OAE arise from?
Ans. is 'd' i.e., Outer hair cell Otoacoustic emissions (OAEs) These are low intensity sounds produced by outer hair cells of a normal cochlea and can be elicited by a very sensitive microphone placed in the external ear canal and analyzed by a computer. Sound produced by outer hair cells travels in a reverse direction : Outer hair cells basilar membrane - Perilymph Oval window Ossicles - Tympanic membrane Ear canal. OAEs are present when outer hair cells are healthy and are absent when they are damaged and thus help to test the function of cochlea. Types of OAEs OAEs are two types : - Spontaneous OAEs : - They are present in healthy normal hearing persons where hearing loss does not exceed 30 dB. They may be absent in 50% of normal persons. Evoked OAEs : - There are produced by sound stimulus and they are subdivided into two types depending on the sound stimulus used to elicit them :- Transient evoked OAEs (TEOAEs) :- Evoked by click. Distoion product OAEs (DPOAEs) :- Two tones are simultaneously presented to the cochlea to produce distoion products. OAEs are absent in 50% of normal individuals, lesions of cochlea, middle ear disorders (as sound travelling in reverse direction cannot be picked up) and when hearing loss exceeds 30 dB. Uses of otoacoustic emissions OAEs are used as a screening test of hearing in neonate and to test hearing in uncooperative or mentally challenged individuals after sedation. Sedation does not interfere with OAEs. They help to distinguish cochlear from retrocochlear hearing loss. OAEs are absent in cochlear lesions, e.g. ototoxic sensorineural hearing loss. They detect ototoxic effects earlier than pure-tone audiometry. OAEs are also useful to diagnose retrocochlear pathology, especially auditory neuropathy. Auditory neuropathy is a neurologic disorder of CN VIII. Audiometric tests, e.g. SNHL for pure tones, impaired speech discrimination score, absent or abnormal auditory brainstem response, show a retrocochlear type of lesion but OAEs are normal.
Oval window
Round window
Inner hair cell
Outer hair cell