Organ of Corti

The organ of Corti (or spiral organ) is the organ in the inner ear of mammals that contains auditory sensory cells, or "hair cells".

Structure and function
It has highly specialized structures that respond to fluid-borne vibrations in the cochlea with a shearing vector in the hairs of some cochlear hair cells. The Organ of Corti contains between 15,000-20,000 auditory nerve recepetors. Each receptor has its own hair cell. The shear on the hairs opens ion channels, leading to neural, electrical signaling to the auditory cortex. The pinna and middle ear amplify sound levels, so that by the time these longitudinal waves reach the Organ of Corti, they are 20 times that of the levels impinging on the pinna. This amplification is partly responsible for the delicacy of the Organ of Corti with respect to excessive sound levels, and helps to understand noise induced health effects.

The discoverer: Alfonso Corti
The organ was named after the Italian anatomist Marquis Alfonso Giacomo Gaspare Corti (1822-1876), who conducted microscopic research of the mammalian auditory system from 1849 to 1851 at the Koelliker laboratory in Würzburg (Germany). He developed new coloring techniques in microscopic anatomy, which enabled him to distinguish and describe individual components inside the highly complex cochlea that had previously been unidentified. In 1851 he was the first to describe the core sensory organ in the mammalian cochlea, the organ of Corti.

Hearing Loss
As stated in the Modern Biology textbook, "Different pitches stimulate different parts of the cochlea. Normally, the human ear can detect sounds ranging from 16 to 20,000 cycles per second. The hair cells that line the cochlea are a delicate and vulnerable part of the ear. Repeated or sustained exposure to loud noise destroys the neurons of the Organ of Corti. Once destroyed, the hair cells are not replaced, and the sound frequencies interpreted by them are no longer heard. Hair cells that respond to high frequency sound are very vulnerable to destruction, and loss of these neurons typically produces difficulty understanding human voices. Much of this type of permanent hearing loss is avoidable by reducing exposure to loud noises in the environment, such as industrial and machinery noise, gunfire, and loud music."