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1. Opthalmology > Physiology of photoreceptors > Flashcards

Physiology of photoreceptors Flashcards

1
Q

What is the direct pathway for signal transmission?

A 
photoreceptors deduce light into electrical current ->
bipolar cells ->
ganglion cells (axons comprise the optic nerve)
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2
Q

What is the role of horizontal cells?

A

recieve input from photoreceptors and project to other photoreceptors and bipolar cells

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3
Q

What is the role of amacrine cells?

A

recieve input from bipolar cells and project to ganglion cells, bipolar cells and other amacrine cells

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4
Q

What is the role of photoreceptors?

A

convert electromagnetic radiation to neural signals

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5
Q

What happens to vertebrate photoreceptor cells membrane potentials when they are exposed to light?

A

membrane potential hyper polarises

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6
Q

Why is a vertebrate photoreceptor cells membrane potential positive?

A

the dark current

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7
Q

What is the dark current?

A

a cGMP gated Na channel that is open in the dark due to the release of neurotransmittors (glutamate) and closed during light

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8
Q

How does the dark current allow the brain to percieve objects?

A

the change of Na due to light signals to the brain

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9
Q

What cells can cause action potentials?

A

ganglion cells

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10
Q

What neurotransmittor is released to open the Na channels?

A

glutamate

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11
Q

What is the membrane potential equation in the dark?

A 
Pna = Pk
Vm = between End and Ek
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12
Q

What is rhodopsin (rods) made up from?

A

retinal - vit A derivative

opsin - G protein coupled receptor

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13
Q

Where are rods present?

A

membrane folds - called discs in outer segment

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14
Q

What does light convert 11-cis-retinal to?

A

all-trans-retinal

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15
Q

What is the role of all-trans-retinal?

A

activates transducin -> molecular cascade -> decrease cGMP which leads to the closure of cGMP gated Na channels

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16
Q

What does decreased Na entry lead to for cGMP gated Na channels?

A

hyperpolarisation

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17
Q

What is transducin?

A

a G protein that activates phosphodiesterase (PDE) which hydrolyses cGMP leading to decreased cGMP levels

18
Q

What are the benefits of rods?

A

good for seeing in dim light - high convergence, low visual acuity

19
Q

What are the benefits of cones?

A

good for seeing in normal daylight with high visual acuity - high density of cones, high visual acuity

20
Q

How do we see shades?

A

cones of different wavelengths overlap

21
Q

What type of cone sees blue?

A

short wave cone

22
Q

What type of cone sees red?

A

long wave cone

23
Q

What type of cone sees green?

A

middle wave cone

24
Q

Where are rods found in the retina?

A

peripheral retina

25
Q

Where are cones found in the retina?

A

center of the retina - fovea

26
Q

What is the monocular visual field?

A

what each eye sees individually

27
Q

What is the binocular visual field?

A

what both eyes overlap to see

28
Q

Where would the right visual field go to?

A

left cortex

29
Q

Where would the superior visual field go to?

A

lower cortex

30
Q

What cells recieve mononoclar vision?

A

4c layer

31
Q

What cells recieve binocular vision?

A

all cells outside the 4c layer

32
Q

What is ambylopia/cortical blindness?

A

no problem with the eye, but one eye has better vision than the other

33
Q

What is ambylopia caused by?

A

strabismus - wandering eye in infancy - must be corrected by eye patch over good eye as signals from eyes need to compete equally

34
Q

What is Hebbs postulate?

A

basis for the loss of binocularity
basically: if axon A is near enough to touch axon B and takes part in exciting it and firing it, a growth process takes place in one or both cells allowing As efficiency to fire cell B to increase - long term potination

35
Q

What can Hebbs postulate lead to?

A

one eye being deprived of axons

36
Q

Where is a colloid cyst found?

A

intravertebral foramen

37
Q

What does an ependymanos arise from?

A

ependymal cells

38
Q

Where is a epidural haematoma found?

A

between skull and dura - arterial bleed

39
Q

Where is a subdural haematoma found?

A

between dura and arachnoid - venous bleed

40
Q

What is hydrocephalus?

A

accumulation of CSF in the ventricular system or around the brain, enlargement of the ventricles increase CSF pressure

41
Q

What is hydrocephalus due to?

A

too much CSF production

obstruction of flow

1. Opthalmology (21 decks)

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