Cochlear partition anatomy and motion in humans differ from the classic view of mammals

Abstract

Mammals detect sound through mechanosensitive cells of the cochlear organ of Corti that rest on the basilar membrane (BM). Motions of the BM and organ of Corti have been studied at the cochlear base in various laboratory animals, and the assumption has been that the cochleas of all mammals work similarly. In the classic view, the BM attaches to a stationary osseous spiral lamina (OSL), the tectorial membrane (TM) attaches to the limbus above the stationary OSL, and the BM is the major moving element, with a peak displacement near its center. Here, we measured the motion and studied the anatomy of the human cochlear partition (CP) at the cochlear base of fresh human cadaveric specimens. Unlike the classic view, we identified a soft-tissue structure between the BM and OSL in humans, which we name the CP “bridge.” We measured CP transverse motion in humans and found that the OSL moved like a plate hinged near the modiolus, with motion increasing from the modiolus to the bridge. The bridge moved almost as much as the BM, with the maximum CP motion near the bridge–BM connection. BM motion accounts for 100% of CP volume displacement in the classic view, but accounts for only 27 to 43% in the base of humans. In humans, the TM–limbus attachment is above the moving bridge, not above a fixed structure. These results challenge long-held assumptions about cochlear mechanics in humans. In addition, animal apical anatomy (inSI Appendix) doesn’t always fit the classic view.

The Correlation of a 2D Volume-Referencing Endolymphatic-Hydrops Grading System With Extra-Tympanic Electrocochleography in Patients With Definite Ménière's Disease

“…Then we adopted the semi-quantification grading system described by Bernaerts et al (13) to separate vestibular hydrops into four degrees (Bernaerts scores). However, as for the cochlear hydrops, the cochlear endolymphatic expand volume was more than twice the volume of the scala media according to the human cochlear anatomy showed by Raufer et al (26) and according to the calculated results (Table 1). So we separated the hydrops of cochlea into four degrees (Figure 1-cochlea) by adding a degree between normal cochlea and Grade I described by Bernaerts et al because we discovered that for some patients the scala media could expand a bit without forming a round dark circle (Figure 1b).…”

Cochlear shape reveals that the human organ of hearing is sex-typed from birth

“…The differences highlighted in our study may induce sex-based hearing properties. However, cochlear mechanics in humans are still debated 52 and structure-function relationships within the cochlea should be considered with caution. When compared to other extant and extinct apes, humans have a longer cochlea than expected for their body mass, a proxy indicating a major auditory change that likely occurred in early representatives of the genus Homo approximately 2 million years ago 20 .…”

Robust data-driven auditory profiling towards precision audiology

“…Finally, conductive presbycusis corresponded to a gently sloping hearing loss at high frequencies, not reflecting morphological alterations in the sensory cells or stria vascularis but yielding elevated thresholds. This type of presbyacusis might reflect an atypical organization in the organ of Corti that affects its mechanical properties (Motallebzadeh, Soons and Puria 2018; Raufer, Guinan and Nakajima 2019). However, recent results obtained with new techniques developed for histopathological analysis suggested that OHC dysfunction might have been underestimated in age-related hearing loss (Wu et al 2020).…”