scholarly journals Hearing at threshold intensities: by slow mechanical traveling waves or by fast cochlear fluid pressure waves

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Haim Sohmer
Keyword(s):  
Soft Tissue ◽  
Hair Cells ◽  
Traveling Wave ◽  
Basilar Membrane ◽  
Fluid Pressure ◽  
Low Frequency ◽  
Frequency Discrimination ◽  
Outer Hair Cells ◽  
Common Mechanism ◽  
Frequency Stimulation

The three modes of auditory stimulation (air, bone and soft tissue conduction) at threshold intensities are thought to share a common excitation mechanism: the stimuli induce passive displacements of the basilar membrane propagating from the base to the apex (slow mechanical traveling wave), which activate the outer hair cells, producing active displacements, which sum with the passive displacements. However, theoretical analyses and modeling of cochlear mechanics provide indications that the slow mechanical basilar membrane traveling wave may not be able to excite the cochlea at threshold intensities with the frequency discrimination observed. These analyses are complemented by several independent lines of research results supporting the notion that cochlear excitation at threshold may not involve a passive traveling wave, and the fast cochlear fluid pressures may directly activate the outer hair cells: opening of the sealed inner ear in patients undergoing cochlear implantation is not accompanied by threshold elevations to low frequency stimulation which would be expected to result from opening the cochlea, reducing cochlear impedance, altering hydrodynamics. The magnitude of the passive displacements at threshold is negligible. Isolated outer hair cells in fluid display tuned mechanical motility to fluid pressures which likely act on stretch sensitive ion channels in the walls of the cells. Vibrations delivered to soft tissue body sites elicit hearing. Thus, based on theoretical and experimental evidence, the common mechanism eliciting hearing during threshold stimulation by air, bone and soft tissue conduction may involve the fast-cochlear fluid pressures which directly activate the outer hair cells.

Timing of spike initiation in cochlear afferents: dependence on site of innervation

1987 ◽  
Vol 58 (2) ◽  
pp. 379-403 ◽  
Author(s):  
M. A. Ruggero ◽  
N. C. Rich
Keyword(s):  
Phase Transition ◽  
Hair Cells ◽  
Basilar Membrane ◽  
Stimulus Frequency ◽  
Low Frequency ◽  
Outer Hair Cells ◽  
Propagation Time ◽  
Paradoxical Response ◽  
Spatial Phase ◽  
Near Threshold

1. The phase of excitation of inner hair cells (IHCs) relative to basilar membrane motion has been estimated as a function of best frequency (BF) (or, equivalently, cochlear location) by recording responses to tones (100–1,000 Hz) from chinchilla cochlear afferent axons at their central exit from the internal auditory meatus. 2. The time of IHC excitation (i.e., the time of chemical transmitter release) was derived from the neural recordings at near-threshold levels by applying a correction for the latency of synaptic processes and the propagation time of action potentials. 3. The phase of basilar membrane motion at the appropriate innervation site was estimated on the basis of previously measured basilar membrane responses at a location close to the basal end of the cochlea and estimates of mechanical travel time from the basal end to the innervation site, derived from the neural latencies to intense rarefaction clicks, as a function of BF. 4. The derived near-threshold excitation of basal IHCs leads basilar membrane displacement toward scala tympani by approximately 40-60 degrees. 5. At BFs corresponding to midcochlear locations (2–6 kHz) there is an abrupt phase transition. The derived excitation for IHCs located at more apical locations (BFs large in relation to stimulus frequency) corresponds approximately to peak velocity of the basilar membrane toward scala vestibuli. 6. Although the derived response phases of apically located IHCs are consistent with intracellular recordings from IHCs, the derived near-threshold response phases of basal IHCs may be inconsistent with intracellular IHC recordings. 7. The foregoing results, based on responses of nearly 1,000 cochlear afferents to tones 100-1,000 Hz at near-threshold stimulus levels, amply confirm our previous conclusions that were based on a smaller sample of responses to very low frequency tones (less than or equal to 100 Hz): there is a spatial transition at midcochlear regions in the mode of excitation of IHCs, which does not seem to simply reflect the macromechanics of the basilar membrane. 8. It has been proposed that both the paradoxical response phases of high-BF afferents and the spatial phase transition arise from an influence of cochlear microphonics on the transmembrane potential of IHCs. The present results, which show that the spatial phase transition occurs for frequencies at least as high as 400 Hz, would appear to make such an electrical influence of outer hair cells on IHCs less likely. An alternative explanation might be that the phase transition has a mechanical basis, perhaps localized to micromechanical events in the subtectorial regio

Tinnitus: some thoughts about its origin

1984 ◽  
Vol 98 (S9) ◽  
pp. 31-37 ◽  
Author(s):  
J. J. Eggermont
Keyword(s):  
Hair Cells ◽  
High Frequency ◽  
Basilar Membrane ◽  
Stimulus Frequency ◽  
Low Frequency ◽  
Nerve Fibers ◽  
Ear Ossicles ◽  
Stimulus Transduction ◽  
Low Levels ◽  
Inner Ear Fluids

An auditory sensation follows generally as the result of the sequence stimulus, transduction, coding, transformation and sensation. This is then optionally followed by perception and a reaction. The stimulus is usually airborne sound causing movements of the tympanic membrane, the middle ear ossicles, the inner ear fluids and the basilar membrane. The movements of the basilar membrane are dependent on stimulus frequency: high frequency tones excite only the basal part of the cochlea, regardless of the stimulus intensity; low frequency tones at low levels only excite the so-called place specific region at the apical end but at high levels (above 60–70 dB SPL) cause appreciable movement of the entire basilar membrane. Basilar membrane tuning is as sharp as that of inner hair cells or auditory nerve fibers (Sellick et al., 1982) at least in the basal turn of animals that have a cochlea in physiologically impeccable condition.

Role of fascia in maintenance of muscle tension and pressure

1981 ◽  
Vol 51 (2) ◽  
pp. 317-320 ◽  
Author(s):  
S. R. Garfin ◽  
C. M. Tipton ◽  
S. J. Mubarak ◽  
S. L. Woo ◽  
A. R. Hargens ◽  
...  
Keyword(s):  
High Frequency ◽  
Muscle Tension ◽  
Fluid Pressure ◽  
Low Frequency ◽  
Testing Procedure ◽  
Force Transducer ◽  
High Frequency Stimulation ◽  
Low Frequency Stimulation ◽  
Frequency Stimulation

The effect of fasciotomy on muscle tension (measured by a force transducer attached to the tendon) and interstitial fluid pressure (measured by Wick catheters in the muscle belly) was studied in the anterolateral compartments of 13 dog hindlimbs. Muscle tension and pressure were monitored in the tibialis cranialis muscle after low- and high-frequency stimulation of the peroneal nerve to produce twitch- and tetanic-type contractions. Fasciotomy decreased muscle force during the low-frequency stimulation by 16% (35.3 +/- 4.9 to 28.4 +/- 3.9 N) and during the high-frequency stimulation by 10% (60.8 %/- 4.9 to 54.8 +/- 3.9 N). Muscle pressure decreased 50% after fasciotomy under both conditions, 15 +/- 2 to 6 +/- 1 mmHg and 84 +/- 17 to 41 +/- 8 mmHg), respectively. Repeated functional evaluations during the testing procedure indicated that muscle fatigue was not a major factor in these results. It was concluded that fascia is important in the development of muscle tension and changes in interstitial pressure. Furthermore, the results raised questions concerning the merits of performing a fasciotomy for athletes with a compartment syndrome.

Prestin Expression in Cochlea of Bats Using Different Echolocation Systems

2014 ◽  
Vol 620 ◽  
pp. 248-252
Author(s):  
Qi Jiu Li ◽  
Xian De Zhang ◽  
Ting Ting Xu ◽  
Jiang Xia Yin
Keyword(s):  
Hair Cells ◽  
High Frequency ◽  
Low Frequency ◽  
Motor Protein ◽  
Outer Hair Cells ◽  
Intracellular Potential ◽  
First Time ◽  
Unique Ability

Outer hair cells (OHCs) have a unique ability to contract and elongate in response to changes in intracellular potential, and Prestin is the motor protein of the cochlea of the OHCs. It is the first time to invest the Prestin expression in different bat species. To invest Prestin expression in different bat species, which have different frequency, we did the coronal sections’ staining of the cochlea using immunhistochemistry. Experiment was designed to determine if the high-frequency bats’ OHCs have more expression than the low-frequency bats’OHCs. We found that the expression in three species was similar and had no obvious difference. Though the study of bats Prestin evolution suggested that Prestin has accelerating evolution in echolocation bats with high frequency, our we showed that the Prestin expression has nothing to do with the frequency, and the Prestin expression in high-frequency bats and low-frequency bats is similar.

scholarly journals Static length changes of cochlear outer hair cells can tune low-frequency hearing

2018 ◽  
Vol 14 (1) ◽  
pp. e1005936 ◽  
Author(s):  
Nikola Ciganović ◽  
Rebecca L. Warren ◽  
Batu Keçeli ◽  
Stefan Jacob ◽  
Anders Fridberger ◽  
...  
Keyword(s):  
Hair Cells ◽  
Low Frequency ◽  
Outer Hair Cells ◽  
Length Changes

scholarly journals Amplification lags nonlinearity in the recovery from reduced endocochlear potential

2020 ◽  
Author(s):  
C. Elliott Strimbu ◽  
Yi Wang ◽  
Elizabeth S. Olson
Keyword(s):  
Hair Cells ◽  
Otoacoustic Emissions ◽  
Basilar Membrane ◽  
Frequency Tuning ◽  
Organ Of Corti ◽  
Endocochlear Potential ◽  
Outer Hair Cells ◽  
Frequency Resolution ◽  
Operating Condition ◽  
Distortion Product

ABSTRACTThe mammalian hearing organ, the cochlea, contains an active amplifier to boost the vibrational response to low level sounds. Hallmarks of this active process are sharp location-dependent frequency tuning and compressive nonlinearity over a wide stimulus range. The amplifier relies on outer hair cell (OHC) generated forces driven in part by the endocochlear potential (EP), the ~ +80 mV potential maintained in scala media, generated by the stria vascularis. We transiently eliminated the EP in vivo by an intravenous injection of furosemide and measured the vibrations of different layers in the cochlea’s organ of Corti using optical coherence tomography. Distortion product otoacoustic emissions (DPOAE) were monitored at the same times. Following the injection, the vibrations of the basilar membrane lost the best frequency (BF) peak and showed broad tuning similar to a passive cochlea. The intra-organ of Corti vibrations measured in the region of the OHCs lost their BF peak and showed low-pass responses, but retained nonlinearity, indicating that OHC electromotility was still operational. Thus, while electromotility is presumably necessary for amplification, its presence is not sufficient for amplification. The BF peak recovered nearly fully within 2 hours, along with a non-monotonic DPOAE recovery that suggests that physical shifts in operating condition are a final step in the recovery process.SIGNIFICANCEThe endocochlear potential, the +80 mV potential difference across the fluid filled compartments of the cochlea, is essential for normal mechanoelectrical transduction, which leads to receptor potentials in the sensory hair cells when they vibrate in response to sound. Intracochlear vibrations are boosted tremendously by an active nonlinear feedback process that endows the cochlea with its healthy sensitivity and frequency resolution. When the endocochlear potential was reduced by an injection of furosemide, the basilar membrane vibrations resembled those of a passive cochlea, with broad tuning and linear scaling. The vibrations in the region of the outer hair cells also lost the tuned peak, but retained nonlinearity at frequencies below the peak, and these sub-BF responses recovered fairly rapidly. Vibration responses at the peak recovered nearly fully over 2 hours. The staged vibration recovery and a similarly staged DPOAE recovery suggests that physical shifts in operating condition are a final step in the process of cochlear recovery.

scholarly journals PIEZO2 mediates ultrasonic hearing via cochlear outer hair cells in mice

2021 ◽  
Vol 118 (28) ◽  
pp. e2101207118
Author(s):  
Jie Li ◽  
Shuang Liu ◽  
Chenmeng Song ◽  
Qun Hu ◽  
Zhikai Zhao ◽  
...  
Keyword(s):  
Hair Cell ◽  
Hair Cells ◽  
Social Communication ◽  
Ex Vivo ◽  
Low Frequency ◽  
Outer Hair Cells ◽  
Freezing Behavior ◽  
Physiological Mechanisms ◽  
Effector Cells ◽  
Mechanosensitive Ion Channel

Ultrasonic hearing and vocalization are the physiological mechanisms controlling echolocation used in hunting and navigation by microbats and bottleneck dolphins and for social communication by mice and rats. The molecular and cellular basis for ultrasonic hearing is as yet unknown. Here, we show that knockout of the mechanosensitive ion channel PIEZO2 in cochlea disrupts ultrasonic- but not low-frequency hearing in mice, as shown by audiometry and acoustically associative freezing behavior. Deletion of Piezo2 in outer hair cells (OHCs) specifically abolishes associative learning in mice during hearing exposure at ultrasonic frequencies. Ex vivo cochlear Ca2+ imaging has revealed that ultrasonic transduction requires both PIEZO2 and the hair-cell mechanotransduction channel. The present study demonstrates that OHCs serve as effector cells, combining with PIEZO2 as an essential molecule for ultrasonic hearing in mice.

A Novel Analysis of the Mechanics of Cochlea, the Inner Ear

2003 ◽  
Author(s):  
Amitava Biswas
Keyword(s):  
Tympanic Membrane ◽  
Traveling Waves ◽  
Hair Cells ◽  
Basilar Membrane ◽  
Oval Window ◽  
Outer Hair Cells ◽  
Acoustic Energy ◽  
Longitudinal Contraction ◽  
Column System ◽  
The Impact

The human ear is often regarded as a paragon of mechanical engineering. To understand how the hearing system works, scientists have proposed detailed models of its specific aspects—the transfer of acoustic energy from the atmosphere to the tympanic membrane via the external ear; the coupling of the tympanic membrane to the oval window of the cochlea via ossicles; the resultant fluidic oscillations in the cochlear ducts; the formation of traveling waves in the basilar membrane of the cochlea; the mechanical stimulation of inner hair cells by the basilar membrane; and the consequential transduction of nerve impulses. Scientists have also proposed models to explain the phenomenon of enhancement of the traveling waves in the basilar membrane by synchronized co-contraction in the length of outer hair cells (OHCs). Although it is unrealistic that any OHC would contract in length without expanding in diameter, the models proposed by other analysts have so far incorporated the longitudinal contraction of OHCs only, suggesting that the impact of any diametric expansion of OHCs would be relatively trival. Here we show that the basilar membrane would behave like a Beam-Column system, which may be significantly influenced by the diametric expansion of OHCs.

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