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Special Senses Lecture
(Day 1:Eye anatomy & Vision)
The eye…..
•Works somewhat like a camera. It takes in light but for image
to be “understood/seen”, it must be processed in the brain.
•Eyes are actually extensions of the brain
•(i.e. the retina, which is on the back of the eye is all nervous tissue)
Anatomy of the Eye:
The eye is round, like a ball or a balloon.
It is made of many separate components and tunics (layers).
Only 1/6 of the eye is exposed/visible (the rest is enclosed
in fat and bone).
Diagram of the Eye
(frontal view)
sclera
conjunctiva (membrane)
medial canthus
lateral canthus
.
ciliary
glands
(lubricate eye)
.
.
.
.
meibomium
glands (oily)
iris
pupil
Interior apparatus associated with the eye:
lacrimal glands
nasolacrimal
duct
Tears contain antibodies and lysozymes (enzymes that kill bacteria).
Six external eye muscles control eye movement:
4 rectus muscles (up, down, left and right)
2 oblique muscles
Inferior oblique (elevates eye & moves it laterally)
Superior oblique (depresses eye & moves it laterally)
Now let’s learn the parts of the eye itself….
Tunic Layers :
a) Sclera (outermost layer): thick, tough, whites of the eye.
b) Choroid (middle layer of eye): blood rich tunic, that contains
a dark pigment that prevents light from scattering in the eye.
c) Retina (inner back of the eye): innermost delicate tunic, that
contains millions of receptor cells (rods & cones) that receive
and respond to light.
sclera
choroid
retina
Internal Anatomy of the Eye:
Two hard lenses (cornea & lens) help bend light
appropriately in order to focus light onto the retina
so image can be clearly seen.
cornea
lens
Attached to the lens are ciliary bodies (smooth muscles)
and the iris (pigmented “color” part of the eye).
The ciliary bodies pull on the iris which dilates
and constricts to regulate light input.
Two “liquids” in eye:
a) Aqueous humor: watery liquid just behind
cornea. Helps bathe cornea and give it oxygen
& nutrients.
b) Vitreous humor: thick, jelly-like substance which
makes up bulk of eyeball. Give eye structure and
maintains ocular pressure.
Aqueous humor
Vitreous humor
On the back of the eye is the retina.
The retina contains thousands of photoreceptors.
Photoreceptors are nerve cells that receive light.
Light passing
through
eyeball
Retina
(& photoreceptors)
The role of photoreceptors…
•Photoreceptors are distributed all over the entire retina,
at the back of the eye (except where the optic nerve leaves
the eyeball = optic disc/“blind spot”).
•When light from an object is focused on the optic disc, it disappears
from our view.
“blind spot”
There are two types of photoreceptors:
a) Rods:slender, elongated neurons. Rods allow us to
see in black, white, and shades of gray.
Rods also allows for peripheral vision.
rods
cones
b) Cones: fatter, more pointed neurons
(blue cones, green cones, and red cones).
Rods (skinny)
Cones allow us to see in color.
Cones
Also allows us to focus clearly
on objects in the center of our view.
(fatter)
Vision results from:
Light enters eye as wavelengths. These stimulate neurons at
back of eye (retina). These neurons start an action potential
(electrical impulse) which pass from the photoreceptors to
bipolar cells, then to ganglion cells, and then leave the optic
nerve.
Photoreceptors on retina get stimulate
and pass electrical impulses to brain via
optic nerve.
The nerve impulses travel very quickly along optic nerve to
the occipital lobe of the the cerebral cortex which allows
us to process and interpret these electrical signals, resulting
in “vision”.
eyes
occipital
lobe
Yes, I see!
The End of Part
ne !