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