How We See 2 - Transduction Flashcards

1
Q

What is visible light an example of?

A

Electromagnetic wave

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2
Q

What is phototransduction?

A

Conversion of light energy to an electrochemical response by photoreceptors (rods and cones)

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3
Q

Where are photoreceptors?

A

On the retina

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4
Q

What do the phototransduced rods and cones activate and how?

A

Optic nerve cells by generating an action potential

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5
Q

What is each lamellae made up of?

A

Cell membrane which has the visual pigment rhodopsin in rods and coneopsins S, M and L in cones

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6
Q

What is the cell in the retina called where rods and cones exist?

A

Muller cell

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7
Q

What is integrated into the cell membrane of lamellae in rods?

A

Rhodopsin

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8
Q

What is integrated into the cell membrane of lamellae in cones?

A

Coneopsins S, M and L

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9
Q

What do the molecules rhodopsin, conopsins S, M and L differ in?

A

Spectral sensitivity

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10
Q

Where on the Muller cells in the retina are photoreceptors found?

A

On stacks of lamellae in the outer segment

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11
Q

What wavelength does the blue cone best absorb?

A

437nm

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12
Q

What wavelength do rods best absorb?

A

498nm

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13
Q

What wavelength do green cones best absorb?

A

533nm

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14
Q

What wavelength do red cones best absorb?

A

564nm

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15
Q

What is the structure of rhodopsin?

A

Integral transmembrane helical protein

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16
Q

What is chromosphore?

A

Part of a molecule responsible for changing its colour

17
Q

What is opsin?

A

Protein which forms part of the visual pigment rhodopsin and is released by the action of light

18
Q

Where is chomosphore found in rhodopsin?

A

Nesting in the opsin

19
Q

Why is vitamin A important for sight?

A

It is used to form opsin within rhodopsin

20
Q

What are the two importnat parts of rhodopsin?

A

Opsin and retinal

21
Q

What happens to 11-cis retinal when light falls on it?

A

Isomerises to all trans retinal

22
Q

Why does rhodosin split from all trans retinal

A

All-trans retinal cnnot fir into the opsin, resulting in bleaching of the visual pigment purple

23
Q

Explain the process of rhodopsin causing the phototransduction cascade?

A

1) Chomophore nests in the protein opsin which is part of retinal
2) When light falls on 11-cis retinal it isomerises to all-trans retinal
3) All-trans retinal cannot fit into the opsin so rhodopsin splits
4) Results in bleaching of the visual purple which causes photoconduction due to the phototransduction cascade

24
Q

What vitamin is responsible for visual pigment regeneratoin?

A
25
Q

When are photoreceptor cells at rest, and in what polar state are they?

A

At rest in th edark in a depolarised state by open Na/Ca channels

26
Q

What maintains at rest photoreceptor cells in a depolarised state?

A

Open Na/Ca channels

27
Q

Explain the phototransduction cascade?

A

1) Photo of ligh hits rhodopsin
2) Which becomes activated rhodopsin
3) Becomes transducin-GTP, then phosphodiesterase (acitvated) then GMP

4) Na channel closes

5) Relative hyperpolarisation of photoreceptor cell
6) hyperpolarisation transmitted by a flux of Ca ions to the synapse with bipolar cell
7) Stimulates ultimately the retinal cell

28
Q

Explain visual pigment regeneration?

A
29
Q

What does vitamin A deficiency lead to in relation to the eyes?

A

Since vitamin A is supplied through the diet any condition that affects vitamin A absorption will affect vision, causing blindness

Also essential for healthy epithelium so conjunctiva and corneal epithleium are also abnormal

30
Q

What are examples of conditions where vitamin A deficiency can occur?

A

Malnutrition

Malabsorption conditions such as coeliac disease or sprue

31
Q

What are signs of vitamin A deficiency?

A

Bitot’s spot in conjunctiva

Corneal ulceration

Corneal melting which leads to opacification of the cornea