Physiology/Clinical Aspects of Hearing and Balance Flashcards
What is the effect of otitis media with effusion
Affects movement of tympanic membrane
Causes conductive hearing loss
What is the effect of otosclerosis?
The deposition of new bone where the footplate of stapes fits into oval window reduces movement of stapes footplate causing a conductive hearing loss
What is the pathway of a pressure wave in the cochlea?
Up scala vestibuli from piston action of the stapes
Through helictotrema at apex
Down scala tympani
Pressure differential deflects the basilar membrane of scala media
What is the hearing mechanism in the cochlea?
Footplate of stapes moves in and out oval window creates wave
Causes movement of basilar membrane and movement of inner and outer hair cells in organ of corti
Cilia of hair cells are deflected = ion channels open
Cations flow from endolymph to hair cells
Depolarisation occurs = sends impulse up cochlear nerve
Inner hair cells activate afferent nerves
Outer hair cells modify response of inner hair cells
What is the tonotopic arrangement on the basilar membrane?
For every frequency = specific place on basilar membrane where the hair cells are most sensitive to that specific frequency
What are the 2 types of tuning fork tests?
Weber = lateralisation Rinne = compares loudness of perceive air to bone conduction (one ear at a time)
What are the different types of audiometry?
Pure tone
Visual reinforcement
Play
Tympanometry
What is pure tone audiometry?
Determines faintest tones a person can hear at selected pitches from low to high
What is conductive hearing loss?
Bone conduction perception is greater than air conduction
What types of audiometry tests are used for testing children?
Play audiometry
Visual reinforcement audiometry
What is otoacoustic emission testing?
Sound stimulates cochlea
Outer hair cells vibrate
Vibration produces nearly inaudible sound that echoes back into middle ear
Picked up with small probe inserted into ear canal
What is tympanometry?
Air pressure pushed into ear canal
Makes eardrum move back and forth
Test measures pressure within the middle ear and mobility of eardrum
Can detect fluid in middle ear, eardrum perforation or wax blocking ear canal
How is hearing loss managed?
Surgery
Sound amplification (hearing aids)
Direct stimulus of cochlear nerve cells (cochlear implants)
What is a bone anchored hearing aid?
An osseous integrated screw into the skull
Microphone + amplifier clipped onto abutment or attached via magnet
Sound conducts through skull to cochlea
When is a bone anchored hearing aid used?
In people that cannot make use of conventional hearing aid
e.g. persistent otitis externa, external canal atresia
What is a cochlear implant?
Very strong hearing aid
Electrode placed into cochlea
When is a cochlear implant used?
In those with profound hearing loss
What are the 2 otolith organs?
Utricle
Saccule
What is the sensory epithelium in the otolith organs called?
Macula
horizontal in utricle
vertical in saccule
What is embedded on the surface of the otolithic membrane?
Calcium carbonate crystals called otoliths
What are ampullae?
Expanded areas at each end of the semicircular canals that contain the crista (sensory organ)
What is the role of the crista?
Movement of the crista is the stimulus for the vestibulo-ocular reflex
What is the role of the vestibulo-ocular reflex?
Stabilises gaze by moving eyes to compensate for head and body movement
Fixes image on retina for clear sight
What is benign paroxysmal positional vertigo?
Loose otoconia move out of utricle into SC canals
When moving head, otoconia move in canal which stimulates the cristae and provokes vertigo and nystagmus
What is the test for benign paroxysmal positional vertigo?
Dix-Hallpike maneouvre
What is the treatment for benign paroxysmal positional vertigo?
Epley manouvre
What are the initial presentations of vestibular neuritis?
Acute onset verigo
Nausea and vomiting
Rarely hearing loss
Nystagmus (if seen early enough)
What are the potential causes of vestibular neuritis if hearing loss is present?
Mumps
Measules
Infectious mononucleosis
What is meniere’s disease?
Rare condition Classic triad (vertigo, hearing loss, tinnitus)
What vertigo signs are present in meniere’s disease?
Unpredictable
Severe
Lasts 30 minutes - 24 hours
May ‘burn out’
What are the hearing loss signs present in meniere’s disease?
Unilateral
Sensorineural
Initially recovers but with time usually develops low tone sensorineural hearing loss
What is a common clinical condition that affects balance?
Migraine: common cause of episodic vertigo abortive treatments rarely work lifestyle management important prophylactic medication helpful
