Hearing and Balance

Question 1

What does the middle ear do in hearing?

Answer 1

Amplifies sound (tympanic membrane area:stapes footplate area should be 17:1 for this ideally)
Transforms acoustic energy from air to fluid

Question 2

What are some conditions affecting hearing?

Answer 2

OM with effusion
(glue ear - affects movement of tympanic membrane)
Small perforation
(effect variable, main indication for repair is recurrent infection)
Subtotal perforation
Otosclerosis
(New bone deposition where footplate of stapes fits into oval window, reduces movement of stapes footplate)

Question 3

What is the cochlea?

Answer 3

Spiral cavity of inner ear containing the organ of Corti

Question 4

Describe the sequence of events involved in hearing.

Answer 4

• Pressure wave transmitted by piston action of the stapes
• Travels through the helicotrema at the apex
• Down the scala tympani
• Pressure differential deflects the basilar membrane of the scala media
• 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
• Signal reaches temporal lobe

Question 5

What is tonotopic arrangement?

Answer 5

There is a specific place on the basilar membrane where hair cells are maximally sensitive to specific frequencies

Question 6

What are some useful assessments for hearing?

Answer 6

Weber
Rinne
Pure tone/visual reinforcement/play audiometry
Tympanometry (tests condition of middle ear and mobility of tympanic membrane)

Question 7

What are some modes of management of hearing loss?

Answer 7

Open fit hearing aid
Bone anchored hearing aid (BAHA)
BAHA abutment
Cochlear implant (essentially a really strong hearing aid)

Question 8

What are the otolith organs?

Answer 8

Utricle
Saccule
Both are indicators of gravity, balance, movement and direction

Question 9

What is the otolithic membrane?

Answer 9

A fibrous structure which serves to determine if the body or the head is tilted, in addition to the linear acceleration of the body

Question 10

What are the ampulla of the semicircular canals and what do they do?

Answer 10

Dilated sacs at the end of the semicircular canals.

They contain the crista which move to stimulate the vestibulo-occular reflex which moves eyes to compensate for movement

Question 11

What are some conditions affecting balance?

Answer 11

• Benign paroxysmal positional vertigo (loose otoconia)
• Vestibular neuritis
• Migraine

Question 12

What are otoconia?

Answer 12

Bio-crystals which move through semi-circular canals, transferring mechanical force on the sensory hair cells