Hearing Loss Flashcards
Describe the process of sound transduction
- SOund waves enter the external auditory canal and bounce off the tympanic membrane.
- The tympanic membrane thn moves the malleus, incus and stapes
- When the STAPES FOOTPLATE moves, the pressure in the fluid filled inner ear changes and that triggers a travelling wave in the basilar membrane of the cochlea
Inside the cochlea, hair cells are found where?
Organ of corti which rests on basilar membrane
High frequency sounds displace the the basilar membrane where
Near the base of the cochlea
As frequency decreases, the point of maximal membrane displacement moves in what direction?
Toward the apex
What stimulates electrical activity along the auditory nerve?
The distortion of stereocilia on hair cells causes depolarization of the cell and that results in electrical activity along the auditory nerve
Causes of conductive hearing loss?
Transmission of sound through the air is blocked.
You can mimic this by sticking your finger in your ear. Thus, anything blocking the external auditory canal causes it.
Cuases of conductive hearing loss
- wax
- foreign object
- otitis externa
- tympanic membrane perforation
- otitis media with effusion
- otosclerosis
Sensorineural heaing loss
Disorders of the cochlea, cochlear nerve, central pathways
- can be congenital
- Presbyacusis (age related hearing loss)
- viral infxn
- ototoxic drugs
- trauma
- meniere’s
- vestibular schwannoma
What is otosclerosis
bony overgrowth of the stapes
Meniere’s disease symptoms
-vertigo, fluctuating sensorineural hearing loss, tinnitus
What causes Meniere’s
Decreased reabsorption of endolymphatic fluid causes hydrops (fluid build-up) which causes rupture of the membrane separating the endolymph from the perilymph. These two fluids have very different compositions and their mixture produces a sudden change in vestibular pressure and electric firing properties.
In the early stages of meniere’s, symptoms remit between attacks and patients may be symptom free for a year or more.
Eventually hearing loss persists and worsens
Tx of menieres
- low salt diet and diuretics
- vestibular sedatives when the pt has an attack
Conductive hearing loss audiogram
fairly equal threshold elevation for each frequency.
Otosclerosis audiogram
Can result in a much greater threshold elevation in the lower frequencies