The fluid-membrane interaction in the cochlear outer hair cell wall
J.T. Ratnanather, A.A. Spector, A.S. Popel and W. E. Brownell
Presented as Membrane viscoelastic properties of dancing outer hair cells of the inner ear at Mathematics and Molecular Biology IV, Santa Fe, NM, November 11-15, 1995.
Also presented as The fluid-membrane interaction in the cochlear outer hair cell wall at Euromech 344: Fluid-structure interactions in biomechanics, Imperial College London, April 10-13, 1996.
Also presented as Is the outer hair cell wall viscoelastic? at Diversity in Auditory Mechanics, University of California, Berkeley. June 24-28, 1996. Click here for a pdf copy of the paper.
Also presented as Viscosity effects on the dynamics of the cochlear outer hair cell at Society for Mathematical Biology Annual Meeting, North Carolina State University, Rayleigh. August 3-6, 1997.
Also presented as Analysis of viscoelastic deformations of the cochlear outer hair cell wall at the American Mathematical Society Annual Meeting, Baltimore. January 7-10, 1998.
Summary
Brownell et al (1985) discovered the phenomenon of cochlear outer hair cell
(OHC) electromotility in which the cylindrically shaped OHC elongates and
shortens in response to electrical stimuli at acoustic frequencies. Evidence
suggest that the OHCs are responsible for the remarkable frequency selectivity
of the mammalian cochlea. The OHC is a hydrostat: its lateral wall is both
elastic and mechanically reinforced and its shape is maintained by a pressurized
fluid core. Brundin and Russell (1994) found that mechanically induced OHC
deformations could be described in terms of a damped mechanical oscillator.
The question is whether the damping results from either the viscosity of the
cytoplasm and the surrounding fluid or the viscoelastic cell wall or both.
The OHC wall is assumed to be viscoelastic in which the effect of membrane
viscosity is considered together with a model of a cylindical elastic membrane.
A slender body perturbation approximation based on the OHC aspect ratio is used
to obtain expressions for the longitudinal membrane tension (which is balanced
by the fluid stresses from inside and outside the OHC) and the pressure
difference across the membrane. Assuming harmonic oscillations, preliminary
results indicate that when a mechanical stimulus is applied at one end of
the OHC, a peak displacement is attained at a length-dependent frequency
location.
References
Brownell, W.E., Bader, C.R., Bertrand, D., and Ribaupierre, Y. de (1985)
Evoked mechanical responses of isolated cochlear outer hair cells.
Science, 227, 194-196.
Brundin, L. and Russell, I. J. (1994) Tuned phasic and tonic motile responses of isolated outer hair cells to direct mechanical stimulation of the cell body. Hearing Research, 74, 35-45.
Evans, E.A. and Skalak, R. (1980) Mechanics and thermodynamics of biomembranes. CRC Press.
Iwasa, K.H. and Chadwick, R.S. (1992) Elasticity and active force generation of cochlear outer hair cells. J. Acoust. Soc. Am., 92, 3169-3173
Jen, D.H. and Steele, C.R. (1986) Electrokinetic model of cochlear outer hair cell motility. J. Acoust. Soc. Am., 82, 1667-1678
Tolomeo, J. (1996) Models of the structure and motility of the auditory outer hair cell. Ph.D. thesis, Stanford University.