Sound waves traveling through the air are collected through the auricle or pinna, which directs them into the external auditory canal. These two structures comprise the outer ear. The sound waves pass to the end of the canal and cause pressure changes on the ear drum or tympanic membrane. The tympanic membrane moves back and forth in response, reproducing the vibrations of the sound wave source. The auditory ossicles, consisting of the malleus or hammer, incus or anvil, and stapes or stirrup are attached to the wall of the tympanic cavity by tiny ligaments. The malleus is attached to the ear drum, so when the ear drum vibrates; the malleus vibrates in unison with it. The malleus causes the incus to vibrate and it passes the movement onto the stapes. Vibration of the stapes at the oval window causes motion in a fluid within the scala vestibuli of the inner ear, called perilymph.

In short, the ossicles help amplify incoming sound waves and convert the sound vibrations into mechanical energy. The vibrations now pass through the vestibule membrane and enter the endolymph of the cochlear duct, where they cause movement in the basilar membrane. The hearing receptors, called hair cells, are located in the organ of Corti on the upper surface of the basilar membrane. As the sound vibrations pass through the inner ear, the hair cells are bent, or pulled, across the tectorial membrane, which lies over them. As the hair cells bend, they mediate the vibrations into nerve impulses; converting mechanical energy into electrochemical energy. The impulse is then transmitted along the cochlear nerve to the vestibulocochlear nerve. This nerve carries the impulses to the auditory cortex in the temporal lobe of the brain where interpretation of the sound, or hearing, occurs.

Next Steps

The tympanic membrane, or eardrum, serves as the window into the middle ear. Direct observation of the tympanic membrane and external auditory canal though an otoscope, offers valuable information about possible disease within the middle ear.

Ear Pathologies