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A role for tectorial membrane mechanics in activating the cochlear amplifier
Amir Nankali1, Yi Wang2, Clark Elliott Strimbu2
1Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI, 48109, USA.
Scientific Reports
|October 20, 2020
Summary
Acoustic stimuli trigger nonlinear cochlear responses due to outer hair cells (OHCs). A discovered phase shift in OHC voltage enables efficient power transfer, enhancing sound amplification.
Area of Science:
- Auditory Neuroscience
- Bioacoustics
- Biophysics
Background:
- Mammalian cochlear responses to sound are nonlinear and frequency-tuned.
- Outer hair cells (OHCs) drive an active amplification process in the cochlea.
- Previous studies noted a phase shift in OHC voltage relative to basilar membrane displacement near characteristic frequency (CF).
Purpose of the Study:
- To investigate the physical mechanism behind the observed phase shift in cochlear electromechanical responses.
- To validate experimental findings using a comprehensive mathematical model.
Main Methods:
- Utilized a comprehensive electromechanical mathematical model of cochlear sound response.
- Analyzed the phase relationship between OHC-generated extracellular voltage and basilar membrane displacement.
- Investigated the role of tectorial membrane impedance in the observed phenomenon.
Main Results:
- The mathematical model successfully predicted the ~0.3 cycle phase shift in extracellular voltage at approximately one-half octave below CF.
- This phase shift was found to originate from a minimum in the radial impedance of the tectorial membrane and its limbal attachment.
- The model supports the hypothesis that this impedance minimum enables efficient electrical-to-mechanical power transfer.
Conclusions:
- Experimental and theoretical results confirm a significant phase shift in cochlear voltage.
- A tectorial membrane resonance is proposed as the mechanism responsible for the phase shift.
- This resonance is crucial for enabling the cochlear amplifier by optimizing power transfer.
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