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Two passive mechanical conditions modulate power generation by the outer hair cells
Yanju Liu1, Sheryl M Gracewski1,2, Jong-Hoon Nam1,2
1Department of Mechanical Engineering, University of Rochester, Rochester, New York, United States of America.
Plos Computational Biology
|September 8, 2017
Summary
Outer hair cells amplify cochlear vibrations through active feedback. Organ of Corti mechanics, not just rigid body motion, explain why amplification is greater at the cochlea's base than apex.
Area of Science:
- Auditory Neuroscience
- Bioengineering
- Mechanics of Hearing
Background:
- Mammalian cochlear amplification relies on outer hair cell (OHC) electro-mechanical feedback.
- Amplification gradients exist along the cochlea, with greater gain at the base than apex.
- Previous models assumed rigid body kinematics for organ of Corti (OC) mechanics.
Purpose of the Study:
- To investigate the role of OC mechanics and OHC electro-mechanics in location-dependent cochlear amplification.
- To develop a more comprehensive model of cochlear active feedback.
- To identify the specific mechanical factors driving cochlear amplification gradients.
Main Methods:
- Utilized a fully deformable 3D finite element model of the cochlea.
- Incorporated physiological properties of OHCs, including active force gain, mechano-transduction, and membrane RC time constant.
- Explicitly modeled OC mechanics and OHC electro-mechanics.
Main Results:
- OC mechanics significantly influence the longitudinal trend of cochlear amplification.
- Two key mechanical conditions drive location-dependent amplification: OHC force phase relative to elongation rate and local OC stiffness.
- These factors explain the greater amplification observed towards the cochlear base.
Conclusions:
- Cochlear amplification is not solely determined by OHC feedback but is critically modulated by OC mechanics.
- The spatial variation in OHC force phase and local OC stiffness are the primary drivers of the base-apex amplification gradient.
- A detailed mechanical model is essential for understanding the complexities of auditory frequency tuning and amplification.
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