Vision System Flashcards
Half of the total brain mass is devoted to visual processing
holy shit
Occipital cortex serves what function
Perception
Visual memories stored where?
Parietal and Temporal Lobes
Visual reflex
Brainstem and spinal cord
Visual system provides information required for setting of the circadian rhythms, general metabolic rate, mood, etc…
These parts of vision occur in the pineal gland (circadian rhythm) and diencephalon
HTN often diagnosed through analyses of the retina before blood pressure changes are noted by the patient
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Functions of the sympathetic nervous system can be tested by pupil dilation
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Fine focusing of incoming light is accomplished by
Fovea which is at teh center of the macula of the eye. Many animals do not have a macula or a fovea which is why their vision is not as crisp as ours.
Lens refraction abilitites are controlled by
Cilliary muscles that are under sympathetic and parasympathetic nervous system control
What is the sclera
a protective layer for the retina and choroid
What is the choroid
The vascular bed of the outer retina
Retinal blood flow is provided by
- Central Retinal Artery that enters through the optic nerves and supplies about 20% of the blood in the human retina.
- Choroid supplies the vast majority of blood to the retina
Fovea is devoid of vessels
If vessels grow there it distorts the image
Pigment cells in the retina are called what and serve what purpose
Retinal Pigmented Epithelial cells. They provide a barrier to the Retina from the choroid
Photoreceptor cell bodies lie where
outer nuclear layer, their projections lie in the outer plexiform layer
Retinal pathway
Photoreceptors (rods and cones) -> bipolar cells -> to ganglion cells
What is the purpose of interneurons
They help in convergence of the image from the millions of photoreceptors to hundreds of bipolar cells to tens of ganglion cells.
Interneurons located where
Outer plexiform layer (horizontal cells)
Inner plexiform layer (amacrines)
Ganglion cell axons coalesce to do what
Form optic nerve head.
Where is the blind spot
Optic nerve entry into the retina
RPE main function
separate vascular choroid from neural retina
Macular degeneration results when….
blood vessels damage the RPE and break through their barrier to the macular region of the eye. This causes visual distortion of the image
What is the other main function of the RPE
To eat outer rod segments every 10 days. As we age, this becomes less effective. Proteins are left in the RPE and they can autoflouresce. This is called Drusen which is a key factor of macular degeneration
Melanin in the RPE does what
absorbs some of the light that comes to the photoreceptors
Rods are responsible for
black and white vision
Light transduction occurs in what segment of rods
outer segment
KNOW that the outermost outer segment of rods is phagocytosed by the RPE cell layer every 10 days. A new outer segment extends from the inner segment and joins up with the other segments.
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Cones are responsible for
color vision
3 types of cones
L- long wavelenghts
M- Medium wavelengths
S- Shorter wavelengths
M and L cones are carried on what chromosome
X…thats why men are more likely to be colorblind, because they have only 1 x chromosome.
L cones
red
M cones
green
S cones
blue
Vision occurs when rods and cones…….. to light
hyperpolarize!!! This is the only sensory system where hyperpolarization is the key response to light
KNOW slide 15
ok…Most important slide of presentation
Once photoreceptors have processed the light, signal is passed to what
Bipolar cels
Rod Photoreceptors transduce their signal to rod bipolar cells and cone photoreceptors transduce their signal to
Cone bipolar cells
What cell types help to converge the signal from a bunch of rod photoreceptors to fewer rod bipolar cells
horizontal cells
Ganglion cells
There are different types. They activate based on image and project to different regions of the brain
Alpha ganglion cells
Most from rods.Teir job is to help locate the object in space. Project to magnocellular layer of LGN
Beta ganglion cells
Found Primarily in central retina. Define color and texture. Respond predominantly to cones. Project to Parvocellular region of LAG
What alows for crisp image representation
in teh fovea there is 1 photoreceptor/1 ganglion cell
NO CONVERGENCE!!!
Left visual field is processed where
Right visual cortex
So we know that images are inverted and shrunk once they cross through the eye. What is it about the eye that causes the image to shrink
Refracted by the LENS and CORNEA
Lens refraction is under control of what?
Ciliary muscles
Note that convergence does not occur in the fovea!!! One photoreceptor supplies one ganglion cell
This is why the image is crisp.
WHich fibers cross in the optic chiasm
only the nasal fibers
Once passing through the optic chiasm, where do fibers move?
Into the Lateral Geniculate ganglion and into the visual cortex
Diabetic retinopathy
changes in vasculature (GF)
Changes in
Dry macular degen vs wet
Dry: LIttle vision loss in one eye usually. 90% of cases
Wet: blood vessels grow into macula and cause significant visual loss…both eyes
