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"Ear Physiology."
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Convergent Evolution Between Insect and Mammalian Audition
In mammals, hearing is dependent on three canonical processing stages: (i) an eardrum collecting sound, (ii) a middle ear impedance converter, and (iii) a cochlear frequency analyzer. Here, we show that some insects, such as rainforest katydids, possess equivalent biophysical mechanisms for auditory processing. Although katydid ears are among the smallest in all organisms, these ears perform the crucial stage of air-to-liquid impedance conversion and signal amplification, with the use of a distinct tympanal lever system. Further along the chain of hearing, spectral sound analysis is achieved through dispersive wave propagation across a fluid substrate, as in the mammalian cochlea. Thus, two phylogenetically remote organisms, katydids and mammals, have evolved a series of convergent solutions to common biophysical problems, despite their reliance on very different morphological substrates.
Journal Article
A mechanical lumped-element model of the human middle ear for bone conduction hearing
Bone conduction (BC) is an important modality of hearing. It enables us to differentiate conductive and sensorineural hearing loss, perceive sounds despite a disabled middle ear, and listen to conversation and music privately without blocking the ear canal. Yet the mechanism underlying BC is not fully understood mainly because the bone-conducted vibrations in the skull simultaneously stimulate the outer ear, the middle ear, and the cochlea. The nature of the parallel stimulation on those interconnected parts makes it difficult to contemplate the dynamics in each compartment and the influences they impose on each other. In the present study, a computational lumped-element human ear model for BC is developed. The model comprises lumped mechanical components—masses, springs and dampers—to represent structures such as eardrum, ossicles, ligaments, joints, and cochlear fluid. The parameters of those components are determined by fitting the simulated ossicular vibrations to the measured counterparts reported by Stenfelt et al., the most extensive BC middle-ear dataset. The results show that the model-predicted vibrations of the umbo and stapes generally match the experimental results not just in the normal ear condition (with a fitting error of 1.8 dB and 3.9 dB, respectively, for the umbo and stapes) but also after various perturbations such as adding mass on the eardrum and separating the incudostapedial joint (with fitting errors ranging from 1.3 to 10 dB). It is believed this is the first lumped-element model that can correctly simulate the vibrations of the human middle ear in BC. The model can serve as the bedrock not only for better understanding the dynamics of the entire ear in BC but also for developing new diagnostics for middle-ear conditions and assisting design of novel hearing prostheses.
Journal Article
3D Finite Element Model of Human Ear with 3-Chamber Spiral Cochlea for Blast Wave Transmission from the Ear Canal to Cochlea
Blast-induced auditory trauma is a common injury in military service members and veterans that leads to hearing loss. While the inner ear response to blast exposure is difficult to characterize experimentally, computational models have advanced to predict blast wave transmission from the ear canal to the cochlea; however, published models have either straight or spiral cochlea with fluid-filled two chambers. In this paper, we report the recently developed 3D finite element (FE) model of the human ear mimicking the anatomical structure of the 3-chambered cochlea. The model consists of the ear canal, middle ear, and two and a half turns of the cochlea with three chambers separated by the Reissner’s membrane (RM) and the basilar membrane (BM). The blast overpressure measured from human temporal bone experiments was applied at the ear canal entrance and the Fluent/Mechanical coupled fluid–structure interaction analysis was conducted in ANSYS software. The FE model-derived results include the pressure in the canal near the tympanic membrane (TM) and the intracochlear pressure at scala vestibuli, the TM displacement, and the stapes footplate (SFP) displacement, which were compared with experimentally measured data in human temporal bones. The validated model was used to predict the biomechanical response of the ear to blast overpressure: distributions of the maximum strain and stress within the TM, the BM displacement variation from the base to apex, and the energy flux or total energy entering the cochlea. The comparison of intracochlear pressure and BM displacement with those from the FE model of 2-chambered cochlea indicated that the 3-chamber cochlea model with the RM and scala media chamber improved our understanding of cochlea mechanics. This most comprehensive FE model of the human ear has shown its capability to predict the middle ear and cochlea responses to blast overpressure which will advance our understanding of auditory blast injury.
Journal Article
Translational Perspectives in Auditory Neuroscience
The second book in the three-book series, Translational Perspectives in Auditory Neuroscience.
eBook
The Roles of the External, Middle, and Inner Ears in Determining the Bandwidth of Hearing
The view seems to prevail that the frequency range of hearing is determined by the properties of the outer and middle ears. We argue that this view is an oversimplification, in part because the reactive component of cochlear input impedance, which affects the low-frequency sensitivity of the cochlea, is neglected. Further, we use comparisons of audiograms and transfer functions for stapes (or columella) velocity or pressure in scala vestibuli near the stapes footplate to show that the middle ear by itself is not responsible for limiting high-frequency hearing in the few species for which such comparisons are possible. Finally, we propose that the tonotopic organization of the cochlea plays a crucial role in setting the frequency limits of cochlear sensitivity and hence in determining the bandwidth of hearing.
Journal Article
Transitional mammalian middle ear from a new Cretaceous Jehol eutriconodont
The transference of post-dentary jaw elements to the cranium of mammals as auditory ossicles is one of the central topics in evolutionary biology of vertebrates. Homologies of these bones among jawed vertebrates have long been demonstrated by developmental studies; but fossils illuminating this critical transference are sparse and often ambiguous. Here we report the first unambiguous ectotympanic (angular), malleus (articular and prearticular) and incus (quadrate) of an Early Cretaceous eutriconodont mammal from the Jehol Biota, Liaoning, China. The ectotympanic and malleus have lost their direct contact with the dentary bone but still connect the ossified Meckel’s cartilage (OMC); we hypothesize that the OMC serves as a stabilizing mechanism bridging the dentary and the detached ossicles during mammalian evolution. This transitional mammalian middle ear narrows the morphological gap between the mandibular middle ear in basal mammaliaforms and the definitive mammalian middle ear (DMME) of extant mammals; it reveals complex changes contributing to the detachment of ear ossicles during mammalian evolution.
The road from jaw to ear
The lower jaw of reptiles is made up of several bones. In mammals, however, it consists of just one, the tooth-bearing dentary. Most of the rest have become the ossicles that transmit sound through the middle ear. This transformation is an iconic example of evolutionary change, but direct fossil evidence of the transition has been hard to find. That's why a fossil described by Jin
et al
. is so important. It is from a triconodont (a type of extinct mammal) from the Cretaceous period in China. In it, the lower-jaw elements have started to resemble middle-ear ossicles, but are still joined to the lower jaw by a sliver of ossified cartilage. This element, Meckel's cartilage, is an important part of the inner surface of the lower jaw; the new fossil shows that it was a vital piece in the evolutionary jigsaw that led to the formation of the mammalian middle ear.
Journal Article
Age and Gender Related Variability in the Strength of Auricular Cartilage in Living Humans
Background
Despite previous studies on auricle morphology, research on its biomechanical properties remains limited. This study aims to assess age- and gender-related variations in auricle strength in living humans.
Methods
A prospective, clinical study was conducted to assess auricle stiffness at three antihelix points (superior, middle, and inferior) using a digital Newton meter. Measurements were conducted in two modes to assess the force needed to move the auricle medially by 1, 2, 3, and 4 mm, and the peak force required to displace the auricle medially to a distance of 1 mm from the mastoid skin. Morphological measurements were also recorded to assess the auricle dimensions and projections at various levels of the auricle. Data were analyzed to examine age-related and gender-related distributions, as well as to investigate correlations between morphological parameters and resistance measurements.
Results
The study included 226 ears from 52 women and 61 men, aged 2–85 years. Age significantly influenced most anthropometric measurements, with males generally exhibiting larger ears. Resistance values increased with age, particularly in age groups over 35 and 50. Gender did not significantly affect resistance values. Positive correlations were found between auricle dimensions and resistance values, indicating increased resistance with increased auricle projection.
Conclusions
This study provides a comprehensive mechanical resistance map of the auricle, demonstrating age-related changes in stiffness and regional variations in mechanical properties. These findings are valuable for refining surgical techniques, tissue engineering, and potentially for forensic applications. Further research on diverse populations and standardization of measurement protocols are recommended.
Level of Evidence III
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Journal Article
Testing a Method for Quantifying the Output of Implantable Middle Ear Hearing Devices
This report describes tests of a standard practice for quantifying the performance of implantable middle ear hearing devices (also known as implantable hearing aids). The standard and these tests were initiated by the Food and Drug Administration of the United States Government. The tests involved measurements on two hearing devices, one commercially available and the other home built, that were implanted into ears removed from human cadavers. The tests were conducted to investigate the utility of the practice and its outcome measures: the equivalent ear canal sound pressure transfer function that relates electrically driven middle ear velocities to the equivalent sound pressure needed to produce those velocities, and the maximum effective ear canal sound pressure. The practice calls for measurements in cadaveric ears in order to account for the varied anatomy and function of different human middle ears.
Journal Article
Morphology of the Auditory and Vestibular Organs in Mammals, with Emphasis on Marine Species
This monograph describes the directions of the structural evolution of the peripheral part of the auditory system in representatives of different ecological groups of mammals. Special attention is paid to the least studied orders of marine mammals (pinnipeds, cetaceans), being of great interest both with regards to the echolocating abilities in dolphins and the influence of the aquatic environment on the development of morphological adaptations in the structure of the outer, middle and inner ears. Undertaken for the first time, a comparative embryological study of the peripheral part of the auditory system in marine mammals allowed the author to reveal the developmental pattern of the auditory and equilibrium organs in animals with a different auditory specialization. The influence of ecological factors on the adaptive trait development in the structural organization of the outer, middle and inner ears in semi-aquatic and aquatic species is discussed. The book is illustrated with a large number of high-quality micro-photos. Other volumes in the Russian Academic Monographs series: - Terrestrial Paleoecology and Global Change, Russian Academic Monographs, No 1 ISBN 978-954-642-153-7 (2003) Author: V.A. Krassilov - Fish and Dolphin Swimming, Russian Academic Monographs, No 2 ISBN 978-954-642-150-2 (2002); Author: E.V. Romanenko - Analytical Methods in Nonlinear Wave Theory, Russian Academic Monographs 3 ISBN 978-954-642-248-7 (2005) Author: I.A. Molotkov - Riccati Equations, Russian Academic Monographs 5 ISBN 978-954-642-296-5 (2007); Author: A.I. Egorov Available through our partner publisher Pensoft (www.pensoft.net).
eBook