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Neuro weeks4-6 - Keith > 40- Vision > Flashcards

40- Vision Flashcards

1
Q

What is purpose of fovea?

A

fine focusing of incoming light

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2
Q

What inverts the image in vision?

A

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

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3
Q

What is pathway of light as it enters the eye?

A

light is refracted by the cornea

  • inverted through pupil
  • variable refratction by lens
  • projeted on the fovea in center of the macula
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4
Q

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

A

they lack a fovea

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5
Q

What is the purpose of the sclera?

A

protection

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6
Q

What is the choroid of the eye?

A

vascular layer

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7
Q

Fovea is devoid of blood vessels

A

fact

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8
Q

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

A

choroid

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9
Q

Where does retinal blood flow come from?

A

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

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10
Q

When are there blood vessels in the fovea?

A

macular degeneration (blood distorts the image)

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11
Q

What are the layers of the retina in order?

A 
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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12
Q

What layer of the retina will light hit first?

A

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.

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13
Q

What interneurons are in the outer plexiform?

A

horizontal cells

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14
Q

What interneurons are in the inner plexiform?

A

amacrines

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15
Q

Why is there a blind spot?

A

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

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16
Q

What is main function of RPE?

A

to separate vascular choiroid from neural retina

RPE stands for retinal pigment epithelium

17
Q

What consumes rod cell outer segments every 10 days?

A

RPE

18
Q

What causes drusen?

A

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

19
Q

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

A

rods

20
Q

Which cells are responsible for night vision?

A

rods

21
Q

Which cells process color vision?

A

cones

22
Q

What are the different cone cell types?

A

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

23
Q

Which cone types process blue color? Red?

A 
S cones (blue has a short wavelength)
L cones process Red, which has a long wavelength
green is somewehre between so M cones
24
Q

Why are men more likely to be colorblind than women?

A

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)

25
Q

How do rods and cones respond to light?

A

they HYPERPOLARIZE

26
Q

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

A

rods and cones rods and cones

27
Q

What is chemical pathway of light reception in rods?

A

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

28
Q

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

A

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

29
Q

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

A

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

30
Q

What is main function of alpha ganglion cells?

A

locate an object in space

31
Q

What is main function of beta ganglion cells?

A

for fine texture and color recognition

32
Q

Where are alpha ganglion cells mostly found? beta?

A

predominate in peripheral retina

beta ganglion found in the central retina

33
Q

Where do beta ganglion cells project to?

A

parvocellular region in lateral geniculate nucleus

34
Q

What is unique about the fovea and convergence?

A

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

35
Q

Where is the left visual field processed?

A

right visual cortex

36
Q

What is the M pathway of the visual cortex?

A

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

37
Q

What is P pathway?

A

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

38
Q

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

A

central field loss for macular

complete vision loss for diabetic

39
Q

What is difference between dry and wet madcular degeneration?

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

Neuro weeks4-6 - Keith (37 decks)

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