Lecture 11: Hearing 1

Question 1

How prevelant is hearing loss in NZ?

Answer 1

Large component of community medical practice. Significant global health issue.

Hearing problems may be invisible unless you check

Question 2

What is the function of hearing?

Answer 2

Hearing for social interaction and communication

• Social engagement
• Emotion
• Relationships
• Work
• Learning
• Awareness and safety

Question 3

Are there health inequities when it comes to hearing loss in NZ?

Answer 3

• More prevalent in MAPAS

- Service uptake less in these communities

Question 4

What are the impacts of hearing loss?

Answer 4

• Delayed speech, language and cognitive development
• Poor environmental awareness of sound, risk of falls
• Academic underachievement, poorer employment opportunities
• Social isolation and social stigmatization
• Depression, cognitive decline

Question 5

What are the comorbidities of hearing loss?

Answer 5

Cognitive decline
Dementia
Dizziness and fall
CV
Diabetes

Question 6

How does the cochlea work broadly?

Answer 6

Transduces the vibrations passed from the stapes through the fluid and this causes the movement of the basilar membrane, which is mapped tonotopically, covered in inner and outer hair cells with stereocilia.

30,000 nerve fibres convert mechanical vibration into nerve impulses

Question 7

Describes the neural pathway from the cochlea:

Answer 7

Cochlear projects to the cochlear nucleus and sup. olivary nucleus. This projects onto the inf. colliculus and is relayed to the medial geniculate body of the thalamus and then on to the primary auditory cortex.

NB sound is processed in the primary, but emotion, understanding of speech etc is processed elsewhere i.e hippo and wernickes.

Question 8

What can happen to the brain areas following loss of hearing?

Answer 8

Loss of input can have big impacts on sound processing

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

May also impact other cognitive functions

Question 9

What is the function of having two ears?

Answer 9

Information from both ears give us spatial hearing: Localize sounds in environment, identify and follow their movement

Question 10

What are the types of hearing loss?

Answer 10

Conductive

Sensorineural

Question 11

What is conductive hearing loss and what are some examples?

Answer 11

Outer and middle ear disease i.e Glue ear and infections

Question 12

What is sensorineural hearing loss and what are some exampels?

Answer 12

Reduced sensory input; Inner ear disease i.e Ageing, noise exposure, ototoxic drugs, trauma and infections

Question 13

What are some disorders in processing sound by the brain and what are the causes?

Answer 13

• Auditory processing disorders, auditory neuropathy spectrum disorder, tinnitus

Caused by; Peripheral injury, developmental, neurological disorders

Question 14

What is the physiology of the outer ear?

Answer 14

• Collects sound
• Protects middle ear
• Sound localization
• Skin lining contains cerumen glands (wax)
• Canal self-cleaning

Question 15

Describe the epithelium of the outer ear canal:

Answer 15

• Canal epithelium shed from the centre of the eardrum and wax is pushed out of the canal via the epithelial conveyer belt formed by the outer ear.
• 0.05mm/day

Question 16

What is cerumen? What does it do?

Answer 16

Ear wax, important.

• Secreted by sebaceous and sweat glands in the outer 1/3 canal.

Cleaning, lubrication, antibacterial

Build up in elderly can cause hearing loss.

Question 17

What are the types of ear wax?

Answer 17

Wet wax: Dominant, more caucasians and africans

Dry wax: Recessive, more asians, native americans

Question 18

What are some medical conditions of the outer ear?

Answer 18

Trauma
Atresia
Microtia
Infection of the tympanic membrane

Question 19

Describe the middle ear:

Answer 19

Tympanic membrane
- Malleus
- Incus
- Stapes
Footplate of stapes sits in oval window of cochlea

• Eustachian tube, connects to nasopharynx to equalize the middle ear and make sure the tympanic membrane isnt met with resistance

Question 20

Write some notes on the bones of the middle ear

Answer 20

Synovial- Acts as levers to apply all the pressure from the tympanic membrane on the small footplate of the stapes.

Only 1db loss.

Question 21

What is the tympanic membrane composed of?

Answer 21

Epithelium
Fibrous
Mucosal

Can self repair

Question 22

What sort of cells line the middle ear?

Answer 22

Middle ear mucosa

• Secretes mucous
• Ciliated cells transfer mucous to eustachian tube

Question 23

What happens to the middle ear with a cold etc

Answer 23

Conductive hearing loss can develop

Question 24

What is the function of the middle ear?

Answer 24

Acts as a transformer to match low impedance of air to high impedance of inner ear fluid

i.e if there was no middle ear, most sound would be reflected going from ear to inner ear fluid or would have a 40-50db earing loss for the same force.

Question 25

What features of the middle ear make it a good transformer?

Answer 25

• Greater area of eardrum transfers more pressure on smaller stapes footplate
• Malleus arm longer than incus generate greater force at stapes
  = OVERCOMES resistance of inner ear fluids

97% energy is transferred vs 3% without middle ear.