Fluid dynamics of the cochlea

Structure of the cochlea

The figure below shows the structure of the human ear. The cochlea is part of the inner ear which is indicated in blue.

Structure of the human ear
Structure of the human ear (from Encyclopaedia Britannica Inc.)

As can be seen in the following figure, the cochlea is a coiled system of three ducts: scala vestibuli, scala tympani, and scala media (or cochlear duct). All of them are filled by lymphatic fluid - the scalae vestibuli and tympani by perilymph and the scala media by endolymph.
Furthermore, the cochlea contains a partition which is often called, for simplification, the "basilar membrane". It comprises, amongst others, the scala media, the organ of Corti, the tectorial membrane, and the basilar membrane. This partition is essential for our sense of hearing.
The uncoiled cochlea shows a length of about 35 mm and a diameter of 1.5 mm.

Cross section of the human cochlea
Cross section of the cochlea (from Encyclopaedia Britannica, Inc.)

Transmission of sounds

Sound waves reaching the ear lead to oscillatory motions of the middle ear ossicles. This stimulation is transmitted through the oval window into the cochlea. Here, the fluid in the outer ducts, scalae vestibuli and tympani, is set in motion, as well as the basilar membrane.
The latter is moved by a travelling wave. The location of the maximal amplitude of this wave depends on the frequency of the incoming sound signal: a frequency analysis takes place.
The motion of the basilar membrane leads to a stimulation of nerve cells which are located in the organ of Corti. They send electrical signals to the brain, the sound is perceived. Furthermore, the movement of the basilar membrane is amplified by the so-called outer hair cells situated in the organ of Corti. This process is called active amplification. It takes place in a nonlinear way: relative to the ossicular displacement, low input signals evoke larger basilar membrane displacements than high sound levels. In addition, the travelling wave of the active basilar membrane is tuned much more sharply than that of the passive basilar membrane. So active amplification enables the perception of softer sounds and smaller frequency differences.

Basilar membrane analysis of sound frequencies
Basilar membrane motions at different frequencies (from Encyclopaedia Britannica, Inc.)

Our studies of cochlear fluid flow

In our studies we focus on the transient dynamics of fluid flow in the cochlea. This signifies that, e.g., we solve for the response to non-harmonic stimulation of the cochlea, such as clicks and changing frequencies.
The aspects listed below of fluid flow in the cochlea and of basilar membrane motion are being investigated:

Cooperation with the Department of Otorhinolaryngology of the University Hospital Zurich

In our studies of cochlear fluid flow we cooperate with a group of the Department of Otorhinolaryngology of the University Hospital Zurich (group Prof. A.M. Huber ).

Related Research Projects on the Fluid Flow in the Inner Ear

The Institute of Fluid Dynamics investigates also the fluid flow in the semi-circular canals.

Refereed Journal Articles and Conference Papers related to the Current Projects

Abstracts & Posters (conferences without proceedings)

Student Projects


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