Lab 6

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Lab 6

• VISION, EYEBALL MOVEMENT AND BALANCE SYSTEMS I

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The 5 Ls Lower retina (upper visual
field) Lateral part of LGN Loop of Meyer
Lower part (temporal) of optic radiations Lingual
Gyrus
In the conscious visual path, impulses travel
from receptors in the retina to the visual cortex
for perception of light stimuli. Visual impulses
traverse rod and cone, bipolar, and then ganglion
cells in the retina. Axons of ganglion cells exit
the eyeball in the optic nerve and traverse the
optic tract (after 50 decussation in the
chiasm). The optic tract terminates in the
lateral geniculate nucleus of the thalamus.
Thalamic neurons then send axons through the
optic radiations (retrolenticular fibers) to the
primary visual (calcarine) cortex.
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The eyeball consists of 3 concentric coats (1)
external or fibrous coat sclera (posteriorly)
and cornea (anteriorly) (2) middle or vascular
coat choroid, ciliary body, iris (3) internal
or retinal coat outer layer of pigmented cells
and inner layers of neural elements posterior to
the ora serrata
The four refractive media
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Black Board 42
Light
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-adapted for ion-pumping -pumps fluid from the
corneal stroma, preventing corneal opacification
from excessive hydration
- the main layer of the cornea and consists of
some 70 broad sheets of tightly bound, parallel
collagen fibers embedded in an extracellular
matrix  -the direction of the collagen fibers
differs in each layer for maximum mechanical
strength - the absence of blood vessels in the
cornea and the regular arrangement of the
 collagen fibers make the cornea translucent,
allowing it to transmit light
-stratified non-keratinized squamous
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The anterior and posterior aqueous chambers
communicate with each other via the aperture of
the pupil. Aqueous humor resembles cerebrospinal
fluid in composition and is secreted by the
epithelial cells of the ciliary processes in the
posterior chamber. It flows from there to the
anterior chamber through the pupil and provides
nutrients to the structures that it bathes. The
following figure indicates the path for the flow
of the aqueous humor
Glaucoma results from abnormal drainage of the
aqueous humor and is characterized by a rise in
the intraocular pressure. If not treated,
blindness can result from damage to the nerve
cells of the retina.
After filtering through a network of spaces
(spaces of Fontana ) lined by endothelium
(trabecular meshwork), which runs around the
circumference of the root of the iris at the
periphery of the anterior chamber, the aqueous
humor enters the canal of Schlemm . This canal
runs around the whole circumference of the limbus
within the sclera and drains into venous vessels.
It should be mentioned that there is normally a
resistance to the flow of aqueous humor through
the trabecular meshwork. Consequently, continued
secretion and resorption of the aqueous humor is
responsible for the normal intraocular pressure
(10-22 mg Hg).
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The axons of the retinal ganglion cells all
collect at the optic disc where they penetrate
the sclera to form the optic nerve. This disc is
also called the blind spot
The pigmented, vascular layer, the choroid (the
middle layer of the posterior 2/3 of the eyeball)
. extends from the ora serrata (the anterior
margin of the neural retina) to the optic
nerve contains blood vessels and lymphatics
supporting the retina. It will appear as a dark
brown sheet which blends with the sclera in its
outer portion The inner portion is attached to
the pigmented epithelium of the retina.
Separation of the retina occurs between the
rods and cones and the pigment epithelium   The
blood supply to the neural retina arises from the
ophthalmic artery ( central artery of the retina
and the ciliary arteries ). The central artery
of the retina branches out from the region of the
optic disc to serve inner portions of the
retina (four branches go to the four quadrants
of the retina). These branches are end arteries
and, if occluded, will result in death of the
ganglion cells and therefore total blindness
from that quadrant of the eye. The posterior
ciliary arteries penetrate the sclera around the
optic disc and form the choroidocapillary plexus
in the choroid. Materials from this plexus
provide nutrients to the outer portions of the
neural retina (the rods and cones).
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    outer coat  sclera posteriorly               
        cornea anteriorly     middle coat
choroid layer, containing pigmented
cells                       ciliary body (with
unstained ciliary muscle)                      
iris     inner coat  retina (in general, deep to
the pigmented layer)
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LENS is held in position by a suspensory ligament
composed of zonular fibers . The lens is a soft,
biconvex structure and has an outer capsule of
hyaline material the lens epithelium (below the
capsule), which is a layer of cuboidal epithelial
cells the center region composed of tightly
packed cells, which have lost their nuclei and
are, chock full of special transparent proteins
(crystallins).
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Pretectal Area
Occulomotor N.? Edinger Westphall
Parasympathetic fibers from ciliary ganglion
Cilliary Body
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note the thickened, black circular ciliary body,
which extends from the base of the iris to the
ora serrata (saw-toothed, black margin) at which
point it is continuous with the choroid (the
pigmented, vascular middle layer).     The
ciliary body contains the ciliary muscle (smooth
muscle), which you will see in microscopic views.
Contraction of this muscle decreases the tension
on the suspensory ligament of the lens and allows
the lens to round up and become more spherical.
The iris is a sheet-like diaphragm anterior to
the lens and separates the anterior and posterior
chambers of the eyes. The pupil is the circular
aperture, which can be constricted or dilated by
the actions of the circular fibers of the
constrictor pupillae (parasympathetic
innervation) and radial fibers of the dilator
pupillae (sympathetic innervation) muscles
respectively (you will see muscles in the eyeball
slide).
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GROSS RELATIONS
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Haines 3-7
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Haines 2-26
Lower visual field
Upper visual field
Calcarine Cortex (V1, Area 17) is along banks of
calcarine sulcus
V2 and V3 surround V1
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Haines 3-4
optic tract - ends at lateral geniculate nucleus
(not visible)
optic nerve
optic radiations
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Haines 4-12
LGN is on Haines 4-13
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Haines 4-13
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Conscious Visual Path
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Haines 4-1
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Haines 5-36
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Haines 4-34
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Haines 5-26
LGN
Optic Tract
Rostral Midbrain Level
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Optic Radiations are thalamic fibers traveling to
the primary visual cortex
Optic Radiations