How We Hear


Sound waves (vibrations of air molecules) enter into the ear canal, travel to the eardrum or tympanic membrane, and cause it to vibrate.  These vibrations transfer movement to the boney ossicles within the middle ear through mechanical energy.  Then the tiny bones relay the movements to the oval window on the cochlear nerve where they are transduced into hydraulic vibrations within the inner ear.  In turn, the fibers of the cochlear nerve send electrical impulses to the brain where they are interpreted as sound.





 The external fleshy part of the ear is called the pinna.  At the center of the pinna is the ear canal or external auditory meatus.  The ear canal ends at the ear drum (tympanic membrane) and is responsible for channeling the sound waves down to the eardrum.  This portion of our hearing mechanism is called the outer ear.





The middle ear consists of three tiny bones that are hooked together to form the ossicular chain.  The individual ossicles are the malleus (hammer), the incus (anvil), and the stapes (stirrup).  The handle of the malleus is attached to the eardrum.  The footplate of the stapes fits in the oval window of the cochlea.  The middle ear transforms the acoustic energy into mechanical energy.





The inner ear is a complicated bony labyrinth that is made up of the cochlea and three semicircular canals.  The three semicircular canals control the vestibular or balance system.  The cochlea is a small snail shape organ that contains 20,000 hair-like sensory fibers that transmit electrical impulses to the brain.  Within the cochlea, the inner ear transforms the mechanical energy received from the ossicular chain to hydro-electric impulses.  Finally, the eighth cranial nerve transmits the electrical impulses up the brain stem to the temporal area of the brain where the impulses are decoded into meaningful information.