Browse - AIP Conference Proceedings

Select this Article FREE

Preface: What Fire is in Mine Ears: Progress in Auditory Biomechanics

Christopher Shera and Elizabeth Olson

AIP Conf. Proc. 1403, pp. 1-1; doi:http://dx.doi.org/10.1063/1.3658051 (1 page)

Online Publication Date: 7 November 2011

Full Text: Download PDF

Abstract Unavailable

+

Show PACS

43.64.Bt	Models and theories of the auditory system
43.64.Kc	Cochlear mechanics
43.64.Ha	Acoustical properties of the outer ear; middle-ear mechanics and reflex

Select this Article FREE

MoH 101: Basic Concepts in the Mechanics of Hearing

Christopher Bergevin, Bastian Epp, and Sebastiaan W. F. Meenderink

AIP Conf. Proc. 1403, pp. 7-14; doi:http://dx.doi.org/10.1063/1.3658052 (8 pages)

Online Publication Date: 7 November 2011

Full Text: Download PDF

+

Show Abstract

We provide a synopsis of selected questions and answers from the second triennial Mechanics of Hearing 101 session held at the 11th International Mechanics of Hearing Workshop in Williamstown, Massachusetts. The MoH 101 session offers a non‐intimidating forum for students, postdocs, and others new to the field to explore issues and ideas relevant to the Workshop. We have augmented the discussion content by giving some basic background and references.

+

Show PACS

43.64.Dw	Anatomy of the cochlea and auditory nerve
02.30.Oz	Bifurcation theory
43.64.Fy	Anatomy of the auditory central nervous system
43.64.Nf	Cochlear electrophysiology

Select this Article FREE

Damping Properties of the Hair Bundle

Johannes Baumgart, Andrei S. Kozlov, Thomas Risler, and A. J. Hudspeth

AIP Conf. Proc. 1403, pp. 17-24; doi:http://dx.doi.org/10.1063/1.3658053 (8 pages)

Online Publication Date: 7 November 2011

Full Text: Download PDF

+

Show Abstract

The viscous liquid surrounding a hair bundle dissipates energy and dampens oscillations, which poses a fundamental physical challenge to the high sensitivity and sharp frequency selectivity of hearing. To identify the mechanical forces at play, we constructed a detailed finite‐element model of the hair bundle. Based on data from the hair bundle of the bullfrog's sacculus, this model treats the interaction of stereocilia both with the surrounding liquid and with the liquid in the narrow gaps between the individual stereocilia. The investigation revealed that grouping stereocilia in a bundle dramatically reduces the total drag. During hair‐bundle deflections, the tip links potentially induce drag by causing small but very dissipative relative motions between stereocilia; this effect is offset by the horizontal top connectors that restrain such relative movements at low frequencies. For higher frequencies the coupling liquid is sufficient to assure that the hair bundle moves as a unit with a low total drag. This work reveals the mechanical characteristics originating from hair‐bundle morphology and shows quantitatively how a hair bundle is adapted for sensitive mechanotransduction.

+

Show PACS

43.64.Ld	Physiology of hair cells
47.85.lb	Drag reduction
43.66.Fe	Discrimination: intensity and frequency
02.70.Dh	Finite-element and Galerkin methods

Select this Article FREE

New Devices for Investigating Hair Cell Mechanical Properties

Joseph C. Doll, Anthony Peng, Anthony Ricci, and Beth L. Pruitt

AIP Conf. Proc. 1403, pp. 25-26; doi:http://dx.doi.org/10.1063/1.3658054 (2 pages)

Online Publication Date: 7 November 2011

Full Text: Download PDF

+

Show Abstract

Cochlear hair cell mechanics are typically probed using a flexible glass fiber. Fibers are individually produced and can vary substantially in their mechanical properties. The fiber is actuated using a macroscale piezoelectric stack and the fiber deflection is monitored optically, which both have a variety of limitations. We have developed micromachined silicon force probes that improve upon these characteristics.

+

Show PACS

43.64.Dw	Anatomy of the cochlea and auditory nerve
43.64.Ld	Physiology of hair cells
43.64.Nf	Cochlear electrophysiology
72.20.Fr	Low-field transport and mobility; piezoresistance

Select this Article FREE

Hair Bundle Dynamics Under Steady‐State Deflection

Lea Fredrickson‐Hemsing, Seung Ji, Robjin Bruinsma, and Dolores Bozovic

AIP Conf. Proc. 1403, pp. 27-31; doi:http://dx.doi.org/10.1063/1.3658055 (5 pages)

Online Publication Date: 7 November 2011

Full Text: Download PDF

+

Show Abstract

Spontaneous oscillations exhibited by stereociliary bundles of the bullfrog sacculus provide a useful probe for the study of the hair cells' internal dynamic state. We apply deflections to hair cell bundles both in the form of steady‐state offsets and slow ramps. We find that these offsets lead to significant modulation of the characteristic frequency of response, exhibiting characteristics of an infinite‐period bifurcation in addition to a supercritical Hopf bifurcation.

+

Show PACS

43.64.Ld	Physiology of hair cells
43.64.Kc	Cochlear mechanics
43.66.Fe	Discrimination: intensity and frequency
02.30.Oz	Bifurcation theory

Select this Article FREE

Sound‐Evoked Length Changes of the Outer Hair Cell Stereocilia Bundle are Modulated by Endocochlear Currents

Pierre Hakizimana, William E. Brownell, Stefan Jacob, and Anders Fridberger

AIP Conf. Proc. 1403, pp. 32-37; doi:http://dx.doi.org/10.1063/1.3658056 (6 pages)

Online Publication Date: 7 November 2011

Full Text: Download PDF

+

Show Abstract

The apical surface of vertebrate inner ear sensory cells is characterized by a bundle of giant microvilli commonly known as stereocilia. Stereocilia bend about a neck‐like thinning near their base and more than three decades of research has established that the direction and magnitude of sideways bundle deflection is the basis of the mechanoelectrical signalling that initiates sound perception. Aside from its ability to bend at the neck, the stereocilium is usually considered as a stiff inelastic rod. Here we show that the length of OHC stereocilia changes during sound transduction, demonstrating their axial compliance, and that the magnitude of the length change is modulated by currents that mimic in vivo endocochlear currents. A reciprocal relation between length change and bundle deflection is evident: the smaller the length changes, the larger the bundle deflection.

+

Show PACS

43.64.Nf	Cochlear electrophysiology
43.66.Gf	Detection and discrimination of sound by animals
87.64.mk	Confocal
82.45.Fk	Electrodes

Select this Article FREE

Effects of Electrical and Mechanical Overstimulus on Spontaneous Oscillations in Hair Bundles

Albert Kao, C. Elliott Strimbu, and Dolores Bozovic

AIP Conf. Proc. 1403, pp. 38-43; doi:http://dx.doi.org/10.1063/1.3658057 (6 pages)

Online Publication Date: 7 November 2011

Full Text: Download PDF

+

Show Abstract

Spontaneous oscillations constitute one of the manifestations of the active process operant in hair cells and provides a sensitive probe for their internal dynamics. The influx of ions into the stereocilia can be modulated by applying an electrical current across the epithelium and has been previously shown to strongly affect the oscillatory profiles. We applied strong transient stimuli and demonstrated that they can induce a transition from the oscillatory to the quiescent state, an effect that can last over several seconds post stimulus cessation. The dynamics of recovery to the oscillatory state was found to be dependent on the amplitude and the duration of the stimulus. Similar dynamics were observed after high‐amplitude mechanical stimulus, which mimics the effects of loud sound on an individual bundle.

+

Show PACS

43.64.Kc	Cochlear mechanics
43.64.Nf	Cochlear electrophysiology
43.66.Fe	Discrimination: intensity and frequency
02.60.Lj	Ordinary and partial differential equations; boundary value problems

Select this Article FREE

Horizontal Top Connectors Mediate a Sliding Adhesion to Hair Cell Stereocilia

K. D. Karavitaki and D. P. Corey

AIP Conf. Proc. 1403, pp. 44-49; doi:http://dx.doi.org/10.1063/1.3658058 (6 pages)

Online Publication Date: 7 November 2011

Full Text: Download PDF

+

Show Abstract

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

+

Show PACS

46.55.+d	Tribology and mechanical contacts
43.64.Kc	Cochlear mechanics
43.66.Fe	Discrimination: intensity and frequency
87.16.Xa	Signal transduction and intracellular signaling

Select this Article FREE

Elastostatic Analysis of the Membrane Tenting Deformation of Inner‐Ear Stereocilia

Jichul Kim, Peter M. Pinsky, Anthony J. Ricci, Sunil Puria, and Charles R. Steele

AIP Conf. Proc. 1403, pp. 50-52; doi:http://dx.doi.org/10.1063/1.3658059 (3 pages)

Online Publication Date: 7 November 2011

Full Text: Download PDF

+

Show Abstract

The tented shape assumed by the plasma membrane at the top of inner‐ear stereocilia suggests a stretching of the lipid bilayer as a direct result of tension in the tip link (TL). We analyzed a model problem based on the detailed geometry of a stereociliary tip complex. We characterized the elastic properties of the plasma membrane in response to a tip load. The results suggest that the stiffness of the membrane deformation due to the TL load may serve as the hair‐cell gating spring.

+

Show PACS

87.19.lt	Sensory systems: visual, auditory, tactile, taste, and olfaction
43.64.Nf	Cochlear electrophysiology
43.64.Kc	Cochlear mechanics
43.64.Ld	Physiology of hair cells

Select this Article FREE

Dynamic Aspects of Cochlear Microphonic Potentials

Sebastiaan W. F. Meenderink and Marcel van der Heijden

AIP Conf. Proc. 1403, pp. 53-58; doi:http://dx.doi.org/10.1063/1.3658060 (6 pages)

Online Publication Date: 7 November 2011

Full Text: Download PDF

+

Show Abstract

Cochlear microphonic potentials were recorded from the Mongolian gerbil in response to low‐frequency auditory stimuli. Provided that contamination of the potentials by the phase‐locked neurophonic is avoided, these recordings can be interpreted “as if recorded from a single outer hair cell”. It is found that the instantaneous I∕O‐curves resemble the well‐known Boltzmann activation curve. The dynamic aspect of the I∕O‐curves does reveal hysteresis and a level‐dependent gain that is not observed in static measures of these curves. We explore a model that simulates CM generation from hair cell populations, but find it inadequate to reproduce the data. Rather, there seem to be fast, adaptive mechanisms probably at the level of the transduction channels themselves.

+

Show PACS

87.19.lt	Sensory systems: visual, auditory, tactile, taste, and olfaction
43.66.Fe	Discrimination: intensity and frequency
43.71.Qr	Neurophysiology of speech perception
43.64.Kc	Cochlear mechanics

Select this Article FREE

High‐Pass Filtering at Vestibular Frequencies by Transducer Adaptation in Mammalian Saccular Hair Cells

Jocelyn E. Songer and Ruth Anne Eatock

AIP Conf. Proc. 1403, pp. 59-63; doi:http://dx.doi.org/10.1063/1.3658061 (5 pages)

Online Publication Date: 7 November 2011

Full Text: Download PDF

+

Show Abstract

The mammalian saccule detects head tilt and low‐frequency head accelerations as well as higher‐frequency bone vibrations and sounds. It has two different hair cell types, I and II, dispersed throughout two morphologically distinct regions, the striola and extrastriola. Afferents from the two zones have distinct response dynamics which may arise partly from zonal differences in hair cell properties. We find that type II hair cells in the rat saccular epithelium adapt with a time course appropriate for influencing afferent responses to head motions. Moreover, striolar type II hair cells adapted by a greater extent than extrastriolar type II hair cells and had greater phase leads in the mid‐frequency range (5–50 Hz). These differences suggest that hair cell transduction may contribute to zonal differences in the adaptation of vestibular afferents to head motions.

+

Show PACS

43.66.Wv	Vibration and tactile senses
43.64.Dw	Anatomy of the cochlea and auditory nerve
43.64.Nf	Cochlear electrophysiology
43.66.Fe	Discrimination: intensity and frequency

Select this Article FREE

Molecular Mechanics of Tip‐Link Cadherins

Marcos Sotomayor, Wilhelm A. Weihofen, Rachelle Gaudet, and David P. Corey

AIP Conf. Proc. 1403, pp. 64-69; doi:http://dx.doi.org/10.1063/1.3658062 (6 pages)

Online Publication Date: 7 November 2011

Full Text: Download PDF

+

Show Abstract

The hair‐cell tip link, a fine filament directly conveying force to mechanosensitive transduction channels, is likely composed of two proteins, protocadherin‐15 and cadherin‐23, whose mutation causes deafness. However, their complete molecular structure, elasticity, and deafness‐related structural defects remain largely unknown. We present crystal structures of extracellular (EC) tip‐link cadherin repeats involved in hereditary deafness and tip link formation. In addition, we show that the deafness mutation D101G, in the linker region between the repeats EC1 and EC2 of cadherin‐23, causes a slight bend between repeats and decreases Ca²⁺ affinity. Molecular dynamics simulations suggest that tip‐link cadherin repeats are stiff and that either removing Ca²⁺ or mutating Ca²⁺‐binding residues reduces rigidity and unfolding strength. The structures and simulations also suggest mechanisms underlying inherited deafness and how cadherin‐23 may bind with protocadherin‐15 to form the tip link.

+

Show PACS

43.64.Ld	Physiology of hair cells
43.64.Kc	Cochlear mechanics
87.16.Xa	Signal transduction and intracellular signaling
87.14.E-	Proteins

Select this Article FREE

Exploring the Role of Mechanotransduction Activation and Adaptation Kinetics in Hair Cell Filtering Using a Hodgkin‐Huxley Approach

Gregg B. Wells and Anthony J. Ricci

AIP Conf. Proc. 1403, pp. 70-75; doi:http://dx.doi.org/10.1063/1.3658063 (6 pages)

Online Publication Date: 7 November 2011

Full Text: Download PDF

+

Show Abstract

In the auditory system, mechanotransduction occurs in the hair cell sensory hair bundle and is the first major step in the translation of mechanical energy into electrical. Tonotopic variations in the activation kinetics of this process are posited to provide a low pass filter to the input. An adaptation process, also associated with mechanotransduction, is postulated to provide a high pass filter to the input in a tonotopic manner. Together a bandpass filter is created at the hair cell input. Corresponding mechanical components to both activation and adaptation are also suggested to be involved in generating cochlear amplification. A paradox to this story is that hair cells where the mechanotransduction properties are most robust possess an intrinsic electrical resonance mechanism proposed to account for all required tuning and amplification. A simple Hodgkin‐Huxley type model is presented to attempt to determine the role of the activation and adaptation kinetics in further tuning hair cells that exhibit electrical resonance. Results further support that steady state mechanotransduction properties are critical for setting the resting potential of the hair cell while the kinetics of activation and adaptation are important for sharpening tuning around the characteristic frequency of the hair cell.

+

Show PACS

43.64.Kc	Cochlear mechanics
43.64.Pg	Electrophysiology of the auditory nerve
43.64.Ld	Physiology of hair cells
87.16.Xa	Signal transduction and intracellular signaling

Select this Article FREE

Time Domina One‐Dimensional Cochlear Model with Integrated Tectorial Membrane and Outer Hair Cells

Oded Barzelay and Miriam Furst

AIP Conf. Proc. 1403, pp. 79-84; doi:http://dx.doi.org/10.1063/1.3658064 (6 pages)

Online Publication Date: 7 November 2011

Full Text: Download PDF

+

Show Abstract

Recent studies of the tectorial membrane (TM) revealed mechanical properties that are changing along the cochlear partition. In our previous cochlear model, the basilar membrane (BM) motion was derived from the cochlear fluid dynamics along with the outer hair cells (OHCs) electromotility force. In order to achieve a match between the resonances of both the BM and the OHCs gain, a set of constraints were obtained. In particular, the OHCs electrical properties were changed along the cochlear partition. However, although plausible differences found between conductance of the OHCs at different locations along the Cochlea, it seems negligible compared to the change in the characteristic frequency. In the current model the TM is included in the model. Since the OHCs are embedded in the TM, we assume that they are gaining their electromotility force from both the BM and TM. The electrical properties of the OHCs are held constant along the cochlear partition, while the TM stiffness and resistance are changing along the cochlear partition in correspondence to the BM dependence. The boundary conditions were derived from the middle ear model. A non‐linear, odd‐order, mechanism related to the OHCs motility was included in the model. The OHCs length change depends nonlinearly on its membrane electrical potential. The model was solved numerically in the time domain in response to various input signals. The basilar and tectorial membranes gain were derived for a wide range of input levels and frequencies. Both BM and TM revealed traveling waves with a maximum response for every input frequency at the same distance from the stapes. The BM sensitivity gain was greater than that of the TM. The difference between the two increased with the increase of the input level.

+

Show PACS

46.40.Ff	Resonance, damping, and dynamic stability
43.64.Ha	Acoustical properties of the outer ear; middle-ear mechanics and reflex
43.64.Nf	Cochlear electrophysiology
43.66.Fe	Discrimination: intensity and frequency

Select this Article FREE

Tectorial Membrane Traveling Waves Underlie Impaired Hearing in Tectb Mutant Mice

Roozbeh Ghaffari, Shirin Farrahi, Alexander J. Aranyosi, Guy P. Richardson, and Dennis M. Freeman

AIP Conf. Proc. 1403, pp. 85-89; doi:http://dx.doi.org/10.1063/1.3658065 (5 pages)

Online Publication Date: 7 November 2011

Full Text: Download PDF

+

Show Abstract

We show that the Tectb mutation reduces the spatial extent and propagation velocity of tectorial membrane (TM) traveling waves. These results can account for all of the hearing abnormalities associated with the Tectb mutation, as follows. By reducing the spatial extent of TM waves, the Tectb mutation decreases spread of excitation and thereby increases frequency selectivity at mid‐ to high frequencies. Furthermore, the decrease in Tectb TM wave velocity at low frequencies reduces the number of hair cells that effectively couple energy to the basilar membrane, which thereby reduces sensitivity.

+

Show PACS

43.66.Fe	Discrimination: intensity and frequency
43.64.Ld	Physiology of hair cells
43.64.Tk	Physiology of sound generation and detection by animals
43.20.Bi	Mathematical theory of wave propagation

Select this Article FREE

Mechanical Excitation of IHC Stereocilia: An Attempt to Fit Together Diverse Evidence

John J. Guinan, Jr.

AIP Conf. Proc. 1403, pp. 90-96; doi:http://dx.doi.org/10.1063/1.3658066 (7 pages)

Online Publication Date: 7 November 2011

Full Text: Download PDF

+

Show Abstract

The output of the cochlea is controlled by the bending of inner‐hair‐cell (IHC) stereocilia, but the mechanisms that produce this bending are poorly understood. Relevant evidence comes from several sources: measurements of cochlear motion from in‐vitro and live preparations, as well as inferences about cochlear motions from responses of auditory‐nerve fibers. The common conception that IHC excitation is due to shearing between the reticular lamina (RL) and the tectorial membrane (TM) does not explain the data. A hypothesis is presented that fits many of the observations into a coherent picture of how IHCs are excited. The key new concept is that stretching of outer‐hair‐cell (OHC) stereocilia (defined broadly) changes the RL‐TM gap and produces fluid flow within the gap that bends the IHC stereocilia. Changes in the RL‐TM gap and the resulting bending of IHC stereocilia provide a mechanism by which OHC active processes can enhance cochlear output without a corresponding enhancement of basilar‐membrane motion.

+

Show PACS

43.64.Ld	Physiology of hair cells
43.64.Ha	Acoustical properties of the outer ear; middle-ear mechanics and reflex
43.64.Nf	Cochlear electrophysiology
46.55.+d	Tribology and mechanical contacts
43.66.Fe	Discrimination: intensity and frequency

Select this Article FREE

Unraveling Traveling Waves Using WKB Modeling

Jessica S. Lamb and Richard S. Chadwick

AIP Conf. Proc. 1403, pp. 97-103; doi:http://dx.doi.org/10.1063/1.3658067 (7 pages)

Online Publication Date: 7 November 2011

Full Text: Download PDF

+

Show Abstract

We calculate traveling waves in the cochlear partition using a WKB‐based mechanical model in which motions of the fluid‐interacting tectorial membrane (TM) and basilar membrane (BM) are degrees of freedom. We find that the two modes of motion that result manifest themselves as two traveling waves, each carried on both the BM and on the TM. The waves produce distinct tuning curves for the TM and the BM. We discuss the influence of the TM and coupling stiffnesses on the waves and tuning curves. We speculate how the two modes of motion we calculate and the differential motions they cause could influence the cochlear amplifier. We also discuss the possibility that mode conversion could occur in the cochlea.

+

Show PACS

43.64.Dw	Anatomy of the cochlea and auditory nerve
43.66.Fe	Discrimination: intensity and frequency
43.66.Wv	Vibration and tactile senses
41.20.Cv	Electrostatics; Poisson and Laplace equations, boundary-value problems

Select this Article FREE

Coupling the Subtectorial Fluid with the Tectorial Membrane and Hair Bundles of the Cochlea

Yizeng Li, Julien Meaud, and Karl Grosh

AIP Conf. Proc. 1403, pp. 104-109; doi:http://dx.doi.org/10.1063/1.3658068 (6 pages)

Online Publication Date: 7 November 2011

Full Text: Download PDF

+

Show Abstract

Two different kinds of flow—(i) shearing of fluid between the reticular lamina (RL) and tectorial membrane (TM) and (ii) so‐called pulsating flow in the RL‐TM gap—have been implicated as the dominant source of fluidic stimulation of the inner hair cell (IHC) hair bundle (HB). However, the frequency and spatial dependence of these flows for IHC stimulation is unresolved in vivo and estimates of the effect of the cochlear amplifier on these flows has not been quantified. Indeed, the relative importance these flow modalities and active processes likely varies with tonotopic location. In this paper, a microfluidic model is developed which features the interaction of the subtectorial fluid with the TM, IHC HBs, and the outer hair cell HBs. The framework of the model allows for incorporation into active macroscopic models as well as for comparison of experiments performed on excised sections of the cochlea.

+

Show PACS

43.64.Ld	Physiology of hair cells
43.66.Fe	Discrimination: intensity and frequency
43.64.Pg	Electrophysiology of the auditory nerve
43.64.Dw	Anatomy of the cochlea and auditory nerve

Select this Article FREE

The Effect of Superior Semicircular Canal Dehiscence on Intracochlear Sound Pressures

Hideko Heidi Nakajima, Dominic V. Pisano, Saumil N. Merchant, and John J. Rosowski

AIP Conf. Proc. 1403, pp. 110-115; doi:http://dx.doi.org/10.1063/1.3658069 (6 pages)

Online Publication Date: 7 November 2011

Full Text: Download PDF

+

Show Abstract

Semicircular canal dehiscence (SCD) is a pathological opening in the bony wall of the inner ear that can result in conductive hearing loss. The hearing loss is variable across patients, and the precise mechanism and source of variability is not fully understood. We use intracochlear sound pressure measurements in cadaveric preparations to study the effects of SCD size. Simultaneous measurement of basal intracochlear sound pressures in scala vestibuli (SV) and scala tympani (ST) quantifies the complex differential pressure across the cochlear partition, the stimulus that excites the partition. Sound‐induced pressures in SV and ST, as well as stapes velocity and ear‐canal pressure are measured simultaneously for various sizes of SCD followed by SCD patching. At low frequencies (<600 Hz) our results show that SCD decreases the pressure in both SV and ST, as well as differential pressure, and these effects become more pronounced as dehiscence size is increased. For frequencies above 1 kHz, the smallest pinpoint dehiscence can have the larger effect on the differential pressure in some ears. These effects due to SCD are reversible by patching the dehiscence.

+

Show PACS

43.64.Bt	Models and theories of the auditory system
43.64.Dw	Anatomy of the cochlea and auditory nerve
43.66.Fe	Discrimination: intensity and frequency
43.20.Hq	Velocity and attenuation of acoustic waves

Select this Article FREE

Biophysical Mechanisms Underlying Hearing Loss Associated with a Shortened Tectorial Membrane

John S. Oghalai, Anping Xia, Christopher C. Liu, Simon S. Gao, Brian E. Applegate, Sunil Puria, Itay Rousso, and Charles Steele

AIP Conf. Proc. 1403, pp. 116-121; doi:http://dx.doi.org/10.1063/1.3658070 (6 pages)

Online Publication Date: 7 November 2011

Full Text: Download PDF

+

Show Abstract

The tectorial membrane (TM) connects to the stereociliary bundles of outer hair cells (OHCs). Herein, we summarize key experimental data and modeling analyses that describe how biophysical alterations to these connections underlie hearing loss. The heterozygous C1509G mutation in alpha tectorin produces partial congenital hearing loss that progresses in humans. We engineered this mutation in mice, and histology revealed that the TM was shortened. DIC imaging of freshly‐dissected cochlea as well as imaging with optical coherence tomography indicated that the TM is malformed and only stimulates the first row of OHCs. Noise exposure produced acute threshold shifts that fully recovered in Tecta^+/+ mice although there was some OHC loss within all three rows at the cochlear base. In contrast, threshold shifts only partially recovered in Tecta^C1509G/+ mice. This was associated with OHC loss more apically and nearly entirely within the first row. Young′s modulus of the TM, measured using atomic force microscopy, was substantially reduced at the middle and basal regions. Both the wild‐type and heterozygous conditions were simulated in a computational model. This demonstrated that the normalized stress distribution levels between the TM and the tall cilia were significantly elevated in the middle region of the heterozygous cochlea. Another feature of the Tecta^C1509G/+ mutation is higher prestin expression within all three rows of OHCs. This increased electricallyevoked movements of the reticular lamina and otoacoustic emissions. Furthermore, electrical stimulation was associated with an increased risk of OHC death as measured by vital dye staining. Together, these findings indicate that uncoupling of the TM from some OHCs not only leads to partial hearing loss, but also puts the OHCs that remain coupled at higher risk. Both the mechanics of the malformed TM and increased electromotility contribute to this higher risk profile.

+

Show PACS

43.64.Bt	Models and theories of the auditory system
43.64.Jb	Otoacoustic emissions
43.64.Ld	Physiology of hair cells
43.66.Fe	Discrimination: intensity and frequency

Select this Article FREE

Numerical Study of the Complex Temporal Pattern of Spontaneous Oscillation in Bullfrog Saccular Hair Cells

Yuttana Roongthumskul, Lea Fredrickson‐Hemsing, Albert Kao, and Dolores Bozovic

AIP Conf. Proc. 1403, pp. 122-127; doi:http://dx.doi.org/10.1063/1.3658071 (6 pages)

Online Publication Date: 7 November 2011

Full Text: Download PDF

+

Show Abstract

Hair bundles of the bullfrog sacculus display spontaneous oscillations that show complex temporal profiles. Quiescent intervals are typically interspersed with oscillations, analogous to bursting behavior observed in neural systems. By introducing slow calcium dynamics into the theoretical model of bundle mechanics, we reproduce numerically the multi‐mode oscillations and explore the effects of internal parameters on the temporal profiles and the frequency tuning of their linear response functions. We also study the effects of mechanical overstimulation on the oscillatory behavior.

+

Show PACS

43.64.Dw	Anatomy of the cochlea and auditory nerve
43.64.Ld	Physiology of hair cells
43.28.Js	Numerical models for outdoor propagation
43.80.Lb	Sound reception by animals: anatomy, physiology, auditory capacities, processing

Select this Article FREE

Magnetic Bead Actuation of Saccular Hair Cells

David Rowland, Damien Ramunno‐Johnson, Jae‐Hyun Lee, Jinwoo Cheon, and Dolores Bozovic

AIP Conf. Proc. 1403, pp. 128-132; doi:http://dx.doi.org/10.1063/1.3658072 (5 pages)

Online Publication Date: 7 November 2011

Full Text: Download PDF

+

Show Abstract

When decoupled from the overlying membrane, hair bundles of the amphibian sacculus exhibit spontaneous oscillation. To explore the dynamics of this innate motility without an imposed external load, we recorded their oscillations with a high‐speed CMOS camera, and applied mechanical manipulation that minimally alters the geometry of an individual hair bundle. We present a technique that utilizes micron‐sized magnetic particles to actuate the stereociliary bundle with a magnetized probe. Quasi‐steady‐state displacements were imposed on freely oscillating bundles. Our data indicate that deflection of the bundle affects both the frequency and the amplitude of the oscillations, with a crossing of the bifurcation that is dependent on the direction and speed of the applied offset.

+

Show PACS

43.64.Dw	Anatomy of the cochlea and auditory nerve
43.64.Ld	Physiology of hair cells
43.80.Lb	Sound reception by animals: anatomy, physiology, auditory capacities, processing
02.30.Oz	Bifurcation theory

Select this Article FREE

Active Motion of Hair Bundles Coupled to the Otolithic Membrane in the Frog Sacculus

C. Elliott Strimbu, Lea Fredrickson‐Hemsing, and Dolores Bozovic

AIP Conf. Proc. 1403, pp. 133-138; doi:http://dx.doi.org/10.1063/1.3658073 (6 pages)

Online Publication Date: 7 November 2011

Full Text: Download PDF

+

Show Abstract

Active hair bundle motility has been proposed to provide the basis for the active process in the auditory organs of non‐mammalian vertibrates, and has been extensively studied in mechanically decoupled or free‐standing hair bundles from in vitro preparations of the frog sacculus. A number of studies have, however, suggested that cooperativity between hair cells plays an important role in the response of an intact organ. We use a semi‐intact in vitro saccular preparation in which the hair cells are coupled and loaded by the otolithic membrane. While the hair bundles do not spontaneously oscillate beneath the membrane, they exhibit active movements in response to transient stimuli, demonstrating that the active process remains operant under these conditions. The coupled system however displays a striking decrease in frequency selectivity compared to freely oscillating bundles.

+

Show PACS

43.64.Dw	Anatomy of the cochlea and auditory nerve
43.64.Bt	Models and theories of the auditory system
43.66.Fe	Discrimination: intensity and frequency
05.45.Xt	Synchronization; coupled oscillators

Select this Article FREE

Otoancorin Knockout Mice Reveal Inertia is the Force for Hearing

Thomas Weddell, P. Kevin Legan, Victoria A. Lukashkina, Richard J. Goodyear, Lindsy Welstead, Chistine Petit, Ian J. Russell, Andrei N. Lukashkin, and Guy P. Richardson

AIP Conf. Proc. 1403, pp. 139-140; doi:http://dx.doi.org/10.1063/1.3658074 (2 pages)

Online Publication Date: 7 November 2011

Full Text: Download PDF

+

Show Abstract

We demonstrate that in Otoa^−/− mice, in which the inner‐ear‐specific protein otoancorin is absent, excitation of the outer hair cells and cochlear amplification is normal. This finding is remarkable because the tectorial membrane (TM), although remaining functionally attached to the outer hair cell bundles, is completely detached from the spiral limbus. Therefore, as in ancestral vertebrate auditory organs, where inertia provides the excitatory force to the hair cells, it is the inertia of the TM that must be important for exciting the outer hair cells, setting the sensitivity of their transducer conductance, and determining the precise timing of cochlear amplification.

+

Show PACS

43.64.Dw	Anatomy of the cochlea and auditory nerve
43.64.Ha	Acoustical properties of the outer ear; middle-ear mechanics and reflex
43.64.Tk	Physiology of sound generation and detection by animals
43.38.Kb	Microphones and their calibration
43.66.Dc	Masking

Select this Article FREE

Evaluating Prestin's Changing Biophysical Attributes in Development Using a Tet‐Induced Cell Line

Shumin Bian, Bon W. Koo, Stephen Kelleher, Joseph Santos‐Sacchi, and Dhasakumar Navaratnam

AIP Conf. Proc. 1403, pp. 143-147; doi:http://dx.doi.org/10.1063/1.3658075 (5 pages)

Online Publication Date: 7 November 2011

Full Text: Download PDF

+

Show Abstract

The motor protein prestin is a member of the SLC26 anion transporter family, and expressed in the lateral wall of OHCs. It is now widely recognized that prestin is required for mammalian cochlear amplification. Expression of prestin precedes the onset of hearing in mice and undergoes a functional maturation within the membrane coincident with the onset of hearing. We have developed several tetracycline‐inducible prestin expressing cell lines that duplicate prestins functional maturation in vivo. Thus, following induction there is an initial stage of increase in the charge carried by an individual motor (z) that accompanies a phase of slow growth in charge density. A plateau in z follows and is accompanied by rapid increase in charge density. The latter strongly correlates with an increasing ratio between an apparently larger and smaller monomer of prestin, suggesting that the latter exerts a dominant negative effect on function. Through the experimental period there is a progressive shift in the voltage of peak capacitance, similar to that observed in developing OHCs. Finally, we observed a non‐selective ionic current after induction, the size of which correlated with charge density.

+

Show PACS

43.64.Kc	Cochlear mechanics
43.64.Ha	Acoustical properties of the outer ear; middle-ear mechanics and reflex
43.64.Ld	Physiology of hair cells
43.64.Dw	Anatomy of the cochlea and auditory nerve

Find articles by AUTHORNAME