The transformation of sound stimuli into electrical signals

Our sense of hearing depends on the correct performance of about 15 000 hair cells in each cochlea that serve as an interface between the mechanical vibrations of speech, music and other sounds and the electrical signals of the brain. Hair cells can detect vibrations of atomic dimensions down to 0.2 nm, and can respond more than 20 000 times a second. These cells cannot regenerate, so their atrophy in old age or destruction by loud sounds or drugs like streptomycin causes permanent deafness. Loss of sensation is often restricted to higher frequencies, and is linked to degeneration of hair cells near one end of the cochlea. This chapter explains how acoustic stimuli are detected by the hair cells and converted into a stream of electrical impulses that are relayed to the brain. It also describes the mechanisms by which each cell is affiliated with certain input frequencies.