( by a pebble thrown into a pond. This en...)St. Jude study solves mystery of mammalian ears

In mammals, the rod-shaped body of the outer hair cell contracts and then vibrates in response to the sound waves, amplifying the sound. In a previous study, Zuo and his colleagues showed that a protein called prestin is the motor in mammalian outer hair cells triggers this contraction. And that is where the debate begins.

While both mammals and non-mammals have cilia on their outer hair cells, only mammalian outer hair cells have prestin, which drives this cellular contraction, or somatic motility. The contraction pulls the tufts of cilia downward, which maximizes the force of their vibration. In mammals, both the cilia and the cell itself vibrate. Thus far the question has been whether the cilia are the main engine of sound amplification in both mammals and non-mammals.

One group of scientists believes that somatic motility in mammalian outer hair cells is simply a way to change the height of the cilia in the fluid to maximize the force with which the cilia oscillate. That, in turn, would amplify the sound. An opposing group of scientists maintains that although the vibration of the outer hair cell body itself—somatic motility—does maximize the vibration of the cilia, the cell body works independently of its cilia. That is, vibration of the mammalian cell dominates the work of amplifying sound in mammals.

“If somatic motility is the dominant force for amplifying sound in mammals, this would mean that prestin is the reason mammals amplify sound so efficiently,” Zuo said.

In the current study, Zuo and his team conducted a complex series of studies that showed in mammals that the role of somatic mobility driven by prestin is not simply to modify the response of the outer hair cells’ cilia to incoming sound waves in the cochlea fluid. Instead, somatic motility itself appea
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Source:www.stjude.org