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Results for “Basilar Membrane”

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At least 19 recordsLinked to original sources
PubMed1991

In vivo measurement of basilar membrane stiffness.

Basilar membrane stiffness measurements were made in the base of the gerbil cochlea. Basilar membrane stiffness was determined by contacting the basilar membrane with a stainless steel needle (tip diameter 25 microns) attached to a force transducer, putting the needle/transducer structure through a low-frequency sinusoidal excursion with amplitude 5 or 25 nm, and measuring the restoring force exerted on the needle by the basilar membrane at the applied frequency. Stiffness was calculated as the amplitude of the restoring force divided by the amplitude of the excursion. Stiffness was measured over a 24-microns range of static displacements of the basilar membrane and is presented as stiffness versus static displacement. In cochleas that were not damaged during surgery the stiffness versus displacement characteristic usually had the following features: (1) an initial stiffness plateau with average stiffness 0.6 N/m; (2) a second plateau or level off with average stiffness 9.1 N/m; and (3) an increase in stiffness beyond the second plateau that was consistent with the theoretical stiffness-vs-displacement function of a beam. These features were present both pre- and post-mortem.

Animals↗
PubMed1986

Travelling wave motion along the pigeon basilar membrane.

The basilar membrane (BM) motion in the pigeon was measured using the Mössbauer technique. Tonotopic frequency mapping and travelling wave motion were observed over the basal 35% of the BM. The sensitivity and sharpness of the BM tuning depended on the physiological condition of the cochlea. The observed amplitude responses did not match the frequency threshold tuning curves of single primary auditory fibers.

Acoustic Stimulation↗
PubMedDate not supplied

Modern methods for measurement of basilar membrane displacements.

Basilar membrane displacements in response to sound at threshold intensities are in the fractional Angstrom range. Visual measurements, as used by Bekesy in his pioneering studies, are by definition limited to values above 10 000 A. The present paper discusses a number of modern techniques capable of taking measurements at lower Anstrom levels: One-point methods (capacitive probe, Mossbauer effect, laser interferometry, and optical heterodyne spectroscopy) and pattern-assessing methods (time-averaged and real-time holography). Advantages and disadvantages of these methods are being discussed.

Acoustic Stimulation↗
PubMedDate not supplied

Mechanical properties of basilar membrane.

A fresh basilar membrane has different mechanical properties in the radial and in the longitudinal directions. When pressure with a needle is exerted on the basilar membrane, a narrow radially oriented strip is deflected. The form of the deflection can be deduced from the pathological consequences of the acoustic trauma as well. The observed anisotrophy is a property of the vital membrane and is disturbed by chemical and physical influences and is lost post mortem. The post-mortem changes can explain the results obtained by von Békésy which differ from ours. The physiological meaning of the mechanical properties of the basilar membrane is discussed here.

Animals↗
PubMed1997

Two-tone distortion on the basilar membrane of the chinchilla cochlea.

Basilar membrane responses to pairs of tones were measured, with the use of a laser velocimeter, in the basal turn of the cochlea in anesthetized chinchillas. Frequency spectra of basilar membrane responses to primary tones with frequencies (f1, f2) close to the characteristic frequency (CF) contain prominent odd-order two-tone distortion products (DPs) at frequencies both higher and lower than CF (such as 2f1-f2, 3f1-2f3, 2f2-f1 and 3f2-2f1). For equal-level primaries with frequencies such that 2f1-f2 equals CF, the magnitude of the 2f1-f2 DP grows with primary level at linear or faster rates at low stimulus levels, but it saturates or decreases slightly at higher levels. For a fixed level of one of the primary tones, the magnitude of the 2f1-f2 DP is a nonmonotonic function of the level of the other primary tone. For low intensities of the variable tone, the 2f1-f2 DP grows at a rate of approximately 2 dB/dB with f1 level and 1 dB/dB with f2 level. DP magnitudes decrease rapidly with increasing primary frequency ratio (f2/f1) at low stimulus levels. For more intense stimuli, DP magnitudes remain constant or decrease slowly over a wide range of frequency ratios until a critical value is reached, at which DP magnitudes fall with slopes as steep as -300 dB/octave. As stimulus level grows, DP phases increasingly lag for large f2/f1 ratios, but exhibit leads for small f2/f1 ratios. Cochlear exposure to an intense tone that produces large sensitivity losses for the primary frequencies (but only small losses for tones with frequency equal to 2f1-f2) causes a substantial decrease in magnitude of the 2f1-f2 DP. This result demonstrates that the 2f1-f2 DP originates at the basilar membrane region with CFs corresponding to the primary frequencies and propagates to the location with CF equal to the DP frequency. 2f1-f2 DPs on the basilar membrane resemble those measured in human psychophysics in most respects. However, the magnitude of basilar membrane DPs does not show the nonmonotonic dependence on f2/f1 ratio evident in DP otoacoustic emissions.

Animals↗
PubMed1997

Basilar membrane velocity noise.

Basilar membrane (BM) noise, measured as a velocity signal under the quiet acoustic condition, was investigated in the guinea pig. The cochleas of anesthetized young healthy guinea pigs were surgically exposed and a hole was made on the lateral wall of the scala tympani of the first cochlear turn for visualization of the BM and measurement of the BM velocity with a laser interferometer. The amplitude and frequency of the BM velocity noise were analyzed by a spectrum analyzer under different conditions. The spectrum of the BM velocity noise was a band limited function with a peak velocity at the topographic best frequency of the measured location on the BM. The peak velocity ranged to about 8 microm/s and depended on the physiological condition of the cochlea. Saline blockage of the external auditory canal or the middle ear did not change the BM noise. BM noise was much smaller, or was not evident, when the cochlear sensitivity decreased. The suppression tuning curve of the BM velocity noise indicates that the maximum suppression caused by an acoustic pure tone occurred at the best frequency location. A low sound level wide band acoustic noise given to the external ear canal produced a spectrum function having the same frequency and amplitude response as the BM noise. Electrical stimulation of the crossed olivocochlear bundle significantly depresses the BM velocity noise. These data demonstrate that the BM noise is a representation of internal rather than external noise. The amplitude and frequency of the BM noise reflect the usual cochlear sensitivity and frequency selectivity. Since the organ of Corti in the sensitive cochlea is a highly sensitive and tuned mechanical system, the internal (to the animal) noise responsible for the BM noise may originate from mechanical vibrations remote from the cochlea and propagated to the ear, or may be caused by Brownian motion of cellular structures in the cochlea.

Acoustic Stimulation↗
PubMed1984

Histological evaluation of damage in cat cochleas used for measurement of basilar membrane mechanics.

Cochleas utilized in basilar membrane vibration measurements were examined histologically using an epon-embedded surface preparation technique. The amount of damage observed at both the apical and basal ends of the cochleas was variable. The apical damage was probably caused by large, low-frequency movements of the basilar membrane. The basal damage was due to trauma produced directly by the surgical and experimental procedure. The sharpness of turning observed in the basilar membrane frequency response was found to be inversely related to the extent of histological damage.

Animals↗
PubMed1982

Measurement of basilar membrane motion in the guinea pig using the Mössbauer technique.

Basilar membrane motion was measured at the 16-19 kHz place of the guinea pig cochlea using the Mössbauer technique. The threshold of the gross cochlear action potential (CAP) evoked by pure-tone bursts was used as an indication of neural threshold. CAP threshold deteriorated progressively after the cochlea was opened and the Mössbauer source placed on the basilar membrane. A close relationship was found between the amplitude of basilar membrane motion at the source place frequency and CAP threshold. Basilar membrane velocity at CAP threshold SPL was about 0.04 mm/s over a 60-dB range of CAP threshold. Intensity functions for basilar membrane motion were linear for frequencies more than an octave below the source place frequency but demonstrated progressive saturation for frequencies greater than an octave below the CF. This nonlinear behavior was eliminated as the CAP threshold became less sensitive and was absent post mortem. Isovelocity curves at the 0.04 mm/s criterion were remarkably similar to frequency threshold curves from primary afferent fibers innervating a similar place on the basilar membrane. The isovelocity curve was a better fit than the isoamplitude curve suggesting that inner hair cells respond to basilar membrane velocity. As the CAP threshold deteriorated, the isovelocit curves lost sensitivity around the best frequency, whereas sensitivity to frequencies below 10 kHz remained constant even after the animal was killed. We suggested that most of the frequency response and nonlinear behavior of inner hair cells and afferent fibers may be found in basilar motion.

Animals↗
PubMed1986

Relationship between basilar membrane tuning and hair cell condition.

Basilar membrane tuning characteristics were measured in 15 cats using laser interferometry. The experimental procedures introduced varying degrees of cochlear trauma. Variability from animal to animal was also observed in the characteristic frequency (CF) of tuning, the sensitivity at CF and lower frequencies, and the sharpness of tuning. The changes in the tuning characteristics of the basilar membrane are correlated with the extent of outer hair cell (OHC) damage. These observations lead to the conclusion that the tuning properties in the CF region are predominantly determined by the mechanical properties of the OHC and not the basilar membrane.

Animals↗
PubMed1997

The location of the cochlear amplifier: spatial representation of a single tone on the guinea pig basilar membrane.

Acoustic stimulation vibrates the cochlear basilar membrane, initiating a wave of displacement that travels toward the apex and reaches a peak over a restricted region according to the stimulus frequency. In this characteristic frequency region, a tone at the characteristic frequency maximally excites the sensory hair cells of the organ of Corti, which transduce it into electrical signals to produce maximum activity in the auditory nerve. Saturating, nonlinear, feedback from the motile outer hair cells is thought to provide electromechanical amplification of the travelling wave. However, neither the location nor the extent of the source of amplification, in relation to the characteristic frequency, are known. We have used a laser-diode interferometer to measure in vivo the distribution along the basilar membrane of nonlinear, saturating vibrations to 15 kHz tones. We estimate that the site of amplification for the 15 kHz region is restricted to a 1.25 mm length of basilar membrane centered on the 15 kHz place.

Acoustic Stimulation↗
PubMed1998

Vibration of reflective beads placed on the basilar membrane.

Most investigators place reflective beads on the basilar membrane to measure its vibration with optical methods. It is therefore important to find out if the beads faithfully follow the motion of the structures on which they are placed. Vibration of the beads on the basilar membrane and basilar membrane adjacent to the beads are measured in the third turn of the guinea pig cochlea in a temporal bone preparation. It is shown that the beads do not follow the motion of the organ. The mechanism by which this departure may occur is investigated by modeling the motion of the beads on the Claudius' cells.

Acoustic Stimulation↗
PubMed1978

The basilar membrane of the bat, Pteronotus p. parnellii.

The basilar membrane of Pteronotus p. parnellii was studied by light and scanning electron microscopy in order to examine the relationship of membrane structure to the sharply tuned sense of hearing in this bat. The basilar membrane was found to differ from those of other mammals and other bats by showing virtually no change in width except at the extreme ends. Thickenings of the pars pectinata and pars tecta are well developed in Pteronotus; they show no sudden changes in their dimensions and in this way differ from the thickenings found in the European horseshoe bat whose sharply tuned sense of hearing seems at least partially dependent on sudden, marked changes in the structure of the basilar membrane. In Pteronotus the greater part of the basilar membrane, 7.5 mm or approximately 58%, lies within the enormous basal turn and within this turn there are steeply banked curves and one small 0.5-mm region where the membrane is straight. The straight portion is associated with a region of the cochlea where there is a marked change in the density of nerve fibers and where the stria vascularis, spiral ligament and fluid-filled spaces of the ear are enlarged.

Animals↗
PubMed1996

[Direct observation of the vibration and the traveling wave on the basilar membrane of the guinea pig].

Basilar membrane vibration was investigated in guinea pigs by using a laser Doppler velocimeter. To monitor the physiological condition of the cochlea, compound action potentials and distortion product otoacoustic emissions were measured before and after each experiment. Sharply tuned (Q10dB : 4.6-7.0) mechanical vibrations were successfully observed in 190 preparations of 15 animals. In these animals, strong compressive nonlinearity of the basilar membrane response and steep phase lag above the characteristic frequency were observed clearly. These findings strongly support the existence of active mechanical elements that play important roles behind the auditory transduction in the cochlea.

Action Potentials↗
PubMed2000

Basilar membrane responses to broadband stimuli.

Basilar membrane (BM) responses to two types of broadband stimuli-clicks and Schroeder-phase complexes--were recorded at several sites at the base of the chinchilla cochlea. Recording sites (characteristic frequency, CF, in the range of 5.5-18 kHz) span the 1-4-mm basal region of the basilar membrane. BM responses to clicks consisted of undamped oscillations with instantaneous frequency that increased over time until it reached a value around CF. The time constant of this glide is CF dependent. Throughout the entire region under study, BM vibration exceeded umbo motion by up to 60 dB. Nonlinear properties of BM responses to clicks resemble those found in the more studied 8-10-kHz region. Amplitude spectra of Schroeder-phase complex stimuli, which consist of a series of sinusoidal components summed in negative (-SCHR) and positive Schroeder phase (+SCHR), are flat. The envelope of BM responses to +SCHR stimuli contains valleys, or dips, that are wider than those found in responses to the -SCHR stimuli. Hence, BM responses to the former stimuli are "peakier" than responses to the latter. Differences in response waveforms are less obvious in linear cochleae. Suppression of a near-CF tone by -SCHR stimuli was larger than that evoked by +SCHR stimuli.

Acoustic Stimulation↗
PubMed1984

Ultrastructural damage in cochleas used for studies of basilar membrane mechanics.

Cat cochleas used for interferometric studies of basilar membrane mechanics were examined with the electron microscope. The structures most severely damaged in the experimental cochleas are the outer hair cells and the radial afferent fibers to the inner hair cells. Since the basilar membrane and other supporting structures appear to be normal, mechanical changes observed in the experimental cochleas are most probably due to outer hair cell damage. Individual animals with varying degrees of damage showed large differences in the frequency of basilar membrane resonance at the same place in the cochlea. Shifts in tuning of this magnitude could occur as a consequence of hair cell damage only if the stiffness of the stereocilia and associated structures was greater initially than the stiffness of the basilar membrane and gradually decreased with damage. The present series of observations, therefore, suggest that the stiffness of the outer hair cell stereocilia determines basilar membrane tuning.

Animals↗
PubMedDate not supplied

The ultrastructure of the basilar membrane in the cat.

A detailed study of the feline basilar membrane was performed in 13 cochleae with light microscopy and in six with electron microscopy. The distribution of the mesothelial cells and homogeneous ground substance with the filaments was recorded and plotted as a function of length along the cochlear duct. The width, thickness and number of filaments were also measured. In the lower basal turn the basilar membrane was narrowest and its entire thickness was occupied by filaments. In the apical region the width was maximal and the filaments were fewer. The density of the filaments counted in the bundles showed no significant difference along the cochlear duct or across the width of the basilar membrane, but the number of filaments decreased markedly (approximately a ten-fold difference) from base to apex. The number of mesothelial cells increased towards the apex. These morphological characteristics may be related to the different motion pattern of the basilar membrane along the length of the cochlear duct. A discontinuity of the basement membrane was noted in the apical region in all cochleae studied. These gaps seemed to provide structural evidence for the permeability of the basilar membrane in this area. The vas spiralis was present as a blood vessel in two specimens and only in the apical region. Thus, its function as the sole nutritional source for the organ of Corti is doubtful.

Age Factors↗
PubMed1982

Studies on fibrous tissues of the basilar membrane in inner ear.

Of a number of electron microscope studies on the basilar membrane of the inner ear cochlear duct so far reported, none seems to have been conducted using PAM of R.R. staining, excellent stainings especially suited for the observation of connective tissue. In this study the basilar membrane of the cochlear duct in young and mature guinea pigs and human fetuses was examined with an electron microscope using these stainings, and obtained the interesting results described below. Fibrils of the basilar membrane, although strongly PAM-positive, all lacked periodic stripes, indicating that they were collagenous fibrils in an immature state. Young guinea pigs clearly differed from mature ones in that numerous fibroblasts were present. In human fetuses, the basilar membrane exhibited no clear fibrillar structure in the 13th week, but had PAM-positive fibrils in the 20th week. By the 23rd week, it had assumed roughly the same structure as in adults, although numerous fibroblasts were still present, and resembled the basilar membrane in young guinea pigs. The basilar membrane is a part of a unique organ, a sensory organ. Though comparison is difficult because of the extremely complicated anatomy of the organ, it is concluded that the fibrils of basilar membrane are collagenous fibrils in a peculiarly immature state, and similar to those in the cartilage and tympanic membrane.

Aged↗
PubMed1985

Structural implications of basilar membrane compliance measurements.

Static point-load measurements of basilar membrane compliance were made in the basal region of the excised guinea pig cochlea. Points on a radial line across the basilar membrane were displaced in one-half micron increments and the force required to maintain each increment recorded. The results are interpreted in terms of the material layers of the basilar membrane and displayed as compliance curves. In addition, a beam model of the basilar membrane, including the arches of Corti and the actual geometry of the pectinate zone, is constructed from anatomical data. The free parameters in this model are the modulus of elasticity of the transverse filaments and the effective spring stiffness of the arches. Compliance curves for the model are generated with a finite element approach and the parameters are obtained by requiring optimal agreement with the experimental measurements. The results show that the separation between fiber layers in the pectinate zone is relevant to the effective moment of inertia of the cross section and that the longitudinal coupling between the heads of the arches provides a rigidity to the arcuate zone not seen in the pectinate zone where longitudinal coupling is minimal. The elastic modulus calculated for the filaments is 1.8 GPa, approximately one-half that of keratin, while the cells and ground substance are five orders of magnitude softer.

Animals↗