Analysis Tools
hearing/vestibular/ear
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• in the basal coil, Hensen's stripe is absent
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• in the apical end of the apical coil, the marginal band is absent and the TM exhibits a significantly frayed peripheral edge
• in the basal coil, marginal band and Kimura's membrane are retained but Hensen's stripe is absent
• however, in both the apical and basal coils of the mature cochlea, the form, orientation and density of hair bundles on IHCs and OHCs are normal, with normal OHC hair-bundle imprints present in the lower surface of the TM
• the dynamic radial stiffness of the TM is unchanged in the high-frequency basal cochlear region, as shown by normal extracellular OHC receptor potentials in the 53-kHz region in response to tones of 10 kHz
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• in the apical end of the apical coil, the marginal band is absent
• in the basal coil, the marginal band is retained
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• at 3-4 months, homozygotes display complete absence of the striated-sheet matrix throughout the length of the TM, with irregular, wavy filaments, 8-10 nm in diameter, and straight filaments between the collagen fibrils
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• at 3-4 months, the cross-sectional area of the TM in the distal end of the apical coil is increased by ~2-fold relative to wild-type, but is not significantly different in the basal coils
• in the apical cochlear coil, TM thickness is increased by ~2-fold but radial width is unaltered
• in the basal cochlear coil, TM thickness, radial width, and cross-sectional area remain normal
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• at 3-4 months, tone-evoked basilar membrane vibrations at the 53-kHz place indicate enhanced basilar membrane tuning while sensitivity at the tip of the tuning curve is largely preserved
• the high- and low- frequency slopes at either side of the tip are steeper than those of wild-type mice, and the low-frequency tail of the tuning curve is relatively insensitive
• in addition, neural masking tuning curves are far sharper in sensitivity, with steeper high- and low-frequency slopes than those of wild-type mice
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• at 3-4 months, homozygotes display significantly increased CAP thresholds at frequencies below ~20 kHz relative to wild-type mice
• however, neural sensitivities remain normal for frequencies above ~20 kHz
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• DPOAEs are only generated in high-frequency regions of the cochlea at low SPLs, spreading to lower frequencies with increasing level of the primary tones
• at 3-4 months, homozygotes show a 20-30 dB reduction in DPOAE levels in the frequency region below 20 kHz relative to wild-type mice, even at the highest levels of test primary tones
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• at 3-4 months, homozygotes display a low-frequency hearing loss for frequencies below 20 kHz, despite an observed increase in sharpness of cochlear tuning in high-frequency (basal) regions
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nervous system
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• at 3-4 months, homozygotes display significantly increased CAP thresholds at frequencies below ~20 kHz relative to wild-type mice
• however, neural sensitivities remain normal for frequencies above ~20 kHz
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