Eyes and Gustation

By Kevin Tran, Spencer Ayres, Brandon Shaw,

and Morgan Ciehanski

Vision

W

e rely on our vision more than any other special

sense

V

isual receptors are located in the eye

Functions of accessory structures

P

rotection

L

ubrication

S

ecretion of tears

Accessory structures of the eye

S

uperficial Epithelium of the Eye- thin layers of skin around the

eye and covering the eye itself

E

yelashes- robust hairs that help prevent foreign materials from

reaching the eye

E

yelids – continuation of the skin that protect and lubricate the eye

eyelashes

L

ocated along the inner margin of the eye lid

T

arsal Glands- also known as Meibomian, are modified

sebaceous glands

T

arsal glands secrete lipid-rich products that keep the eye

lids from sticking together

Eyelids

E

yelids open and close eye using muscles fibers

O

rbicularis Oculi and Levator Palpebrae

Superioris muscles are responsible for closing the

eye and raising the upper lid

Epithelium of the eye

C

onjunctiva- outer surface of the eye that a mucous membrane

covered in stratified squamous epithelium

P

alpebral Conjunctiva- inner surface of the eyelid

O

cular Conjunctiva- the anterior surface of the eye

C

ornea- a transparent part of the outer fibrous layer

Lacrimal apparatus

L

acrimal Apparatus- produces, distributes, and removes

tears

C

onsists of• Lacrimal Gland and associated ducts• Lacrimal Canaliculi• Lacrimal Sac• Nasolacrimal Duct

Lacrimal apparatus

L

acrimal Gland- tear gland

L

acrimal Canaliculi- small canals that lead to the lacrimal sac

L

acrimal Sac- holds the tears that the lacrimal gland produces

N

asolacrimal Duct- delivers tears to the nasal cavity on that side

The eye

S

ophisticated visual instruments

C

ontains three distinct layers or tunics• Outer Fibrous Tunic• Middle Vascular Tunic• Inner Neural Tunic (retina)

Fibrous tunic

O

utermost layer

C

onsists of sclera and cornea

S

clera- “white of the eye”; made of collagen and elastic fibers

P

rovides mechanical support and some physical protection

S

erves as an attachment site for the eye muscles

C

ontains structures that assist in the focusing process

Vascular tunic

A

lso known as the Uvea

C

ontains blood vessels, lymphatic vessels, and the intrinsic muscles of the

eye

P

rovides a route for blood vessels and lymphatics that supply tissues of the

eye

R

egulating the amount of light the eye receives

Vascular tunic

S

ecreting and reabsorbing the aqueous humor that circulates

the eye

C

ontrols the shape of the lens

C

ontains the iris

Visual receptors, or Photoreceptors, located in neural tunic

Iris

I

ris- visible through the corneal surface, contains the blood

vessels, pigment cells, and smooth muscle fibers

P

upillary muscles- muscles that contract and changes the

diameter of the pupil

P

upil- central opening of the iris

Pupillary muscles

P

upillary Constrictor Muscles- when it contracts,

the pupil decreases (more light)

P

upillary Dilator Muscles- contraction enlarges the

pupil (less light)

Neural Tunic

A

lso known as the Retina

R

etina helps process visual information

C

ontains two parts: pigmented part and neural part

P

igmented part absorbs light

N

eural part is in control of processing

A

lso contains photoreceptors

P

hotoreceptors- cells that detect light

Organization of retina

R

ods and cones

R

ods- highly sensitive to light, don’t ‘see’ colors

C

ones- ‘sees’ colors, provide sharper clearer images

O

ptic Nerve- transmits the visual images picked up from the rods

and cones and delivers them to the brain

Rods and cones

M

acula Lutea- has no rods

F

ovea- contains highest cone concentration

F

ovea is the site of the sharpest vision

Structure of the eye

T

he eye is hollow

T

wo cavities• Posterior cavity• Anterior cavity is filled with aqueous humor

Posterior cavity

Or Vitreous Chamber, contains the vitreous body

Vitreous Body- or Vitreous Humor, gelatinous substance

that makes up most of the volume of the posterior cavity

Helps stabilize the shape of the eye

Anterior Cavity

D

ivided into two chambers• Anterior chamber• Posterior chambers

C

hambers are filled with Aqueous Humor

A

queous Humor- fluid that circulates within the anterior

cavity, passing through the chambers of the pupil

Anterior chamber

E

xtends from the cornea to the iris

Posterior chamber

E

xtends between the iris and the lens

lens

L

ies posterior to the cornea

P

rimary function is to focus the visual image on the photoreceptors

F

ocus happens by the change in shape of the lens

L

ens fibers are in the interior of the lens

Lens fibers

L

ost their nucleus and organelles

S

lender and elongated

F

illed with transparent proteins called crystallins

C

rystallins- responsible for clarity and focusing power of the lens

transparency

D

epends on precise combination of structural and

biochemical characteristics

L

ose of balance produces cataracts

refraction

T

he light that is collected by the photoreceptors in refracted,

or bent when passing from one medium to another

P

encil in water

R

efraction occurs when passing light through the cornea and

then into the lens

refraction

G

reatest amount of refraction occurs when light passes through

the air into the corneal tissues

T

issues have a density similar to water

W

hen you opne your eyes underwater you cant see as easily

because the air-water refraction has been eliminated and

replaced with water to water, thus light remains unbent and

Additional refraction

L

ight passes through the aqueous humor into the dense lens

T

his lens provides extra refraction that’s needed to focus

the light rays from an object to a focal point

F

ocal Point- a specific point of intersection of the retina

Focal distance

F

ocal Distance- distance between the center of the

lens and its focal point

D

etermined by two factors1. Distance from object to the lens2. Shape of the lens

Distance from the object to the lens

T

he closer an object is to the lens, the greater the

focal distance

The shape of the lens

T

he rounder the lens the more refraction occurs, so a

very round lens has a shorter focal distance than a

flatter one

accommodation

A

ccommodation- focusing images on the retina by changing the

shape of the lens to keep the focal length constant

T

o view nearby objects the lens becomes rounder

T

he lens flattens when we view a distant object

L

ens are held in place by suspensory ligaments

accommodation

G

reatest amount of refraction is needed for viewing objects up close

I

nner limit of clear vision is called the near point of vision

C

hildren can see things up close but as time goes on the lens

becomes stiffer and less responsive

A

ging effects the near point of vision

Astigmatism

I

f light doesn’t pass properly the image is distorted

Astigmatism- the degree of curvature in the cornea or

lens varies from one axis to another

I

mage distortion may be so minimal people don’t even

notice the condition

Image reversal

L

ight originates at a single point either near or far

H

owever and object in view is a complex light source that is treated as a

large number of individual points

T

hese individual points creates a miniature image of the original but is

upside down and backwards

T

he brains compensates for this image reversal and we don’t notice it

Visual activity

V

isual activity- clarity of vision

R

ated against a ‘normal’ standard (20/20, 20/15, etc.)

C

onsidered legally blind when vision falls below

20/200, even with glasses or contact lenses

blindness

T

erms implies a total absence of vision due to damage of the

optic pathways

C

ommon causes are• Diabetes mellitus• Cataracts• Glaucoma• Corneal scarring• Detachment of the retina• Hereditary factors

Scotomas

A

bnormal blind spots that may appear in the field of vision

P

ermanent in a fixed position

R

esult from a compression of the optic nerve, damage to the

photoreceptors, of damage to the visual pathway

A

lso Floaters, which a small spots that drift across the field of vision,

generally temporary phenomena

Color vision

O

bjects appear to have color if they reflect or transmit photons from one

portion of the visible spectrum and absorbs the rest

P

hotons stimulate rods and cones

P

hotons of all colors bounce off an object or rods themselves are stimulated,

the object will appear white

I

f photons are absorbed by the object (none reach the retina), the object

appears black

Cone types

B

lue cones, green cones, and red cones

E

ach have a sensitivity to a different range of wavelengths

S

timulation to different combos of wavelength creates color vision

C

olor discrimination results from the integration of info from all three types of

cones

E

XAMPLE: Yellow is formed from a combo of highly stimulate green cones, less

strongly stimulated red cones, and relatively unaffected blue cones

Color blindness

P

eople who are unable to distinguish certain colors have a form of color

blindness

H

appens when one or more classes of cones aren't functional

E

ither lack of cones or unable to function properly

M

ost common type is red-green color blindness; red cones are missing so

a person cant tell the difference between red and green light

Effects of Aging on the eye

S

enile cataracts- lens loses transparency, blurred

vision

A

ccommodation problems- the near point of vision

gradually increases with age

Eye diseases

C

onjunctivitis- or pinkeye, due to damage and/or irritation of the

conjunctival surface

C

ataract- balance in the lens becomes disturbed and the lens loses

transparency; they can result from injury, radiation, or reaction to

drugs, as well as aging

G

laucoma- eye disease in which the optic nerve is damaged in a

characteristic pattern

Professions dealing with the eye

O

ptometrist- concerned with the health of the eyes and related

structures as well as vision, visual systems, etc. ; they are trained to fit

lens to improve vision and diagnose and treat diseases of the eye

O

phthalmologist- a specialist in medical and surgical eye problems

O

ptician-use prescriptions written by an optometrist or an

ophthalmologist to fit and sell eyeglasses, contact lenses and other

eyewear

Taste

S

pecial sense given to us by the tongue

T

aste sensation(s) is due to the presence of taste

receptors on the tongue

Taste buds

M

ade of specialized epithelial cells and taste receptors

C

ontain around 40 cells of different types/stages

B

asal cells -> Stem Cells in the tongue

G

ustatory cells -> Mature daughter cells, grow in stages

A

round 3000 in the adult tongue

Lingual papillae

E

pithelial projections on the tongue

T

hree types: Filiform Papillae, Fungiform Papillae,

Circumvallate Papillae

T

aste Buds located on the papillae

Filiform papillae

D

o not contain taste buds

P

rovide friction to move things around the mouth

Fungiform papillae

A

contain around five taste buds

A

little bigger than filiform papillae

Circumvallate papillae

C

an contain up to 100 taste buds

L

argest of the three types of papillae

F

orms a “V” at the back of the tongue

Gustatory discrimination

F

our Primary sensations: Sweet, sour, salty, bitter

T

wo less well known: Umami Umami, Water

D

ifferent regions of the tongue are more prone to certain tastes than others

A

ll sensations have same structure in the taste bud, just slightly different

receptor mechanisms

R

espond much more readily to unpleasant tastes than to pleasant

Taste receptor underpinnings

D

issolved chemicals bind to the receptor proteins in

gustatory cell

C

ell releases neurotransmitter, which generates action

potential in nervous system

Aging on taste

W

ith age, the number of functioning taste buds

decreases, meaning you’re less sensitive to various

tastes

N

umber decreases dramatically after 50

Taste video link

h

ttp://bigthink.com/videos/from-tongue-to-brain-the-

neurology-of-taste