Researchers have identified a molecule that can transform the mechanical stimulus of a sound wave into an electrical signal recognizable by the brain. The protein forms an ion channel that opens in response to sound, causing electrical impulses that communicate the pitch, volume, and duration of a sound to the brain.
Scientists have long suspected that such a molecule must exist in the tiny cilia extending from receptor cells in the inner ear. Now, researchers led by Howard Hughes Medical Institute investigator David P. Corey, who is at Harvard Medical School, have several lines of evidence that, in vertebrates, this mechanosensitive channel is formed by a protein known as TRPA1. Certain features of the protein suggest that it may serve double, or even triple, duty in the inner ear, not only acting as an ion channel, but also forming a spring that allows the transduction machinery to stretch, and even amplifying incoming auditory signals. The work is published October 13, 2004, in an advance online publication of the journal Nature.
The cells that line the inner ear and convert mechanical sound vibrations into electrical impulses are known as hair cells – named for the tuft of 30-300 cilia, or microscopic hairs, on each cells surface. Thin filaments called tip links connect the channels in adjacent hairs, so that when a vibration stirs the bundle of cilia, the tip links are tightened and pull on the channels. Within 5 to 10 microseconds of this motion, channels in the hair cell open and allow ions to enter – the first step in sending a sound signal to the brain.
Jennifer Michalowski | EurekAlert!
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