40- Vision Flashcards
What is purpose of fovea?
fine focusing of incoming light
What inverts the image in vision?
refracted by the cornea and inverted as it passes through the pupil
What is pathway of light as it enters the eye?
light is refracted by the cornea
- inverted through pupil
- variable refratction by lens
- projeted on the fovea in center of the macula
Why is vision of many animals not as crisp as ours?
they lack a fovea
What is the purpose of the sclera?
protection
What is the choroid of the eye?
vascular layer
Fovea is devoid of blood vessels
fact
What provides blood flow to photoreceptors and RPE (retinal pigmented epithelial) cells?
choroid
Where does retinal blood flow come from?
central retinal artery (20%), the rest by choroid
When are there blood vessels in the fovea?
macular degeneration (blood distorts the image)
What are the layers of the retina in order?
Choroid 1 - pigment cells 2 - photoreceptor layer 3- outer limiting membrane 4 - cell bodies of rods and cones 5 - outer plexiform layer 6 - inner nuclear layer 7 - inner plexiform layer 8 - ganglion layer 9 - optic nerve fibers 10 - inner limiting membrane vitreous body
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What layer of the retina will light hit first?
inner limiting membrane after it passes through the vitreous body. then optic nerve fibres–>all the way to rods and cones and photorectpor layer with the last layer being the pigment cells with choroid behind them.
What interneurons are in the outer plexiform?
horizontal cells
What interneurons are in the inner plexiform?
amacrines
Why is there a blind spot?
ganglion cell axons coalesce to form optic nerve head (blind spot)
What is main function of RPE?
to separate vascular choiroid from neural retina
RPE stands for retinal pigment epithelium
What consumes rod cell outer segments every 10 days?
RPE
What causes drusen?
RPE failure to eat rod outer segments every 10 days. left over proteins start to autofloresce (drusen). Key factor in dry macular degenration
What cells process black and white information (scotopic) in eye?
rods
Which cells are responsible for night vision?
rods
Which cells process color vision?
cones
What are the different cone cell types?
L, M and S cones for Long, medium and short wavelengths.
Which cone types process blue color? Red?
S cones (blue has a short wavelength) L cones process Red, which has a long wavelength green is somewehre between so M cones
Why are men more likely to be colorblind than women?
M and L cones are carried on X-chromosome. This is why red-green colorblindness is so common in males. (they only have 1 x chromosome)
How do rods and cones respond to light?
they HYPERPOLARIZE
What is only sensory system in the body that hyperpolarizes in response to stimulus?
rods and cones rods and cones
What is chemical pathway of light reception in rods?
light converts 11-cis-retinal to all-trans-retinal
which activates rhodopsin
-rhodopsin activates GTP which activattes cGMP phosphodiesterase (PDE)
-active PDE lowers cGMP levels to hyperpolarize embrane and close Na and Ca channels.
-visual response is now signalled.
-Ca is pumped out of cell via Na/Ca exchanger
-cGMP levels rise and re-polarise the membrane to reopen channels
-rhodopsin dephosphorylated and all-trans-retinal converted back to 11-cis retinal so process can repeat.
-Arrestin prevents rhodopsin from being reactivated by rhodopsin kinase until light deactivates the arrestin
What is chemical difference in light reception between rods and cones?
cones have similar process of 11-cis-retinal to all-trans-retinal to GTP to cGMP PDE to lower cGMP to close Na and Ca channels to hyperpolarize, except they have THREE OPSINS INSTEAD OF JUST ONE RHODOPSIN
What input do alpha ganglion cells in the retina mostly recieve and where do they project to?
mostly get input from rods and project to magnocellular layer of lateral geniculate nucleus
What is main function of alpha ganglion cells?
locate an object in space
What is main function of beta ganglion cells?
for fine texture and color recognition
Where are alpha ganglion cells mostly found? beta?
predominate in peripheral retina
beta ganglion found in the central retina
Where do beta ganglion cells project to?
parvocellular region in lateral geniculate nucleus
What is unique about the fovea and convergence?
convergence does NOT occur in the fovea.
1 photorecptor = 1 ganglion cell.
Allows for crisp image.
Where is the left visual field processed?
right visual cortex
What is the M pathway of the visual cortex?
orinates from magnocellular ganglion cells, projects to lateral geniculate layers 1 and 2, and to layer 4c-alpha in cortex for space information
What is P pathway?
originates from parvocellular ganglion and projects to lateral geniculate layers 3-6 to layer 4c-beta in cortex for form information
What visual defect is common with age-related macular degenreation? What about diabetic retinopathy
central field loss for macular
complete vision loss for diabetic
What is difference between dry and wet madcular degeneration?
dry = little vision loss, lots of Drusen, usually 1 eye wet = vision loss, sometimes drusen, both eyes.
