Transcript Chapter 8 The Special Senses

The Special Senses
A. Structure and function of the eye
1. Location
2. Structure of the eye
a. Fibrous tunic
i.
Sclera
ii.
Cornea
sclera
cornea
fibrous
tunic
iris
optic
nerve
sclera
pupil
dura mater
canals of
Schlemm
The Special Senses
A. Structure and function of the eye
2. Structure of the eye
b. Vascular tunic
i.
Choroid
ii.
Ciliary body
iii.
Iris with pupil
a)
Sphincter pupillae
b)
Dilator pupillae
choroid
ciliary
body
iris
pupil
pupil
FULL
CONSTRICTION
FULL
DILATION
The Special Senses
A. Structure and function of the eye
2. Structure of the eye
c.
retina
Nervous tunic (retina)
i.
Photoreceptors
(rods and cones)
ii.
Photopigments
iii.
Optic nerve
iv.
Optic disc
v.
Fovea centralis
optic
disk
optic
nerve
ora
serrata
The Special Senses
A. Structure and function of the eye
posterior
chamber
2. Structure of the eye
anterior
chamber
d. Lens
e. Aqueous humor
f.
Vitreous humor
posterior
cavity
anterior
cavity
The Special Senses
A. Structure and function of the eye
3. Accessory structures
a. Eyelids
lacrimal puncta
lacrimal
gland
b. Conjunctiva
c.
Lacrimal apparatus
lacrimal ducts
d. Extrinsic muscles
nasolacrimal
duct
lacrimal caruncle
superior and
inferior lacrimal
canals
The Special Senses
A. Structure and function of the eye
4. Light refraction and the accommodation reflex
The Special Senses
B. Age-related changes of the eye
1. External changes
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
B. Age-related changes of the eye
2. Internal changes
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
B. Age-related changes of the eye
2. Internal changes
b. Nervous tunic (retina)
c.
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
Vitreous humor
i.
Becomes more liquid, causing light flashes
ii.
Floaters
iii.
More opaque
The Special Senses
B. Age-related changes of the eye
2. Internal changes
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
C. Age-related dysfunctions of the eye
1. Presbyopia (farsightedness)
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
C. Age-related dysfunctions of the eye
3. Glaucoma
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
C. Age-related dysfunctions of the eye
3. Glaucoma
d. Etiology – mostly unknown
e. Onset
f.
Symptomology
g. Treatments
The Special Senses
C. Age-related dysfunctions of the eye
4. Diabetic retinopathy
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
C. Age-related dysfunctions of the eye
5. Cataracts
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
C. Age-related dysfunctions of the eye
6. Age-related macular degeneration
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
C. Age-related dysfunctions of the eye
7. Detached retina
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
D. Structure and function of the ear
1. Location
external auditory meatus
temporal
bone
2. Divisions
a. External (outer) ear
i.
Auricle (pinna)
auricle
(pinna)
ii.
External auditory meatus
iii.
Tympanic membrane (eardrum)
tympanic
membrane
The Special Senses
D. Structure and function of the ear
1. Location
middle ear cavity
2. Divisions
b. Middle ear
i.
Ossicles
(malleus, incus, stapes)
ii.
Auditory (Eustachian) tube
iii.
Oval and round windows
incus
malleus
stapes
oval
window
tympanic
membrane
round
window
The Special Senses
D. Structure and function of the ear
1. Location
inner ear
2. Divisions
c.
Internal (inner) ear
i.
Bony labyrinth
ii.
Membranous labyrinth
iii.
Perilymph and endolymph
iv.
Cochlea (spiral organ)
v.
Vestibular apparatus
vi.
a)
Semicircular ducts
b)
Utricle and saccule
Vestibulocochlear nerve
semicircular ducts
saccule
utricle
cochlea
The Special Senses
D. Structure and function of the ear
3. Functions
a. Hearing
b. Equilibrium
The Special Senses
E. Age-related changes of the ear
1. External 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
E. Age-related changes of the ear
2. Middle 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
F. Age-related dysfunctions of the ear
1. Presbycusis
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
F. Age-related dysfunctions of the ear
2. Tinnitus
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
F. Age-related dysfunctions of the ear
3. Deafness
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
The Special Senses
G. Structure and function of taste
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
H. Age-related changes in 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
I. Structure and function of smell
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
a. Smell identification increases to
age 30-40
b. Smell identification decreases
post-60
c.
70% identification between 20-40,
but 5% >age 70
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
end