Ear

Wednesday, June 27, 2012

The ear is the paired sensory organ of hearing and sense of balance, situated in each side of the head, below and in the temporal bone. It is composed of the external ear, the middle ear, and the inner ear. The external ear consists of the pinna and ear canal; the pinna is the funnel-like external visible organ that collects the acoustic vibrations. The middle ear is made up of the tympanic membrane (eardrum) and the auditory ossicles, which are three small bones called malleus (hammer), incus (anvil), and the stapes (stirrup), which are joined together by ligaments.

The inner ear is composed of the vestibule, the cochlea, and the semicircular canals; the vestibule is the inner ear entrance chamber which has two small holes: the oval window and the round window; the cochlea is a small, snail-shaped, coiled up tube which is divided inside along its full length into three smaller tubes or ducts, all of which are filled with a fluid called perilymph; these three smaller ducts are: the scala vestibuli, the scala tympani, and the scala media (or cochlear duct), which is located in the middle position; the semicircular canals are a series of three fluid-filled looping tubes whose function is balance and equilibrium: superior canal, horizontal canal, and posterior canal.

How It Works

The acoustic vibrations, or sound, produced in the outer world, enter the the ear canal and meet the tympanic membrane, which vibrates at the rhythm of the acoustic vibrations. Then, the tympanic membrane transmits the acoustic vibrations to the auditory ossicles, whose stapes bone passes them onto the inner ear through the oval window. The stapes pumps in and out of the oval window, transforming the acoustic sound into vibratory waves that move throughout the cochlea's tubes fluid. The vibratory waves that travel up the scala vestibuli (upper little tube) of the cochlea, and then down the scala tympani, stimulate the hair cells in the organ of Corti, which is located inside the scala media (the middle little tube). The hair cells then transform these vibratory waves, that travel through the liquid medium of the perilymph, into nervous impulses that are transmitted first to the nervous cells in the modiolus and from here to the auditory nerve, which relays these nerve impulses to the temporal lobe of the brain.