Lecture 11: Hearing 1 Flashcards
How prevelant is hearing loss in NZ?
Large component of community medical practice. Significant global health issue.
Hearing problems may be invisible unless you check
What is the function of hearing?
Hearing for social interaction and communication
- Social engagement
- Emotion
- Relationships
- Work
- Learning
- Awareness and safety
Are there health inequities when it comes to hearing loss in NZ?
- More prevalent in MAPAS
- Service uptake less in these communities
What are the impacts of hearing loss?
- 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
What are the comorbidities of hearing loss?
Cognitive decline Dementia Dizziness and fall CV Diabetes
How does the cochlea work broadly?
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
Describes the neural pathway from the cochlea:
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.
What can happen to the brain areas following loss of hearing?
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
What is the function of having two ears?
Information from both ears give us spatial hearing: Localize sounds in environment, identify and follow their movement
What are the types of hearing loss?
Conductive
Sensorineural
What is conductive hearing loss and what are some examples?
Outer and middle ear disease i.e Glue ear and infections
What is sensorineural hearing loss and what are some exampels?
Reduced sensory input; Inner ear disease i.e Ageing, noise exposure, ototoxic drugs, trauma and infections
What are some disorders in processing sound by the brain and what are the causes?
- Auditory processing disorders, auditory neuropathy spectrum disorder, tinnitus
Caused by; Peripheral injury, developmental, neurological disorders
What is the physiology of the outer ear?
- Collects sound
- Protects middle ear
- Sound localization
- Skin lining contains cerumen glands (wax)
- Canal self-cleaning
Describe the epithelium of the outer ear canal:
- 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
What is cerumen? What does it do?
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.
What are the types of ear wax?
Wet wax: Dominant, more caucasians and africans
Dry wax: Recessive, more asians, native americans
What are some medical conditions of the outer ear?
Trauma
Atresia
Microtia
Infection of the tympanic membrane
Describe the middle ear:
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
Write some notes on the bones of the middle ear
Synovial- Acts as levers to apply all the pressure from the tympanic membrane on the small footplate of the stapes.
Only 1db loss.
What is the tympanic membrane composed of?
Epithelium
Fibrous
Mucosal
Can self repair
What sort of cells line the middle ear?
Middle ear mucosa
- Secretes mucous
- Ciliated cells transfer mucous to eustachian tube
What happens to the middle ear with a cold etc
Conductive hearing loss can develop
What is the function of the middle ear?
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.
What features of the middle ear make it a good transformer?
- 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.
