The cochlea is a minute, bony, spiral-shaped tube of two canals and a duct subdivided by a thin elastic partition called the cochlear partition, which runs the entire length of the spiral. The partition is bound on one side by the basilar membrane and on the other by the vestibular membrane. Sound vibrations reaching the inner |ear| are transmitted through the fluid of the cochlear canals (the tympanic canal and the vestibular canal) and around the cochlear duct which divides them. As the pressure of the waves flows over the basilar membrane, which is the vibrating wall of the cochlear duct, the fluid inside the duct is agitated. This agitations stimulates the organ of corti, which sits on the membrane inside the cochlear partition. It is a hearing sense organ and performs the actual transformation of mechanical vibrations into ~nerve~ impulses. It has a gelatinous tectorial membrane and two sets of hair cells (receptor hair cells), inner and outer, sitting between the basilar and tectorial membranes. When the basilar membrane vibrates it pushes the hair cells against the tectorial membrane, causing the hair cells to produce a chemical that converts the movement into electrical impulses in adjacent |nerve fibers|. There are approximately 30,000 |nerve fibers| in each |ear| transmitting signals to both the |brain| stem and the |brain|'s auditory |cortex|.
