Vision I: Retinal Function

Question 1

Major cells of retina

Answer 1

photoreceptors (rods and cones), bipolar cells, ganglion cells, horitzontal and amacrine cells, muller cells, retinal pigment epithelium, blood vessels, collagen

Question 2

Rods/cones are what order neurons?

Answer 2

First order

Question 3

Ratio of rods and cones

Answer 3

Many more rods (100 million) than cones (5 million)

Question 4

Bipolar cells are what order neurons?

Answer 4

seconds order

Question 5

Ganglion cells

Answer 5

3rd order neurons, connect retina to the brain (LGN), unmyelinated axons transverse inner retina become myelinated by optic nerve oligodendrocytes, involved in convergence

Question 6

Horizontal and amacrine cells

Answer 6

interneurons with specific roles in center and dark vision

Question 7

Which cells work as retinal astrocytes (GFAP+)>

Answer 7

Muller cells

Question 8

RPE

Answer 8

important regulator of PR health

Question 9

Branches of what artery run through retina?

Answer 9

central retinal artery

choroidal vasculature provides supply to PRs

Question 10

Vasculature to fovea?

Answer 10

NOPE. (foveal avascular zone) since it’s involved in processing color

Question 11

Where do we find photoreceptors? (PRs)

Answer 11

in fovea - cones abundant, provide fine detail and color vision
rods - not in fovea, most of them are lateral

Question 12

Compare and contrast structural features of rods and cones

Answer 12

rods - free floating
cones - attached to plasma membrane

rods are longer, steeper
cones - thicker, shorter

both have outer and inner segments, both have cilium

Question 13

How is PR excitability different from other cells?

Answer 13

in the dark, channels open, partially depolarized

AT REST, THE CURRENT FLOW IS ALREADY PARTIALLY DEPOLARIZED “DARK CURRENT”

Question 14

Rhodopsin

Answer 14

involved in activation of phototransduction cascade (coordinates with G-protein transducin, GTP)

vitamin A

Question 15

How does phototransduction signal propogate to second order neuron?

Answer 15

Removal of glutamate

Question 16

What is the waste management dohick in photoreceptors?

Answer 16

RPE! phagocytize the most apical outer segment discs and take to lysosomal system, follow circadian rhythms

Question 17

Other functions of RPE?

important!

Answer 17

1. forms blood PR barrier
2. daily phagocytosis of outer segment discs
3. Vit A metabolism (important in phototransduction, trans to cis)
4. melanin production to allow for high acuity (high density melanosomes around cones, low around rods)
5. neovascular barrier to prevent choroidal vasculature from entering subretinal space

Question 18

How are ganglion cells distributed?

Answer 18

high density in mid fovea! very siimilar in distribution to cones (close to 1:1 ratio of cone to GC at the fovea)

Question 19

How are images perceived by eye?

Answer 19

Images are right- left reversed AND up-down inverted

Question 20

X pathway of RGC

Answer 20

small diameter (midget RGCs)
detect fine detail, sharp edges, color, project ot parvocellular layers of the lateral geniculate nucleus (P cells)

Question 21

Y pathway of RGC

Answer 21

large diameter cells with huge dendritic field, detect motion and general shapes, project to M cells

Question 22

W pathway of RGCs

Answer 22

varied size, large dendritic field, used for detection of LIGHT LEVELS not for acuity, do NOT go to lateral geniculate nuclues

Question 23

Types of cones

Answer 23

L cones - red (long wavelength)
M cones - green (middle wavelength)
S cones - blue (short wavelength)

Question 24

How is color vision mediated?

Answer 24

Genetically (opsins are tightly linked on X chormosome for long and middle wavelength, and on chromosome 7 for short wavelength)

Question 25

Protanopia

Answer 25

Loss of L cone function

Question 26

Deuteranopia

Answer 26

loss of M cone function

Question 27

tritanopia

Answer 27

loss of S cone function

Question 28

Receptive field center and surround?

Answer 28

Receptive field center - provides direct info from PRs to bipolar cells

Receptive field surround - indirect info from PRs to bipolar cells via horizontal cells (lateral inhibition)