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Results for “Tectorial Membrane”

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At least 199 records · Page 11Linked to original sources

PubMed1999

Direct visualization of organ of corti kinematics in a hemicochlea.

The basilar membrane in the mammalian cochlea vibrates when the cochlea receives a sound stimulus. This mechanical vibration is transduced into hair cell receptor potentials and thereafter encoded by action potentials in the auditory nerve. Knowledge of the mechanical transformation that converts basilar membrane vibration into hair cell stimulation has been limited, until recently, to hypothetical geometric models. Experimental observations are largely lacking to prove or disprove the validity of these models. We have developed a hemicochlea preparation to visualize the kinematics of the cochlear micromechanism. Direct mechanical drive of 1-2 Hz sinusoidal command was applied to the basilar membrane. Vibration patterns of the basilar membrane, inner and outer hair cells, supporting cells, and tectorial membrane have been recorded concurrently by means of a video optical flow technique. Basilar membrane vibration was driven in a direction transversal to its plane. However, the direction of the resulting vibration was found to be essentially radial at the level of the reticular lamina and cuticular plates of inner and outer hair cells. The tectorial membrane vibration was mainly transversal. The transmission ratio between cilia displacement of inner and outer hair cells and basilar membrane vibration is in the range of 0.7-1.1. These observations support, in part, the classical geometric models at low frequencies. However, there appears to be less tectorial membrane motion than predicted, and it is largely in the transversal direction.

Animals↗

PubMed1981

Morphological changes in the cochlea of the mouse after the onset of hearing.

The cochleae of 5, 10, 12 and 15 day old mice and of adults (Mus musculus, strain NMRI) were studied by light and electron microscopy. In each case the same part of the organ of Corti (2.8-3.3 mm from the helicotrema) was examined. The results were correlated with the development of auditory thresholds (in mice of the same strain) obtained by Ehret (Ehret, G. (1971) J. Am. Audiol. Soc. 1, 179-184). It was demonstrated that morphological development of the organ of Corti is by no means complete at the onset of behavioural responses to acoustic stimuli. After this event the following morphological changes occur: (1) The basilar membrane filaments stain more intensely and the tympanic cover layer is greatly reduced in thickness and almost completely disappears. (2) The filaments of the pillar cells stain more intensely and apparently increase in number, and the angle between the outer and inner pillar cells increases so that the cross-sectional area of the tunnel of Corti expands. (3) Hook-shaped connections (marginal pillars) between the reticular membrane and the tectorial membrane disappear. The consequences of these morphological changes for the cochlear mechanics are discussed, especially in respect to the increase of sensitivity of hearing.

Animals↗

PubMed1993

Collagen of accessory structures of organ of Corti.

It was previously demonstrated that about 40% of the protein of the tectorial membrane of the guinea pig consists of collagen type II, with lesser amounts of type IX and XI. In this paper we extend these studies on the tectorial membrane to the basilar membrane and to other accessory structures, the spiral ligament and spiral limbus. Earlier immunohistochemical data indicated that no collagen type II is present in the basilar membrane of the newborn guinea pig, but that it is present in the area of the basilar membrane in the embryo. However, by means of stringent extraction procedures we have determined biochemically that collagen type II and lesser amounts of type XI are present in the basilar membrane of the adult guinea pig, at similar levels (on the basis of total protein) to the tectorial membrane. Levels of collagen type II are much lower in the spiral ligament and spiral limbus. The presented studies demonstrate that classical techniques of collagen chemistry can be applied at the microscale on minute tissue elements. The significance of the presence of collagen in the tectorial membrane and basilar membrane is discussed in the light of known mechanical properties of these structures.

Amino Acids↗

PubMed1997

Quantitative uronic acid analysis of the otoconial membrane of the guinea pig.

Histochemical and biochemical studies have shown that the otoconial membrane, as well as the tectorial membrane and the cupula, contains glycoproteins and proteoglycans. However, uronic acids, which are essential elements of glycosaminoglycans (GAGs), have not so far been directly detected or quantitatively measured in inner ear samples. In the present study, we quantitatively analyzed the glucuronic acid (GlcA) content of the otoconial membrane of the guinea pig by methanolysis combined with reversed-phase high-performance liquid chromatography (RP-HPLC). The utricular otoconial membrane was treated with thermolysin to separate the supernatant (OM-sup; gelatinous layer) and precipitate (OM-ppt; otoconia). The samples were then subjected to methanolysis followed by brief TFA hydrolysis, incubated with 1-phenyl-3-methyl-5-pyrazolone for labeling, and then analyzed by RP-HPLC coupled with the detection of UV absorbance at 245 nm. The GlcA contents of OM-sup and OM-ppt were 2.1 and 5.8 pmol/100 ng protein, respectively. Based on this result, GlcA-containing GAGs estimated as (GlcA+monosulfo-N-acetylhexosamine)n would be 1.0% of protein in OM-sup and 2.61% of protein in OM-ppt, indicating that this type of glycoconjugate is a minor component in both fractions. It is, accordingly, presumed that both the gelatinous layer and otoconia of the otoconial membrane have totally different properties from those of the tectorial membrane and cartilaginous matrix, which contain abundant GAGs.

Animals↗

PubMed1991

Stereociliary bundles reorient during hair cell development and regeneration in the chick cochlea.

We have examined changes in the orientation of stereociliary bundles of hair cells in the cochlear sensory epithelium that occur during normal embryonic development and during the regeneration of hair cells that follows acoustic trauma. At the time when hair cell surfaces become recognizable in the embryonic cochlea, the bundles of stereocilia exhibit a range of orientations, as indicated by the position of the kinocilium and later, by the location of the tallest row of stereocilia. With time, the orientations of bundles on neighboring hair cells become more uniform, a condition that is maintained in the adult. Changes in stereocilia orientation are also observed during the regeneration of hair cells after acoustic trauma. When new hair cells first differentiate at sites of trauma in the recovering sensory epithelium, their stereociliary bundles are not uniformly oriented. Then as the cells mature over a period of days, the bundles become aligned both with the neighboring bundles in the region of the previous lesion and with the pre-existing bundles that surround the site of regeneration. We conclude that the stereociliary bundles of hair cells are reorienting as the cells differentiate. A common mechanism may guide reorientation both during embryonic development and during regeneration. Observations in living cochleae indicate that differentiating stereociliary bundles establish asymmetric linkages to the extracellular matrix of the developing tectorial membrane. During the growth of the tectorial membrane, its progressive extension across the surface of the sensory epithelium may exert traction forces through those asymmetric linkages that pull the bundles of the hair cells into uniform alignment.

Animals↗

PubMed1980

Theory of cochlear mechanics.

This paper attempts to define the current state of the theory of cochlear mechanics on the basis of past and current experimental and theoretical work. It begins with von Békésy's discovery of traveling transversal waves in the cochlea and with related early mathematical theory and ends with insights engendered by Russell and Sellick's demonstration that inner hair cells are as sharply tuned as the auditory-nerve fibers and by the finding of the M.I.T. groups of Weiss and Peake that sharp tuning of hair cells can exist in the absence of basilar-membrane tuning. Evidence for a sharpening of tuning beyond basilar-membrane vibration is reviewed and two mechanisms for such sharpening are considered--one arising from an interaction between basilar-membrane wavelength and longitudinal coupling within the tectorial membrane and one from the radial-mode resonance of the tectorial membrane and its viscoelastic coupling to the organ of Corti. Simple calculation reveals that damping of the radial-mode vibration should be small enough to allow such a resonance.

Animals↗

PubMed2006

Audiological evaluation of affected members from a Dutch DFNA8/12 (TECTA) family.

In DFNA8/12, an autosomal dominantly inherited type of nonsyndromic hearing impairment, the TECTA gene mutation causes a defect in the structure of the tectorial membrane in the inner ear. Because DFNA8/12 affects the tectorial membrane, patients with DFNA8/12 may show specific audiometric characteristics. In this study, five selected members of a Dutch DFNA8/12 family with a TECTA sensorineural hearing impairment were evaluated with pure-tone audiometry, loudness scaling, speech perception in quiet and noise, difference limen for frequency, acoustic reflexes, otoacoustic emissions, and gap detection. Four out of five subjects showed an elevation of pure-tone thresholds, acoustic reflex thresholds, and loudness discomfort levels. Loudness growth curves are parallel to those found in normal-hearing individuals. Suprathreshold measures such as difference limen for frequency modulated pure tones, gap detection, and particularly speech perception in noise are within the normal range. Distortion otoacoustic emissions are present at the higher stimulus level. These results are similar to those previously obtained from a Dutch DFNA13 family with midfrequency sensorineural hearing impairment. It seems that a defect in the tectorial membrane results primarily in an attenuation of sound, whereas suprathreshold measures, such as otoacoustic emissions and speech perception in noise, are preserved rather well. The main effect of the defects is a shift in the operation point of the outer hair cells with near intact functioning at high levels. As most test results reflect those found in middle-ear conductive loss in both families, the sensorineural hearing impairment may be characterized as a cochlear conductive hearing impairment.

Adult↗

PubMed2000

Histopathological differences between temporary and permanent threshold shift.

The structural changes associated with noise-induced temporary threshold shift (TTS) were compared to the damage associated with permanent threshold shift (PTS). A within-animal paradigm involving survival-fixation was used to minimize problems with data interpretation from interanimal variability in response to noise. Auditory brainstem response thresholds for clicks and tone pips were determined pre- and 1-2 h post-exposure in 11 chinchillas. The animals were exposed for 24 h to an octave band of noise with a center frequency of 4 kHz and a sound pressure level of 86 dB. Three animals (0/0-day) had both cochleas terminal-fixed 2-3 h post-exposure. Two animals (27/27-day) had threshold shifts determined every other day for 1 week, every week thereafter, and underwent terminal-fixation of both cochleas 27 days after exposure. Six animals (0/n-day) had threshold shifts determined in both ears upon removal from the noise; their left cochlea was then survival-fixed 2-3 h post-exposure. Threshold shifts were determined in their right ear every 2-3 days until their hearing either returned to pre-exposure values or stabilized at a reduced level at which time their right cochlea was terminal-fixed (4-13 days post-exposure). All cochleas were prepared as plastic-embedded flat preparations. Missing hair cells were counted and supporting cells and nerve fibers were evaluated throughout the organ of Corti using phase-contrast microscopy. Post-exposure, all animals had moderate TTSs in their left and right ears which averaged 43 dB for 4-12 kHz. In the 0/0-day animals, the only abnormality which correlated with TTS was a buckling of the pillar bodies. In the 0/n-day animals, their left cochlea (survival-fixed 2-3 h post-exposure) had outer hair cell (OHC) stereocilia which were not embedded in the tectorial membrane in the region of the TTS whereas OHC stereocilia were embedded in the tectorial membrane throughout the cochleas of non-noise-exposed, survival-fixed controls. Three of six right cochleas (terminal-fixed 4-13 days post-exposure) from the 0/n-day animals developed a PTS and two of these cochleas had focal losses of inner and outer hair cells and afferent nerve fibers at the corresponding frequency location. The other cochlea with PTS had buckled pillars in the corresponding frequency region. These results suggest that with moderate levels of noise exposure, buckling of the supporting cells results in an uncoupling of the OHC stereocilia from the tectorial membrane which results in a TTS. The mechanisms resulting in TTS appear to be distinct from those that produce permanent hair cell damage and a PTS.

Acoustic Stimulation↗

PubMed1988

Histopathology of the temporal bones of deaf dogs.

Histopathological studies were done in 22 deaf dogs consisting of 10 Dalmatians, 5 English setters, 2 Great Danes, 2 foxhounds, 1 shepherd, 1 bulldog and 1 Australian sheep dog. Hypoplasia or aplasia of the sensory cells of the organ of Corti, stria vascularis and macula sacculi (pars inferior) was noted in all deaf dogs examined, indicating the pathology of inner ear malformation in these dogs to be of Scheibe's type. A solidified and calcified tectorial membrane was noted in 19 out of the 22 deaf dogs. A calcified sclerosis of the tectorial membrane is thought to be a characteristic finding of genetically inherited anomaly of the inner ear in deaf dogs. Distortion of the tectorial membrane, absence of the sensory cells in the organ of Corti, agenesis of the stria vascularis and abnormalities of the saccule described Scheibe's dysgenesis of the pars inferior as the pathological correlate for deafness in these dogs as assessed functionally.

Animals↗

PubMed1986

Developmental aspects of glycoprotein secretion and migration in the endolymphatic space.

Secretion and migration of sulphated glycoproteins during the early postnatal development of the rat inner ear was studied autoradiographically with the use of 35SO4. This isotope was found to be selectively incorporated into the embryonal sulcus cells and subsequently expelled into the tectorial membrane. This process decreased simultaneously with the replacement of the tall sulcus cells by cuboidal cells and the detachment of the tectorial membrane from these cells. A two stage development of the tectorial membrane is postulated: formation of filaments followed by incorporation of glycoproteins. Incorporation of isotope was also observed in the sensory epithelium of the vestibular part of the labyrinth, followed by migration into the cupulae and otolithic membranes. The accumulation of labelled material in the lumen of the endolymphatic sac 6 hours after isotope administration, suggests the existence of endolymph flow towards the endolymphatic sac in the early postnatal period.

Animals↗

PubMed1995

Expression of the carbohydrate epitope 3-fucosyl-N-acetyl-lactosamine (CD 15) in the adult guinea pig inner ear.

The expression of the CD 15 (3-fucosyl-N-acetyl-lactosamine) epitope was immunohistochemically studied on paraffin sections of adult guinea pig inner ears. Two regions of the inner ear expressed the epitope for CD 15: the tectorial membrane of the cochlea and the endolymphatic sac. The upper part of the main body of the tectorial membrane was deeply stained. In the rugosal and distal part of the endolymphatic sac several unevenly distributed cells showed strong intra- and extracellular localization of the CD15 epitope. The CD15 epitope is associated with a transduction structure (tectorial membrane) and with a "volume regulating" compartment (endolymphatic sac) and may be involved in the maintenance of the structural integrity of both.

Animals↗

PubMedDate not supplied

What basilar-membrane tuning says about cochlear micromechanics.

Experiments performed within the last 15 years on cochleas of live animals indicate that the cochlear sound analysis is much sharper than was expected from Békésy's experiments on postmortem preparations. The mechanism underlying the sharp analysis has not yet been ascertained experimentally. However, details of mechanical tuning curves defined by the amplitude of basilar-membrane vibration as a function of sound frequency ofr a constant amplitude of stapes displacement, together with structural and physical properties of he basilar and tectorial membranes and of the organ of Corti, strongly suggest a mechanism. The mechanism is assumed to result from a resonance of the tectorial membrane produced by interaction of the membrane's mass with its viscoelastic attachments to the organ of Corti and the spiral limbus. The resonance would produce a strong vibration of the tectorial membrane in the radial plane and enhance the shear motion between the membrane and the reticular lamina. Mechanical and computer models of the mechanism have allowed the authors to reproduce in detail the empirical basilar membrane as well as corresponding neural tuning curves and to account for associated cochlear nonlinearities.

Animals↗

PubMed1993

Anatomical and roentgenographic features of atlantooccipital instability.

An anatomical study using six fresh, human cadaveric cervical spine specimens was performed. After the dissection of all soft tissue, flexion-extension radiographs were obtained to verify initial stability. A sagittal plane bone cut was then made, centered on the odontoid and sparing the alar ligaments, the tectorial membrane, and the atlantooccipital (AO) ligaments. Repeat flexion-extension radiographs and photographs were taken to document maintenance of stability of these hemisections. The occipital-atlantoaxial ligaments were then individually and sequentially incised, maintaining all other structures each time. After the sectioning of each ligament, flexion-extension radiographs and photographs were obtained to identify subsequent motion patterns. Both gross anatomical and roentgenographic examinations demonstrated the important stabilizing role of the tectorial membrane in flexion. Additionally, contact between the posterior arch of C1 and the occiput limited hyperextension as a secondary restraint once the tectorial membrane was sectioned. Furthermore, the AO ligaments proved to play an insignificant role in the preservation of AO stability through a flexion-extension arc of motion. Under normal circumstances, the AO articulation is not excessively stressed. However, acute AO injury, as well as the insidious failure of these ligaments, has been documented in several cases involving various pathologies. This study demonstrates a mechanism of instability and highlights the essential role of the tectorial membrane in maintaining upper cervical spine stability.

Atlanto-Occipital Joint↗

PubMed1995

Filtering of distortion-product otoacoustic emissions in the inner ear of birds and lizards.

When the output magnitude of more than one order of distortion-product otoacoustic emission (DPOAE) is measured, they reach their maximum at the same DPOAE frequency. This fact led several authors to the assumption that, subsequent to their generation in the cochlea, the DPOAE are band-pass filtered. It was suggested that the tectorial membrane is the structure responsible for this filtering. In this report, we show that the same kind of "DPOAE tuning' is shown by animals which have hearing organs with tectorial structures of very different morphology, or even with no tectorial membrane at all. We therefore conclude that it is unlikely that the filter is the tectorial membrane.

Acoustic Stimulation↗

PubMed2005

Type IX collagen is crucial for normal hearing.

cDNA microarray analysis indicated that COL9A1 and COL9A3 are highly expressed in the human inner ear, suggesting that type IX collagen has a crucial functional role in the inner ear. This study further confirmed, by means of real-time PCR, the presence of collagen type IX genes in the mouse inner ear. Immunocytochemical analysis also revealed that type IX collagen is distributed in the tectorial membrane, where it co-localizes with type II collagen, indicating that type IX collagen may contribute to the three-dimensional integrated structure of type II collagen molecules. Mice with targeted disruption of the col9a1 gene were shown through assessment by auditory brain stem response to have hearing loss, suggesting an important role of type IX collagen in maintaining normal hearing. At the light microscopic level, the tectorial membrane of knock-out mice was found to be abnormal in shape, and electron microscopy confirmed disturbance of organization of the collagen fibrils. An antibody against type II collagen failed to detect type II collagen in the tectorial membrane of type IX collagen knock-out mice, suggesting that a lack of type IX collagen may affect the three-dimensional structure of type II collagen molecules. These findings indicate that genes encoding each chain of type IX collagen may fulfill an important function associated with the tectorial membrane in the auditory system.

Animals↗

PubMed2004

Spatial tuning curves along the chick basilar papilla in normal and sound-exposed ears.

Intense sound exposure destroys chick short hair cells and damages the tectorial membrane. Within a few days postexposure, signs of repair appear resulting in nearly complete structural recovery of the inner ear. Tectorial membrane repair, however, is incomplete, leaving a permanent defect on the sensory surface. The consequences of this defect on cochlear function, and particularly frequency analysis, are unclear. The present study organizes the sound-induced discharge activity of cochlear nerve units to describe the distribution of neural activity along the tonotopic axis of the basilar papilla. The distribution of this activity is compared in 12-day postexposed and age-matched control groups. Spontaneous activity, tuning curves, and rate-intensity functions were measured in each unit. Discharge activity at 60 frequency and intensity combinations was identified in the tuning curves of hundreds of units. Activity at each of these criterion frequency/intensity combinations was plotted against the unit's characteristic frequency to construct spatial tuning curves (STCs). The STCs depict tone-driven cochlear nerve activity along the length of the papilla. Tuning sharpness, low- and high- frequency slopes, and the maximum response were quantified for each STC. The sharpness of tuning increased with increasing criterion frequency. However, within a frequency, increasing sound intensity yielded more broadly tuned STCs. Also, the high-frequency slope was consistently steeper than the low-frequency slope. The STCs of exposed ears exhibited slightly less frequency selectivity than control ears across all frequencies and larger maximum responses for STCs with criterion frequencies spanning the tectorial membrane defect. When rate-intensity types were segregated, differences were observed in the STCs between saturating and sloping-up units. We propose that STC shape may be determined by global mechanical events, as well as localized tuning and nonlinear processes associated with individual hair cells. The results indicated that 12 days after intense sound exposure, global and local contributions to spatially distributed neural activity are restored.

Animals↗

PubMed1995

Shearing motion in the hearing organ measured by confocal laser heterodyne interferometry.

To investigate the presence of the postulated shearing motion in the micromechanics of the inner ear during sound stimulations we measured the vibratory response of the tectorial membrane and the reticular lamina in the third cochlear turn in an isolated temporal bone preparation using confocal laser heterodyne interferometry. The mechanical response of the tectorial membrane had the same frequency of maxima as the underlying reticular lamina, but was not as sharply tuned. When the two-dimensional motion was calculated from measurements made from several viewing angles it was found that the vibration of the reticular lamina had significant components both normal and tangential to its surface. The tectorial membrane motion, however, was primarily in a direction approximately perpendicular to the surface of the reticular lamina. The results indicate that shearing motion is produced predominantly by the radial motion of the reticular lamina.

Acoustic Stimulation↗

PubMedDate not supplied

Incomplete recovery of chicken distortion product otoacoustic emissions following acoustic overstimulation.

Distortion product otoacoustic emissions (DPOAEs) were measured in chickens before and after exposure to a 525-Hz pure tone (120 dB SPL, 48 h). The exposure caused extensive hair cell loss and destroyed the tectorial membrane along the abneural edge of the basilar papilla in the low-to-mid-frequency region of the cochlea. Although the lesion was restricted, DPOAEs were greatly depressed at all frequencies immediately after the exposure. The high-frequency DPOAEs gradually recovered to preexposure values after the exposure; however, there was little or no improvement in DPOAEs at test frequencies equal to or slightly above the exposure frequency even after 16 weeks of recovery. By 28 days of recovery, the previously damaged region of the basilar papilla had been repopulated by hair cells and the lower honeycomb layer of the tectorial membrane had regenerated, but not the upper fibrous layer. The upper fibrous layer of the tectorial membrane was still missing after 16 weeks of recovery and the region of damage corresponded closely to the frequency regions where the DPOAEs were depressed.

Acoustic Stimulation↗