Term
| What is the nerve fibre layer made up of and where in the eye will you find it? |
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Definition
| Nervous ganglia nuclei overlying the retina. |
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Term
| Explain the role of ganglia in the nerve fibre layer |
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Definition
Nervous nuclei and fibres which lead to the optic disc. Approx. 2% are photosensitive to blue light.
They also regulate melatonin productio for circadian rhythms. |
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Term
| What is the role of the inner plexiform layer? |
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Definition
| Synapses between ganglia and bipolar/amacrine cells |
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Term
| What processor and supportive cells make up the inner nuclear layer? |
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Definition
Processor- Bipolar, horizontal and amacrine cells.
Supportive- Muller cells |
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Term
| What is the role of bipolar cells in the inner nuclear layer? |
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Definition
| Relay impulses from photoreceptors to ganglia |
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Term
| What is the role of horizontal cells in the inner nuclear layer? |
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Definition
| Laterally inhibit photoreceptors, no ganglion contact. They help integrate and regulate input from photoreceptor cells. Horizontal cells are responsible for allowing eyes to adjust to bright and dim light conditions. |
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Term
| What is the role of amacrine cells in the inner nuclear layer? |
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Definition
| Laterally inhibit photorecptors AND ganglia. Mechanism of action is unknown. |
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Term
| What is the role of muller cells in the inner nuclear layer? |
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Definition
| Muller cells are glial cells, therefore act as support cells. They have also been shown to dedifferentiate into progenitor cells in response to retinal damage. |
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Term
| What is the role of the outer plexiform layer? |
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Definition
| Synapses between photoreceptors and processor cells. |
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Term
| Where is the photoreceptor layer and what is it composed of? |
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Definition
| Outer nuclear layer, made up of rods (~120m) and cones (~7m)which are concentrated in the fovea. |
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Term
| What are the roles of rods and cones in the photoreceptor layer? |
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Definition
Rods- sense light/darkness
Cones- sense red and green or blue. |
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Term
| How is light transferred into a nervous impulse? |
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Definition
| Rods and cones contain rhodopsin, light causes hyperpolarisation by break down of rhodopsin into large opsin and small retinal molecules, retinal molecule inactivates cGMP molecule and closes NA gate, Ca+ pumped out Na+ cant get in, cell becomes -ve and reduced glutamate production, this signal reaches ganglia and is then transmitted to the optic nerve. |
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Term
| What is the role of the retinal pigment epithelium? |
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Definition
| Prevents reflection of light and phyagocytoses cell debris from inner layers. |
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Term
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Definition
| Vascular supply of the retina but on a seperate layer. |
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Term
| What happens to the photoreceptors in the dark |
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Definition
Become depolarised, Na+ diffusing in, Ca2+ pumped out – cGMP keeps Na+ gate open.
Produce gluatamate. |
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Term
| What occurs in the neural processing of diffuse light? |
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Definition
| Lateral inhibition by horizontal and amacrine cells limits the depolarisation of photoreceptors, therefore impulses are only sent if the light hits a large area of the retina. |
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Term
| How does the action of bipolar centres affect vision? |
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Definition
One bipolar cell connects to many rods.
If centred on a hyperpolarising rod, the bipolar cell will depolarise.
However this is inhibited by horizontal and amacrine cells when a bipolar cell is neighboured by a non hyperpolarising rod.
This allows for increased edge/contour definition. |
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Term
| How do bipolar cells affect foveal acuity? |
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Definition
| One cone is connected to one cone cell therefore acuity is increased. |
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Term
| How does colour blindness occur? |
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Definition
| Red, blue and green cone cells each have different rhodopsin molecules. Colour blindness occurs when the eye is unable to produce one of these rhodopsin molecules. Most commonly red and green, this is a sex linked th.most common in boys. |
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Term
| What stimuli will make the pupils change in size? |
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Definition
| Change in light/dark and close/distant objects. |
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Term
| Describe the pathway of the pupillary light reflex. |
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Definition
| Optic nerve -> optic chiasm -> pretectal nuclei -> erdinger westphal nuclei ->occulomotor nerve/ cillary ganglia/ constrictor muscles of iris. |
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Term
| Why do both eyes respond to a light stimulus in one eye? |
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Definition
| In the optic chiasm, fibres from the medial half of the retina decussate whilst fibres from the lateral half remain ipsilateral. |
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Term
| What would a lesion to the optic nerve anterior to the optic chiasm result in? |
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Definition
| No sensory information passing from that eye. |
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Term
| What pupillary effect would a lesion to the optic nerve behind the optic chiasm result in? |
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Definition
| Will not affect the pupillary light reflex as fibres from the other eye will pass to both erdigner westphal nuclei. |
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Term
| What pupillary effect would a lesion to an occulomotor nerve result in? |
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Definition
| Prevent any response in that eye but have no effect on the other. |
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Term
| What are the three actions of the pupillary near response? |
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Definition
| Convergence, accomodation and constriction. |
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Term
| Describe the sensory pathway |
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Definition
| Optic nerve -> optic chiasm -> lateral geniculate bodies -> optic radiations ->primary visual cortex |
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Term
| What occurs in the sensory pathway at the optic chiasm? |
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Definition
| Fibres from medial half of retina (or lateral visual field) decussate, fibres from lateral half remain on ipsilateral side. |
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Term
| Where are the lateral geniculate bodies found? |
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Definition
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Term
| What occurs in the sensory pathway at the lateral geniculate bodies? |
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Definition
| Fibres synapse and split into those from top and bottom of retina. |
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Term
| What does the superior optic radiation carry and to where? |
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Definition
| Carries fibres from upper retina (lower field of vision) through the parietal lobes. |
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Term
| What does the inferior optic radiation carry and to where? |
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Definition
| Carries fibres from the lower retina (upper field of vision) through the temporal lobes. |
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Term
| What occurs at the visual cortex and where is it? |
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Definition
Neurons from radiations synapse with cortical cells.
In the occipital lobe |
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Term
| What is macular sparing and why does it occur? |
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Definition
Poor blood supply tot he cortex makes it vulnerable to CVA.
However, cells dealing with macula located at the occipital pole dual blood supply, therefore can be spared in CVA. |
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Term
| Describe the motor pathway |
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Definition
| Visual cortex -> frontal eye field -> erdinger westphal nuclei ->oculomotor nerve. |
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Term
| What would a lesion in the optic tract result in? |
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Definition
| Contralateral Hemianopsia |
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Term
| What would a central lesion in the optic chiasm result in? |
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Definition
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