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Excitable Cells > L13-Vision > Flashcards

L13-Vision Flashcards

1
Q

Why are planktons and plants better adapted when they can sense light?

A

They can optimise sun exposure- photosynthesis.

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2
Q

If animals have eyes, why must they be a big advantage?

A
  • Eyes are very metabolically expensive.

- Only have them f they’re really worth it.

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3
Q

What happens to Mexican blind cavefish’s eyes?

A
  • They develop eyes embryologically

- then reabsorb them because they cost too much energy. (probably evolutionary to develop them)..

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4
Q

What do all eyes use to detect light?

A

All use the same basic molecule to detect light- opsins.

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5
Q

What are the differences in different eyes?

A
  • Many different solutions for lenses to focus light.

- Inverse and everse retinas.

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6
Q

What’s the similar developmental genes in eyes?

A

Pax-6.

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7
Q

In vertebrates, where is the retina derived from?

A
  • The ectoderm/ neural tube.

- It’s an extension of the brain.

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8
Q

What does the cornea do?

A

Greatest refracting power in the eye.

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9
Q

What does the lens do?

A

Accommodate the refracting power. Change shape for refracting power.

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10
Q

Where does the light hit at the back of the eye?

A

the fovea

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11
Q

Gross structure of the vertebrate eye

A

look at diagram!

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12
Q

What’s the laminar structure of the retina?

A 
Pigment epithelium
rods + cones
Muller cells
horizontal cells
  \+ bipolar cells
amacrine cells
ganglion cells
nerve fibre layer
inner limiting membrane
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13
Q

Which way is the arrow drawn in the lamina?

A

From the “excitable” cells, nerve fibres towards the photo-receptors, rods + cones.
Towards the detection of light.

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14
Q

What’s the order of cells along the arrow from the Ganglion cells?

A 
Ganglion cells
Amacrine cells
Bipolar cells
Horizontal cells
Muller cells
Rods + cones photoreceptor cells
Retinal pigment epithelium
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15
Q

What’s the RPE?

A

Retinal pigment epithelia
— pigmented layer at the back of the retina.
‘wraps’ outer segment of rods + cones

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16
Q

What is the RPE importance in recycling?

A

Retinaldehyde- an essential co-factor of opsins

17
Q

what is tapetum lucidum (eye shine) ?

A

The layer just behind the RPE.

light absorption and/ or reflection

18
Q

In the retinal pigment cells what do melanin granules and tapetum do?

A

Melanin granules = absorb light

Tapetum = reflects light

19
Q

What are the steps in phototransduction in rods and cones?

A
  1. Photon of light
  2. Conformational change in rhodopsin molecule
  3. Activation of transducing
  4. Activation of phosphodresterase
  5. Reduction in cGMP
  6. Closure of sodium channels—-
    —presence of stimulant = hyperpolarisation.
    Very odd.
20
Q

What is odd about phototransduction in rods and cones?

A
  • Presence of stimulant = hyperpolarisation
  • Usually in cells —depolarisation.
  • In dark they are depolarised with Na channels open,
    in the light cGMP is reduced and Na channels close
    Opposite of usual.
21
Q

What does membrane depolarisation in rods and cones do?

A

Glutamate release.

22
Q

In primates how much of the cortex is devoted to processing visual information?

A

More than 50%. Very important sense.

23
Q

What are 6 common defects in human vision?

A 
1 - Refractive errors
2- Cataracts
3- Diabetic retinopathy
4- Glaucoma- damage to optic nerve
5- Genetic defects in proteins e.g. rhodopsin
6- Tropical diseases e.g. trichoma
24
Q

What is the invertebrate retina made up of?

A

Individual units - ommatidia

Information from all- integrated in the brain.

25
Q

What do pigment cells do in invertebrates?

A

Prevent light scattering into other ommatidia.

26
Q

What are the steps of phototransduction in invertebrates?

A
  1. Photon of light
  2. Conformational change in rhodopsin
  3. Activation of Gq
  4. Activation of phospholipase C
  5. Phosphoinositide hydrolysis
  6. Cation channels open
  7. Depolarisation
27
Q

What’s the main difference in phototransduction between vertebrates and invertebrates?

A

Vertebrates- hyperpolarisation

Invertebrates- depolarisation

28
Q

What do a small proportion of retinal ganglion cells contain?

A

An additional opsin different from rods and cones.–

— melanopsin

29
Q

What does melanopsin do?

A

Measure levels of brightness important in unconscious light detection e.g. circadian rhythms, pupillary light reflex, body temp.

30
Q

In response to light, what happens in ganglion cells?

A
  1. Vertebrate — Na channel closes. Hyperpolarisation.
  2. Invertebrate —Na channel opens. Depolarisation.
    GPCRS —various responses.
31
Q

What does vertebrate vision rely on?

A
  • Rhodopsin
  • Transducin
  • Hyperpolarisation
32
Q

What does invertebrate vision and melanopsin involve?

A

Depolarisation

Excitable Cells (10 decks)

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