July 31, 2007 | David F. Coppedge

Motorized Ears Give Mammals Acoustic Acuity

f=”crev03.htm#amazing11″>03/27/2001), we reported on the discovery of prestin, a motor protein that acts as an amplifier in the inner ear.  One of the fastest-acting molecular motors known (02/21/2002), prestin works by stiffening the rod-shaped cell body with its cilia.  Somehow, the action of this motor protein amplifies hearing in mammalian ears by several orders of magnitude (09/19/2002).
    In the intervening years, cell biologists and physiologists studying prestin have debated its role in amplification.  Some have thought that the cilia were the main players in amplifying the sound, as in non-mammals.  Now, according to an article in Science Daily, prestin’s role is to affect the sensitivity of the entire cell, not just the cilia.  Researchers at St. Jude Children’s Research Hospital bred mice with mutated prestin that extends the cilia instead of pulling them in.  If cilia were the key agents of amplification, they should have shown more gain – but they did not.  Somehow, prestin assists the entire cell to “bounce” more effectively in response to the sound ripples in the cochlear fluid.  This whole-cell response is called somatic motility.
    “The researchers concluded that somatic motility was not simply a way to make cilia do their job better; rather, there is no connection between the hair cell contractions and how the cilia do their job,” the article explained.  “Instead, somatic motility, generated by prestin, is the key to the superior hearing of mammals.”
    The presence of these prestin-assisted outer hair cells in mammals increases sound sensitivity a hundredfold, the article said.  “The finding could explain why dogs, cats, humans and other mammals have such sensitive hearing and the ability to discriminate among frequencies.”

Motors in your ears that amplify sound.  What more could be said?  He who has ears to hear, let him hear.

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