Vision I: Retinal Function Flashcards
(28 cards)
Major cells of retina
photoreceptors (rods and cones), bipolar cells, ganglion cells, horitzontal and amacrine cells, muller cells, retinal pigment epithelium, blood vessels, collagen
Rods/cones are what order neurons?
First order
Ratio of rods and cones
Many more rods (100 million) than cones (5 million)
Bipolar cells are what order neurons?
seconds order
Ganglion cells
3rd order neurons, connect retina to the brain (LGN), unmyelinated axons transverse inner retina become myelinated by optic nerve oligodendrocytes, involved in convergence
Horizontal and amacrine cells
interneurons with specific roles in center and dark vision
Which cells work as retinal astrocytes (GFAP+)>
Muller cells
RPE
important regulator of PR health
Branches of what artery run through retina?
central retinal artery
choroidal vasculature provides supply to PRs
Vasculature to fovea?
NOPE. (foveal avascular zone) since it’s involved in processing color
Where do we find photoreceptors? (PRs)
in fovea - cones abundant, provide fine detail and color vision
rods - not in fovea, most of them are lateral
Compare and contrast structural features of rods and cones
rods - free floating
cones - attached to plasma membrane
rods are longer, steeper
cones - thicker, shorter
both have outer and inner segments, both have cilium
How is PR excitability different from other cells?
in the dark, channels open, partially depolarized
AT REST, THE CURRENT FLOW IS ALREADY PARTIALLY DEPOLARIZED “DARK CURRENT”
Rhodopsin
involved in activation of phototransduction cascade (coordinates with G-protein transducin, GTP)
vitamin A
How does phototransduction signal propogate to second order neuron?
Removal of glutamate
What is the waste management dohick in photoreceptors?
RPE! phagocytize the most apical outer segment discs and take to lysosomal system, follow circadian rhythms
Other functions of RPE?
important!
- forms blood PR barrier
- daily phagocytosis of outer segment discs
- Vit A metabolism (important in phototransduction, trans to cis)
- melanin production to allow for high acuity (high density melanosomes around cones, low around rods)
- neovascular barrier to prevent choroidal vasculature from entering subretinal space
How are ganglion cells distributed?
high density in mid fovea! very siimilar in distribution to cones (close to 1:1 ratio of cone to GC at the fovea)
How are images perceived by eye?
Images are right- left reversed AND up-down inverted
X pathway of RGC
small diameter (midget RGCs) detect fine detail, sharp edges, color, project ot parvocellular layers of the lateral geniculate nucleus (P cells)
Y pathway of RGC
large diameter cells with huge dendritic field, detect motion and general shapes, project to M cells
W pathway of RGCs
varied size, large dendritic field, used for detection of LIGHT LEVELS not for acuity, do NOT go to lateral geniculate nuclues
Types of cones
L cones - red (long wavelength)
M cones - green (middle wavelength)
S cones - blue (short wavelength)
How is color vision mediated?
Genetically (opsins are tightly linked on X chormosome for long and middle wavelength, and on chromosome 7 for short wavelength)
