eyes and gustation by kevin tran, spencer ayres, brandon shaw, and morgan ciehanski
TRANSCRIPT
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