L13-Vision Flashcards
Why are planktons and plants better adapted when they can sense light?
They can optimise sun exposure- photosynthesis.
If animals have eyes, why must they be a big advantage?
- Eyes are very metabolically expensive.
- Only have them f they’re really worth it.
What happens to Mexican blind cavefish’s eyes?
- They develop eyes embryologically
- then reabsorb them because they cost too much energy. (probably evolutionary to develop them)..
What do all eyes use to detect light?
All use the same basic molecule to detect light- opsins.
What are the differences in different eyes?
- Many different solutions for lenses to focus light.
- Inverse and everse retinas.
What’s the similar developmental genes in eyes?
Pax-6.
In vertebrates, where is the retina derived from?
- The ectoderm/ neural tube.
- It’s an extension of the brain.
What does the cornea do?
Greatest refracting power in the eye.
What does the lens do?
Accommodate the refracting power. Change shape for refracting power.
Where does the light hit at the back of the eye?
the fovea
Gross structure of the vertebrate eye
look at diagram!
What’s the laminar structure of the retina?
Pigment epithelium rods + cones Muller cells horizontal cells \+ bipolar cells amacrine cells ganglion cells nerve fibre layer inner limiting membrane
Which way is the arrow drawn in the lamina?
From the “excitable” cells, nerve fibres towards the photo-receptors, rods + cones.
Towards the detection of light.
What’s the order of cells along the arrow from the Ganglion cells?
Ganglion cells Amacrine cells Bipolar cells Horizontal cells Muller cells Rods + cones photoreceptor cells Retinal pigment epithelium
What’s the RPE?
Retinal pigment epithelia
— pigmented layer at the back of the retina.
‘wraps’ outer segment of rods + cones
What is the RPE importance in recycling?
Retinaldehyde- an essential co-factor of opsins
what is tapetum lucidum (eye shine) ?
The layer just behind the RPE.
light absorption and/ or reflection
In the retinal pigment cells what do melanin granules and tapetum do?
Melanin granules = absorb light
Tapetum = reflects light
What are the steps in phototransduction in rods and cones?
- Photon of light
- Conformational change in rhodopsin molecule
- Activation of transducing
- Activation of phosphodresterase
- Reduction in cGMP
- Closure of sodium channels—-
—presence of stimulant = hyperpolarisation.
Very odd.
What is odd about phototransduction in rods and cones?
- 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.
What does membrane depolarisation in rods and cones do?
Glutamate release.
In primates how much of the cortex is devoted to processing visual information?
More than 50%. Very important sense.
What are 6 common defects in human vision?
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
What is the invertebrate retina made up of?
Individual units - ommatidia
Information from all- integrated in the brain.
What do pigment cells do in invertebrates?
Prevent light scattering into other ommatidia.
What are the steps of phototransduction in invertebrates?
- Photon of light
- Conformational change in rhodopsin
- Activation of Gq
- Activation of phospholipase C
- Phosphoinositide hydrolysis
- Cation channels open
- Depolarisation
What’s the main difference in phototransduction between vertebrates and invertebrates?
Vertebrates- hyperpolarisation
Invertebrates- depolarisation
What do a small proportion of retinal ganglion cells contain?
An additional opsin different from rods and cones.–
— melanopsin
What does melanopsin do?
Measure levels of brightness important in unconscious light detection e.g. circadian rhythms, pupillary light reflex, body temp.
In response to light, what happens in ganglion cells?
- Vertebrate — Na channel closes. Hyperpolarisation.
- Invertebrate —Na channel opens. Depolarisation.
GPCRS —various responses.
What does vertebrate vision rely on?
- Rhodopsin
- Transducin
- Hyperpolarisation
What does invertebrate vision and melanopsin involve?
Depolarisation
