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Results for “Basilar Membrane”

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At least 19 recordsLinked to original sources

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.

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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.

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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.

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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.

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PubMed1978

Stiffness gradient along the basilar membrane as a basis for spatial frequency analysis within the cochlea.

Stiffness z of the basilar membrane of the house mouse against a displacement by sound was calculated from data on width and thickness of the membrane. Three functions of the kind log10z = ax + b were obtained which equally express the stiffness change in dependence on the locus x on the basilar membrane. These functions were compared with the one for frequency representation. The result is that the spatial distribution of displacement maxima for frequencies and of stiffness follows the same kind of place-dependent functions over a large portion of the basilar membrane. From this it can be concluded empirically that the frequency and stiffness (calculated from width and thickness of the basilar membrane) scales along the cochlea are generally proportional to each other and that stiffness is a dominant factor for the determination of the locus of the displacement maximum for a given frequency.

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PubMedDate not supplied

[Assessment of the anisotropic stiffness component of the basilar membrane].

The average through the section components Dy and Dx of the basilar membrane anisotropic stiffness are evaluated from Bekesy's hydrostatic and hair probe experiments. A contradiction is found between the values and the behaviour of Dy component, calculated from the hydrostatic experiment and from the hair probe. The solution of the strongly bent plate equation for the average through the section transversal component of the basilar membrane anisotropic stiffness is obtained by the asymptotic method. A significant divergence between effective and bending stiffness can exist if the thickness of the human basilar membrane is about twice of that of the guinea pig.

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PubMed1992

Two-tone suppression in the basilar membrane of the cochlea: mechanical basis of auditory-nerve rate suppression.

1. The vibratory response to two-tone stimuli was measured in the basilar membrane of the chinchilla cochlea by means of the Mössbauer technique or laser velocimetry. Measurements were made at sites with characteristic frequency (CF, the frequency at which an auditory structure is most sensitive) of 7-10 kHz, located approximately 3.5 mm from the oval window. 2. Two-tone suppression (reduction in the response to one tone due to the presence of another) was demonstrated for CF probe tones and suppressor tones with frequencies both higher and lower than CF, at moderately low stimulus levels, including probe-suppressor combinations for which responses to the suppressor were lower than responses to the probe tone alone. 3. For a fixed suppressor tone, suppression magnitude decreased as a function of increasing probe intensity. 4. The magnitude of suppression increased monotonically with suppressor intensity. 5. The rate of growth of suppression magnitude with suppressor intensity was higher for suppressors in the region below CF than for those in the region above CF. 6. For low-frequency suppressor tones, suppression magnitude varied periodically, attaining one or two maxima within each period of the suppressor tone. 7. Suppression was frequency tuned: for either above-CF or below-CF suppressor tones, suppression magnitude reached a maximum for probe frequencies near CF. 8. Cochlear damage or death diminished or abolished suppression. There was a clear positive correlation between magnitude of suppression and basilar-membrane sensitivity for responses to CF tones. 9. Suppression tended to be accompanied by small phase lags in responses to CF probe tones. 10. Because all of the features of two-tone suppression at the basilar membrane match qualitatively (and, generally, also quantitatively) the features of two-tone rate suppression in auditory-nerve fibers, it is concluded that neural two-tone rate suppression originates in mechanical phenomena at the basilar membrane. 11. Because the lability of mechanical suppression parallels the loss of sensitivity and frequency tuning due to outer hair cell dysfunction, the present findings suggest that mechanical two-tone suppression arises from an interaction between the outer hair cells and the basilar membrane.

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PubMed1978

Basilar membrane motion in a spiral-shaped cochlea.

To examine the influence of the spiral coiling of the cochlea upon the motion of the basilar membrane, a mathematical model of the cochlea is constructed. The formulation of the problem leads to Laplace's equation in three dimensions in a curvilinear coordinate system plus corresponding boundary conditions. By basing the choice of the coordinate system upon the form of the helix representing the centerline of the basilar membrane, a relatively simple formulation is obtained. The helix parameters appear only in the Laplacian, not in the boundary conditions. From experimental data the equations of the basilar membrane's centerline are derived for a human cochlea, both in intrinsic form and in regular form. The relative simplicity of the formation permits the tentative conclusion that, in spite of the large curvature near the apex, the spiral shape of the cochlea has only a small influence upon the motion of the basilar membrane.

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PubMed1978

The temporal relationship between basilar membrane motion and nerve impulse initiation in auditory nerve fibers of guinea pigs.

When the helicotrema was obstructed in guinea pigs, trapezoidal displacement of the round window membrane produced a trapezoidal microphonic which indicated a unidirectional displacement of the entire length of the basilar membrane. Responses of single auditory nerve fibers to the trapezoidal displacement of the round window membrane were recorded after obstruction of the helicotrema. About 39% of the 424 fibers showed tonic responses which demonstrated directional sensitivity. More than 90% of these fibers increased their discharge rate during displacement of the basilar membrane toward the scala tympani and decreased their discharge rate during oppositely directed displacement. Less than 5% of the tonic fibers responded in the reverse manner. About 23% of the auditory nerve fibers responded to onset and/or cessation of trapezoidal motion of the basilar membrane. About 28% showed a combination of the tonic and phasic responses. However it is probably that all phasic responses we observed do not arise from velocity-sensitive fibers but some may represent artifacts. Both possibilities remain open until further studies are performed. The transduction mechanism of the cochlea is discussed on the basis of our data obtained by unidirectional displacement of the basilar membrane.

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PubMed1979

Noise-induced hearing losses. Can they be explained by basilar membrane movement?

The development of noise-induced hearing losses must in some way be related to the basilar membrane movement. Our analysis of this relationship is based on Mössbauer effect measurements of the basilar membrane movement in human temporal bone preparations. At a single basilar membrane position in each of seven preparations, the displacement frequency response was measured for a given sound pressure level at the ear drum. The measurements covered the place range 2.2--6.2 kHz. Despite the inadequacy of the experimental data, there seems to be no doubt that low frequency components contribute substantially to the displacement and mechanical strain of the hair cells near the 4 kHz location, where the hair cells are known to be most vulnerable to noise damage. In fact, the analysis performed indicates that these cells will suffer the greatest mechanical strain, almost irrespective of the spectrum shape of the stimulus noise.

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PubMed1992

Using acoustic distortion products to measure the cochlear amplifier gain on the basilar membrane.

Most models of the cochlea developed during the last decade have explained frequency selectivity and sensitivity of the cochlea at threshold by the use of power amplification of the acoustic wave on the basilar membrane. This power amplification has been referred to as the cochlear amplifier (CA). In this paper, a method to measure the cochlear amplifier gain as a function of position along the basilar membrane is derived from a simple model. Next, experimental evidence is presented that strongly restricts the properties of these proposed cochlear amplifier models. Specifically, it is shown that small signals generated by mechanical nonlinearities in the basilar membrane motion are not amplified during basilar membrane propagation, contrary to what would be expected from the cochlear amplifier hypotheses. This paper describes a method of measuring the cochlear power gain as a function of frequency and position, from the stapes to within 2 mm of the place corresponding to the frequency being measured. Experimental results in the cat indicate that the total gain of the cochlear amplifier, over the range of positions measured, must be less than 10 dB. The simplest interpretation of the experimental results is that there is no cochlear amplifier. The results suggest that the cochlea must achieve its frequency selectivity by some other means.

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PubMed1992

Postnatal development of the rat organ of Corti. I. General morphology, basilar membrane, tectorial membrane and border cells.

The development of the rat organ of Corti was studied during the first postnatal weeks. The temporal and the spatial patterns of cochlear development were investigated between 4 and 24 days after birth by means of semi-thin sections at approx. ten equidistant positions along the entire cochlear duct. At all examined positions width, thickness and cross sectional area of basilar membrane, cross-sectional area of tectorial membrane, of cells of Hensen, Claudius and Boettcher and of the organ of Corti were quantitatively analyzed. The most conspicuous maturational changes occur between 8 and 12 days after birth. These are the detachment of the tectorial membrane, the first appearance of filaments within the basilar membrane, the formation of the tunnel of Corti and the opening of the inner spiral sulcus. Quantitative analysis revealed that structures of a given position along the cochlear duct do not develop synchronously. Width of the basilar membrane and cross-sectional area of the tectorial membrane are already mature at the onset of hearing (10-12 days after birth). Length, thickness and cross-sectional area of the basilar membrane as well as cross-sectional area of the organ of Corti and of the cells of Hensen, Claudius and Boettcher still develop after the onset of hearing (up to 20-24 days after birth). We suggest that basic cochlear function is established by structures which are mature before the onset of hearing. Cochlear structures which develop after the onset of hearing might be involved in this improvement during this period.

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PubMedDate not supplied

A study of the vibration of the basilar membrane in human temporal bone preparations by the use of the Mössbauer effect.

Using the Mössbauer technique, we have studied the vibration of the human basilar membrane and malleus head in the sound frequency range 0.2--9.0 kHz and at a sound pressure of 100 dB at the tympanic membrane. The displacement frequency response curves for the basilar membrane and the malleus head have similar shapes, with a maximum at about 1 kHz. Below and above 1 kHz the curves have a slope of about 10 dB/octave and--100 dB/octave, respectively. In addition, the basilar membrane has a maximum displacement at a frequency dependent distance from the stapes. A simple hydrodynamic model for the cochlea is used to interpret the experimental data. A possible mechanism for the frequency resolution of sound by the ear and noise-induced hearing loss is discussed.

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PubMed1992

Basilar membrane mechanics in the hook region of cat and guinea-pig cochleae: sharp tuning and nonlinearity in the absence of baseline position shifts.

A heterodyne laser interferometer was used to observe the movements of small (approximately 20 microns) stainless-steel beads placed on the basilar membrane in the hook region of cat and guinea-pig cochleae. In several preparations, the displacement patterns observed exhibited sharp nonlinear tuning; in one cat this tuning was comparable to that commonly observed in single auditory-nerve fibers. The most sensitive frequencies of the preparations ranged from 31-40 kHz in the cat, and 28-32 kHz in the guinea-pig. The sharp tuning and nonlinearity of the basilar membrane responses was not apparent in surgically or acoustically traumatized preparations. The response nonlinearities were susceptible to temporary threshold shifts and disappeared within a few minutes post-mortem. Stimulus-related shifts in the baseline position of the basilar membrane were not apparent at low stimulus levels. Such shifts were occasionally observed at higher stimulus levels (e.g., > 90 dB SPL), but never approached the fundamental (oscillatory) component of basilar membrane vibration in magnitude. These findings are discussed in relation to previous observations by other workers.

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PubMed1991

Application of a commercially-manufactured Doppler-shift laser velocimeter to the measurement of basilar-membrane vibration.

A commercially-available laser Doppler-shift velocimeter has been coupled to a compound microscope equipped with ultra-long-working-distance objectives for the purpose of measuring basilar membrane vibrations in the chinchilla. The animal preparation is nearly identical to that used in our laboratory for similar measurements using the Mössbauer technique. The vibrometer head is mounted on the third tube of the microscope's trinocular head and its laser beam is focused on high-refractive-index glass microbeads (10-30 microns) previously dropped, through the perilymph of scala tympani, on the basilar membrane. For equal sampling times, overall sensitivity of the laser velocimetry system is at least one order of magnitude greater than usually attained using the Mössbauer technique. However, the most important advantage of laser-velocimetry vis-à-vis the Mössbauer technique is its linearity, which permits undistorted recording of signals over a wide velocity range. Thus, for example, we have measured basilar-membrane responses to clicks whose waveforms have dynamic ranges exceeding 60 dB.

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PubMed1992

Responses to sound of the basilar membrane of the mammalian cochlea.

Recent evidence shows that the frequency-specific non-linear properties of auditory nerve and inner hair cell responses to sound, including their sharp frequency tuning, are fully established in the vibration of the basilar membrane. In turn, the sensitivity, frequency selectivity and non-linear properties of basilar membrane responses probably result from an influence of the outer hair cells.

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PubMed1991

Laser Doppler velocimetry of basilar membrane vibration.

A method is described for the measurement of basilar membrane (BM) vibration velocimeter (LDV). The instrumentation was coupled to a compound microscope which served to visualize reflective glass microbeads placed on the BM. The laser beam of the LDV was focused in the microscope object plane and positioned over the reflective bead. We show examples of frequency tuning curves and displacement input/output intensity functions obtained with the technique.

Acoustic Stimulation↗

PubMed1991

Shapes of rate-versus-level functions of primary auditory nerve fibres: test of the basilar membrane mechanical hypothesis.

Rate-versus level functions (RI functions) for characteristic frequency (CF) stimulation were measured from primary auditory nerve fibres from different spontaneous rate categories in the guinea pig cochlea. Attention was focussed on those fibres that showed clear breakpoints in their RI functions (sloping-saturation fibres). A statistical curve fitting procedure to an empirical equation was used to provide a quantitative estimate of the breakpoint position in individual fibres. It was found that, within the limits of reliability of the curve fitting procedure, the breakpoint position was the same in fibres from the same CF regions in any given animal. This result is consistent with the notion that the breakpoint position is determined by global basilar membrane mechanics and not by processes private to each nerve fibre. However, a subgroup of fibres not easily classifiable as sloping-saturation, showed features of their RI functions suggesting that factors other than basilar membrane mechanics could lead to fibre-to-fibre differences in rate-versus-level behaviour.

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