la pathologie humaine. Les souris mutantes homozygotes sont profondément sourdes, due à une perte rapide et complète des cellules sensorielles cochléaires au moment de leur entrée en fonction. Afin de caractériser les mécanismes moléculaires responsables de la perte de ces cellules, nous avons comparé le protéome de souris sauvages et mutantes par des gels en 2-dimensions. Nous avons ensuite analysé les spots variants par spectrométrie de masse, ce qui nous a permis de reconstruire les réseaux dans lesquels les protéines variantes interviennent. Parmi les réseaux identifiés, nous avons focalisé notre analyse sur celui du canal potassique BK, puisque sa mise en place est concomitante de la dégénérescence des cellules sensorielles. Par des expériences d'immunohistochimie et de patch-clamp, nous avons pu montrer dans les cellules sensorielles de la cochlée, une réduction de l'expression membranaire et de l'activité de ce canal en l'absence de Tmprss3 fonctionnelle. Le résultat original de notre travail est qu'une sérine protéase est capable de réguler le canal potassique BKTMPRSS3 is a type II serine protease mutated in human DFNB8/10 deafness. In order to determine the role of this protein in the cochlear physiology, we generated a mutant mice and phenotyped it. We found that homozygous mutant mice are profoundly deaf, due to a rapid and drastic degeneration of cochlear sensory cells at the onset of hearing. In order to decipher the molecular mechanism leading to sensory cells degeneration, we compared the cochlear proteome of wild type and homozygous mice using 2-dimensions gels. Then, we analyzed variant spots using mass spectrometry. Using bioinformatics, we clustered the protein in signaling pathways. We focused on the network centered on BK potassium channel because this channel appears at the onset of hearing, the time when sensory cells degenerate. Using immunohistochemistry and patch-clamp techniques, we were able to show that in the absence of a functional Tmprss3, membranous expression and activity of BK channel are altered in cochlear sensory cells. The original finding of our work is that a serine protease is able to modulate BK potassium channel
14
Newbold, Carrie. "Electrode tissue interface : development and findings of an in vitro model /". Connect to thesis, 2006. http://repository.unimelb.edu.au/10187/1692.
Testo completoAbstract (sommario):
In the period immediately following the implantation of a cochlear implant electrode array within the cochlear environment, the power required to stimulate the auditory nerve at preset current levels increases. This rise is due to increases in electrode impedance which in turn is suggested to be a result of tissue growth around the electrode array. The foreign body response initiated by the immune system encapsulates the array in a matrix of fibrous tissue, separating the electrode array from the rest of the body. A second change in electrode impedance occurs with the onset of electrical stimulation. A transitory reduction in impedance has been recorded in animals and humans after stimulation of electrodes. Impedance returns to pre-stimulation levels following the cessation of stimulation. It was suggested that these changes in impedance with stimulation were also related to the tissue growth around the electrode array. A more thorough understanding of the interface was required to ascertain these concepts.
15
O'Beirne, Greg A. "Mathematical modelling and electrophysiological monitoring of the regulation of cochlear amplification". University of Western Australia. School of Biomedical and Chemical Sciences, 2005. http://theses.library.uwa.edu.au/adt-WU2006.0115.
Testo completoAbstract (sommario):
[Truncated abstract] The cochlea presumably possesses a number of regulatory mechanisms to maintain cochlear sensitivity in the face of disturbances to its function. Evidence for such mechanisms can be found in the time-course of the recovery of CAP thresholds during experimental manipulations, and in observations of slow oscillations in cochlear micromechanics following exposure to low-frequency tones (the “bounce phenomenon”) and other perturbations. To increase our understanding of these oscillatory processes within the cochlea, and OHCs in particular, investigations into cochlear regulation were carried out using a combination of mathematical modelling of the ionic and mechanical interactions likely to exist within the OHCs, and electrophysiological experiments conducted in guinea pigs. The electrophysiological experiments consisted of electrocochleographic recordings and, in some cases, measurement of otoacoustic emissions, during a variety of experimental perturbations, including the application of force to the cochlear wall, exposure to very-low-frequency tones, injection of direct current into scala tympani, and intracochlear perfusions of artificial perilymph containing altered concentrations of potassium, sodium, and sucrose. To obtain a panoramic view of cochlear regulation under these conditions, software was written to enable the interleaved and near-simultaneous measurement of multiple indicators of cochlear function, including the compound action potential (CAP) threshold, amplitude and waveshape at multiple frequencies, the OHC transfer curves derived from low-frequency cochlear microphonic (CM) waveforms, distortion-product otoacoustic emissions (DPOAEs), the spectrum of the round-window neural noise (SNN), and the endocochlear potential (EP). ... The mathematical model we have developed provided a physiologically-plausible and internally-consistent explanation for the time-courses of the cochlear changes observed during a number of different perturbations. We show that much of the oscillatory behaviour within the cochlea is consistent with underlying oscillations in cytosolic calcium concentration. We conclude that a number of the discrepancies between the simulation results and the experimental data can be resolved if the cytosolic calcium functions as two distinct pools: one which controls basolateral permeability and one which controls slow motility. This two-calcium-pool model is discussed.
16
Knobloch, Marie [Verfasser]. "Harmoniewahrnehmung mit dem Cochlea-Implantat / Marie Knobloch". Magdeburg : Universitätsbibliothek, 2018. http://d-nb.info/1165650568/34.
Testo completo
17
Brass, David Neil. "Stimulus frequency otoacoustic emissions and cochlea function". Thesis, University College London (University of London), 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261775.
Testo completo
18
Mullaley, Christopher John. "Modelling current flow in the mammalian cochlea". Thesis, University College London (University of London), 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.440459.
Testo completo
19
John, Gabriela Christina [Verfasser]. "Otolithenfunktionsstörung nach Cochlea-Implantation / Gabriela Christina John". Berlin : Medizinische Fakultät Charité - Universitätsmedizin Berlin, 2015. http://d-nb.info/1071088084/34.
Testo completo
20
Ni, Guangjian. "Fluid coupling and waves in the cochlea". Thesis, University of Southampton, 2012. https://eprints.soton.ac.uk/348820/.
Testo completoAbstract (sommario):
The cochlea plays an important role in human hearing. Its basic function is to map sounds of different frequencies onto corresponding characteristic positions on the basilar membrane, BM. When sounds enter the fluid-filled cochlea, deflections of the BM occur due to pressure differences between the cochlear fluid chambers. These deflections propagate along the cochlea to a frequency-dependent characteristic position and then decay away rapidly. The mechanics of the cochlea are modelled using both analytic and numerical models. In this thesis, the passive response of the cochlea is analysed, corresponding to its behaviour at high sound levels, to study the fluid coupling and waves in the cochlea. The fluid coupling is studied in 1D and 3D, uniform and non-uniform, uncoiled and coiled geometries, all with a passive basilar membrane. A ‘uniaxial model’, which is dependent on only a single dimension, is developed to represent the three-dimensional cochlea. The finite element method is also used to provide an independent check of the results from the analytic model. Analytic methods are used to predict waves due to different mechanisms in the passive cochlea, such as 1D and 3D fluid coupling and longitudinal BM dynamics. The wave finite element, WFE, method is then used to decompose the results of a full finite element model of the coupled cochlea into wave components. Results show that apart from the conventional slow wave, other additional types of wave in the passive cochlea do not appear to play a dominant role in normal passive cochlear function.
21
Mann, Zoe Francesca. "Mitochondrial function in the neonatal rat cochlea". Thesis, University College London (University of London), 2008. http://discovery.ucl.ac.uk/1446285/.
Testo completoAbstract (sommario):
The cochlea is a specialised structure that contains the cells responsible for transducing mechanical sound stimuli into neural code within the auditory nerve. Mutations in the mitochondrial genome have been associated with hearing loss, suggesting that they play a key role in cochlear physiology. Alongside ATP production, mitochondria are also intimately involved in processes such as calcium homeostasis and the regulation of cell death. The precise role for mitochondria in inner ear physiology is at present poorly defined. I used neonatal cochlear explants and confocal microscopy to study aspects of mitochondrial physiology. The dye TMRM was used to investigate differences in A j/mt between basal and apical inner (IHC) and outer (OHC) hair cells and supporting cells. Data reveal a base-to-apex difference in mitochondrial function specific to inner hair cells. Mitochondrial function was investigated further using the endogenous autofluorescence of NADH and flavoproteins and revealed a base-to-apex difference in cell redox state, again in the IHCs but not OHCs. Differences in intracellular metabolism were also investigated using fluorescence lifetime imaging of NAD(P)H and revealed metabolic differences between OHCs and supporting cells consistent with a metabolism that is more glycolytic in supporting cells and more oxidative in OHCs. 9+ The role of mitochondria in cochlear Ca homeostasis was also investigated. The amplitude and spatiotemporal properties of intercellular Ca waves initiated by ATP 9+ 9+ were studied. Blocking mitochondrial Ca ( Ca mt) uptake using Ru360 increased the wave amplitude, propagation velocity and extent of spread in cochlear supporting cells, 94- showing that mitochondrial Ca buffering plays a role in shaping calcium signals in the cochlea. 9+ 9+ Finally, neomycin was used to investigate Ca c and Ca mt during neomycin toxicity. 94- Neomycin induced a rapid bi-phasic response in OHC Ca c leading to cell loss of A /mt and cell permeabilsation, which correlated with ATP-dependent intercellular Ca waves in the surrounding supporting cells.
22
Hey, Matthias. "Kanaltrennung bei hochratiger sequentieller pulsatiler Elektrostimulation der Cochlea". [S.l.] : [s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=967060745.
Testo completo
23
Louza, Julia Palo Rodrigues. "Zum Einfluss der Cochlea Implantation auf das Vestibularorgan". Diss., lmu, 2010. http://nbn-resolving.de/urn:nbn:de:bvb:19-124603.
Testo completo
24
Vonier, Andreas. "Cochlea-implantierte Kinder gehörloser bzw. hochgradig hörgeschädigter Eltern". Heidelberg Median-Verl, 2008. http://deposit.d-nb.de/cgi-bin/dokserv?id=3117018&prov=M&dokv̲ar=1&doke̲xt=htm.
Testo completo
25
Fleischer, Mario. "Mehrfeldmodellierung und Simulation der äußeren Haarsinneszelle der Cochlea". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-100717.
Testo completoAbstract (sommario):
Das Innenohr des Säugetieres ist ein hochspezialisiertes sensorisches System, das durch ein komplexes mechanisches Verhalten gekennzeichnet ist. Neben der komplizierten Morphometrie und Geometrie kommen auch dem richtungsabhängigen Materialverhalten eine wesentliche Bedeutung zu. Es zeigt sich, daß im Cortischen Organ mit der äußeren Haarsinneszelle ein Zelltyp vorliegt, der durch seine physikalischen Eigenschaften das Gesamtverhalten des Innenohres maßgeblich beeinflußt. Wie jede tierische Zelle weist die äußere Haarsinneszelle als biomechanisches System eine heterogene Mikrostruktur auf. Vom mechanischen Standpunkt aus gesehen, ist neben der mehrschichtigen basolateralen Zellwand jede Einzelzelle durch ein viskoses inneres Fluid (Zellplasma) und einen Zellkern (Nukleus) gekennzeichnet. Die resultierenden mechanischen Eigenschaften des Gesamtsystems ”äußere Haarsinneszelle” können durch Experimente und eine geeignete Modellierung determiniert werden.
In dieser Arbeit wird ein neuer Ansatz zur Bestimmung der viskoelastischen Materialeigenschaften der basolateralen Wand vorgestellt. Durch Anwendung einer effektiven Fluid-Struktur-Interaktion wird das Gesamtsystem geschlossen untersucht und eine umfangreiche Materialparameterstudie durchgeführt. Dabei werden im Rahmen der Kontinuumsmechanik gültige Materialgesetze angewendet. Das durch partielle Differentialgleichungen formulierte mechanische Feldproblem wird im Rahmen der Finiten-Elemente-Methode approximiert, was zu einem linearen Gleichungssystem führt. Auf dieser Grundlage wird ein Finite-Elemente-Modell der äußeren Haarsinneszelle entwickelt. Die zur Beschreibung notwendigen Systemmatrizen – insbesondere die Dämpfungsmatrix – basieren dabei vollständig auf einem viskoelastischen Materialgesetz. Die benutzte Methodik läßt weiterhin eine effiziente Berechnung im Frequenzbereich zu.
Es zeigt sich, daß eine spezielle Dämpfungsformulierung die experimentell bestimmten dynamischen Eigenschaften der Zelle adäquat widerspiegelt. Eine Analyse auf Materialgesetzebene zeigt, daß dafür reine Schubdämpfung und damit eine spezielle Anisotropie im Viskositätstensor verantwortlich ist. Diese Eigenschaft bestimmt das dynamische Verhalten der äußeren Haarsinneszelle bis mindestens 10 kHz und liegt damit im Hörbereich.
Der Modellierung der Zelle geht eine angepaßte Auswertung der experimentell ermittelten Daten voraus. Die mechanisch geeignete Auswertung der zugrundeliegenden Experimente weist dabei auf mögliche Fehlerquellen bei der Analyse der Rohdaten hin. Das hat zur Konsequenz, daß der experimentellen Umgebung die gleiche Aufmerksamkeit geschenkt werden muß wie dem Meßobjekt selbst. Nur so kann eine geeignete Extraktion der für das Meßobjekt spezifischen Eigenschaften erfolgen.
26
Pan, Shuokai. "Cochlea modelling and its application to speech processing". Thesis, University of Southampton, 2018. https://eprints.soton.ac.uk/427156/.
Testo completoAbstract (sommario):
Models of the cochlea provide a valuable tool for both better understanding its mechanics and also as an inspiration for many speech processing algorithms. Realistic modelling of the cochlea can be computationally demanding, however, which limits its applicability in signal processing applications. To mitigate this issue, an efficient numerical method has been proposed for performing time domain simulations, based on a nonlinear state space formulation. This model has then been contrasted with another type of cochlear model, that is established from a cascade of digital filters. A comparison of the responses from these two models has been conducted, in terms of their realism in simulating the measured nonlinear cochlear response to single tones and pairs of tones. Guided by these results, the filter cascade model is chosen for subsequent signal processing applications because it is significantly more efficient than the state space model, while still producing realistic responses. Using this nonlinear filter cascade model as a front-end, two speech processing tasks have been investigated: voice activity detection and supervised speech separation. Both tasks are tackled within a machine learning framework, in which a neural network is trained to reproduce target outputs. The results are compared with those using a number of other simpler auditory-inspired analysis methods. Simulation results show that although the nonlinear filter cascade model can be more effective in many testing scenarios, its relative advantage against other analysis methods is small. The incorporation of temporal context information and network structure engineering are found to be more important in improving the performance of these tasks. Once a suitable context expansion strategy has been selected, the difference between various front-end processing methods considered is marginal.
27
Zhak, Serhii M. "Modeling and design of an active silicon cochlea". Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/45863.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2008.Includes bibliographical references.
Silicon cochleas are inspired by the biological cochlea and perform efficient spectrum analysis: They realize a bank of constant-Q Nth-order filters with O(N) efficiency rather than O(N²) efficiency due to their use of an exponentially tapered filter cascade. They are useful in speech-recognition front ends, cochlear implants, and hearing aids, especially as architectures for improving spectral analysis in noisy environments and for performing low-power spectrum analysis. In this thesis I describe four contributions towards improving the state-of-the-art in silicon-cochlea design, two of which involve theoretical modeling, and two of which involve integrated-circuit design. On the theoretical side, I first show that a simple rational approximation to distributed partition impedances in the biological cochlea captures its essential features and enables an efficient artificial implementation achieving maximum gain in a minimum number of stages while still maintaining stability. In particular, I show that the terminating impedance of the cochlea is crucial for its stability and discuss various analytic methods for termination. Second, I derive a novel composite artificial cochlear architecture composed of a cascade of all-pass second-order filters from a first-principles analysis of the biological cochlear transmission line. The novel all-pass architecture reduces phase lag and group delay in the silicon cochlea, a problem in prior designs, sharpens its high-frequency rolloff slopes, increases its frequency selectivity, and improves its nonlinear compression characteristics. On the circuit side, I first present a novel current-mode log-domain topology that simultaneously increases signal-to-noise ratio (SNR) and dynamic range while lowering power consumption in resonant filters with high quality factor Q.
(cont.) The novel topology is validated in a second-order low-pass resonant filter, which is employed in the silicon cochlea, demonstrating a reduction in power consumption and increase in SNR by a factor of Q. When bias currents in the filter are adjusted as the signal level varies, this technique enables an improvement in maximum SNR by a factor of Q and an increase in maximum non-distorted signal power and dynamic range by a factor of Q⁴. Measurements from a chip in a 0.18-[mu]m 1.1-V CMOS technology achieve a quiescent power consumption of 580-nW at a 15-kHz center frequency with a maximum SNR of 41.3dB and dynamic range of 76dB for a Q=4. Finally, I describe a current-mode -stage 0.18-[mu]m silicon cochlea that achieves 79dB of dynamic range with 41-[mu]W power consumption on a 1-V power supply over a usable 3.5kHz-14kHz frequency range. These numbers represent an 18dB improvement in dynamic range and a 12.5x reduction in power consumption over prior state-of-the-art silicon cochleas.
by Serhii M. Zhak.
Ph.D.
28
Schulze-Gattermann, Heide. "Kosten-Nutzen-Analyse der Cochlea-Implantation bei Kindern /". Berlin : Springer, 2002. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=009735549&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
Testo completo
29
Wong, Paul Chun Hymn. "High Fidelity Bioelectric Modelling of the Implanted Cochlea". Thesis, The University of Sydney, 2015. http://hdl.handle.net/2123/14445.
Testo completoAbstract (sommario):
Cochlear implants are medical devices that can restore sound perception in individuals with sensorineural hearing loss (SHL). Since their inception, improvements in performance have largely been driven by advances in signal processing, but progress has plateaued for almost a decade. This suggests that there is a bottleneck at the electrode-tissue interface, which is responsible for enacting the biophysical changes that govern neuronal recruitment. Understanding this interface is difficult because the cochlea is small, intricate, and difficult to access. As such, researchers have turned to modelling techniques to provide new insights. The state-of-the-art involves calculating the electric field using a volume conduction model of the implanted cochlea and coupling it with a neural excitation model to predict the response. However, many models are unable to predict patient outcomes consistently. This thesis aims to improve the reliability of these models by creating high fidelity reconstructions of the inner ear and critically assessing the validity of the underlying and hitherto untested assumptions. Regarding boundary conditions, the evidence suggests that the unmodelled monopolar return path should be accounted for, perhaps by applying a voltage offset at a boundary surface. Regarding vasculature, the models show that large modiolar vessels like the vein of the scala tympani have a strong local effect near the stimulating electrode. Finally, it appears that the oft-cited quasi-static assumption is not valid due to the high permittivity of neural tissue. It is hoped that the study improves the trustworthiness of all bioelectric models of the cochlea, either by validating the claims of existing models, or by prompting improvements in future work. Developing our understanding of the underlying physics will pave the way for advancing future electrode array designs as well as patient-specific simulations, ultimately improving the quality of life for those with SHL.
30
Mammano, Fabio. "Biophysics of the Cochlea. Theory, Experiments and Applications". Doctoral thesis, SISSA, 1992. http://hdl.handle.net/20.500.11767/4438.
Testo completoAbstract (sommario):
This work attempts to bring together theoretical and experimental aspects of cochlear
biophysics. In both cases, the focus is on the relationship between the motility of
outer hair cells and the filtering properties of the basilar membrane, as this seems
the key for understanding the functioning of the peripheral auditory system.
From the theoretical side, the hydrodynamics of the cochlea is studied in detail. A
possible mechanism for coupling the outer hair cells to the mechanics of the basilar
membrane is proposed and analysed mathematically. From the experimental side,
the effects of stimulating the cochlea with extracellular current are investigated by
means of laser interferometry. The necessary apparatus and the software for data
acquisition were engineered in the course of this investigation. A rapid return in
the realm of mathematical modelling concludes this work, with an eye on possible
applications of physiological knowledge to speech recognition.
The newcomer is given a succint introduction to the cochlear world in Chapter 1. A
new model of cochlear biomechanics is presented in Chapter 2. A set of experiments
aiming at clarifying the role of outer hair cell motility in the control of the vibration
pattern of the basilar membrane are described in Chapter 3. The role of active
cochlear mechanics in the processing of speech is explored in Chapter 4. Chapters
2 and 4 are the result of an intense collaboration with Prof. Renato Nobili at
the Department of Physics of Padova University, Italy, following a preparatory
period with Prof. Campbell L. Searle at the Massachusetts Institute of Technology,
Boston, U .S.A. The results of Chapter 3 were obtained thanks to the expertise
of Dr. Jonathan Ashmore, in his laboratory at the Department of Physiology of
Bristol University, England.
31
Jäger, Wanje. "Physiological aspects of cochlear excitation and neurotransmitter release /". Stockholm, 1998. http://diss.kib.ki.se/1998/91-628-3294-8/.
Testo completo
32
Cheng, Jun. "Signal processing approaches on otoacoustic emissions /". Stockholm, 2000. http://diss.kib.ki.se/2000/91-628-4058-4.
Testo completo
33
McMahon, Catherine. "The mechanisms underlying normal spike activity of the primary afferent synapse in the cochlea and its dysfunction : an investigation of the possible mechanisms of peripheral tinnitus and auditory neuropathy". University of Western Australia. School of Biomedical and Chemical Sciences, 2004. http://theses.library.uwa.edu.au/adt-WU2003.0034.
Testo completoAbstract (sommario):
[Truncated abstract] One of the problems in researching tinnitus is that it has often been assumed that the physiological mechanisms underlying the tinnitus percept cannot be objectively measured. Nonetheless, it is generally accepted that the percept results from altered spontaneous neural activity at some site along the auditory pathway, although it is still debated whether it is produced by: synchronisation of activity of adjacent neurones; a change in the temporal pattern of activity of individual neurones; or an increase in the spontaneous firing rate per se. Similarly, it is possible that the recently coined “auditory neuropathy” is produced by under-firing of the primary afferent synapse, although several other mechanisms can also produce the symptoms described by this disorder (normal cochlear mechanical function but absent, or abnormal, synchronous neural firing arising from the cochlea and auditory brainstem, known as the auditory brainstem response, or ABR). Despite an absent ABR, some subjects can detect pure tones at near-normal levels, although their ability to integrate complex sounds, such as speech, is severely degraded in comparison with the pure-tone audiogram. The aim of the following study was to investigate the normal mechanisms underlying neural firing at the primary afferent synapse, and its regulation, to determine the possible mechanisms underlying over-firing (tinnitus) or under-firing (auditory neuropathy) of primary afferent neurones.
34
Waleka, Oliver Julian [Verfasser]. "Hörrehabilitation bei einseitiger Ertaubung mittels Cochlea-Implantat: Der Einfluss der subjektiven Ertaubungsdauer auf das postoperative Einsilberverstehen nach Cochlea-Implantation / Oliver Julian Waleka". Mainz : Universitätsbibliothek der Johannes Gutenberg-Universität Mainz, 2020. http://d-nb.info/1224810813/34.
Testo completo
35
Wachtlin, Bianka, e Blanca Schäfer. "Phonologische Bewusstheit bei deutschsprachigen Kindern mit bilateraler Cochlea-Implantat Versorgung : eine Pilotstudie". Universität Potsdam, 2014. http://opus.kobv.de/ubp/volltexte/2014/7148/.
Testo completo
36
Wright, A. "Structural changes in the human cochlea during drug treatment". Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371567.
Testo completo
37
Huss, M. "Dead regions in the cochlea : diagnosis and perceptual consequences". Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604839.
Testo completoAbstract (sommario):
“Threshold equalising noise” (TEN) was designed to produce approximately equal masked thresholds for all signal frequencies for people without DRs. When the signal falls inside a DR and is therefore detected via neurones with characteristic frequencies different from the signal frequency, the masked threshold is unusually high. the TEN test was validated by comparison with psychophysical tuning curves and was found to be an appropriate clinical tool for the identification of DR. Hearing-impaired subjects who do not perceive pure tones with a clear pitch were often assumed to have DRs. A systematic study based on subjective ratings of tone clarity showed that tones falling more than ~ 1.5 octaves inside a DR were indeed always rated as somewhat unclear, but a noise-like percept was not necessarily associated with a DR. No correlation was found between noisiness ratings and absolute thresholds across frequencies within ears, but average ratings increased with the severity of the hearing loss. An extensive study of perceived pitch was conducted by obtaining pitch matches across ears of unilaterally hearing-impaired subjects, or within ears using octave matches. The results indicate that tones falling within a DR are perceived with an unclear pitch that is different from “normal”, particularly for tones falling well inside low- or high-frequency DRs. The results indicate that the pitch of low-frequency tones is not conveyed solely by a temporal code, although some temporal information is still available. Possibly, a correspondence between place and temporal information is necessary for a “normal” pitch to be perceived. The pitch of high-frequency tones falling in a DR is probably solely determined by place information. Normally, a sustained tone remains audible when presented at a level well above threshold, except at the upper frequency limit of hearing. In an extensive study using subjects with and without DRs, no consistent association was found between the degree of tone decay and the presence of a DR.
38
Lahne, Manuela. "Damage-induced signalling mechanisms in the neonatal rat cochlea". Thesis, University College London (University of London), 2007. http://discovery.ucl.ac.uk/1444911/.
Testo completoAbstract (sommario):
Sound overstimulation and exposure to ototoxic drugs damage cochlear hair cells (HCs) and cause their death. The surrounding support cells maintain an epithelial barrier and the appropriate physiological environment for surviving HCs during pathological conditions. Coordination of this homeostatic process requires cellular signalling. However, the signalling events that are activated during damage in the mammalian cochlea, are poorly understood. Neonatal rat cochlear explants were subjected to mechanical damage or exposed to neomycin - an ototoxin. Mechanical damage triggered the immediate propagation of an intercellular wave of increased intracellular Ca2+ from the lesion site into distinct cochlear regions. The properties of the Ca2+ wave and the source of Ca2+ required were specific to the cochlear region. IP3-mediated release from intracellular stores and influx of extracellular Ca2+ contribute differentially to the rise in intracellular Ca2+. The release of extracellular ATP is crucial for the propagation of the damage-induced Ca2+ wave. Gap junctions or connexin hemichannels also contribute to its formation. A subsequent damage-induced signalling event is the transient phosphorylation of ERK1/2 that arises within minutes of the insult occurring in support cells specifically. Similarly to the formation of the Ca2+ wave, release of extracellular ATP and gap junctions are critical for ERK1/2 activation. UTP-induced activation of ERK1/2 reveals the involvement of P2Y receptors. In addition, a requirement for the influx of extracellular Ca2+ also suggests a role for ion channels - potentially P2X receptors. P2X2,3,4 and P2Y2.4, n receptors were expressed in cochlear explants with P2X2 and P2Y2 being exclusive to support cells. Damage-induced currents were recorded from Deiters' cells in a syncytium during mechanical damage of the cochlea. Finally, when HCs were specifically targeted using neomycin, ERK1/2 activation occurred in support cells surrounding pyknotic HC nuclei. Inhibition of ERK1/2 delayed HC death.
39
Hüttenbrink, Karl-Bernd, Thomas Zahnert, Uwe Vogel e Gert Hofmann. "Biologic Fixation of the Electrode Cable of Cochlea Implants". Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-135236.
Testo completoAbstract (sommario):
Objectives: To verify the necessity for special surgical techniques or clips for fixation of the electrode cable of a cochlea implant against dislocation, and to test the stability of postoperative biologic cicatrization as the sole and solid anchoring of the cable. Material: Temporal bone experiments with a simulated connective tissue sheath around conventional (Med El Combi 40+) and prototype (profiled surface) electrode cables. Results and Conclusions: The electrode cable is anchored securely in a sheath of scar tissue, since unphysiologic loads are needed for pulling it out of its anchorage. The drag during one extraction trial with a profiled cable even resulted in the rupture of the cable. These results confirm our confidence in this biologic fixation of the electrode cable inside its postoperative cicatric tissue sheath. More than 80 cochlea implantations with the electrode simply imbedded in a drop of fibrin glue in the posterior tympanotomy never demonstrated a shift of the electrodes in the last 8 years. Therefore, special fixation of the electrode cable with clips or surgical techniques is not necessaryFragestellung: Muss das Elektrodenkabel eines Kochlearimplantats durch spezielle operative Techniken oder Halterungen gegen ein Herausrutschen aus der Kochlea gesichert werden, oder genügt die Einscheidung in dem postoperativ sich ausbildenden Narbengewebe für eine ausreichend stabile Fixierung? Material: Felsenbeinexperimente mit einer Simulation der narbigen Einbettung konventioneller und modifizierter (geriffelter Oberfläche) Elektrodenkabel eines Kochlearimplantats (Med El Combi 40+). Ergebnisse und Schlussfolgerungen: Ein Herausziehen eines in simuliertem Narbengewebe eingescheideten Elektrodenkabels gelang erst bei erheblichen, unphysiologischen Kräften; eine Rifflung der Oberfläche des Silikonkabels erhöhte den Reibungswiderstand über die Reissfestigkeit des Kabels. Das Vertrauen in die biologische Fixierung des Elektrodenkabels durch die Verankerung im Narbengewebe ist somit gerechtfertigt, und wird auch durch unsere klinische Erfahrung bestätigt: in über 80 Operationen, bei denen das Kabel des Kochlearimplantats nur durch Einbettung in Fibrinkleber am Rahmen der posterioren Tympanotomie gesichert worden war, liess sich in den letzten 8 Jahren in keinem Fall eine Elektrodenverlagerung nachweisen. Eine gezielte Fixation des Elektrodenkabels durch künstliche Halterungen oder spezielle OP-Techniken erscheint somit nicht erforderlich
Problématique: Afin d’éviter tout glissement de l’électrode de l’implant cochléaire, est-il préférable d’en assurer la fixation par une technique opératoire particulière ou bien est-il suffisant de gainer l’électrode dans les tissus cicatriciels qui se forment après l’opération? Méthode: Nous avons procédé à des expériences sur le rocher en simulant une inclusion cicatricielle d’un câble-électrode classique (Med El Combi 40+), d’une part, et modifié (surface cannelée), d’autre part. Résultats et conclusion: Une force dépassant les réalités physiologiques a été nécessaire pour retirer le câble-électrode gainé dans les tissus cicatriciels simulés. Le câble avec la surface cannelée s’avérait encore plus résistant: il déchirait même lorsqu’on a essayé de le retirer. Ceci vient donc conforter la confiance que nous avons dans la fixation biologique, c’est-à-dire dans l’ancrage de l’électrode dans les tissus cicatriciels. Une confiance qui est d’ailleurs confirmée par les expériences que nous avons pu faire dans notre clinique. Ainsi, en 8 ans, sur 80 opérations, au cours desquelles le câble de l’implant a été fixé en étant simplement placé dans de la fibrine, dans le cadre d’une tympanotomie postérieure, aucun déplacement de l’électrode n’a été constaté. Par conséquent, il ne s’avère pas nécessaire d’avoir recours à une fixation artificielle ou à une technique opératoire particulière pour assurer le bon maintien de l’électrode
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich
40
De, Boer Jessica. "Electrical properties of Deiters cells of the mammalian cochlea". Thesis, University College London (University of London), 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.397252.
Testo completo
41
Page, Scott Lawrence. "Sound-induced micromechanical motions in an isolated cochlea preparation". Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/37926.
Testo completoAbstract (sommario):
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.Includes bibliographical references (p. 44-45).
The mechanical processes at work within the organ of Corti can be greatly elucidated by measuring both radial motions and traveling-wave behavior of structures within this organ in response to sound stimuli. To enable such measurements, we have developed a new preparation for observing three-dimensional motions of micromechanical structures in the apical region of an isolated gerbil cochlea. The cochlea is submerged in a low-chloride, low-calcium artificial perilymph solution and cemented to the bottom of a Petri dish at an angle. The bone above scala vestibuli of one half of the apical turn is removed to allow optical imaging with a 40x, 0.8 NA water-immersion objective. Reissner's membrane is left intact. Illumination is provided with a blue LED coupled to an optical fiber. The fiber is positioned next to the bone surrounding scala tympani of the apical turn, so that the organ of Corti is illuminated from below. The resulting optical access allows imaging of a variety of structures that have been proposed to play a role in cochlear mechanics, including inner and outer hair cell bundles, the tectorial membrane, inner and outer pillar cells, and efferent fibers in the tunnel of Corti. In some preparations, individual stereocilia of inner hair cell bundles can be resolved.
(cont.) Motions are stimulated by driving the stapes with a piezoelectric probe, and are measured using a stroboscopic computer microvision system. Measurements of sub-micrometer motions of key structures in three dimensions are quantified, including longitudinal motion of the organ of Corti and relative radial motion between the tectorial membrane and hair cells. Longitudinal motion of the Efferent fibers in the tunnel of Corti is found to have a phase lead with respect to the hair cell bodies. This system enables quantitative studies of both the relative motions of structures within the organ of Corti in response to sound and the propagation of traveling waves along structures within the organ of Corti.
by Scott Lawrence Page.
S.M.
42
Aranyosi, Alexander James 1970. "Measuring sound-induced motions of the alligator lizard cochlea". Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/16829.
Testo completoAbstract (sommario):
Thesis (Ph.D.)--Harvard--Massachusetts Institute of Technology Division of Health Sciences and Technology, 2002.Includes bibliographical references (p. 219-235).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
The sensitivity and frequency selectivity of the hearing sense are determined primarily by mechanical properties of the cochlea. These mechanical properties are poorly understood in any species. This thesis contributes to our understanding of cochlear mechanics by presenting measurements of sound-induced motion of the alligator lizard cochlea. Novel methods were developed to maintain the cochlea in vitro for the time required to measure three-dimensional motions. Three-dimensional images of cochlear motion were taken by illuminating the cochlea with a light-emitting diode stroboscopically at predetermined phases of the acoustic stimulus. The resulting images were analyzed using computer vision algorithms to extract three-dimensional motions of all visible structures with nanometer precision. The sound-induced motion of the entire basilar papilla and of individual hair bundles of hair cells were simultaneously measured. The basilar papilla, in which the hair cells reside, moved as a rigid body, exhibiting simultaneous translational and rotational modes of motion. Both modes apply shearing forces to hair bundles. A simple mechanical model of the basilar papilla, based on these measurements, provides a physical basis for a mechanical low-pass filter hypothesized in previous models. In the tectorial region of the cochlea, motion of the tips of hair bundles and of the tectorial membrane (TM) were in phase with motion of the basilar papilla. None of the motions had significant frequency dependence, suggesting that this region does not exhibit appreciable mechanical frequency selectivity. In the free-standing region, which has no TM, hair bundle deflection depended on stimulus frequency and hair bundle height.
(cont.) At high frequencies, hair bundle deflection was proportional to basilar papilla displacement. At low frequencies, hair bundle deflection was proportional to a linear combination of basilar papilla velocity and acceleration. Measured hair bundle deflections were well fit by a simple hydrodynamic model (Freeman and Weiss, 1990) of this region of the cochlea. The measurements in this study provide the first characterization of the three-dimensional motion of all structures in a vertebrate cochlea.
by Alexander James Aranyosi.
Ph.D.
43
Alkhairy, Samiya Ashraf. "An analytic model of the Cochlea and functional interpretations". Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/113732.
Testo completoAbstract (sommario):
Thesis: Ph. D. in Biomedical Engineering, Harvard-MIT Program in Health Sciences and Technology, 2017.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 120-125).
The cochlea is part of the peripheral auditory system that has unique and intriguing features - for example it acts as a wave-based frequency analyzer and amplifies traveling waves. The human cochlea is particularly interesting due to its critical role in our ability to process speech. To better understand how the cochlea works, we develop a model of the mammalian cochlea. We develop the model using a mixed physical-phenomenological approach. Specifically, we utilize existing work on the physics of classical box-representations of the cochlea, as well as the behavior of recent data-derived wavenumber estimates. We provide closed-form expressions for macromechanical responses - the pressure difference across the Organ of Corti (OoC), and the OoC velocity, as well as the response characteristics - such as bandwidth and group delay. We also provide expressions for the wavenumber of the pressure traveling wave and the impedance of the OoC that underlie these macromechanical responses and are particularly important variables which provide us with information regarding how the cochlea works; they are a window to properties such as effective stiffness, positive and negative damping or amplifier profile, incremental wavelengths, gain and decay, phase and group velocities, and dispersivity. The expressions are in terms of three model constants, which can be reduced to two constants for most applications. Spatial variation is implicitly incorporated through an assumption of scaling symmetry, which relates space and frequency, and reduces the problem to a single independent dimension. We perform and discuss various tests of the model. We then exemplify a model application by determining the wavenumber and impedance from observable response characteristics. To do so, we determine closed-form expressions for the model constants in terms of the response characteristics. Then, using these expressions, along with values for human response characteristics that are available from psychoacoustic measurements or otoacoustic emissions, we determine the human wavenumber and impedance. In addition, we determine the difference in the wavenumber and impedance in the human base (where the OoC velocity responds maximally to high frequencies), and the human apex (where the OoC velocity responds maximally to low frequencies) and discuss their interpretations. The model is primarily valid near the peak region of the traveling wave, and is linear - therefore the model, as is, does not account for cochlear nonlinearity, and hence is primarily suitable for low stimulus levels. Finally, we discuss other scientific and engineering model applications which we can pursue, as well as potential modifications to the model, including suggestions regarding incorporating nonlinearity.
by Samiya A Alkhairy.
Ph. D. in Biomedical Engineering
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Andor, Daniel Ardó. "Energy transport, reflections and noise in the active cochlea". Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615187.
Testo completo
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Burghard, Alice [Verfasser]. "Einflussfaktoren auf proliferative Vorgänge nach Cochlea Implantation / Alice Burghard". Hannover : Bibliothek der Tierärztlichen Hochschule Hannover, 2013. http://d-nb.info/1046662295/34.
Testo completo
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Hüttenbrink, Karl-Bernd, Thomas Zahnert, Uwe Vogel e Gert Hofmann. "Biologic Fixation of the Electrode Cable of Cochlea Implants". Karger, 2000. https://tud.qucosa.de/id/qucosa%3A27630.
Testo completoAbstract (sommario):
Objectives: To verify the necessity for special surgical techniques or clips for fixation of the electrode cable of a cochlea implant against dislocation, and to test the stability of postoperative biologic cicatrization as the sole and solid anchoring of the cable. Material: Temporal bone experiments with a simulated connective tissue sheath around conventional (Med El Combi 40+) and prototype (profiled surface) electrode cables. Results and Conclusions: The electrode cable is anchored securely in a sheath of scar tissue, since unphysiologic loads are needed for pulling it out of its anchorage. The drag during one extraction trial with a profiled cable even resulted in the rupture of the cable. These results confirm our confidence in this biologic fixation of the electrode cable inside its postoperative cicatric tissue sheath. More than 80 cochlea implantations with the electrode simply imbedded in a drop of fibrin glue in the posterior tympanotomy never demonstrated a shift of the electrodes in the last 8 years. Therefore, special fixation of the electrode cable with clips or surgical techniques is not necessary.Fragestellung: Muss das Elektrodenkabel eines Kochlearimplantats durch spezielle operative Techniken oder Halterungen gegen ein Herausrutschen aus der Kochlea gesichert werden, oder genügt die Einscheidung in dem postoperativ sich ausbildenden Narbengewebe für eine ausreichend stabile Fixierung? Material: Felsenbeinexperimente mit einer Simulation der narbigen Einbettung konventioneller und modifizierter (geriffelter Oberfläche) Elektrodenkabel eines Kochlearimplantats (Med El Combi 40+). Ergebnisse und Schlussfolgerungen: Ein Herausziehen eines in simuliertem Narbengewebe eingescheideten Elektrodenkabels gelang erst bei erheblichen, unphysiologischen Kräften; eine Rifflung der Oberfläche des Silikonkabels erhöhte den Reibungswiderstand über die Reissfestigkeit des Kabels. Das Vertrauen in die biologische Fixierung des Elektrodenkabels durch die Verankerung im Narbengewebe ist somit gerechtfertigt, und wird auch durch unsere klinische Erfahrung bestätigt: in über 80 Operationen, bei denen das Kabel des Kochlearimplantats nur durch Einbettung in Fibrinkleber am Rahmen der posterioren Tympanotomie gesichert worden war, liess sich in den letzten 8 Jahren in keinem Fall eine Elektrodenverlagerung nachweisen. Eine gezielte Fixation des Elektrodenkabels durch künstliche Halterungen oder spezielle OP-Techniken erscheint somit nicht erforderlich.
Problématique: Afin d’éviter tout glissement de l’électrode de l’implant cochléaire, est-il préférable d’en assurer la fixation par une technique opératoire particulière ou bien est-il suffisant de gainer l’électrode dans les tissus cicatriciels qui se forment après l’opération? Méthode: Nous avons procédé à des expériences sur le rocher en simulant une inclusion cicatricielle d’un câble-électrode classique (Med El Combi 40+), d’une part, et modifié (surface cannelée), d’autre part. Résultats et conclusion: Une force dépassant les réalités physiologiques a été nécessaire pour retirer le câble-électrode gainé dans les tissus cicatriciels simulés. Le câble avec la surface cannelée s’avérait encore plus résistant: il déchirait même lorsqu’on a essayé de le retirer. Ceci vient donc conforter la confiance que nous avons dans la fixation biologique, c’est-à-dire dans l’ancrage de l’électrode dans les tissus cicatriciels. Une confiance qui est d’ailleurs confirmée par les expériences que nous avons pu faire dans notre clinique. Ainsi, en 8 ans, sur 80 opérations, au cours desquelles le câble de l’implant a été fixé en étant simplement placé dans de la fibrine, dans le cadre d’une tympanotomie postérieure, aucun déplacement de l’électrode n’a été constaté. Par conséquent, il ne s’avère pas nécessaire d’avoir recours à une fixation artificielle ou à une technique opératoire particulière pour assurer le bon maintien de l’électrode
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.
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Weddell, Thomas David. "Mechanisms of excitation and amplification in the mammalian cochlea". Thesis, University of Brighton, 2013. https://research.brighton.ac.uk/en/studentTheses/0f9db6ef-c538-4db9-a714-ea04154959fa.
Testo completoAbstract (sommario):
Mechanisms of cochlea excitation and amplification were investigated experimentally across a range of mammalian species. Distortion product otoacoustic emissions (DPOAEs) are used to clinically assess hearing. DPOAEs recorded from the ears of human subjects in the presence of a low frequency, high level tone were compared with similar recordings made from guinea pigs. Both guinea pig and human data were found to originate from a common cochlear nonlinearity; the Boltzmann model of DPOAE generation at the output of a spatially localised single-saturating non-linearity. Accordingly, the guinea pig cochlea can be used as a human model system for the study of DPOAE generation.
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Ghosh, Sumana. "CANNABINOID RECEPTORS (CB) IN COCHLEA: CHARACTERIZATION AND OTOPROTECTIVE FUNCTIONS". OpenSIUC, 2017. https://opensiuc.lib.siu.edu/dissertations/1486.
Testo completoAbstract (sommario):
Endocannabinoid (eCB) system is composed of endogenous CB ligands including anandamide (AEA) and 2-Arachidonyl glycerol (2-AG), enzymes involved in their biosynthesis and degradation such as diacylglycerol lipase-α (DAGL- α), and CB receptors. Primarily, there are three types of CB receptors - CB receptor 1(CB1), CB receptor 2 (CB2) and non CB1 non CB2 types of CB receptor (e.g. GPR, TRPV1) and they belong to G-protein (Gi/o) coupled receptors (GPCR) family.CB1 receptors are abundant in the brain where they modulate neuronal activities. On the other hand, CB2 receptors are predominantly expressed in the immune cells and regulate the growth and proliferation of different immune cells and modulate the activities of cytokines network and anti-oxidant machinery in stress conditions. Inflammation plays a central role in hearing loss (HL) caused by different ototoxic insults including anti-neoplastic agents such as cisplatin, aminoglycosides and acoustic trauma. These insults can trigger chronic production of reactive oxygen species (ROS) in regions of cochlea such as organ of Corti, stria vascularis (SVA), spiral ligament (SL) and spiral ganglion neurons (SG). This leads to increased synthesis of pro-inflammatory cytokines, disruption of mitochondrial membrane integrity, activation of DNA damage/repair pathways and activation of pro-apoptotic enzymes. Jeong et al. (2007) have shown that CB2 receptor specific agonist (JWH-015) protects the HEI-OC1 hair cell cultures against cisplatin-induced cytotoxicity in-vitro. The goal of the current study was to examine the distribution and function of CB receptors (mainly CB2) in the cochlea and determine whether activation of these receptors could protect the cochlea by altering the expression of ROS generating proteins, along with pro-inflammatory and pro-apoptotic proteins. This study also investigated whether inhibition of eCB synthesis can causes HL. Aim 1 of the current study investigated the expression of CB receptors in the cochlea using different in-vivo models such as male Wistar rat and knock-in mice with GFP-tagged CB2 receptors, in-vitro models such as organotypic culture of neonatal mouse (C57BL/6) cochlea and University of Bristol organ of Corti (UB/OC1) cells. We show that both CB1 and CB2 receptors are expressed in the outer and the inner hair cells (OHCs and IHCs), SV, SG and supporting cells (SCs) included outer and inner pillar cells. The distribution of DAGL- α was also examined in the male Wistar rats and we found the similar distribution pattern of this enzymes as CB2. DAGL- α catalyzes the hydrolysis of DAG to synthesize 2-AG, which acts as a chief endogenous CB2 ligand. Our initial studies suggested a role of CB2 and not CB1 in protection, leading us to focus on CB2 receptors for subsequent studies. Aim 2 examined the otoprotective role of trans-tympanic application of CB2 specific agonist (JWH-015) against cisplatin-induced hearing loss in male Wistar rats. Activation of CB2 receptors restored cisplatin-induced elevations in ABR thresholds which was significantly reversed by CB2 antagonist AM-630. Pre-treatment with JWH-015 protected against cisplatin-induced loss of hair cell and synaptic ribbons. In-vitro studies in UB/OC-1 cells demonstrated that pre-treatment of JWH-015 modulates the activities of signal transducer and activator of transcription 1 and 3 (STAT1 and STAT3), increases the expression of anti-apoptotic protein Bcl-xL, indicating its role in regulating the apoptosis Activation of CB2 also abrogated cisplatin-induced decrease in Na+/K+ATPase- α in the SV and SL fibrocytes and ameliorated the expression of different pro-inflammatory genes including TRPV1, COX2, NOX3, KIM1, iNOS and TNF- α. We also found that blocking of CB2 by AM630 itself resulted in hearing loss and loss in CB2 receptors, indicating eCB system is tonically active and could be important for physiological function of the cochlea. Indeed, we observed that inhibition of DAGL- α by RHC80267 results in HL. Aim 3 of this current study investigated whether pre-treatment of CB2 agonist will interfere with anti-cancer efficacy of cisplatin against various cancer cell lines head and neck cancer cells (UMSCC10B), and colon cancer cells (HCT116). Our data indicate that JWH-015 did not interfere with cisplatin-induced apoptosis in these cells. Overall, this study provides novel insights into the essential role eCBs plays in protection the cochlea under non-stressed conditions and following exposure to ototoxic agents. It also demonstrates that application of exogenous CB2 agonist (JWH-015) could serve as an effective protective agent against cisplatin ototoxicity These data suggest that localized delivery of CB2 agonists should be studied in human for protection against hearing loss.
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Tobin, Mélanie. "Gradients in the mechanical properties of auditory hair cells". Thesis, Sorbonne Paris Cité, 2016. http://www.theses.fr/2016USPCC183/document.
Testo completoAbstract (sommario):
Notre capacité à communiquer et à apprécier la musique repose sur une discrimination de fréquences couvrant une large gamme de fréquences sonores. Cette propriété résulte de cellules mécanosensorielles « ciliées », qui sont réglées pour répondre de façon maximale à une fréquence caractéristique qui varie monotoniquement le long de l’axe de l’organe auditif, la cochlée. Les mécanismes cellulaires et moléculaires qui définissent la fréquence d’une cellule ciliée et régulent sa valeur pour différentes cellules afin de couvrir la gamme auditive demeurent néanmoins inconnus. Notre hypothèse de travail est que cette fréquence est réglée en partie par les propriétés mécaniques passives et actives de la « touffe ciliaire », l’antenne mécanosensorielle de la cellule ciliée. A l’aide d’une préparation excisée de la cochlée du rat, nous avons combiné l’iontophorèse de chélateurs de calcium (BAPTA ou EDTA) pour casser les liens de bout-de-cil qui connectent les stéréocils voisins de la touffe ciliaire, une stimulation grâce à un micro-jet de fluide pour estimer la raideur de la touffe ciliaire et des enregistrements en « patch-clamp » de courants de transduction afin de compter le nombre de liens de bout-de-cil intacts qui contribuent à la réponse. Avec les mouvements évoqués par la rupture des liens de bout-de-cil et avec nos mesures de raideur, nous avons pu estimer la tension dans toute la touffe ciliaire, ainsi que la tension dans un seul lien de bout-de-cil en connaissant le nombre de liens qui contribuent à cette tension. Dans les cellules ciliées externes, qui sont impliquées dans l’amplification du stimulus sonore mais qui n’envoient pas d’information neuronale au cerveau, nous avons observé un gradient de tension et de raideur lorsque la fréquence caractéristique de la cellule ciliée augmente, suggérant que ces paramètres physiques peuvent être impliqués dans le réglage d’une cellule ciliée à sa fréquence caractéristique. Au contraire, pour les cellules ciliées internes, les vraies cellules sensorielles de la cochlée, nos observations ne montrent pas de gradient significatif. De plus, nous avons observé des mouvements de la touffe ciliaire induits par la variation de la concentration en calcium, correspondant à une tension accrue pour des concentrations en calcium plus faibles. Ces mouvements sont similaires à ceux évoqués dans d’autres classes de vertébrés, tels que chez la grenouille ou chez la tortue. Ainsi, nos résultats réconcilient les expériences faites chez les vertébrés inférieurs et chez le mammifère, et montrent l’implication des gradients de la mécanique de la touffe ciliaire pour l’importante sélectivité fréquentielle de la cochléeOur ability to communicate and appreciate music relies on acute frequency discrimination over a broad range of sound frequencies. This property results from the operation of mechanosensory “hair" cells, which are each tuned to respond maximally to a characteristic frequency that varies monotonically along the axis of the auditory organ, the cochlea. The cellular and molecular mechanisms that set the characteristic frequency of a hair cell and regulate its value among different cells to cover the auditory range have remained elusive. Our working hypothesis is that tuning results in part from passive and active mechanical properties of the “hair" bundle, the mechanosensory antenna of the hair cell.Using an excised preparation from the rat cochlea, we combined iontophoresis of a calcium chelator (BAPTA or EDTA) to break the tip links that interconnect neighbouring stereocilia of the hair-cell bundle, fluid-jet stimulation to estimate hair-bundle stiffness and patch-clamp recordings of transduction currents to count the number of intact transduction channels contributing to the response. From the movements evoked by tip-link breakage and our stiffness measurements, we were able to estimate tension in the whole hair bundle as well as, knowing the number of tip links contributing to this tension, in a single tip link.In outer hair cells, which are involved in sound amplification but do not send neural information to the brain, we observed a gradient of tension and stiffness from the low-frequency to the high-frequency end of the cochlea, suggesting that these physical parameters may help tune the hair cell to its characteristic frequency. Interestingly, with inner hair cells - the true sensors of the cochlea, our observations do not show any significant gradient. Furthermore, we observed calcium-evoked hair-bundle movements corresponding to an increased tension in the tip links at decreased concentrations of calcium. These movements were similar to those evoked in other classes of vertebrates, such as the frog or the turtle. Together, our results reconcile experiments performed in lower vertebrates with those performed in mammals and show the implication of hair-bundle mechanical gradients in the sharp frequency tuning of the cochlea
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Berninger, Erik. "Quinine as a model for the study of cochlear hearing loss in humans /". Stockholm, 2000. http://diss.kib.ki.se/2000/91-628-4272-2/.
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