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Smell- Olfactory bulbs
Taste- Taste buds
Sight- Eyes
Hearing- Ears
• Also static and dynamic equilibrium
The Sense of Sight
• Accessory organs:
– Eyelids- 4 layers:
skin, muscle,
connective tissue,
conjunctiva
(mucous
membrane) moved
by orbicularis oculi
muscles (close)
and levatator
palpebrae
superioris (open)
– Lacrimal apparatus- lacrimal gland- secretes
tears continuously– tears contain lysozyme
which protects against bacteria
– 6 extrinsic muscles- movement of eye
Structure of the Eye
• Cornea
– Helps focus
entering light rays
– Connective tissue
with thin layer of
epithelium
– No blood vessels
– Unusually regular
fiber pattern
• Sclera (white of
eye)
– Opaque due to
large,
disorganized
collagenous and
elastic fibers
– For protection
and attachment
• Choroid coat
– Contains blood
vessels
– Produces
melanin which
absorbs excess
light
• Ciliary body
– Forms internal
ring around front
of eye (muscle
fibers and
ligaments)
• Iris
– Colored portion of eye (pigmented
versus non-pigmented)
– Thin diaphragm composed of
connective tissue and muscle fibers
– Circular and radial muscle fibers
control size of pupil (stimulated by
photons of light)
• Aqueous humor
– Fills space
between cornea
and lens
– Nourishes, helps
hold shape
Glaucoma- aqueous
humor made
quicker than can
be removed;
pressure builds,
damage results
• Lens
– Lies directly
behind iris and
pupil
– Epithelial cells
(cytoplasm is
transparent part)
– Change shape to
focus
Cataract- fluid in lens becomes cloudy and
opaque
Light entering the eye is refracted
• Retina- contains
photoreceptors
– Rods- more sensitive
in low light, gives
general outline, seen
as black and white
– Cones- less sensitive
in low light, sharp
picture, color
• Fovea- cones only, sharpest vision
• Optic disk- where
nerve fibers from
retina enter optic
nerve
– Known as the
“blind spot”
Night blindnessfewer working rods
(lack of vitamin A)
Day blindness- lack
of working cones
Visual pigments
• In rods- rhodopsin breaks down into opsin
and retinal when struck by photons. This
initiates a chemical rxn (action potential)
which is sent to the visual cortex. (occipital
lobe)
• In bright light nearly all rhodopsin is
broken down, reducing rod sensitivity
• In cones- 3 different light sensitive proteins
connected to retinal
– Depending on which one is stimulated, brain
interprets that color
– Erythrolabe- red
– Chlorolabe- green
– Cyanolabe- blue
If all are stimulated at once- white
4 Sex-Linked Traits:
1. Normal Color Vision:
A: 29, B: 45, C: --, D: 26
2. Red-Green Color-Blind:
A: 70, B: --, C: 5, D: -3. Red Color-blind:
A: 70, B: --, C: 5, D: 6
4. Green Color-Blind:
A: 70, B: --, C: 5, D: 2
• Axons of the retina
form optic nerves
which join at optic
chiasma in which
certain fibers cross
(medial) and other
fibers do not (lateral)
• A few enter the thalamus to stimulate
visual reflexes