Flashcards in Hearing Loss Deck (26)
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
- foreign object
- otitis externa
- tympanic membrane perforation
- otitis media with effusion
Sensorineural heaing loss
Disorders of the cochlea, cochlear nerve, central pathways
- can be congenital
- Presbyacusis (age related hearing loss)
- viral infxn
- ototoxic drugs
- 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.
Can result in a much greater threshold elevation in the lower frequencies
Middle ear effusion audiogram
Greater elevation of thresholds in the higher frequencies
Sensorineural hearing loss audiogram
usually the higher the frequency the worse the hearing
Noise induced hearing loss generally shows a selectively greater loss at what frequency
Meniere's disease audiogram
Hearing thresholds elevated in the lower frequencies...hearing usually worse at lower than higher
In perforation of the tympanic membrane, the degree of hearing loss depends on
The size of the hole
Growth of abnormal bone around the otic capsule is called
otosclerosis.....leads to fixation of the stapes
Otosclerosis is often accompanied by what type of hearing loss
At what age range does otosclerosis generally start
20's and 30's and is BILATERAL (prob means I don't have it)
Family history for otosclerosis
Tumor of the cerebellar pontine angle?
Often a vestibular schwannoma (acoustic neuroma