Visual Systems 1 Flashcards
Describe the physical parts of the eye from exterior –> interior
Cornea, aq. humor, lens, vitreous humor, retina
What contracts the lens?
Ciliary muscles and zonule fibers
What are cataracts?
The accumulation of protein residue in the lens
What is glaucoma?
Abnormal high pressure in the eye that leads to optic nerve damage
Whats the center of the retina called?
Fovea
Whats diabetic retinopathy?
blood vessel damage in the retina
What process is done by the lens when looking at near objects? What’s the loss of this ability called?
Accommodation; presbyopia
What wave length is UV light?
<400nm
Once light hits the retina, what does it have to go through to get to the optic nerve?
Pigmented epithelium, the outer nuclear layer, the outer plexiform layer, the inner nuclear layer, the inner plexiform layer, the ganglion cell layer
What extra cells are present in between the plexiform layers?
The horizontal cells & amacrine cells
What is the purpose of the horizontal & amacrine cells
local retinal processing (quick processing)
What is the role of rods vs cones?
Rods - night vision, peripheral
Cones - color, concentrated area, foveal concentration
In the central retina, what allows for high resolution vision?
Each receptor cell is connected to one bipolar cell and one ganglion cell
In the peripheral retina, what allows for high light sensitivity?
convergence allows 1 ganglion for many photoreceptors
What is retinal isomerization triggered by?
photon absorption
What large transmembrane protein binds to retinal?
Rhodopsin
Why is red/green blindness more common in men?
The photoreceptor gene is close to the x-chromosome
What chromosome are blue color receptor genes located on?
Chromosome 7
what is the first step in the visual transduction mechanism?
G-protein coupling activated by photon input
what happens to the cell membrane of photoreceptors when the G-protein is coupled?
Hyperpolarizes
List the steps to the phototransduction pathway (light)
Light –> rhodopsin activated –> transducin & GTP activated –> PDE activation –> cGMP cleavage to GMP –> Na+ channels close (polarization)
In a neurotransmitter receptor, what happens to the second messenger vs a light photoreceptor?
Neurotransmitter increase in second messenger photoreceptor/decreases second messenger
What is the term for the photoreceptor, horizontal cell, and bipolar cell?
Tripartite synapse
Which pathway depolarizes in response to lights on? And is the synapse sign conserving or inverting?
ON pathway; sign inverting
The OFF pathway has a sign conserving synapse. This means the bipolar cell activates in response to what?
Turning lights off
What happens to photoreceptors in the dark and why?
Photoreceptors are activated because the lack of light allows glutamate to be released and depolarize horizontal cells (which release GABA)
Which types of bipolar cell are inhibitory or excitatory?
ON –> inhibitory
OFF –> excitatory
Whats the role of glutamate in a depolarized ON cell?
There is more glutamate release –> more hyperpolarized bipolar cell
What happens when OFF photoreceptors are exposed to light in terms of glutamate?
Less glutamate is released –> less GABA is released by horizontal cells. Other photoreceptors depolarize more which means the bipolar cell is more hyperpolarized
What are the two types of ganglion cells? And what are their characteristics?
M (magno) - large Rf, fast adaptation, 5%
P (parvo) - small Rf, slow adaptation, 90%
What is the role of the superior colliculus?
Directs the eyes toward signals of interest
What does the optic nerve project to?
The superior colliculus and the LGN in the thalamus
