Do microfluid pumps enhance hearing

Do microfluid pumps enhance hearing in mammals? The cochlea is the part of the mammalian inner ear that converts pressure waves of various frequencies into nerve impulses. Fluid-filled ducts, separated by a sensory epithelium called the organ of Corti, run the length of the spiral-shaped cochlea. The organ’s outer hair cells generate membrane voltage changes in response to sound and change their length in response to changes in membrane voltage. At the November meeting of the Acoustical Society of America in Austin, Texas, researchers presented visual evidence of contracting outer hair cells pushing fluid back and forth in a tiny channel—the tunnel of Corti—running lengthwise through the sensory organ. David Mountain (Boston University) and Domenica Karavitaki (Harvard Medical School) used stroboscopic illumination that flashed up to 10 000 times a second to create slow-motion movies of hair and nerve cell motions. Less than 1/1000 the length of the cell, the tiny motions were synchronized in a manner suggesting a pump action that can provide an electromechanical feedback loop. Such a loop supports the researchers’ theory that the pumped fluid within the organ amplifies the motion of the membrane on which the organ of Corti sits, and thus increases hearing sensitivity. (Movies available at http://www.physicstoday.org .)