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Human and Biomimetic Sensors
Published in Patrick F. Dunn, Fundamentals of Sensors for Engineering and Science, 2019
Sound can be characterized by its amplitude (loudness) and frequency (pitch). The minimum auditory amplitude threshold in humans is 20.4 μPa of pressure (a slight whisper in a quiet room), corresponding to 0 dB by definition. The maximum pressure that potentially damages the cochlea is 10 million times higher, which is 200 Pa or 140 dB. The threshold varies with frequency, as shown in Figure 3.9. Sound frequencies audible to humans range from approximately 16 Hz to 28 kHz. A human can distinguish an average of about 2000 different frequencies. Changes in frequency as small as 0.03 % can be detected in the most sensitive frequency ranges. The structure of the cochlear duct establishes sensitivity to various frequencies. The duct spirals two and three-quarter revolutions inward over a length of ~35 mm. The width at its inlet (apex) is 500 μm. This width gradually decreases to 40 μm at its end (base). Pressure waves with 200 Hz frequencies give maximum displacement near the apex, while those with 20 kHz frequencies give maximum displacement near the base.
Restoration: Nanotechnology in Tissue Replacement and Prosthetics
Published in Harry F. Tibbals, Medical Nanotechnology and Nanomedicine, 2017
The cochlea is a hollow tapering helix supported by a bony spiral shelf, the osseous spiral lamina, which winds around a central core, the modiolus. The cochlea’s spiral cone geometry, like a French horn or conch shell, acts as a mechanical acoustical transform to select for different vibration frequencies along its interior. The interior of the cochlea is separated into two fluid-filled chambers (the scala vestibuli and scala tympani or upper and lower ducts) by a thin sac, called the cochlear duct, filled with gelatinous material. The large end of the spiral is sealed from the outer ear by two membranes, the oval and round windows, on either side of the cochlear duct. The duct separates the two chambers all the way up the spiral to its apex, where there is a small opening between them. The sensory hair cells are inside the cochlear duct adjacent to a thin layer of tissue (the tectorial membrane). Each hair cell has a group of stereo-cilia projecting into the viscous gelatin, which resonate with sound [286,287].
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 membrane separating the scala tympani from the cochlear duct is called the basilar membrane (see figure 3.15), and the motion of this membrane plays a key role in the generation of the nerve impulses associated with the sense of hearing. The basilar membrane runs the full length of the spiral, and spans across from a bony shelf to a ligament. The membrane contains many fibres, each approximately 1–2 µm in diameter, that run spanwise across it. The length of these fibres varies from approximately 75 µm near to the oval window up to about 475 µm at the helicotrema. Inside the cochlear duct, and supported on the basilar membrane, is the organ of Corti. It is this organ that accomplishes the transformation of mechanical to electrical energy.
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
In order to explore the effects of continuous noise (headphones) on the cochlea and BM, a cochlear model of the human ear was constructed. The cochlea is an important part of the inner ear and takes the shape of a 3 D spiral similar to a snail’s shell. The cochlear cavity of a normal person rotates 2.5 to 2.75 turns around the cochlear axis, with a length of about 35 mm. The outer part of the cochlea is a bony structure, the inner part contains a membranous labyrinth, and three chambers: the scala vestibular, scala tympani, and the cochlear duct. Only scala vestibular and scala tympani are filled with perilymph fluid. The cochlear duct is filled with endolymph fluid.