Sound-Evoked Radial Strain in the Hearing Organ

AbstractThe hearing organ contains sensory hair cells, which convert sound-evoked vibration into action potentials in the auditory nerve. This process is greatly enhanced by molecular motors that reside within the outer hair cells, but the performance also depends on passive mechanical properties, such as the stiffness, mass, and friction of the structures within the organ of Corti. We used resampled confocal imaging to study the mechanical properties of the low-frequency regions of the cochlea. The data allowed us to estimate an important mechanical parameter, the radial strain, which was found to be 0.1% near the inner hair cells and 0.3% near the third row of outer hair cells during moderate-level sound stimulation. The strain was caused by differences in the motion trajectories of inner and outer hair cells. Motion perpendicular to the reticular lamina was greater at the outer hair cells, but inner hair cells showed greater radial vibration. These differences led to deformation of the reticular lamina, which connects the apex of the outer and inner hair cells. These results are important for understanding how the molecular motors of the outer hair cells can so profoundly affect auditory sensitivity

Successor Liability in Bankruptcy: Some Unifying Themes of Intertemporal Creditor Priorities Created by Running Covenants, Products Liability, and Toxic-Waste Cleanup

The exceptional sensitivity of mammalian hearing organs is attributed to an active process, where force produced by sensory cells boost sound-induced vibrations, making soft sounds audible. This process is thought to be local, with each section of the hearing organ capable of amplifying sound-evoked movement, and nearly instantaneous, since amplification can work for sounds at frequencies up to 100 kHz in some species. To test these fundamental precepts, we developed a method for focally stimulating the living hearing organ with light. Light pulses caused intense and highly damped mechanical responses followed by traveling waves that developed with considerable delay. The delayed response was identical to movements evoked by click-like sounds. This shows that the active process is neither local nor instantaneous, but requires mechanical waves traveling from the cochlear base toward its apex. A physiologically-based mathematical model shows that such waves engage the active process, enhancing hearing sensitivity.Funding Agencies|NIH [DC-004554, DC-004084]; Swedish Research Council [K2011-63X-14061-11-39]; Research Council for Health, Working Life and Welfare [2006-1526]; Horselskadades Riksforbund; Tysta skolan foundation</p

Розробка модуля Ethernet контролю для дистанційного керування електроживильною установкою

Sound processing in the inner ear involves separation of the constituent frequencies along the length of the cochlea. Frequencies relevant to human speech (100 to 500 Hz) are processed in the apex region. Among mammals, the guinea pig cochlear apex processes similar frequencies and is thus relevant for the study of speech processing in the cochlea. However, the requirement for extensive surgery has challenged the optical accessibility of this area to investigate cochlear processing of signals without significant intrusion. A simple method is developed to provide optical access to the guinea pig cochlear apex in two directions with minimal surgery. Furthermore, all prior vibration measurements in the guinea pig apex involved opening an observation hole in the otic capsule, which has been questioned on the basis of the resulting changes to cochlear hydrodynamics. Here, this limitation is overcome by measuring the vibrations through the unopened otic capsule using phase-sensitive Fourier domain optical coherence tomography. The optically and surgically advanced method described here lays the foundation to perform minimally invasive investigation of speech-related signal processing in the cochlea. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License.Funding Agencies|NIH NIDCD [R01DC000141]; NIH [R01DC004554, R01DC010201, R01DC011796]; Swedish Research Council [K2014-63X-14061-14-5]; Torsten Soderberg Foundation</p

Влияние параметров торцовой фрезы на характер обработанной поверхности

Материалы ХI Международной науч.-техн. конф. студентов, магистрантов и аспирантов [28-29 апреля 2011 г., г. Гомель]. - Гомель, 2011

A mechanoelectrical mechanism for detection of sound envelopes in the hearing organ

To understand speech, the slowly varying outline, or envelope, of the acoustic stimulus is used to distinguish words. A small amount of information about the envelope is sufficient for speech recognition, but the mechanism used by the auditory system to extract the envelope is not known. Several different theories have been proposed, including envelope detection by auditory nerve dendrites as well as various mechanisms involving the sensory hair cells. We used recordings from human and animal inner ears to show that the dominant mechanism for envelope detection is distortion introduced by mechanoelectrical transduction channels. This electrical distortion, which is not apparent in the sound-evoked vibrations of the basilar membrane, tracks the envelope, excites the auditory nerve, and transmits information about the shape of the envelope to the brain.Funding Agencies|Swedish Research Council [K2014-63X-14061-14-5, 2017-06092]; Torsten Soderberg foundation; Strategic research area for systems neurobiology (Region Ostergotland); Linkoping University; NIH-NIDCD [R01 DC-004554, R01 DC 000141]</p

In Vivo Outer Hair Cell Length Changes Expose the Active Process in the Cochlea

BACKGROUND: Mammalian hearing is refined by amplification of the sound-evoked vibration of the cochlear partition. This amplification is at least partly due to forces produced by protein motors residing in the cylindrical body of the outer hair cell. To transmit power to the cochlear partition, it is required that the outer hair cells dynamically change their length, in addition to generating force. These length changes, which have not previously been measured in vivo, must be correctly timed with the acoustic stimulus to produce amplification. METHODOLOGY/PRINCIPAL FINDINGS: Using in vivo optical coherence tomography, we demonstrate that outer hair cells in living guinea pigs have length changes with unexpected timing and magnitudes that depend on the stimulus level in the sensitive cochlea. CONCLUSIONS/SIGNIFICANCE: The level-dependent length change is a necessary condition for directly validating that power is expended by the active process presumed to underlie normal hearing

Hair cell and organ of corti responses to normal and intense acoustic stimulation

The principal aims of the studies described in this thesis were to develop an in vitro model for studying acoustic overstimulation at the cellular level, to define the electrical and mechanical response characteristics of the perfused temporal bone preparation, and to investigate the effects of intense sound stimulation on the calcium levels of the hair cells in the intact hearing organ. In the in vitro model for acoustic overstimulation, isolated cochlear outer hair cells were subjected to a pressure jet emanating from a glass micropipette aimed at the cell body. The pressure jet was generated by the vibrating shaft of a minishaker, hydraulically coupled to the micropipette. Such stimulation was found to cause increases of the cytoplasmic calcium concentration in most auditory sensory cells. The calcium changes were sustained, and no evidence of recovery of the elevated levels were seen after the termination of the stimulus. A system was also developed to measure the pressures delivered to the cells. This system was based on a piezoresistive pressure transducer connected to a glass micropipette brought into the immediate vicinity of cells subjected to the pressure jet, allowing highly localized pressure changes to be measured. The peak pressure that could be generated by the stimulus system was found to be 144 dB SPL. Taking the middle ear transfer function into account, this level would correspond to approximately 120 dB SPL at the tympanic membrane during normal sound stimulation. Using laser heterodyne interferometry, the sound-induced vibrations of the low-frequency regions of the inner ear were investigated. The responses of the perfused isolated temporal bone preparation was found to be similar to that of living animals, both in terms of sharpness of tuning and the presence of nonlinearities. These characteristics were also reflected in the extracellularly recorded receptor potentials of the hair cells. The mechanical and electrical responses of the low-frequency regions of the cochlea were substantially different from the high-frequency regions, however. Methods were developed to load the organ of Corti with fluorescent dyes and to measure the fluorescence after various experimental manipulations, using video-enhanced microscopy. The fluorescence images were further processed off-line, using a computerized algorithm, to remove out-of-focus information. When the isolated temporal bone preparation was subjected to acoustic overstimulation, large increases of the calcium concentration of the outer hair cells were seen. In addition, overstimulation caused contractions of the hearing organ that were reversible after the termination of the stimulus. Both the calcium changes and the contraction response could be expected to have severe effects on the function of the inner ear. Keywords: Cochlea, outer hair cells, calcium, pressure changes, micromechanics, noise-induced hearing loss, fluorescent indicators, laser interferometry, temporal bone preparation, guinea pig ISBN 91-628-2353-