Ear

About the Ear

The ear has three divisions. The outer ear includes the auricle pinna collecting sound and the external auditory canal 2.5 cm leading to the tympanic membrane eardrum. The middle ear tympanic cavity contains three ossicles malleus hammer, incus anvil, stapes stirrup, the smallest bones, amplifying sound vibrations approximately 22x and transmitting them from air to fluid. The stapes footplate sits on the oval window of the cochlea. The Eustachian tube connects middle ear to nasopharynx for pressure equalization. The inner ear labyrinth has two functional divisions. The cochlea snail shaped organ of hearing contains the organ of Corti with inner hair cells approximately 3,500 transducers and outer hair cells approximately 12,000 amplifiers, tuned by place to different frequencies tonotopic organization high frequencies at base, low at apex. The vestibular system includes semicircular canals three, detecting rotational acceleration, utricle and saccule detecting linear acceleration and gravity, via otoliths. Hair cells are mechanoreceptors with stereocilia deflected by sound or motion, opening ion channels. Cochlear implants bypass damaged hair cells, directly stimulating the auditory nerve. Hearing loss is conductive outer or middle ear or sensorineural inner ear or auditory nerve. Presbycusis age related hearing loss affects high frequencies first.