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Chapter 3 Physics of the Senses
Published in B H Brown, R H Smallwood, D C Barber, P V Lawford, D R Hose, Medical Physics and Biomedical Engineering, 2017
The cochlea is essentially a tapered tube approximately 30 mm in length. The tube is not straight but is wound into a spiral shape, so that its external appearance is much like the shell of a snail. The diameter of the tube tapers downwards from the outside of the spiral, at the interface to the middle ear, to the apex. The tube is divided along its length into three chambers. The two outer chambers, the scala vestibuli and the scala tympani, are connected at the apex of the cochlea through an opening called the helicotrema. The fluid in the scalae is called perilymph. The vibration of the oval window, induced by the stirrup, gives rise to a wave travelling inwards away from the oval window. The outer boundaries of the cochlea are rigid, and, since the fluid is basically incompressible, some flexibility is required to allow the system to move under the applied loads. This flexibility is provided by the round window at the outer boundary of the scala tympani. The cochlear duct, sandwiched between the two scalae, contains a fluid called endolymph.
Study of fatigue damage to the cochlea
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2023
Lei Gao, Jiakun Wang, Junyi Liang, Wenjuan Yao, Lei Zhou, Xinsheng Huang
The BM is given in Figure 3. The BM in the cochlea is a linear elastic material, and its modulus of elasticity has been measured in previous experiments to decrease gradually from the base to the apex, here from 600 MPa (base) to 10 MPa (apex). The perilymph fluid in the scala vestibular and scala tympani of the cochlea is a low viscosity compressible fluid, which was measured to be similar to water with a density of 1000 kg/m3 and a viscosity coefficient of 0.001 Ns/m2. The fluid-structure interface is indicated as the junction between the inner surface of the cochlear duct and the BM. The inlet boundary is at the oval window, the inlet boundary condition is a given pressure, and the outlet boundary is at the round window, its condition is fixed at a pressure 0 constraint. In the model calculation, the initial liquid condition is 0. The controlling equation for the fluid is: where is the fluid density, is the fluid velocity, is the dynamic viscosity coefficient, is the pressure, is the volume force density on the solid, I is 3rd order unit matrix, and K is the dissipation function containing the compressible term, T express matrix transpose.