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