Asymmetric cupula displacement due to endolymph vortex in the human semicircular canal
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The vestibular system in the inner ear senses angular head manoeuvres by endolymph fluid which deforms a gelatinous sensory structure (the cupula). We constructed computer models that include both the endolymph flow (using CFD modelling), the cupula deformation (using FEM modelling), and the interaction between both (using fluid–structure interaction modelling). In the wide utricle, we observe an endolymph vortex. In the initial time steps, both the displacement of the cupula and its restorative forces are still small. As a result, the endolymph vortex causes the cupula to deform asymmetrically in an S-shape. The asymmetric deflection increases the cupula strain near the crista and, as a result, enhances the sensitivity of the vestibular system. Throughout the head manoeuvre, the maximal cupula strain is located at the centre of the crista. The hair cells at the crista centre supply irregularly spiking afferents, which are more sensitive than the afferents from the periphery. Hence, the location of the maximal strain at the crista may also increase the sensitivity of the semicircular canal, but this remains to be tested. The cupula overshoots its relaxed position in a simulation of the Dix-Hallpike head manoeuvre (3 s in total). A much faster head manoeuvre of 0.222 s showed to be too short to cause substantial cupula overshoot, because the cupula time scale of both models (estimated to be 3.3 s) is an order of magnitude larger than the duration of this manoeuvre.
KeywordsVestibular system Fluid–structure interaction Computational fluid dynamics Time constant Navier–Stokes equations Balance Finite element model
This research was financially supported by FWO Project G0E02.14N to prof. Peter Aerts, FWO postdoctoral fellowship 12R5118N to J.G. and FWO travel Grant V428716N to J.G. for a long stay abroad at the Laboratory for Aero and Hydrodynamics at the TUDelft. Simulation software licences and computers were funded by FWO research Grant 1504018N to J.G and by Grant BOF/KP 24346 of University of Antwerp to prof. Peter Aerts. The authors wish to thank Dr. Sam Van Wassenbergh for advice on the construction of the simulation model, Ms. Josie Meaney-Ward for language correction, and two anonymous referees for their valuable comments and remarks.
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Conflict of interest
The authors declare that they have no conflict of interest.
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