Vision

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  • Created by: Jess
  • Created on: 15-05-14 09:29
What is the purpose of the cornea and the lens?
To focus light onto the fovea.
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What is the fovea?
The direct point of gaze on the back of the retina.
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Where are the photoreceptors located in the eye?
On the very back of the retina.
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What is a plexiform layer and how many are there in the retina?
A synaptic layer at which all synapses are found. 2 (inner and outer).
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Where does the optic nerve travel to?
The back of the cerebellum.
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In what conditions are rod and cone cells used?
Rod cells detect light in dark conditions whereas cone cells are used in bright ambient light.
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How do rod and cone cells communicate with ganglion and amacrine cells?
Via bipolar cells.
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Which cells are involved in developing contrast and edge detection?
Horizontal and Amacrine cells.
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Describe the structure of a rod cell.
Three layers: Outer and inner segement and synaptic terminal. Invaginations are internalised to form intermembranous discs. Likelihood of meeting pigment is high.
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What type of vision are rod cells involved in?
Monochromatic vision.
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Describe the structure of a cone cell.
Three layers: inner and outer segment and synaptic terminal. Less invaginations and never pinch off to form discs. Three types: red, green and blue.
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What type of vision are cone cells involved in?
Colour vision.
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What is the main job of the photoreceptors?
To transduce a neural signal from information encoded in the spectrum of visible light.
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What molecule do the opsin proteins need to join with to form the visual pigment?
11-cis retinal.
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Name the four opsin proteins.
Red opsin, green opsin, blue opsin and rhodopsin.
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Which receptor superfamily does rhodopsin belong to?
GPCR.
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Where does 11-cis retinal bind in the receptor?
At residue 296 within the 7 trasmembrane domains.
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What conformational change underpins phototransduction?
Absorption of light by 11-cis retinal causes the backbone to become linear forming all-trans retinal.
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Describe the cell signalling that leads from rhodopsin activation to hyperpolarisation.
Activation of rhodopsin leads to activation of the G protein transducin, activates cGMP phosphodiesterase - conveerts cGMP to 5-GMP, less available to act on cGMP gated Na channels, they shut blocking Na influx, leading to hyperpolarisation.
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How does signalling in photoreceptors amplify?
One rhodopsin molecule can act on hundreds of transducin which can activate thousands of phosphodiesterase. Results in the breakdown of 10,000s of cGMP molecules.
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Describe the dark current.
Na flows into the outer segment through cGMP-gated Na channels. An active transporter in the inner segment swaps Na for K and K flows out through K selective channels in the inner segment. Causes a loop of positive current flow.
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Which cells in the retina produce action potentials?
The ganglion cells that travel to the optic nerve.
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How do most cells in the retina communicate?
Passively propagating signals.
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Which channels in the synaptic terminal of a cone cell are likely to be open in the dark and what occurs as a consequence of this?
Calcium channels will be open in the dark and the influx of calcium leads to the release of glutamate.
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What happens to the calcium channels in the synaptic terminal in the light?
The channels close and glutamate release decreases.
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How is the light response terminated?
The kinases arrestin and opsin kinase phosphorylate rhodopsin to ensure the response is very short.
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Why does the light response need to be short?
To ensure high fidelity and accurate track of visual fields.
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Where are the rod cells not present?
In the central fovea.
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Where are cone cells highly concentrated?
In the central fovea.
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Why is there more photopigment in rod cells?
To capture more photons of light in low light conditions. There is then high amplification for single photon detection.
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Other cards in this set

Card 2

Front

What is the fovea?

Back

The direct point of gaze on the back of the retina.

Card 3

Front

Where are the photoreceptors located in the eye?

Back

Preview of the front of card 3

Card 4

Front

What is a plexiform layer and how many are there in the retina?

Back

Preview of the front of card 4

Card 5

Front

Where does the optic nerve travel to?

Back

Preview of the front of card 5
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