Impedance analysis of the organ of corti with magnetically actuated probes.

Abstract:

:An innovative method is presented to measure the mechanical driving point impedance of biological structures up to at least 40 kHz. The technique employs an atomic force cantilever with a ferromagnetic coating and an external magnetic field to apply a calibrated force to the cantilever. Measurement of the resulting cantilever velocity using a laser Doppler vibrometer yields the impedance. A key feature of the method is that it permits measurements for biological tissue in physiological solutions. The method was applied to measure the point impedance of the organ of Corti in situ, to elucidate the biophysical basis of cochlear amplification. The basilar membrane was mechanically clamped at its tympanic surface and the measurements conducted at different radial positions on the reticular lamina. The tectorial membrane was removed. The impedance was described by a generalized Voigt-Kelvin viscoelastic model, in which the stiffness was real-valued and independent of frequency, but the viscosity was complex-valued with positive real part, which was dependent on frequency and negative imaginary part, which was independent of frequency. There was no evidence for an inertial component. The magnitude of the impedance was greatest at the tunnel of Corti, and decreased monotonically in each of the radial directions. In the absence of inertia, the mechanical load on the outer hair cells causes their electromotile displacement responses to be reduced by only 10-fold over the entire range of auditory frequencies.

journal_name

Biophys J

journal_title

Biophysical journal

authors

Scherer MP,Gummer AW

doi

10.1529/biophysj.103.037184

subject

Has Abstract

pub_date

2004-08-01 00:00:00

pages

1378-91

issue

2

eissn

0006-3495

issn

1542-0086

pii

S0006-3495(04)73617-6

journal_volume

87

pub_type

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