Inner Ear + Hearing Flashcards
What is the function of the inner ear
Convert mechanical signs to electrical which can be detected by brain
Maintain balance by detecting position and movement
What is the inner ear made up of and what fluid
Bony labyrinth - endolymph
Membranous labyrinth - perilymph
What is in the bony labyrinth
Cochlea
Vestibule
Semi-circular canals
What is in membranous labyrinth
Duct of cochlea
Semi-circular duct
Utricle and saccule
What nerves to inner ear
Vestibulocochlear nerve
- Vestibular for balance
- Cochlear for hearing
Facial nerve passes but doesn’t innervate
What is the cochlea
Organ of hearing
Consists of three adjacent tubes separate by membranes
Stapes (final ossicular bone) moves back and forth against window creating pressure wave in cochlea which travel up and down tubes
What are tubes called
Scala vestibule- travels up
Basilar membrane
Scala tympani - travels down
What is the organ of corti and how is it involved in hearing
Structure containing tiny hair cells on basilar membrane
If wave with certain frequency reaches that resonant point, membrane releases burst of energy
Moves the hair cels
Send electrical impulse to cochlear nerve
What hearing problems do problems with outer or middle ear cause
Prevents conduction so conductive hearing loss
What do problems with cochlea or cochlear nerve cause
Sensory neural loss
What is bone conduction
Sound goes right through bone directly to inner ear
i.e. if you put tuning fork directly on mastoid bone
Measures purely inner ear function
What is air conduction
Normal pathway of sound through the ear
- Through canal, hits ear drum which vibrates causing ossicular bones to vibrate which connect to cochlea
What are tuning fork tests
Weber’s
Rinne’s
What does Weber test
Lateralisation
Put tuning fork in middle of head
If localise to side of deafness = conductive hearing loss
If localise to other side = sensorineural
What does Rinne’s test
Compares loudness of air compared to bone conduction
AC > BC = positive (what you want)
If BC > AC = conductive loss as doesn’t have to travel through outer and middle ear where as if outer and middle ear not working then air conduction can’t happen
If AC > BC if deaf ear then sensorineural
What should you check first if hearing loss
Look for wax
What is 1st line investigation of hearing difficulty and how do you interpret
Audiometry
Test different sound levels and freq
Test for air conduction and bone conduction
Plot the lowest volume patient can ear
If bone conduction normal and air abnormal
- Problem is in outer ear
If bone conduction abnormal then even if sensorineural fine won’t work as won’t conduct
If gap between air and bone conduction
- Conductive hearing loss
If both lines at same level
- Sensorineural loss
What types of audiometry
Pure tone - determines faintest tone a person can hear Visual reinforcement Play audiometry Can also test air or bone conduction Sensorineural = both imapired Conductive = only conduction
What is tympanomery
Measures pressure in ear drum
Detects fluid / perforation or blocked wax
Measures mobility of the drum
What are objective testing of hearing loss
Otoacoustic emissions
Auditory brainstem response
What is otoacoustic emissions
Small sounds given off by hair cells vibrating when cochlea stimulated
Echo back into middle ear and ca be measured
If hearing loss = no sounds
Used in newborn
What is auditory brain stem response
Electrodes place on head and record brain activity
What is prescbycusis
Old age hearing loss due to damage to hair cell
High frequency bilateral sensorineural
How do you investigate
Otoscopy to rule out
Tympanometry
Audiometry
Bloods normal
What does otoscope rule out
Wax
Cholessteastoma
Otosclerosis
How do you manage hearing loss
Hearing aid
Cochlear / middle ear implant
What is irreversible
Sensorineural loss
What is tinnitus and types
Any perception of sound in the ear
Often ringing or buzzing
Non-pulsatile
- False perception heard by individual only
Pulsatile
- Synchronus with heartbeat and caused by turbulent flow
- More likely has treatbable cause
What contributes
Hearing loss
Stress
What can cause non-pulsatile tinnitus
Age - presbycuis Inner ear damage Sensorineural hearing loss Noise induced hearing loss Wax Infection - otitis media Meniere's Head injury Drugs - aspirin / gent / loop / quinine Acoustic neuroma Cholesteatoma
If pustule what should you exclude
Carotid artery stenosis
Carotid artery dissection
AV malformation
AV fistula
Non-vascular
Paget
Otosclerosis
How do you investigate and treat
Investigation = audiometry and tympanogram
MRI if unilateral to exclude acoustic neuroma
If pulsatile = MR / CT angio / carotid duplex
Rx Reassurance Hearing aid may help if hearing loss Sound enrichment therapy CBT Stress management
What can it lead too
Insomina
Depression
What type of hearing loss from gentamicin
High freq sensorineural
What type of hearing loss from vestibular schawomma
Unilateral sensorineural
Refer for MRI
How does head injury affect hearing
Damages hair cells
What does Menieres cause
Low frequency loss
How does noise cause hearing loss
Damages hair cells
Causes bilateral sensorineural hearing loss +- tinnitus
What causes conductive deafness
- What Sx suggest cause
- What Dx
Conital ossicular / pinna abnormality Wax = most common - Otoscopy FB Otosclerosis - AD + tinnitus - Onset usually 20-40 - CT Cholesteatoma - Chronic smelly discharge - May need CT to assess extent Otitis media Otitis media + effusion (glue ear) - Otoscopy = fluid level TM perforation - May have discharge - Otoscopy
What causes acute sensorineural
Idiopathic / SSNHL Trauma Noise Drug ototoxicity - Aminoglycoside - Cytotoxic - Diuretics / aspirin Mumps Viral Acoustic neuroma MS Stroke Vasculitis
What causes chronic sensorineural
Age Peri-natal / congenital Environment noise toxicity - Often with tinnitus Presbyacusis Menieres Menignitis Head injury Cerebral palsy Inherited
What needs urgent referral and what do you do
Acute sensorineural loss as steroids may cure ENT EMERGENCY Give steroids as well - 1mg / kg MRI + audiometry Bloods + autoimmune screen often don't find out cause
What investigations
Hx - Sudden vs gradual - Associated Sx FBC, LFT, pANCA, viral titre, TB, ESR Autoimmune screen Otoscopy to look at EAC / TM = normal Pure tone Audiometry Rinne / Webber CXR MRI LN and nasopharyngeal biopsy
What must you exclude if unilateral tinnitus
Acoustic neuroma
How do you manage hearing loss
Hearing aid
Surgery
- Stapdectomy in otosclerosis
Chcolear implant
What is common in children
Wax
Otits externa
Otitis media with effusion
What is the hum test
Louder = conductive Quieter = sensorineural
