Abstract
The mammalian basilar membrane (BM) consists of two collagen-fiber layers responsible for the frequency-to-place tonotopic mapping in the cochlea, which together form a flat beam over at least part of the BM width. The mechanics of hearing in rodents such as gerbil pose a challenge to our understanding of the cochlea, however, because for gerbil the two layers separate to form a pronounced arch over the remaining BM width. Moreover, the thickness and total width normally thought to determine the local stiffness, and tonotopic mapping in turn, change little along the cochlear length. A nonlinear analysis of a newly developed model, incorporating flat upper and arched lower fiber layers connected by ground substance, explains the initial plateau and subsequent quadratic increase found in measured stiffness vs. deflection curves under point loading, while for pressure loading the model accurately predicts the tonotopic mapping. The model also has applicability to understanding cochlear development and to interpreting evolutionary changes in mammalian hearing.
Highlights
Greenwood presented a function relating the cochlear location to the best frequency (BF), which was shown to be valid for several mammalian cochleae[29]
The present analysis has been for a gerbil BM without loading from the organ of Corti (OoC)
Only about half of the BM stiffness comes from the OoC7, 22, and most of this comes from the stiffness of the coupled pillar heads[23, 31]
Summary
The lower fiber band is modeled as a segmental arch with radius R. The lower arch thickness t1 and upper flat beam thickness t2 are from Schweitzer et al.[5]. Namely the PZ width Lp and the height h, for computing the BM stiffness under a point load at the mid-point of the arch (Q in Fig. 1c), are taken from Edge et al.[14].
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