Waves of sound fill the world. Your ears translate these waves into ripples in the fluid that washes over these structures within your ears’ hair cells called stereocilia — sitting atop sensory hair cells in the ear. They bundle together, arranged in rows of varying heights like organ pipes. Some bundles flex for higher notes while other bundles flex for lower notes.
Over the last two decades, researchers have discovered that this flexing pulls on thin threads known as “tip links,” that connect the tops of lower rows of stereocilia to the sides of the taller upper rows. The tip links bind one row to the next, stiffening the bundle, so they all sway together. They also attach directly to gated channels that pull open as the group sways, letting molecules rush through into the hair cells to set off an electrical signal in the connecting nerve that your brain hears as sound. Damaging tip links — by blasting them with loud sounds, for instance, can affect the swaying of the whole bundle. Stereocilia that are not connected by tip links can cause deafness or may trigger ringing of the ears, tinnitus.
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