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The Special Senses
1. Location
2. Structure of the eye
A. Structure and function of the eye
a. Fibrous tunic
i. Sclera
ii. Cornea
sclera pupil
iris
sclera
cornea
canals of Schlemm
fibrous tunic
dura mater
optic nerve
The Special Senses
2. Structure of the eye
A. Structure and function of the eye
b. Vascular tunic
i. Choroid
ii. Ciliary body
iii. Iris with pupil
choroid ciliary body
iris
pupilpupil
FULL DILATION
FULL CONSTRICTION
a) Sphincter pupillae
b) Dilator pupillae
The Special Senses
2. Structure of the eye
A. Structure and function of the eye
c. Nervous tunic (retina)
i. Photoreceptors (rods and cones)
ii. Photopigments
iii. Optic nerve
iv. Optic disc
v. Fovea centralis
retina
ora serrata
optic disk
optic nerve
The Special Senses
2. Structure of the eye
A. Structure and function of the eye
d. Lens
e. Aqueous humor
f. Vitreous humor
anterior cavity
posterior chamber
anterior chamber
posterior cavity
The Special Senses
3. Accessory structures
A. Structure and function of the eye
a. Eyelids
b. Conjunctiva
c. Lacrimal apparatus
d. Extrinsic muscles
lacrimal gland
lacrimal ducts
lacrimal puncta
lacrimal caruncle
nasolacrimal duct
superior and inferior lacrimal
canals
The Special Senses
4. Light refraction and the accommodation reflex
A. Structure and function of the eye
The Special Senses
1. External changes
B. Age-related changes of the eye
a. Wrinkles and sags
b. Eyelids tend to not meet when eyes are closed
c. Upper eyelids tend to droop
d. Conjunctival changes
e. Fibrous tunic
i. Sclera yellows and has transparent spots
ii. Cornea becomes more translucent and less spherical, leading to astigmatism
iii. Senile ring may form
The Special Senses
2. Internal changes
B. Age-related changes of the eye
a. Vascular tunic
i. Retinal surface becomes uneven and fragile
ii. Less aqueous humor produced
iii. Ciliary muscles lose mass due to atrophy
iv. Iris hardens, color fades, dilator pupillae atrophies (senile miosis)
The Special Senses
2. Internal changes
B. Age-related changes of the eye
b. Nervous tunic (retina)
i. General decline in photoreceptors (?)
ii. Decreased total rhodopsin, regeneration rate, adaptation
iii. Less efficient removal of debris and wastes
iv. Increased atherosclerotic blood vessels
c. Vitreous humor
i. Becomes more liquid, causing light flashes
ii. Floaters
iii. More opaque
The Special Senses
2. Internal changes
B. Age-related changes of the eye
d. Lens
i. Yellows and becomes less transparent
ii. Increased cell growth on outside of lens
e. Functional changes
i. Altered refraction
ii. Less light reaching the retina
iii. Reduced light sensitivity
iv. Decreased central visual processing times
The Special Senses
1. Presbyopia (farsightedness)
C. Age-related dysfunctions of the eye
a. Practically universal post-40
b. Results from loss of elasticity, flattening, and increased density of the lens
c. Loss accommodation during near vision
2. Blindness
a. Incidence of blindness increases with age
b. 16% of people 75 – 84 legally blind
c. Variety of causes
The Special Senses
3. Glaucoma
C. Age-related dysfunctions of the eye
a. Most serious eye problem of aging
b. 20% of blindness in the US
c. Caused by increased intraocular pressure
i. Poor drainage of aqueous humor from anterior cavity
ii. Elevated pressure presses against retinal blood vessels
iii. Leads to degeneration of optic nerve fibers where they exit the eye
iv. “Tunnel” vision
The Special Senses
3. Glaucoma
C. Age-related dysfunctions of the eye
d. Etiology – mostly unknown
e. Onset
f. Symptomology
g. Treatments
The Special Senses
4. Diabetic retinopathy
C. Age-related dysfunctions of the eye
a. 7% of blindness in US (40,000 people)
b. Microaneurysms form in retinal capillaries
c. Areas of hemorrhage vs. areas of starvation
d. Symptomology
e. Treatments
The Special Senses
5. Cataracts
C. Age-related dysfunctions of the eye
a. 70% of people over 70 have some level
b. Cloudy (opaque) lens interfering with light passage
c. Causes
i. Compression of old lens fibers by newer ones
ii. Oxidative reactions in lens proteins
d. Symptomology
e. Treatments
The Special Senses
6. Age-related macular degeneration
C. Age-related dysfunctions of the eye
a. Disease of the macula lutea (100% cone cells)
b. Loss of central vision (acuity and color) -- the opposite of tunnel vision
c. Cause
d. Two forms
i. Dry (atrophy) – more common and very gradual
ii. Wet (hemorrhage) – rare and sudden
e. No medical treatment
The Special Senses
7. Detached retina
C. Age-related dysfunctions of the eye
a. Retina attached to vascular pigment only at optic disc and ora serrata
b. Pressure exerted by vitreous humor “holds” the rest of the retina in place
c. As vitreous diminishes with age, detachment risk increases
d. Effects
e. Treatments
The Special Senses
1. Location
2. Divisions
D. Structure and function of the ear
a. External (outer) ear
i. Auricle (pinna)
ii. External auditory meatus
iii. Tympanic membrane (eardrum)
external auditory meatus
temporal bone
tympanic membrane
auricle (pinna)
The Special Senses
1. Location
2. Divisions
D. Structure and function of the ear
b. Middle ear
i. Ossicles
(malleus, incus, stapes)
ii. Auditory (Eustachian) tube
iii. Oval and round windows
middle ear cavity
malleus
incus
stapes
round window
oval window
tympanic membrane
The Special Senses
1. Location
2. Divisions
D. Structure and function of the ear
c. Internal (inner) ear
i. Bony labyrinth
ii. Membranous labyrinth
iii. Perilymph and endolymph
iv. Cochlea (spiral organ)
v. Vestibular apparatus
inner ear
a) Semicircular ducts
b) Utricle and saccule
vi. Vestibulocochlear nerve
semicircular ducts
utricle
saccule
cochlea
The Special Senses
3. Functions
D. Structure and function of the ear
a. Hearing
b. Equilibrium
The Special Senses
1. External ear
E. Age-related changes of the ear
a. Auricles increase in size, lose flexibility
b. External auditory meatus becomes wider, causing skin within to become dry and brittle
c. Ear hairs become stiffer and grow longer
d. Earwax becomes drier, causing it to build-up
The Special Senses
2. Middle ear
E. Age-related changes of the ear
a. Tympanic membrane becomes thinner and less rigid
b. Ossicular joints ossify
c. Minor loss of hearing
3. Internal ear
a. Some degeneration of spiral organ cells, ganglion cells, and equilibrium receptor cells by age 50
b. Loss of nerve fibers in vestibulocochlear nerve
c. Changes especially noticeable post-70 years
The Special Senses
1. Presbycusis
F. Age-related dysfunctions of the ear
a. Hearing loss as a result of aging
b. Loss of high-pitch (20kHz at childhood drops to 8kHz by age 65
c. Post-65 there is also loss of low-range frequencies = difficult understanding speech
d. Interrupted pattern or rate of speech, or interference from background noises affects understanding of conversation
e. Environmental factors contribute significantly
f. Hearing loss is usually not severe
The Special Senses
2. Tinnitus
F. Age-related dysfunctions of the ear
a. Constant background ringing, hissing, whistling in one or both ears
b. Usually accompanied with some hearing loss
c. Mechanism unknown
i. Obstruction of ear canal
ii. Middle ear infection
iii. Meningitis
iv. Hypertension
d. 10% over age 65 complain of tinnitus
The Special Senses
3. Deafness
F. Age-related dysfunctions of the ear
a. Complete loss of hearing is not common
b. Conduction deafness vs. nerve deafness
4. Dizziness and vertigo
a. What’s the difference between the two?
b. 90% of elderly complain of one or the other
c. Often caused by inflammation of inner ear or vesitibulocochlear nerve
d. People tend to compensate by standing with feet wider apart and arms away from the body
1. Location of taste buds
2. Taste bud cells
3. Taste sensations
a. Substances must be dissolved
b. Sweet, salty, sour, bitter
c. Most of taste is olfaction
The Special Senses
G. Structure and function of taste
1. General decrease in taste with age, thought to be due to decreased central sensation, not loss of cells
2. Decreased salivary secretion and volume
3. Fissure and furrow formation on tongue
4. Effects of tobacco
The Special Senses
H. Age-related changes in taste
1. Slow generalized loss of olfactory cells
2. Loss of neurons in olfactory bulbs
3. Gradual decline in smell beginning in middle age, also related to decline in central processing
The Special Senses
I. Structure and function of smell
a. Smell identification increases to age 30-40
b. Smell identification decreases post-60
c. 70% identification between 20-40, but 5% >age 70
end
The Special Senses
J. Take home messages
1. Generalized loss of receptors
2. Eye – changes in lens, pupil size, and corneal curvature; loss of vitreous humor; adaptation time increases
3. Ear – loss of nerve fibers and sensory cells allows loss of hearing and balance with aging
4. General decline in taste and smell
5. Much decline attributed to decreased central processing
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