The Probert Encyclopaedia of Medicine

COCHLEA

The cochlea is a minute, bony, spiral-shaped tube in the ear, comprised of two canals and a duct subdivided by a thin partition called the cochlear partition, which runs the entire length of the spiral. The basilar membrane lies on one side of the partition and the vestibular membrane lies on the other side. 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 movement of the fluid stimulates the organ of corti, which sits on the membrane inside the cochlear partition. The organ of corti is a hearing sense organ and performs the actual transformation of mechanical vibrations into nerve impulses. It has a gelatinous membrane and two sets of hair cells (receptor hair cells). The two sets of receptor hair cells, the inner and outer receptor cells, are located between the basilar and gelatinous membrane of the organ of cporti. When the basilar membrane vibrates it pushes the hair cells against the gelatinous membrane, causing the hair cells to produce a chemical that converts the movement into electrical impulses which are transmitted to the adjacent nerve fibres. There are approximately 30,000 nerve fibres in each ear transmitting signals to both the brain stem and the brain's auditory cortex.
Research Cochlea