Sound-Induced Motions of Individual Cochlear Hair Bundles (original) (raw)
Related papers
High-Frequency Force Generation in the Constrained Cochlear Outer Hair Cell: A Model Study
Journal of the Association for Research in Otolaryngology, 2005
Cochlear outer hair cell (OHC) electromotility is believed to be responsible for the sensitivity and frequency selectivity of the mammalian hearing process. Its contribution to hearing is better understood by examining the force generated by the OHC as a feedback to vibration of the basilar membrane (BM). In this study, we examine the effects of the constraints imposed on the OHC and of the surrounding fluids on the cell's high-frequency active force generated under in vitro and in vivo conditions. The OHC is modeled as a viscoelastic and piezoelectric cylindrical shell coupled with viscous intracellular and extracellular fluids, and the constraint is represented by a spring with adjustable stiffness. The solution is obtained in the form of a Fourier series. The model results are consistent with previously reported experiments under both low-and high-frequency conditions. We find that constrained OHCs achieve a much higher corner frequency than free OHCs, depending on the stiffness of the constraint. We analyze cases in which the stiffness of the constraint is similar to that of the BM, reticular lamina, and tectorial membrane, and find that the force per unit transmembrane potential generated by the OHC can be constant up to several tens of kHz. This model, describing the OHC as a local amplifier, can be incorporated into a global cochlear model that considers cochlear hydrodynamics and frequency modulation of the receptor potential, as well as the graded BM stiffness and OHC length.
Effectiveness of Hair Bundle Motility as the Cochlear Amplifier
Biophysical Journal, 2009
The effectiveness of hair bundle motility in mammalian and avian ears is studied by examining energy balance for a small sinusoidal displacement of the hair bundle. The condition that the energy generated by a hair bundle must be greater than energy loss due to the shear in the subtectorial gap per hair bundle leads to a limiting frequency that can be supported by hairbundle motility. Limiting frequencies are obtained for two motile mechanisms for fast adaptation, the channel re-closure model and a model that assumes that fast adaptation is an interplay between gating of the channel and the myosin motor. The limiting frequency obtained for each of these models is an increasing function of a factor that is determined by the morphology of hair bundles and the cochlea. Primarily due to the higher density of hair cells in the avian inner ear, this factor is~10-fold greater for the avian ear than the mammalian ear, which has much higher auditory frequency limit. This result is consistent with a much greater significance of hair bundle motility in the avian ear than that in the mammalian ear.
Static length changes of cochlear outer hair cells can tune low-frequency hearing
PLoS computational biology, 2018
The cochlea not only transduces sound-induced vibration into neural spikes, it also amplifies weak sound to boost its detection. Actuators of this active process are sensory outer hair cells in the organ of Corti, whereas the inner hair cells transduce the resulting motion into electric signals that propagate via the auditory nerve to the brain. However, how the outer hair cells modulate the stimulus to the inner hair cells remains unclear. Here, we combine theoretical modeling and experimental measurements near the cochlear apex to study the way in which length changes of the outer hair cells deform the organ of Corti. We develop a geometry-based kinematic model of the apical organ of Corti that reproduces salient, yet counter-intuitive features of the organ's motion. Our analysis further uncovers a mechanism by which a static length change of the outer hair cells can sensitively tune the signal transmitted to the sensory inner hair cells. When the outer hair cells are in an el...
Outer hair cell active force generation in the cochlear environment
The Journal of the Acoustical Society of America, 2007
Outer hair cells are critical to the amplification and frequency selectivity of the mammalian ear acting via a fine mechanism called the cochlear amplifier, which is especially effective in the high-frequency region of the cochlea. How this mechanism works under physiological conditions and how these cells overcome the viscous ͑mechanical͒ and electrical ͑membrane͒ filtering has yet to be fully understood. Outer hair cells are electromotile, and they are strategically located in the cochlea to generate an active force amplifying basilar membrane vibration. To investigate the mechanism of this cell's active force production under physiological conditions, a model that takes into account the mechanical, electrical, and mechanoelectrical properties of the cell wall ͑membrane͒ and cochlear environment is proposed. It is shown that, despite the mechanical and electrical filtering, the cell is capable of generating a frequency-tuned force with a maximal value of about 40 pN. It is also found that the force per unit basilar membrane displacement stays essentially the same ͑40 pN/ nm͒ for the entire linear range of the basilar membrane responses, including sound pressure levels close to hearing threshold. Our findings can provide a better understanding of the outer hair cell's role in the cochlear amplifier.
Chapter 15. Cochlear Mechanics Cochlear Mechanics Project Staff
2008
The cochlea is responsible for transforming the mechanical vibrations of sound into neural signals that are sent to the brain. The physiological processes underlying this transformation are poorly understood. We have recently presented measurements showing that, in lower vertebrates, mechanical tuning of the sensory hair bundles of receptor cells plays a key role in determining how the cells respond to sound. However, the inner ears of mammals contain specialized structures, such as motile outer hair cells, that are not present in lower vertebrates but play a key role in cochlear function. To study such specializations we have adapted our measurement methods to investigate cochlear mechanics in mammals.
Force generation in the outer hair cell of the cochlea
Biophysical Journal, 1997
The outer hair cell of the mammalian cochlea has a unique motility directly dependent on the membrane potential. Examination of the force generated by the cell is an important step in clarifying the detailed mechanism as well as the biological importance of this motility. We performed a series of experiments to measure force in which an elastic probe was attached to the cell near the cuticular plate and the cell was driven with voltage pulses delivered from a patch pipette under whole-cell voltage clamp. The axial stiffness was also determined with the same cell by stretching it with the patch pipette. The isometric force generated by the cell is around 0.1 nN/mV, somewhat smaller than 0.15 nN/mV, predicted by an area motor model based on mechanical isotropy, but larger than in earlier reports in which the membrane potential was not controlled. The axial stiffness obtained, however, was, on average, 510 nN per unit strain, about half of the value expected from the mechanical isotropy of the membrane. We extended the area motor theory incorporating mechanical orthotropy to accommodate the axial stiffness determined. The force expected from the orthotropic model was within experimental uncertainties.
Pfl�gers Archiv European Journal of Physiology, 1998
The function of the hearing organ is based on mechanical processes occurring at the cellular level. The mechanical properties of guinea-pig isolated sensory cells were investigated using two different techniques. The stiffness of the outer hair cells along the longitudinal axis was measured by compressing the cell body using stiffness-calibrated quartz fibres. For cells with a mean length of 69 µm, the mean axial compression stiffness was 1.1±0.8 mN/m (±SD). There was an inverse relation between stiffness and cell length. The stiffness of the cell membrane perpendicular to the longitudinal axis of the sensory cell was measured by indenting the cell membrane with a known force. The mean lateral indentation stiffness was 3.3±1.5 mN/m (±SD) for cells with a mean length of 64 µm. Longer cells were less stiff than short cells. Modelling the hair cell as a shell with bending resistance, finite element calculations demonstrated that the axial compression stiffness correlated well with the lateral indentation stiffness, and that a simple isotropic model is sufficient to explain the experimental observations despite the different stress strain states produced by the two techniques. The results imply that the two different stiffness properties may originate from the same cytoskeletal structures. It is suggested that the mechanical properties of the outer hair cells are designed to influence the sound-induced motion of the reticular lamina. In such a system, stiffness changes of the outer hair cell bodies could actively control the efficiency of the mechanical coupling between the basilar membrane and the important mechanoelectrical transduction sites at the surface of the hearing organ.
Some observations on cochlear mechanics
Journal of The Acoustical Society of America, 1978
A set of experiments was conducted using the MSssbauer effect to determine the vibratory characteristics of the basilar membrane, Reissner's membrane, the malleus, incus, and oval window in squirrel monkey.
Nanomechanics of the subtectorial space caused by electromechanics of cochlear outer hair cells
Proceedings of the National Academy of Sciences, 2006
the First Cochlear Turn. Although an almost counterphasic motion of the IHC and overlying TM was found for frequencies in the region of the CF in the second cochlear turn , and in the third turn where CF Ͻ3 kHz , the two surfaces were found to move in phase at CF in the first cochlear turn . That is, here there was no evidence of a pulsating mode. On
The Endocochlear Potential Alters Cochlear Micromechanics
Biophysical Journal, 2011
Acoustic stimulation gates mechanically sensitive ion channels in cochlear sensory hair cells. Even in the absence of sound, a fraction of these channels remains open, forming a conductance between hair cells and the adjacent fluid space, scala media. Restoring the lost endogenous polarization of scala media in an in vitro preparation of the whole cochlea depolarizes the hair cell soma. Using both digital laser interferometry and time-resolved confocal imaging, we show that this causes a structural refinement within the organ of Corti that is dependent on the somatic electromotility of the outer hair cells (OHCs). Specifically, the inner part of the reticular lamina up to the second row of OHCs is pulled toward the basilar membrane, whereas the outer part (third row of OHCs and the Hensen's cells) unexpectedly moves in the opposite direction. A similar differentiated response pattern is observed for sound-evoked vibrations: restoration of the endogenous polarization decreases vibrations of the inner part of the reticular lamina and results in up to a 10-fold increase of vibrations of the outer part. We conclude that the endogenous polarization of scala media affects the function of the hearing organ by altering its geometry, mechanical and electrical properties.