40- Vision

Question 1

What is purpose of fovea?

Answer 1

fine focusing of incoming light

Question 2

What inverts the image in vision?

Answer 2

refracted by the cornea and inverted as it passes through the pupil

Question 3

What is pathway of light as it enters the eye?

Answer 3

light is refracted by the cornea

• inverted through pupil
• variable refratction by lens
• projeted on the fovea in center of the macula

Question 4

Why is vision of many animals not as crisp as ours?

Answer 4

they lack a fovea

Question 5

What is the purpose of the sclera?

Answer 5

protection

Question 6

What is the choroid of the eye?

Answer 6

vascular layer

Question 7

Fovea is devoid of blood vessels

Answer 7

fact

Question 8

What provides blood flow to photoreceptors and RPE (retinal pigmented epithelial) cells?

Answer 8

choroid

Question 9

Where does retinal blood flow come from?

Answer 9

central retinal artery (20%), the rest by choroid

Question 10

When are there blood vessels in the fovea?

Answer 10

macular degeneration (blood distorts the image)

Question 11

What are the layers of the retina in order?

Answer 11

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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Question 12

What layer of the retina will light hit first?

Answer 12

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.

Question 13

What interneurons are in the outer plexiform?

Answer 13

horizontal cells

Question 14

What interneurons are in the inner plexiform?

Answer 14

amacrines

Question 15

Why is there a blind spot?

Answer 15

ganglion cell axons coalesce to form optic nerve head (blind spot)

Question 16

What is main function of RPE?

Answer 16

to separate vascular choiroid from neural retina

RPE stands for retinal pigment epithelium

Question 17

What consumes rod cell outer segments every 10 days?

Answer 17

RPE

Question 18

What causes drusen?

Answer 18

RPE failure to eat rod outer segments every 10 days. left over proteins start to autofloresce (drusen). Key factor in dry macular degenration

Question 19

What cells process black and white information (scotopic) in eye?

Answer 19

rods

Question 20

Which cells are responsible for night vision?

Answer 20

rods

Question 21

Which cells process color vision?

Answer 21

cones

Question 22

What are the different cone cell types?

Answer 22

L, M and S cones for Long, medium and short wavelengths.

Question 23

Which cone types process blue color? Red?

Answer 23

S cones (blue has a short wavelength)
L cones process Red, which has a long wavelength
green is somewehre between so M cones

Question 24

Why are men more likely to be colorblind than women?

Answer 24

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)

Question 25

How do rods and cones respond to light?

Answer 25

they HYPERPOLARIZE

Question 26

What is only sensory system in the body that hyperpolarizes in response to stimulus?

Answer 26

rods and cones rods and cones

Question 27

What is chemical pathway of light reception in rods?

Answer 27

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

Question 28

What is chemical difference in light reception between rods and cones?

Answer 28

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

Question 29

What input do alpha ganglion cells in the retina mostly recieve and where do they project to?

Answer 29

mostly get input from rods and project to magnocellular layer of lateral geniculate nucleus

Question 30

What is main function of alpha ganglion cells?

Answer 30

locate an object in space

Question 31

What is main function of beta ganglion cells?

Answer 31

for fine texture and color recognition

Question 32

Where are alpha ganglion cells mostly found? beta?

Answer 32

predominate in peripheral retina | beta ganglion found in the central retina

Question 33

Where do beta ganglion cells project to?

Answer 33

parvocellular region in lateral geniculate nucleus

Question 34

What is unique about the fovea and convergence?

Answer 34

convergence does NOT occur in the fovea. 1 photorecptor = 1 ganglion cell. Allows for crisp image.

Question 35

Where is the left visual field processed?

Answer 35

right visual cortex

Question 36

What is the M pathway of the visual cortex?

Answer 36

orinates from magnocellular ganglion cells, projects to lateral geniculate layers 1 and 2, and to layer 4c-alpha in cortex for space information

Question 37

What is P pathway?

Answer 37

originates from parvocellular ganglion and projects to lateral geniculate layers 3-6 to layer 4c-beta in cortex for form information

Question 38

What visual defect is common with age-related macular degenreation? What about diabetic retinopathy

Answer 38

central field loss for macular complete vision loss for diabetic

Question 39

What is difference between dry and wet madcular degeneration?

Answer 39

``` dry = little vision loss, lots of Drusen, usually 1 eye wet = vision loss, sometimes drusen, both eyes. ```