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Journal of Audiology & Otology Apr 2015Mass and stiffness affect on the peculiar characteristics of transmission of the middle ear and the distinctive behavior of the cochlear mechanics. Applying the... (Review)
Review
Mass and stiffness affect on the peculiar characteristics of transmission of the middle ear and the distinctive behavior of the cochlear mechanics. Applying the principle of the mass and stiffness, the band-pass characteristic transfer function of the middle ear has been explained. The greatest transfer function of the middle ear, approximately 24-29 dB, is observed at 1-2 kHz in both cat and human species. However, at lower frequencies, the transfer function was disturbed by the stiffness of the middle ear primarily due to middle ear cavity. At higher frequencies, the transfer function was disturbed by the stiffness of the middle ear primarily due to middle ear bones. Several examples, such as an acoustic reflex, otitis media, and otosclerosis are discussed. For understanding the traveling wave of the basilar membrane, different place tuning at certain stimulus frequencies, contrastingly shaped basilar membrane to the cochlear duct, and the structural and physical characteristics of the whole cochlear partition were reviewed in terms of changing width, mass, and stiffness from the base to apex. Being about ten times wider, more massive, and one hundredfold stiffer at the base than the apex, the nature of the cochlear partition to absorb high-frequency energy changes in fluid pressure declines toward the apex. Consequently, at the base of the cochlea, high frequencies stimuli are decoded while low frequencies stimuli are decoded at the apex of the cochlea. Due to these characteristics of the cochlear partition, the direction of the traveling wave was also proved to be in the fashion of base-to-apex always.
PubMed: 26185784
DOI: 10.7874/jao.2015.19.1.1 -
Frontiers in Bioengineering and... 2021Cochlear implants (CIs) have become the standard treatment for severe-to-profound sensorineural hearing loss. Conventional CIs have some challenges, such as the use of...
Cochlear implants (CIs) have become the standard treatment for severe-to-profound sensorineural hearing loss. Conventional CIs have some challenges, such as the use of extracorporeal devices, and high power consumption for frequency analysis. To overcome these, artificial basilar membranes (ABMs) made of piezoelectric materials have been studied. This study aimed to verify the conceptual idea of a totally implantable ABM system. A prototype of the totally implantable system composed of the ABM developed in previous research, an electronic module (EM) for the amplification of electrical output from the ABM, and electrode was developed. We investigated the feasibility of the ABM system and obtained meaningful auditory brainstem responses of deafened guinea pigs by implanting the electrode of the ABM system. Also, an optimal method of coupling the ABM system to the human ossicle for transducing sound waves into electrical signals using the middle ear vibration was studied and the electrical signal output according to the sound stimuli was measured successfully. Although the overall power output from the ABM system is still less than the conventional CIs and further improvements to the ABM system are needed, we found a possibility of the developed ABM system as a totally implantable CIs in the future.
PubMed: 34336805
DOI: 10.3389/fbioe.2021.693849 -
Comprehensive Physiology Sep 2017Sound pressure fluctuations striking the ear are conveyed to the cochlea, where they vibrate the basilar membrane on which sit hair cells, the mechanoreceptors of the... (Review)
Review
Sound pressure fluctuations striking the ear are conveyed to the cochlea, where they vibrate the basilar membrane on which sit hair cells, the mechanoreceptors of the inner ear. Recordings of hair cell electrical responses have shown that they transduce sound via submicrometer deflections of their hair bundles, which are arrays of interconnected stereocilia containing the mechanoelectrical transducer (MET) channels. MET channels are activated by tension in extracellular tip links bridging adjacent stereocilia, and they can respond within microseconds to nanometer displacements of the bundle, facilitated by multiple processes of Ca2+-dependent adaptation. Studies of mouse mutants have produced much detail about the molecular organization of the stereocilia, the tip links and their attachment sites, and the MET channels localized to the lower end of each tip link. The mammalian cochlea contains two categories of hair cells. Inner hair cells relay acoustic information via multiple ribbon synapses that transmit rapidly without rundown. Outer hair cells are important for amplifying sound-evoked vibrations. The amplification mechanism primarily involves contractions of the outer hair cells, which are driven by changes in membrane potential and mediated by prestin, a motor protein in the outer hair cell lateral membrane. Different sound frequencies are separated along the cochlea, with each hair cell being tuned to a narrow frequency range; amplification sharpens the frequency resolution and augments sensitivity 100-fold around the cell's characteristic frequency. Genetic mutations and environmental factors such as acoustic overstimulation cause hearing loss through irreversible damage to the hair cells or degeneration of inner hair cell synapses. © 2017 American Physiological Society. Compr Physiol 7:1197-1227, 2017.
Topics: Animals; Calcium; Hair Cells, Auditory; Humans; Ion Channels; Mechanotransduction, Cellular; Synaptic Transmission
PubMed: 28915323
DOI: 10.1002/cphy.c160049 -
Proceedings of the National Academy of... Jul 2016Low-frequency hearing is critically important for speech and music perception, but no mechanical measurements have previously been available from inner ears with intact...
Low-frequency hearing is critically important for speech and music perception, but no mechanical measurements have previously been available from inner ears with intact low-frequency parts. These regions of the cochlea may function in ways different from the extensively studied high-frequency regions, where the sensory outer hair cells produce force that greatly increases the sound-evoked vibrations of the basilar membrane. We used laser interferometry in vitro and optical coherence tomography in vivo to study the low-frequency part of the guinea pig cochlea, and found that sound stimulation caused motion of a minimal portion of the basilar membrane. Outside the region of peak movement, an exponential decline in motion amplitude occurred across the basilar membrane. The moving region had different dependence on stimulus frequency than the vibrations measured near the mechanosensitive stereocilia. This behavior differs substantially from the behavior found in the extensively studied high-frequency regions of the cochlea.
Topics: Acoustic Stimulation; Animals; Basilar Membrane; Guinea Pigs; Hair Cells, Auditory, Outer; Hearing; Interferometry; Motion; Organ of Corti; Sound; Tomography, Optical Coherence
PubMed: 27407145
DOI: 10.1073/pnas.1606317113 -
The Journal of Physiology Oct 2006Medial olivocochlear efferent (MOCE) neurones innervate the outer hair cells (OHCs) of the mammalian cochlea, and convey signals that are capable of controlling the... (Review)
Review
Medial olivocochlear efferent (MOCE) neurones innervate the outer hair cells (OHCs) of the mammalian cochlea, and convey signals that are capable of controlling the sensitivity of the peripheral auditory system in a frequency-specific manner. Recent methodological developments have allowed the effects of the MOCE system to be observed in vivo at the level of the basilar membrane (BM). These observations have confirmed earlier theories that at least some of the MOCE's effects are mediated via the cochlea's mechanics, with the OHCs acting as the mechanical effectors. However, the new observations have also provided some unexpected twists: apparently, the MOCEs can enhance the BM's responses to some sounds while inhibiting its responses to others, and they can alter the BM's response to a single sound using at least two separate mechanisms. Such observations put new constraints on the way in which the cochlea's mechanics, and the OHCs in particular, are thought to operate.
Topics: Animals; Basilar Membrane; Calcium Channels; Calcium Channels, L-Type; Cochlea; Exocytosis; Hair Cells, Auditory, Outer; Mechanoreceptors; Mice; Neurons, Efferent
PubMed: 16901947
DOI: 10.1113/jphysiol.2006.114991 -
International Journal of Molecular... Nov 2023Tinnitus is the perception of noise in the absence of acoustic stimulation (phantom noise). In most patients suffering from chronic peripheral tinnitus, an alteration of... (Review)
Review
Tinnitus is the perception of noise in the absence of acoustic stimulation (phantom noise). In most patients suffering from chronic peripheral tinnitus, an alteration of outer hair cells (OHC) starting from the stereocilia (SC) occurs. This is common following ototoxic drugs, sound-induced ototoxicity, and acoustic degeneration. In all these conditions, altered coupling between the tectorial membrane (TM) and OHC SC is described. The present review analyzes the complex interactions involving OHC and TM. These need to be clarified to understand which mechanisms may underlie the onset of tinnitus and why the neuropathology of chronic degenerative tinnitus is similar, independent of early triggers. In fact, the fine neuropathology of tinnitus features altered mechanisms of mechanic-electrical transduction (MET) at the level of OHC SC. The appropriate coupling between OHC SC and TM strongly depends on autophagy. The involvement of autophagy may encompass degenerative and genetic tinnitus, as well as ototoxic drugs and acoustic trauma. Defective autophagy explains mitochondrial alterations and altered protein handling within OHC and TM. This is relevant for developing novel treatments that stimulate autophagy without carrying the burden of severe side effects. Specific phytochemicals, such as curcumin and berberin, acting as autophagy activators, may mitigate the neuropathology of tinnitus.
Topics: Humans; Tinnitus; Hair Cells, Auditory, Outer; Stereocilia; Sound; Acoustic Stimulation
PubMed: 38068993
DOI: 10.3390/ijms242316664 -
Korean Journal of Audiology Dec 2012The main objective of this study is to provide an overview of the basic mechanisms of blast induced hearing loss and review pharmacological treatments or interventions... (Review)
Review
The main objective of this study is to provide an overview of the basic mechanisms of blast induced hearing loss and review pharmacological treatments or interventions that can reduce or inhibit blast induced hearing loss. The mechanisms of blast induced hearing loss have been studied in experimental animal models mimicking features of damage or injury seen in human. Blast induced hearing loss is characterized by perforation and rupture of the tympanic membrane, ossicular damage, basilar membrane damage, inner and outer hair cell loss, rupture of round window, changes in chemical components of cochlear fluid, vasospasm, ischemia, oxidative stress, excitotoxicity, hematoma, and hemorrhage in both animals and humans. These histopathological consequences of blast exposure can induce hearing loss, tinnitus, dizziness, and headache. The pharmacological approaches to block or inhibit some of the auditory pathological consequences caused by blast exposure have been developed with antioxidant drugs such as 2,4-disulfonyl α-phenyl tertiary butyl nitrone (HXY-059, now called HPN-07) and N-acetylcysteine (NAC). A combination of antioxidant drugs (HPN-07 and NAC) was administered to reduce blast induced cochlear damage and hearing loss. The combination of the antioxidant drugs can prevent or treat blast induced hearing loss by reducing damage to the mechanical and neural component of the auditory system. Although information of the underlying mechanisms and treatment of blast induced hearing loss are provided, further and deep research should be achieved due to the limited and controversial knowledge.
PubMed: 24653882
DOI: 10.7874/kja.2012.16.3.103 -
Communications Biology Jun 2023The human auditory system is designed to capture and encode sounds from our surroundings and conspecifics. However, the precise mechanisms by which it adaptively...
The human auditory system is designed to capture and encode sounds from our surroundings and conspecifics. However, the precise mechanisms by which it adaptively extracts the most important spectro-temporal information from sounds are still not fully understood. Previous auditory models have explained sound encoding at the cochlear level using static filter banks, but this vision is incompatible with the nonlinear and adaptive properties of the auditory system. Here we propose an approach that considers the cochlear processes as envelope interpolations inspired by cochlear physiology. It unifies linear and nonlinear adaptive behaviors into a single comprehensive framework that provides a data-driven understanding of auditory coding. It allows simulating a broad range of psychophysical phenomena from virtual pitches and combination tones to consonance and dissonance of harmonic sounds. It further predicts the properties of the cochlear filters such as frequency selectivity. Here we propose a possible link between the parameters of the model and the density of hair cells on the basilar membrane. Cascaded Envelope Interpolation may lead to improvements in sound processing for hearing aids by providing a non-linear, data-driven, way to preprocessing of acoustic signals consistent with peripheral processes.
Topics: Humans; Hearing; Cochlea; Sound; Basilar Membrane
PubMed: 37355702
DOI: 10.1038/s42003-023-05040-5 -
Micromachines May 2022Based on the modern microelectromechanical systems technology, we present a revolutionary miniaturized artificial cochlear sensory epithelium for future implantation...
Based on the modern microelectromechanical systems technology, we present a revolutionary miniaturized artificial cochlear sensory epithelium for future implantation tests on guinea pigs. The device was curved to fit the spiral structure of the cochlea and miniaturized to a maximum dimension of <1 mm to be implanted in the cochlea. First, the effect of the curved configuration on the oscillation characteristics of a trapezoidal membrane was evaluated using the relatively larger devices, which had a trapezoidal and a comparable curved shape designed for high-precision in vitro measurements. Both experimental and numerical analyses were used to determine the resonance frequencies and positions, and multiple oscillation modes were clearly observed. Because the maximum oscillation amplitude positions, i.e., the resonance positions, differed depending on the resonance frequencies in both trapezoidal and curved membrane devices, the sound frequency was determined based on the resonance position, thus reproducing the frequency selectivity of the basilar membrane in the organ of Corti. Furthermore, the resonance frequencies and positions of these two devices with different configurations were determined to be quantitatively consistent and similar in terms of mechanical dynamics. This result shows that despite a curved angle of 50−60°, the effect of the curved shape on oscillation characteristics was negligible. Second, the nanometer-scale oscillation of the miniaturized device was successfully measured, and the local resonance frequency in air was varied from 157 to 277 kHz using an experimental system that could measure the amplitude distribution in a two-dimensional (2D) plane with a high accuracy and reproducibility at a high speed. The miniaturized device developed in this study was shown to have frequency selectivity, and when the device was implanted in the cochlea, it was expected to discriminate frequencies in the same manner as the basilar membrane in the biological system. This study established methods for fabricating and evaluating the miniaturized device, and the proposed miniaturized device in a curved shape demonstrated the feasibility of next-generation cochlear implants.
PubMed: 35630235
DOI: 10.3390/mi13050768 -
The Journal of the Acoustical Society... Apr 2023Cochlear mechanics tends to be studied using single-location measurements of intracochlear vibrations in response to acoustical stimuli. Such measurements, due to their...
Cochlear mechanics tends to be studied using single-location measurements of intracochlear vibrations in response to acoustical stimuli. Such measurements, due to their invasiveness and often the instability of the animal preparation, are difficult to accomplish and, thus, ideally require stimulus paradigms that are time efficient, flexible, and result in high resolution transfer functions. Here, a swept-sine method is adapted for recordings of basilar membrane impulse responses in mice. The frequency of the stimulus was exponentially swept from low to high (upward) or high to low (downward) at varying rates (from slow to fast) and intensities. The cochlear response to the swept-sine was then convolved with the time-reversed stimulus waveform to obtain first and higher order impulse responses. Slow sweeps of either direction produce cochlear first to third order transfer functions equivalent to those measured with pure tones. Fast upward sweeps, on the other hand, generate impulse responses that typically ring longer, as observed in responses obtained using clicks. The ringing of impulse response in mice was of relatively small amplitude and did not affect the magnitude spectra. It is concluded that swept-sine methods offer flexible and time-efficient alternatives to other approaches for recording cochlear impulse responses.
Topics: Mice; Animals; Cochlea; Acoustic Stimulation; Basilar Membrane
PubMed: 37092917
DOI: 10.1121/10.0017547