Inner Ear Flashcards
what is the role of the middle ear?
transforms acoustic energy from the medium of air to the medium of fluid
how does the middle ear transform acoustic energy from the medium of air to the medium of fluid?
acts as a sound amplifier
The area effect of the tympanic membrane (TM) – ratio of TM to stapes footplate is 17:1
Lever action of ossicular chain – ratio of pressure on stapes footplate to pressure on malleus is 1.3:1
what is the area effect of the tympanic membrane (TM) – ratio of TM to stapes footplate?
17:1
Lever action of ossicular chain – what is the ratio of pressure on stapes footplate to pressure on malleus?
1.3:1
What are the 3 areas of the ear?
External
Middle
Inner
What is the pinna?
Stratified keratinised epithelium (skin)
Elastic cartilage
What is the external ear canal made of?
Lateral 1/3rd made of skin and cartilage:
Skin containing ceruminous and sebaceous glands (producing wax)
Thick hairs on the outside, become finer on the inside
Protective barrier and disinfectant
Medial 1/3rd made of skin and bone
No hairs or cilia
Doesn’t produce wax
How do the lateral and medial 1/3 of external ear canal differ?
Lateral 1/3rd made of skin and cartilage:
Skin containing ceruminous and sebaceous glands (producing wax)
Thick hairs on the outside, become finer on the inside
Protective barrier and disinfectant
Medial 1/3rd made of skin and bone
No hairs or cilia
Doesn’t produce wax
in a subtotal perforation if sensorineural function is maintained is what?
If sensorineural function is maintained, the maximum hearing loss is in order of 60dB
what is otosclerosis?
Deposition of new bone where footplate of stapes fits into oval window.
Reduces movement of stapes footplate causing a conductive hearing loss.
describe the physiology of the inner ear?
in what direction does the pressure wave flow in?
A pressure wave flows up the scala vestibuli from the piston action 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 does the basilar membrane contain?
The basilar membrane is a stiff structural element within the cochlea of the inner ear which separates two liquid-filled tubes that run along the coil of the cochlea, the scala media and the scala tympani.
describe the hearing mechanism in the cochlea?
Footplate of stapes moves in and out of oval window creating a travelling wave in the scala vestibuli and scala tympani of the cochlea
This causes 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 cilia of the hair cells are deflected and ion channels open
Cations flow from the endolymph into the hair cells
Depolarisation 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 every frequency picked up by our ear specific to?
For every frequency there is a specific place on the basilar membrane where the hair cells are maximally sensitive to that frequency. This is known as a tonotopic arrangement.
what are the four different assessments for hearing?
Clinical testing
Tuning fork tests
Audiometry
Objective testing
what does clinical testing entail?
place your hand on their eye so they are unable to see you and give a very basic hearing test
what does the tuning fork test entail?
vibrations differentiating between conductive loss and neural
what are the two different types of tuning fork tests?
Weber – a test of lateralisation
Rinne – a test that compares loudness of perceived air conduction to bone conduction in one ear at a time
what is the weber test?
A test of two ears - goes in the middle, may sound louder in one ear or the other
neural problem - sounds louder at the front rather than the back
conductive problem - sounds louder at the back
what is the rinner test?
a test that compares loudness of perceived air conduction to bone conduction in one ear at a time
conductive loss - sound will sound louder in poorer ear
neural loss - sound will sound louder in good ear
what are the different types of audiometry?
Pure tone audiometry
Visual reinforcement audiometry
Play audiometry
Tympanometry
What physical properties of sound would be useful in the assessment of hearing ability?
Frequency
Volume
what does pure tone audiometry test for?
Pure-tone air conduction hearing test determines the faintest tones a person can hear at selected pitches (frequencies), from low to high. During this test, earphones are worn so that information can be obtained for each ear.
what is the air-bone gap?
Bone conduction perception is greater than air conduction perception. The differential is known as the air-bone gap
what are examples of objective testing?
Otoacoustic Emissions (OAEs)
Otoacoustic emissions (OAEs) 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 decibels (dB) do not produce these very soft sounds. The OAE test is often part of a newborn hearing screening programme.
what is tympanometry?
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. These can reveal a stiff eardrum, a hole in the eardrum, or an eardrum that moves too much.
how do you manage hearing loss?
Surgery
Sound amplification
Direct stimulus of cochlear nerve cells
when is a hearing aid used?
41 to 65 dB - moderate hearing loss
what is the difference between open fit hearing aid and a hearing aid?
Both devices have the same mechanism i.e. the microphone, amplifier, and speaker. The behind-the-ear hearing aid has an earmold that goes into the ear canal, whereas the open fit hearing aid has a slim tube and a dome that fits into the ear canal
when is a bone anchored hearing aid do?
for people without an ear canal, blockage or pain with a hearing aid
what is a bone anchored hearing aid?
Osseous integrated screw into skull
Microphone and amplifier clip onto an abutment or attach by magnet
Sound conducts through skull to cochlea
Requires 50dB sensorineural thresholds or better
Used by those whose anatomy makes use of conventional aid difficult e.g. persistent otitis externa, external canal atresia
when is a cochlear implant needed?
Essentially a very strong hearing aid
Electrode placed inside cochlea
For those with profound hearing loss
100 decibels
what are the two otolith organs?
utricle and saccule
what do both the utricle and saccule contain?
a sensory epithelium (macula)
horizontally oriented in utricle
vertically orientated in saccule
what are embedded in otolithic membrane?
cilia of hair cells
what are embedded on the surface area of the otolithic membrane?
calcium carbonate crystals (otoliths)
what are ampullae?
The ampullae are the expanded areas at each end of the semicircular canals. They contain the sensory organ – the crista. Movement of the crista is the stimulus for the vestibulo-ocular reflex.
what is the function of the semicircular canals?
The semicircular canals are three tiny, fluid-filled tubes in the inner ear that help you keep your balance. When your head moves around, the liquid inside the semicircular canals sloshes around and moves the tiny hairs that line each canal.
what is the function of the ampullae?
They are the sensory organs of rotation. They are located in the ampullae of each of the inner ear’s semicircular canals, making a total of three pairs. The crista ampullaris is responsible for detecting angular deceleration and acceleration.
what is the function of the vestibular nerve?
The vestibular nerve innervates the vestibular system of the inner ear, which is responsible for detecting balance. The cochlear nerve travels to cochlea of the inner ear, forming the spiral ganglia which serve the sense of hearing.
what is the VESTIBULO-OCULAR REFLEX?
To maintain a stable perception of the world around us while we engage in normal movements throughout our day, such as walking, we have something known as the vestibulo-ocular reflex (VOR). This reflex keeps us steady and balanced even though our eyes and head are continuously moving when we perform most actions
how does the VOR stabilise gaze?
The VOR stabilises gaze by moving eyes in order to compensate for head and body movement. This fixes image on retina for clear sight.
what are clinical conditions of the inner ear?
Benign Paroxysmal Positional Vertigo
Vestibular Neuritis
Meniere’s Disease
what is benign paroxysmal vertigo?
BPPV is an inner ear problem that causes short periods of vertigo when your head is moved in certain positions. The term ‘Vertigo’ means a sensation of spinning and movement affecting you or your surroundings.
Loose otoconia move out of utricle into semicircular canals, most commonly the posterior canal
When moving the head, the otoconia move in the canal, stimulate the cristae and provoke vertigo and nystagmus
what is the test for BPPV?
The test for posterior canal is the Dix-Hallpike maneouvre
what is the Dix-Hallpike maneouvre?
It consists of a series of movements you perform while your provider observes your response. The Hallpike test only takes a few minutes.
what is treatment for BPPV?
Epley maneouvre
what is the eply manouver?
This is a simple treatment that involves you turning your head in a series of movements.
what is vestibular neuritis?
Vestibular neuritis, also known by the name vestibular neuronitis, is thought to be caused by inflammation of the vestibular portion of the eighth cranial nerve and classically presents with vertigo, nausea, and gait imbalance. It is believed to be associated with preceding or accompanying viral infection
what is the initial clinical presentation of vestibular neuritis?
Acute onset of vertigo
nausea and vomiting
Rarely hearing loss (if present, then can be truly called labyrinthitis)
Nystagmus present if seen early enough
what is histological evidence of having vestibular neuritis?
Histological evidence points to viral damage of vestibular nerve rather than sensory cells of labyrinth (similar to Bell’s palsy)
If hearing loss is present, mumps, measles or infectious mononucleosis may be responsible
what is menieres disease?
Ménière’s disease is a rare inner ear condition that can affect your balance and hearing. It cannot be cured, but treatment can help the symptoms.
It is episodic - comes in clusters
what is the classic triad of menieres disease?
Vertigo
Hearing loss – unilateral
Tinnitus
Often also sensation of fullness in ear
what is the pathophysiology of menieres disease?
Endolymphatic hydrops
?cause or effect
Endolymph produced by stria vascularis
Hydrops due to malabsorption of endolymph in endolymphatic duct and sac
how does the vertigo present in menieres disease/
Severe
Lasts 30 mins – 24 hours
May “burn out”
how does hearing loss present in menieres disease
Unilateral, at least at first
Sensorineural in nature
Initially recovers
With time – usually develop low tone sensorineural hearing loss
what is a common cause of episodic vertigo?
migraine
