Inner Ear Pathology And Physiology Flashcards
What is the physiology of hearing in the outer and middle ear?
Sound enters the ear caught by the pinna, goes through the auditory canal and hits the tympanic membrane. This vibrates and sound pressure is transmitted through the ossicles, last one being the scapes.
The scapes vibrates against the membrane of ova window and transmits sound into the inner ear.
What does the middle ear do?
Transforms acoustic energy from the medium of air to fluid
What does the middle ear act as?
A sound amplifier
How does the middle ear act as a sound amplifier?
The area effect of the tympanic membrane- ration of TM to stapes footplate is 17:1
Lever action of ossicular chain- ratio of pressure on tapes to footplate to pressure on malleus is 1.3:1
What does otitis media cause?
Affects the movement of tympanic membrane. Causes conductive hearing loss
How does small perforation affect hearing?
Variable effect.
Main indication for repair is recurrent infection
How can subtotal perforation effect hearing?
If sensorineural function is maintained, the maximum hearing loss is in order of 60dB.
Even if whole drum is gone, some sound will go through hitting the ossicles and ova window
What is otosclerosis
Deposition of new bone where footplate of scapes fits into oval window
How does otosclerosis effect hearing?
Reduces movement of stapes footplate causing a conductive hearing loss
Describe the structure of the cochlea
A pressure wave flows up fron the vestibule from the piston of the stapes, through the helictotrema at the apex and down the scala tympani. The pressure differential deflects the basilar membrane of the scala media
What is the hearing mechanism of the cochlea?
Footplate of the stapes moves in and out of the oval window creating a traveling wave in the scala vestibule and scala tympani of the cochlea
This causes the movement of the basilar membrane and movement of the inner and outer hair cells in the organ of corti in relation to the tectorial membrane
The iliac of the hair cells are deflected and ion channel opens
Cations flow from the endolymoh into the hair cells
Depolorisation takes place and an impulse is sent up the cochlear nerve
Inner hair cells activate the afferent nerves
Outer hair cells modify the response of the inner hair cells
What is tonotopic arrangement?
For every frequency there is a specific place on the basilar membrane where the hair cells are maximally sensitive to that frequency
Where does the tonotopic arrangement continue to?
Through the auditory pathway up to the acoustic area of the temporal lobe
What can be used to assess hearing?
Clinical testing
Tuning fork test
Audiometry
Objective testing
What are the two different tuning fork tests?
Weber
Rinne
What is Webers test?
Compare the two ears
Fork in middle of forehead and sound radiates to both ears.
If equal hearing on both side= sound in middle
If sound loss in one ear - in conductive, sound work be louder in affected ear
- in senseroneural hearing loss, sound louder in unaffected ear
What is conductive hearing loss?
Something blocking the sound getting into the inner ear
What is sensory neural hearing loss?
Issue with cochlea or cochlear nerve or both
What is rinne test?
A test that compares loudness of perceived air conduction to bone conduction in one ear at a time
In Rinnes test, what would be seen in normal hearing function?
Sound louder at front of ear than back
In rinnes test, what would be heard in conductive hearing loss?
Louder on the bine at back than in front of ear
What are the different types of audiometry?
Pure tone audiometry
Visual reinforcement audiometry
Play audiometry
Tympanometry
What is different about tympanometry?
Don’t need a response from an individual
Wha can you measure for hearing?
Frequency and volume
What is pure tone audiometry?
Pure-tone air conduction hearing test determines the faintest tones a person can hear at selected pitches, from low to high. During this test, earphones are worn so that information can be obtained for search ear
What is the air-bone gap?
Bone conduction perception is greater than air conduction perception
What are OAEs?
Otoacoustic emissions are sounds given off by the inner ear when the cochlea is stimulated by a sound. When sound stimulates the cochlea, the outer hair cells vibrate. The vibration produces a nearly inaudible sound that echoes back into the middle ear. The sound can be measured with a small probe inserted into the ear canal.
People with normal hearing produce emissions. Those with hearing loss greater than 25-30 dB, do not produce these very soft sounds. The OAE test is often part of a newborn hearing screening programme.
What is tympanometry?
Assists in the detection of fluid in the middle ear, perforation of the eardrum, or wax blocking the ear canal. Tympanometry pushes air pressure into the ear canal, making the eardrum move back and forth. The test measures the pressure within the middle ear and the mobility of the eardrum. Graphs are created, called tympanograms.
What can tympanometry reveal?
Stiff eardrum
Hole in the eardrum
Eardrum that moves too much
What is the management of hearing loss?
Surgery
Sound amplification
Direct stimulus of cochlear nerve cells
What is a bone anchored hearing aid?
Osseous integrated screw into the skull
Microphone and amplifier clip onto an abutment or attached by magnet
Sound conducts through skull to cochlea
What sensorineural threshold does BAHA require?
5dB or better
Who uses BAHA?
Used by those whose anatomy makes use of conventional aid difficult e.g. persistent otitis externa, external canal atresia
What is a cochlear implant?
A very strong hearing aid
Electrode placed inside cochlea
Who uses a cochlear implant?
Those were profound hearing loss
What is the balance part of the inner ear?
The vestibule
What is the vestibule made up of?
2 otilist organs
-uricle
-saccule
3 semicircular canals
-connect to uricle
Blind ending part
-endolymphatic sac
What is the sensory epithelium in cochlea?
Organ of corti
What is the sensory epithelium in otolith organs?
Macula
What are the ampullae of semi-circular canals?
Expanded areas at each end of the semicircular canals.
They contain the sensory organ- the crista
What does the movement of crista cause?
Stimulus for the vestibulo-ocular reflex
What does the vestibulo-ocular reflex cause?
Stabilises gaze by moving eyes in order to compensate for head and body movement, this fixes images on retina for clear sight
What would a disorder in VOR cause?
Dizziness and vestibular problems
What 3 main systems regulate balance?
Inner ear
Vision
Feet, hips, knees and ankles
What’s does the inner ear help with in balance?
Rotation and gravity
What does feet, hips, knees and angles help with in balance?
Pressure and Proprioception
What happens if one balance system stop working?
It is manageable
What happen if more than 1 balance system stops working?
There is a problem
What are clinical conditions of inner ear that affect balance?
Benign paroxysmal postional vertigo
Vestibular neuritis
Ménière’s disease
What happens in benign paroxysmal postional vertigo?
Loose otoconia move out of the uricle, into semicircular canals, most commonly the posterior
When moving te head, the otoconia move into the canal, stimulate the cristae and provoke vertigo and nystagmus
What is the test for BPPV?
Dix - hallpike maneouvre
What is the treatment for BPPV?
Epley maneouvre
What is the initial clinical presentation of vestibular neuritis?
Acute onset of vertigo - nausea and vomiting
Rarely hearing loss nystagmus present if seen early enough
What does the hitological evidence of vestibular neuritis show?
Viral damage of vestibular nerve rather than sensory cell labyrinth
What may be the cause of hearing loss in vestibular neuritis?
Mumps, measles or infectious mononucleosis may be responsible
What is the classic triad of Ménière’s disease?
Vertigo
Hearing loss- unilateral
Tinnitus
What is the pathophysiology of Ménière’s disease?
Endolymohatic hydrops
- unknown cause or effect
- endolymph produced by stria vascularis
Hydrops drug to malabsorption of endolymph in endolymphatic duct and sac
what is the vertigo like in Ménière’s disease?
Unpredictable
Severe
Last 30mins - 24 hours
May burn out
What is hearing loss like in Ménière’s disease?
Unilaterlat at first
Sensorineural in nature
Initially removes
With time usually develop low tone sensorineural hearing loss
What is a common clinical condition affecting balance?
Migraine
What do migraines cause?
Episodic vertigo
How are migraines managed ?
Lifestyle management and propohylacic medication
