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5 Hearing

Figure 5.2: The inner ear with the basilar membrane.

membrane stiffness. The membrane can control the stiffness of its different sections by

first modifying the composition of a section (i. e., more cholesterol generally stiffens a

membrane) as well as anchoring it at specific points to the cytoskeleton at the inside of

the cell and possibly the outside via special proteins [5]. Stiffer parts dampen vibrations,

softer ones enhance them.

Let’s summarize: sound waves in air are transferred into sound waves in liquids,

which makes membranes vibrate. The long path of the vibrations results in the sepa-

ration and amplification of the different wavelengths of the sound. The transduction of

the vibration to the electrical signal occurs because stretching of a protein according to

those vibrations mechanically opens an ion channel, which releases a neurotransmitter

that starts the electrical transduction throughout the nerves and brain. Only the work-

up of the electrical signal puts all of the wavelengths together again and identifies the

original signal as a specific sound. Can the molecules and methods of the human audi-

tory system be used to make an artificial, molecular-sized auditory sensor with similar

functions?