The organ of Corti is a neural apparatus located within the cochlear duct, which separates the upper (vestibular canal) and lower (tympanic canal) chambers in the cochlea. It is a highly sensitive structure responsible for peripheral neural transduction of sound by converting mechanical energy into electrical energy. In addition, the organ of Corti lies on the basilar membrane, and contains hair cells, tectorial membrane, and a number of supporting cells. It was named after Marquis Alfonso Giacomo Gaspare Corti, an Italian anatomist who discovered it.
Furthermore, the basilar membrane serves as a sound frequency analyzer that distributes the sound stimulus along the hair cells. Thus, different hair cells respond to different frequencies of sound. These receptor cells are specialized for hearing and are found along the full length of the organ of Corti. They are elongated cells with hairlike extensions called stereocilia.
In humans, the organ of Corti contains 3,500 inner hair cells and 15,000 outer hair cells that are stimulated and highly sensitive to sounds. The lower ends of hair cells are attached to nerve fibers that relay information to and from the brain via the eighth cranial nerve, which controls auditory functions. A single row of inner hair cells transmits most of the neural information about sound signals to the brain. Three rows of outer hair cells arranged in parallel rows carry information from the brain.
The transduction of sound is not a simple process. When sound waves reach the ear, they cause the tympanic membrane to oscillate. In effect, the fluid within the upper and lower chambers of the cochlea moves due to oscillations. The energy of these fluid movements causes the basilar membrane to move and, with it, the organ of Corti. In turn, the hair cell stereocilia bend, causing a change in membrane potential that results in the transduction of sound.
Destruction of hair cells can lead to sensorineural hearing loss. Hair cells can be damaged either selectively or completely by exposure to industrial noise, trauma from high-intensity sounds, drugs that cause ear toxicity such as antibiotics, accidents, and infections or diseases, including Ménière’s disease. Damage of hair cells is irreversible, and this results in a compromised sound transduction due to loss of sensitivity and disorder in amplification function, causing deafness and sound distortion, respectively. Hair cells that respond to high frequencies are usually damaged first, because the basilar membrane moves vigorously when responding to high frequencies.
