Ageing special sensory system Flashcards
What senses constitute the special senses?
Hearing, Balance, Vision, Taste and Olfaction
Which two physiological systems undergo age-related changes in ALL individuals:
Hearing and vision
What percentage of adults and over 60s experience hearing loss?
20% of adults and 75% of over 60s have mild hearing loss
Why are auditory and visual decline not much of a problem in modern society?
~ hearing aids increase volume and change pitch of sound
~ contact lenses and glasses improve vision
Why are age related changes in olfaction important?
Effect both taste and smellas they are linked
What is amplitude?
the amplitude of waves
What is pitch?
wave frequency?
What is he human range of pitch?
1000-4000Hz
What is the purpose and structure of the middle ear?
Middle ear bones (ossicles: malleus, incus & stapes) amplify & transfer sound to the oval window
What is the function of the inner ear?
The inner ear has hair cell
receptors for hearing in the cochlea and equilibrium in semi-circular canals (balance)
Which part of the ear protects against loud noises and how?
• Middle ear reflexes protect against loud noises but respond
poorly to sudden loud sounds (eg gun shot), risking damage
• The tensor tympani muscle & stapedius muscle both contract in
response to loud sounds
What is the cause of presbycusis?
Reduced movement of the tympanic membrane (ear drum) and middle ear bones
How do AGEs contribute to presbycucis?
~ tendons attached to the ossicles become cross-linked due
to Advanced Glycation End products (AGEs) and stiffen
~ this reduces sensitivity to loudness and pitch
~ it is a non-enzymatic process which gets worse with age
What is prebycusis?
Loss of hearing in old age
What are possible causes of presbycusis
~ can be caused by conductive problem in the middle ear
~ usually caused by loss of hair cells or stereocilia therefore less neurotransmitter is released in response to sound which decreases sensation of loudness and pitch
What age related changes occur to the auditory cortex and auditory nerves?
~ neuron losses in ageing sensory pathways reduces hearing
~ blood vessel thickening reduces blood flow and hearing
~ cochlear implants may help
What can cause sensorineural hearing loss?
Ototoxic drugs such as aminoglycoside antibiotics
What is the neuronal sequence of events to perceive sound
The nerves go to thalamus, then the auditory cortex ~ superior temporal gyrus ~ left has hearing and pitch dominance ~ right has music dominance Many cross to opposite side & ascend via the inferior colliculus ~ role in acoustic reflexes ~ direction detection 1st order neurones synapse in medulla (cochlear nucleus) Afferent fibres form the cochlear branch of the vestibulocochlear nerve enter the brain stem
What is the vestibular apparatus?
~ contains 3 semicircular canals at right angles to each
other which respond to movement 3 planes
• Semicircular canals transduce rotational movement in 3
directions using cupula hair cells located in ampullla
~ the Utricle and Saccule transduce linear acceleration
using otolith (calcium carbonate crystals) linked hair cells
What age related changes occur to the vestibular apparatus?
40% less vestibular nerve
fibres the by age 80
18,000 ↓ to 11,000 by 80
• Age related changes affect balance, equilibrium & dizziness in
14 – 30% of the over 60s mainly due to hair cell loss
What age related changes occur to vestibular hair cells?
- Vestibular hair cell degeneration occurs with age
* By age 90 vestibular function can fall by 40%
How are utricles and saccules effected by ageing?
33000 normal, reduction of 20% by age of 80
Saccules contain about 19000 hair cells decreasing to 14000 in old age
What wavelengths are detected by he retina?
Wavelengths between 400-700nm
What age related changes occur to vision?
Age-related changes reduce acuity, sensitivity, adaption
thresholds and nerve number
What is presbyopia?
inability of the lens to recoil, from a spherical shape, to
increase it’s refractive power to focus on near objects
How do AGEs contribute to presbyopia?
Collagen cross links stiffen the lens
Why does vision decline irreparably as we age?
• Terminally differentiated cells in the lens are not relaced when they die ~ lens damage is not repaired as we age • A slight decrease in smooth muscle cell number occurs in the ciliary body
what is the purpose of the lens changing shape?
to make adjustments for far and near objects
Why does ageing reduce the ability to focus on an object
elasticity reduction makes changing the lens shape less effective
What type of retinal cells reduce in number as we age?
Ganglion cells and optic nerve axons
What is cataracts?
a cataract is an opaque lens caused by photo-oxidation and a lack of lens repair as cells die
it is crystalin proteins in the lens denature
what are age related frequency for cataracts?
- 7% of 50-59s;
- 2% of 60-69s;
- 5% of 70-79s
- 8% of 80+
what are age related frequency for Glycoma?
- 1% of 50-59s;
- 2% of 60-69s;
- 3% of 70-79s
- 7% of 80+
What is glycoma?
Glaucoma is a group of disorders in which intraocular pressure
causes optic neuropathy and to blindness
what are age related frequencies for Macular degeneration?
<0.1% of 50-59s;
- 05% of 60-69s;
- 15% of 70-79s
- 5% of 80+
Name 3 general facts regarding taste buds
~ taste receptor cells die within about 10 days and are
continually replaced by new receptor cells
~ they are chemoreceptors found within taste buds
~ each taste bud contains 40 - 150 receptor cells
at what age does taste bud number decline?
about 50
What is loss of olfactory sense called?
anosmia
what percentage 80+ year olds have major olfactory impairment
75%
