Thousands of microscopic hair cells are located in the auditory and vestibular system of the inner ear. They are responsible for sensing sound and balance information.
The auditory hair cells are located in the organ of Corti, along a thin membrane called the basilar membrane in the cochlea. There are two types of hair cells: outer hair cells and inner hair cells. When sound reaches the organ of Corti, the hair cells are moved. The inner hair cell movement creates an electrical impulse to the cochlear nerve, where the signal is then received by the brain. The brain can determine the pitch and loudness of the sound based on how many hair cells are activated, and the position of the activated hair cells. Outer hair cells have been shown to be responsible for amplifying low-level sounds.
Damage to these hair cells can occur with loud noise exposure, the aging process, and certain medications. In mammals, once the hair cells are damaged, they do not reproduce. This leads to a sensorineural hearing loss. Researchers are making progress on the regeneration of hair cells in mammals with the use of gene and stem-cell therapies.