The Eye part 1

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The 6 extraoccular muscle pairs
lateral and medial rectus (horizontal), superior and inferior rectus (vertical and inwards), Superior and inferior oblique (vertical and outward)
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What is accomodation and what controls it
changing in the shape of the lens to focus on near objects, caused by ciliary muscles.
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Describe how accomodation works
the ciliary muscle contracts and swells in size, releasing tension in the zonule of zinn ligaments, making the area inside the muscle smaller. the Lens becomes rounder and thicker, which increases the refractive power.
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What fibres attach the lens to the muscles in the ciliary body
zonule fibres
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The pupillary light reflex. Describe
sphincter and dialator muscles work antagonistically following signals sent from the retina to the brain stem - pretectal nuclei -> eidenger westphal -> cicillary ganglion
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What are the names for constriction and dialation?
Miosis - constriction, adaption to strong light. Dilation - mydriasis, adaption to low light.
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Describe the 6 layers of the retina
ganglion cell layer, inner plexiform layer, inner nuclear layer, outer plexiform, outer nuclear layer, layer of photoreceptor outer segments.
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The direct pathway
photoreceptors, bipolar cells, ganglion cells which fire afferents down the optic nerve
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two types of cell that can influence retinal processing
Horizontal cells, recieve input from photoreceptors. Amacrine cells recieve input from bipolar cells.
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Why is the inside out organisation useful?
The pigmented epithelium is needed to maintain the photoreceptors, and it absorbs any excess light
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Where are the connections of the horizontal and amacrine cells?
Horizontal connects with photoreceptors in the outer plexiform layer. Amacrine cells make connections with ganglion cells in the inner plexiform layer
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The four common features of all photoreceptors. Draw.
Outer segment (variable stacks of membrenous discs) , inner segment, cell body, synaptic terminal
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Why are rods more senstive to light?
They have a greater number of discs and a higher photopigment concentration
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What 'type' of retina uses cones, and which type uses rods.
Scotopic - nighttime - uses rods. Photopic - daytime - uses cones
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Describe the difference in regional density of retinal structure
peripery has higher concentration of rods to cones. the fovea has high concentration of cones.
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Why is the fovea better for high resolution vision
lateral displacement of the cells above it means that light can strike the cones with out passing through other retinal cell layers
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What are saccades
Little darty eye movements to adjust the fovea to the centre of focus
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In phototransduction - what is the effect of light on photopigment
hyperpolarisation. change in protein conformation, which causes a G-protein to bind GTP and decrease the conc of cGMP, and decrease Na conductance
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Describe the receptive field properties of p cells
small receptive field, fine grained, high resolution, colour detection.
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Describe the receptive field of M cells
Large receptive fields, coarse grained detection, low resolution, no colour, sensitive to movement and flicker
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How many different classes of RGC are there
~20
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What does this number of RGCs tell us about what the brain has to do?
The brain will receive 20+ parralell inputs about different features of the visual scene that it has to enterpret.
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Draw the human visual field
large binocular zone, partial l and r only zones
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Describe the quadrant organisation of the visual feilds
superior/ inferioir and temporal/nasal
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What views the temporal visual feild?
The nasal retinal
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What veiws the left visual feild? Draw it
Left visual field - nasal retina of left eye, temporal retina of right eye
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Where do most of the RGCs synapse
the lateral geniculate nucleus
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Where do melanopsin containing RGCs project to?
the suprachiasmatic nucleus
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Describe what happens at the optic chiasm
RGC's partially dessucate. Nasal axons project in the contralateral optic tract, temporal axons project in the ipsilateral optic tract.
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What does lesion in the left optic tract cause
blindess in the right half of the visual field of both eyes - contralateral homonymous hemaniopia
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What do lesions at the chiasm cause??
bitemporal hemianopia- pituitary tumour or aneyrism can cause this
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How is information about location of objects in the visual field relayed to the brain
retinotopic maps. eg, anterior superior colluculus means that something in the visual feild was seen by the temporal retina
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How many layers in the LGN?
SIX - 1-2 are magnocellular, 3-6 are parvocellular
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What comes out of the dorsal and lateral borders of the LGN
Optic radiations projecting to the ipsilateral cortex
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Other cards in this set

Card 2

Front

What is accomodation and what controls it

Back

changing in the shape of the lens to focus on near objects, caused by ciliary muscles.

Card 3

Front

Describe how accomodation works

Back

Preview of the front of card 3

Card 4

Front

What fibres attach the lens to the muscles in the ciliary body

Back

Preview of the front of card 4

Card 5

Front

The pupillary light reflex. Describe

Back

Preview of the front of card 5
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