Lecture 14: Hearing 1

Question 1

What are the causes of Hearing loss

Answer 1

• Aging

- Noise exposure

Question 2

What is the epidemiology of hearing loss

Answer 2

• Prevalence in NZ is high- 13-18% hearing loss and tinnitus major disabilities, will rise with ageing population
• Higher in developing nations
• Younger people at risk of
• Accounts for 4.8% of DALYs

Question 3

What are 4 areas of the impacts of hearing loss

- overall reduced connectedness

Answer 3

• Social isolation and stigmatization leading to depression, cognitive decline
• Hearing loss from mid life associated with increased risk of developing dementia
• CVS disease and Diabetes are comorbidities
• In old there is poor 3D awareness of environmental sounds so higher risk of falls
• In young there is delayed speech, language and cognitive development leading to academic underachievement, poorer employment opportunities.

Question 4

What is the difference between conductive and sensorineural hearing loss + causes

Answer 4

-Conductive: disease or damage of the outer and middle ear leads to reduced hearing sensitivity - muffled, worse at low frequencies.

Due to congenital malformations, otitis media, trauma to ear drum and middle ossicles, otosclerosis, cholesteatoma.

Sensorineural is to do with damage to sensory cells or neural elements of the inner ear.

Due to ageing, exc noise exposure, ototoxic drug, trauma and infections

Question 5

What is the presentation of disorders in processing sound by brain (what ability is gone) and what types of disorders are there

Answer 5

Disorders:
Auditory neuropathy spectrum disorder, Tinnitus and
Auditory processing disorders:

Gone is

• Ability to hear speech in background noise
• Ability to localise sound
• Ability to order sounds accurately

May also affect other cognitive function (emotion and memory)

Question 6

What are auditory processing disorders caused by

Answer 6

Losing neural input from both ears on auditory centres in brain as this interacts with speech and higher cognitive centres- (so small hearing loss causes big effect on sound processing)

Caused by

Peripheral injury (loss of nerve fibres,

• Developmental,
• Neurological disorders (eg. Parkinsons)

Question 7

What are the components of the outer ear, their structure and function

Answer 7

1. Cartilaginous pinna and external auditory meatus.

Funct:

1. Collection and direction of sound towards the inner ear,
2. Protects middle ear,
3. Pinna Helps sound localisation through folds in shape (regardless of direction) which enhance/reflect certain high frequencies

Question 8

What lines the auditory canal and what is its function

Answer 8

Epithelium: contains cerumen + sweat glands in outer 1/3 of canal, which helps with cleaning, lubrication and mild antibacterial.

• Can be wet (w/af) or dry (Ea/Na)
• Canal skin shed from centre of eardrum to out.

Question 9

What are the components of the Middle ear

Answer 9

It is an air filled cavity within the temporal bone (Tympanum).

Separated from the auditory canal by the Tympanic membrane, which conducts airborne sound through the ossicular chain:
Malleus, Incus and Stapes to the Oval window of the inner ear.

It is connected to the nasopharynx via the Eustachian tube anterior/inferiorly.

Question 10

What is the function of the Eustachian tube, and the problems associated with it

Answer 10

It aerates and drains the middle ear, maintains equal air pressure across tympanic membrane for conduction of sound.

However this tube can allow infections to enter the middle ear: otitis media. More common in children with flatter tube

Failure of ciliated cells to transfer mucous produced by the middle ear mucosa through tube can lead to otitis media with effusion (glue ear)

Question 11

What are the 3 cell tissue layers of the tympanic membrane and its special feature

Answer 11

Eardrum:
Epithelial layer on ear canal side
Fibrous: circular and radial collagen to maintain cone shape
Mucosal : tissues of inner ears.

It can self repair

Question 12

Why do we need middle ear

Answer 12

It is a transformer to match the low impedance of air to the high impedance (resistance to flow of energy) of inner ear fluid.
It does this by having greater area of eardrum to smaller stapes footplate and Malleus arm is longer than incus, to make greater force at stapes

Without it 97-99% of vibrations would be reflected, only 1% would be transmitted leading to 30-40db loss. Its the opposite for with the middle ear.