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
The ear is the organ used for hearing. It converts sound into electrical impulses that are fed to the brain. The external ear is composed of the auricle (the pinna), and the auditory canal (the meatus auditorius externus). The Pinna or auricle surrounds the entrance to the auditory canal. It consists of cartilage covered by skin, with small muscles connecting it to the scalp. At the base of the ear is a fleshy lobe. The meatus auditorius is a canal about three centimeters long in the adult, partly bony and partly cartilaginous, leading from the pinna of the ear to the drum. The lining cells secrete the waxy substance found in the canal. In young children the canal is much shorter. The ear drum (tympanic membrane) is a thin oval-shaped membrane, inserted into a groove around the auditory canal. Normally it is white, glistening and somewhat transparent, so that some of the structures of the middle ear are partly visible when viewed through an auroscope. It separates the auditory canal from the middle ear.
The Tympanum or middle ear is a cavity within the temporal bone. It contains several important structures, including three small bones which connect the drum with the internal ear; they are the malleus or hammer, the incus or anvil, and the stapes or stirrupbone. They transmit the vibrations of sound waves to the inner ear. The Eustachian Tube is a channel of communication between the tympanum and the upper part of the pharynx. It admits air from the throat to the tympanum and so maintains an equal pressure on both sides of the drum. The Labyrinth or internal ear is a series of chambers through the petrous bone, comprising the vestibule, a three-cornered cavity within the tympanum; the semicircular canals communicating with the vestibule; and the cochlea, which makes two and a half turns around an axis called the modiolus. The human ear is capable of detecting sounds in the frequency range 20 hz to 20 khz, approximately. Research Ear
The semicircular canals comprise the organ of balance occupying mush of the inner ear, next to the cochlea. The three semicircular canals are set at right angles to one another: one parallel to the ground, a second parallel to the side of the head, and a third parallel to the front of the head or face. The canals are responsible for sensing the movements of the head in three dimensions. Each fluid-filled canal contains sensory hairs connected to receptor cells that provide information to the cerebellum. As the head is tilted, the fluid presses on the sensory hairs of the receptor cells. The receptor cells convert the pressure into electrical signals which are sent to the brain via nerve impulses. Other receptor cells are situated in and near the semicircular canals. The nerve impulses are essential to the control of balance. Research Semicircular Canals
The vestibulocochlear nerve (nervus vestibulaocochlearis) is a group of sensory nerves that innervate the receptor cells within the labyrinth of the cochlea. It is a branch of the eighth cranial nerve. The acousticnerve is the eighth cranial nerve, extending from the ear to the brain. The cochlear portion of the acousticnerve conveys sound impulses from the inner ear to the brain and the vestibular portions convey the sensations of balance from the semicircular canals in the inner ear to the brain. The acousticnerve is an important nerve to the sense of hearing and the sense of balance. Research Vestibulocochlear Nerve
The Probert Encyclopaedia was designed, edited and programed by
Matt and Leela Probert
Abbreviations
Research Cochlea
