How the Body Works: The Organ of Corti

Situated in the spiral-shaped cochlea of the inner ear is the organ of Corti. Only one inch long if uncoiled, it bears about twenty-five thousand sound receptor cells with hairlike projections arranged in rows on the basilar membrane. The tips of the receptors are fixed in a gelatinous tectorial membrane. As the basilar membrane vibrates, the hairs press against the tectorial membrane and are stimulated. The membrane vibrates because the fluid waves created in the cochlea, initiate a traveling wave within it. Receptor cells in the membrane become stimulated at and around points of maximum amplitude that are determined by the sound frequency. The greater the amplitude of the wave, the louder the noise that is heard. Impulses are then generated in some of the thirty thousand nerve fibers which lead to the auditory cortex of the brain.