inner ear (week 1) Flashcards
what is conductive hearing loss?
problems with outer and middle ear (such as otitis media with effusion)
when should we repair small perforation?
this has a variable effect on hearing
repair if recurrent infection
what is a subtotal perforation?
when whole drum is gone, sound still hits ossicles (loss of 60dB)
otosclerosis?
due to trauma and new bone forms and fits the footplate of stapes to oval window (stops it moving and reduces sound)
what does the vestibule and cochlea do in the inner ear?
vestibule - balance
cochlea - hearing (pressure wave goes up Scala vestibuli and down the Scala tympani, with the Scala media in the middle which contains the basilar membrane which has the organs of corti)
describe the hearing mechanism in the cochlea?
footplate moves in and out oval window, creates a wave that travels up Scala
this leads to movement of inner and outer hair cells in the organ of corti
cilia are deflected and causes ion channels to open, so positive ions flow from endolymph (like extracellular fluid) into hair cells
then depolarisation takes place and impulse sent up the cochlear nerve
inner hair cells activate afferent nerves (inner cells convert vibrations in fluid to electrical signals)
outer hair cells modify response of the inner hair cells - such as amplifying lower-level sounds (more outer hair cells)
what cells are sensitive to what frequencies?
innermost ear is sensitive to higher frequencies, gets sensitive to lower at the outermost ear cells
describe the clinical test for hearing?
stand side on with patient, get them to cover their eyes so they can’t lip read and repeat a number to them at different volumes to see their range of hearing
what are the two types of tuning fork tests and its reason?
tuning fork tests are to see if hearing is obstructive or nervous damage
weber - checks hearing capabilities between both ears (tap the tuning fork and place it in the middle of forehead, if ear damage, will hear louder on one side)
Rinne - compares loudness of perceived air conduction to bone conduction in one ear at time (sound conducts to ear with the problem in this test - place the tuning fork behind the ear)
what physical property of sound would be useful in assessing hearing ability
frequency and volume
what is a pure tone audiometry?
detects the faintest tones a person can hear at certain frequencies
this test checks the threshold of hearing (quietest they can hear)
what are otoacoustic emissions and why are they significant in diagnosis?
very quiet sounds given off by the cochlea when it is stimulated by sound when the outer hair cells vibrate.
They can be detected with a probe that goes into the ear to detect them and CANNOT be heard in hearing loss greater than 25 - 30dB
can be used in babies as part of newborn hearing screening programme
tympanometry
pushes air into the ear canal to make the drum go back and forth (measures pressure in the middle ear and motility of ear drum)
used to detect fluid in middle ear, perforation, or wax blocking the ear canal
when do we use a cochlear implant?
severe hearing loss (90 - 100dB)
its a strong hearing air with electrode placed in cochlea.
for bilateral profound hearing loss
what does the vestibule consist of?
2 otolith organs -utricle and saccule
3 semicircular canals that connect to utricle
endolymphatic sac
what do the otolith organs pick up?
balance - they have sensory epithelium called macula. these are horizontal in the utricle and vertical in the saccule
otolithic organs sense head positions and linear movements
what do the semicircular canals pick up?
rotational movements
they are all at a right angle to each other and are filled with endolymph.
have ampulla at each end of the canals which is where response is made (watch video of this in detail, too much detail to explain)
inner ear conditions that affects balance?
benign paroxysmal positional vertigo
vestibular neuritis
what happens when an otolymph gets into vestibule (BPPV)?
mostly goes into the posterior canal if it breaks off (causes eye to move up and down when lie the patient flat and tilt the head)
can affect the horizontal canal too (causes eyes to move sideways)
(test for the posterior canal is called Dix-Hallpike manoeuvre)
treated by the Epley manoeuvre
what is vestibular neuritis
inflammation of the vestibular nerve
presents with nausea and vomiting, acute onset of vertigo (spinning feeling when sitting perfectly still)
nystagmus will be present if caught early (involuntary eye movement)
can rarely cause labyrinthitis (effects whole inner ear, so hearing loss) - hearing loss too can mean mumps, measles and glandular fever cause
what is Meniere’s disease
vertigo, hearing loss, and tinnitus, often fullness of one ear sensation
it is episodic and it is severe
