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Scientific Reports Nov 2022Within the cochlea, the basilar membrane (BM) is coupled to the reticular lamina (RL) through three rows of piezo-like outer hair cells (OHCs) and supporting cells that...
Within the cochlea, the basilar membrane (BM) is coupled to the reticular lamina (RL) through three rows of piezo-like outer hair cells (OHCs) and supporting cells that endow mammals with sensitive hearing. Anatomical differences across OHC rows suggest differences in their motion. Using optical coherence tomography, we measured in vivo and postmortem displacements through the gerbil round-window membrane from approximately the 40-47 kHz best-frequency (BF) regions. Our high spatial resolution allowed measurements across the RL surface at the tops of the three rows of individual OHCs and their bottoms, and across the BM. RL motion varied radially; the third-row gain was more than 3 times greater than that of the first row near BF, whereas the OHC-bottom motions remained similar. This implies that the RL mosaic, comprised of OHC and phalangeal-process tops joined together by adhesion molecules, is much more flexible than the Deiters' cells connected to the OHCs at their bottom surfaces. Postmortem, the measured points moved together approximately in phase. These imply that in vivo, the RL does not move as a stiff plate hinging around the pillar-cell heads near the first row as has been assumed, but that its mosaic-like structure may instead bend and/or stretch.
Topics: Animals; Organ of Corti; Cochlea; Basilar Membrane; Hair Cells, Auditory, Outer; Motion; Gerbillinae
PubMed: 36333415
DOI: 10.1038/s41598-022-23525-x -
Physiological Reviews Jul 2010The ability to determine the location of a sound source is fundamental to hearing. However, auditory space is not represented in any systematic manner on the basilar... (Review)
Review
The ability to determine the location of a sound source is fundamental to hearing. However, auditory space is not represented in any systematic manner on the basilar membrane of the cochlea, the sensory surface of the receptor organ for hearing. Understanding the means by which sensitivity to spatial cues is computed in central neurons can therefore contribute to our understanding of the basic nature of complex neural representations. We review recent evidence concerning the nature of the neural representation of auditory space in the mammalian brain and elaborate on recent advances in the understanding of mammalian subcortical processing of auditory spatial cues that challenge the "textbook" version of sound localization, in particular brain mechanisms contributing to binaural hearing.
Topics: Animals; Auditory Pathways; Brain; Cues; Hearing; Humans; Mammals; Sound; Sound Localization
PubMed: 20664077
DOI: 10.1152/physrev.00026.2009 -
American Family Physician May 2000Hearing loss caused by exposure to recreational and occupational noise results in devastating disability that is virtually 100 percent preventable. Noise-induced hearing...
Hearing loss caused by exposure to recreational and occupational noise results in devastating disability that is virtually 100 percent preventable. Noise-induced hearing loss is the second most common form of sensorineural hearing deficit, after presbycusis (age-related hearing loss). Shearing forces caused by any sound have an impact on the stereocilia of the hair cells of the basilar membrane of the cochlea; when excessive, these forces can cause cell death. Avoiding noise exposure stops further progression of the damage. Noise-induced hearing loss can be prevented by avoiding excessive noise and using hearing protection such as earplugs and earmuffs. Patients who have been exposed to excessive noise should be screened. When hearing loss is suspected, a thorough history, physical examination and audiometry should be performed. If these examinations disclose evidence of hearing loss, referral for full audiologic evaluation is recommended.
Topics: Adolescent; Audiometry; Female; Hearing Loss, Noise-Induced; Hearing Loss, Sensorineural; Humans; Male; Middle Aged; Referral and Consultation
PubMed: 10821155
DOI: No ID Found -
Hearing Research Aug 2018The cochlea contains macrophages. These cells participate in inflammatory responses to cochlear pathogenesis. However, it is not clear how and when these cells populate... (Comparative Study)
Comparative Study
The cochlea contains macrophages. These cells participate in inflammatory responses to cochlear pathogenesis. However, it is not clear how and when these cells populate the cochlea during postnatal development. The current study aims to determine the postnatal development of cochlear macrophages with the focus on macrophage development in the organ of Corti and the basilar membrane. Cochleae were collected from C57BL/6J mice at ages of postnatal day (P) 1 to P21, as well as from mature mice (1-4 months). Macrophages were identified based on their expression of F4/80 and Iba1, as well as their unique morphologies. Two sets of macrophages were identified in the regions of the organ of Corti and the basilar membrane. One set resides on the scala tympani side of the basilar membrane. These cells have a round shape at P1 and start to undergo site-specific differentiation at P4. Apical macrophages adopt a dendritic shape. Middle and basal macrophages take on an irregular shape with short projections. Basal macrophages further differentiate into an amoeboid shape. The other set of macrophages resides above the basilar membrane, either beneath the cells of the organ of Corti or along the spiral vessel of the basilar membrane. As the sensory epithelium matures, these cells undergo developmental death with the phenotypes of apoptosis. Macrophages are also identified in the spiral ligament, spiral limbus, and neural regions. Their numbers decrease during postnatal development. Together, these results suggest a dynamic rearrangement of the macrophage population during postnatal cochlear development.
Topics: Age Factors; Animals; Animals, Newborn; Antigens, Differentiation; Apoptosis; Biomarkers; Calcium-Binding Proteins; Cell Differentiation; Cell Shape; Cochlea; Female; Leukocyte Common Antigens; Macrophages; Male; Mice, Inbred C57BL; Microfilament Proteins; Phenotype
PubMed: 29804721
DOI: 10.1016/j.heares.2018.05.010 -
BioRxiv : the Preprint Server For... Oct 2023Auditory sensation is based in nanoscale vibration of the sensory tissue of the cochlea, the organ of Corti complex (OCC). Motion within the OCC is now observable due to...
Auditory sensation is based in nanoscale vibration of the sensory tissue of the cochlea, the organ of Corti complex (OCC). Motion within the OCC is now observable due to optical coherence tomography. In the cochlear base, in response to sound stimulation, the region that includes the electro-motile outer hair cells (OHC) was observed to move with larger amplitude than the basilar membrane (BM) and surrounding regions. The intense motion is based in active cell mechanics, and the region was termed the "hotspot" (Cooper et al., 2018, Nature comm). In addition to this quantitative distinction, the hotspot moved qualitatively differently than the BM, in that its motion scaled nonlinearly with stimulus level at all frequencies, evincing sub-BF activity. Sub-BF activity enhances non-BF motion; thus the frequency tuning of the hotspot was reduced relative to the BM. Regions that did not exhibit sub-BF activity are here defined as the OCC "frame". By this definition the frame includes the BM, the medial and lateral OCC, and most significantly, the reticular lamina (RL). The frame concept groups the majority OCC as a structure that is largely shielded from sub-BF activity. This shielding, and how it is achieved, are key to the active frequency tuning of the cochlea. The observation that the RL does not move actively sub-BF indicates that hair cell stereocilia are not exposed to sub-BF activity. A complex difference analysis reveals the motion of the hotspot relative to the frame.
PubMed: 37873430
DOI: 10.1101/2023.06.29.547111 -
Biogerontology Jun 2020The cochlear basilar membrane (CBM) contains inner hair cells and outer hair cells that convert sound waves into electrical signals and transmit them to the central...
The cochlear basilar membrane (CBM) contains inner hair cells and outer hair cells that convert sound waves into electrical signals and transmit them to the central auditory system. Cochlear aging, the primary reason of age-related hearing loss, can reduce the signal transmission capacity. There is no ideal in vitro aging model of the CBM. In this study, we cultured the CBM, which was dissected from the cochlea of the C57BL/6 mice 5 days after birth, in a medium containing 20 mg/mL, 40 mg/mL, or 60 mg/mL D-galactose (D-gal). Compared with the control group, the levels of senescence-associated β-galactosidase were increased in a concentration-dependent manner in the CBM of the D-gal groups. In addition, levels of the mitochondrial superoxide and patterns of an age-related mitochondrial DNA3860-bp deletion were significantly increased. The ATP levels and the membrane potential of the mitochondrial were significantly decreased in the CBM of the D-gal groups compared with the control group. Furthermore, in comparison with the control group, damaged hair cell stereocilia and a loss of inner hair cell ribbon synapses were observed in the CBM of the D-gal groups. A loss of hair cells and activation of caspase-3-mediated outer hair cell apoptosis were also observed in the CBM of the high-dose D-gal group. These insults induced by D-gal in the CBM in vitro were similar to the ones that occur in cochlear natural aging in vivo. Thus, we believe that this is a successful in vitro aging model using cultured CBM. These results demonstrate the effects of mitochondrial oxidative damage on presbycusis and provide a reliable aging model to study the mechanisms of presbycusis in vitro.
Topics: Animals; Basilar Membrane; Cochlea; DNA, Mitochondrial; Galactose; Mice; Mice, Inbred C57BL; Mitochondria; Oxidative Stress; Rats; Rats, Sprague-Dawley
PubMed: 32026209
DOI: 10.1007/s10522-020-09859-x -
Hearing Research Sep 2022Intra organ of Corti (OC) vibrations differ from those measured at the basilar membrane (BM), with higher amplitudes and a wide-band nonlinearity extending well below a...
Intra organ of Corti (OC) vibrations differ from those measured at the basilar membrane (BM), with higher amplitudes and a wide-band nonlinearity extending well below a region's best frequency. The vibrations are boosted by the cochlear amplifier, the active processes within the mammalian hearing organ, and are thus sensitive to metabolic or pharmacological manipulation. We introduced salicylate, a known blocker of outer hair cell (OHC) based electromotility, into the perilymphatic space by applying sodium salicylate onto the round window membrane. Vibration patterns of an area of the OC were mapped with phase sensitive optical coherence tomography before and after treatment; distortion product otoacoustic emissions (DPOAEs) were measured at similar times to assess the cochlear condition. Following treatment, all regions showed a loss of vibration amplitude and tuning while OHC-region vibrations retained their wide-band nonlinearity. OC vibrations, which had been relatively confined in a region including OHCs and extending to the BM at the outer pillar foot, became less confined with structures lateral to the OHCs sometimes exhibiting the highest amplitudes. Vibrations and DPOAEs could recover to baseline levels over approximately three hours post treatment. This article is part of the Special Issue Outer hair cell Edited by Joseph Santos-Sacchi and Kumar Navaratnam.
Topics: Animals; Basilar Membrane; Cochlea; Hair Cells, Auditory, Outer; Mammals; Organ of Corti; Salicylates; Vibration
PubMed: 34774368
DOI: 10.1016/j.heares.2021.108389 -
Zoological Letters Oct 2022The inner ear morphology and size are linked to hearing and balance ability. The goal of this study was to determine the morphology and morphometrics of the dromedary...
BACKGROUND
The inner ear morphology and size are linked to hearing and balance ability. The goal of this study was to determine the morphology and morphometrics of the dromedary camel's inner ear and how it influences hearing accommodation and equilibrium in the desert environment.
MATERIALS AND METHODS
Gross morphology, computed tomography images, and the endocast were used to show the inner ear morphology. A caliper and ImageJ software were used to take measurements on a plastic endocast.
RESULTS
The presence of the subarcuate fossa, flat cochlea, radii curvature of the semicircular canals, particularly the lateral semicircular canal, orthogonality, and the union between the semicircular canals, along with slightly increased saccule and utricle size, maintains camel balance on sandy ground, even during heavy sandstorms. The cochlear basilar membrane length and cochlea radii ratio aided low-frequency hearing and perception over a wide octave range.
CONCLUSION
The camel's cochlear characteristics revealed a lengthy basilar membrane, a high radii ratio, 3.0 cochlear canal turns, and a very broad cochlea. The orthogonality of the semicircular canals, the high curvature of the lateral semicircular canal, the presence of the subarcuate fossa, and the confluence between the lateral and posterior semicircular canal were particular specifications that allowed the inner ear of the camel to adapt to desert living.
PubMed: 36303215
DOI: 10.1186/s40851-022-00196-0 -
Journal of the Association For Research... Apr 2020The cochlea's wave-based signal processing allows it to efficiently decompose a complex acoustic waveform into frequency components. Because cochlear responses are...
The cochlea's wave-based signal processing allows it to efficiently decompose a complex acoustic waveform into frequency components. Because cochlear responses are nonlinear, the waves arising from one frequency component of a complex sound can be altered by the presence of others that overlap with it in time and space (e.g., two-tone suppression). Here, we investigate the suppression of basilar-membrane (BM) velocity responses to a transient signal (a test click) by another click or tone. We show that the BM response to the click can be reduced when the stimulus is shortly preceded or followed by another (suppressor) click. More surprisingly, the data reveal two curious dependencies on the interclick interval, Δt. First, the temporal suppression curve (amount of suppression vs. Δt) manifests a pronounced and nearly periodic microstructure. Second, temporal suppression is generally strongest not when the two clicks are presented simultaneously (Δt = 0), but when the suppressor click precedes the test click by a time interval corresponding to one to two periods of the best frequency (BF) at the measurement location. By systematically varying the phase of the suppressor click, we demonstrate that the suppression microstructure arises from alternating constructive and destructive interference between the BM responses to the two clicks. And by comparing temporal and tonal suppression in the same animals, we test the hypothesis that the asymmetry of the temporal-suppression curve around Δt = 0 stems from cochlear dispersion and the well-known asymmetry of tonal suppression around the BF. Just as for two-tone suppression, BM responses to clicks are most suppressed by tones at frequencies just above the BF of the measurement location. On average, the frequency place of maximal suppressibility of the click response predicted from temporal-suppression data agrees with the frequency at which tonal suppression peaks, consistent with our hypothesis.
Topics: Algorithms; Animals; Basilar Membrane; Gerbillinae; Hearing
PubMed: 32166602
DOI: 10.1007/s10162-020-00747-2 -
Hearing Research Nov 2015Bone conduction (BC) hearing relies on sound vibration transmission in the skull bone. Several clinical findings indicate that in the human, the skull vibration of the... (Review)
Review
Bone conduction (BC) hearing relies on sound vibration transmission in the skull bone. Several clinical findings indicate that in the human, the skull vibration of the inner ear dominates the response for BC sound. Two phenomena transform the vibrations of the skull surrounding the inner ear to an excitation of the basilar membrane, (1) inertia of the inner ear fluid and (2) compression and expansion of the inner ear space. The relative importance of these two contributors were investigated using an impedance lumped element model. By dividing the motion of the inner ear boundary in common and differential motion it was found that the common motion dominated at frequencies below 7 kHz but above this frequency differential motion was greatest. When these motions were used to excite the model it was found that for the normal ear, the fluid inertia response was up to 20 dB greater than the compression response. This changed in the pathological ear where, for example, otosclerosis of the stapes depressed the fluid inertia response and improved the compression response so that inner ear compression dominated BC hearing at frequencies above 400 Hz. The model was also able to predict experimental and clinical findings of BC sensitivity in the literature, for example the so called Carhart notch in otosclerosis, increased BC sensitivity in superior semicircular canal dehiscence, and altered BC sensitivity following a vestibular fenestration and RW atresia.
Topics: Biomechanical Phenomena; Bone Conduction; Cochlea; Ear, Inner; Electric Impedance; Humans; Labyrinthine Fluids; Models, Biological; Oval Window, Ear; Round Window, Ear; Vibration
PubMed: 25528492
DOI: 10.1016/j.heares.2014.12.003