The Eye

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  • Created by: jessica
  • Created on: 16-12-12 13:42
List the structures of the eye
Pupil, Iris, Cornea, Scleara, Conjunctiva, Optic nerve, Retinal vessels, Macula, Fovea, Lens
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What is the purpose of the Pupil?
allows light to enter the eye, reaching the Retina
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What is the purpose of the Iris?
It is the two pigmented muscles that vary the size of the pupil
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What is the purpose of the Cornea?
It covers the pupil and iris and is continuos with the scleara. Also has a refractive power of 42 diopters.
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What is the purpose of the Scleara?
It is the white of the eye, forming the tough wall of the eyeball and has 3 pairs of extraocular muscles that move the eyeball
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What is the purpose of the Conjunctiva?
It is the membrane that folds from the inside of the eyelids attaching to the scleara, protecting the eye.
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What is the purpose of the Optic nerve?
Carrys axons from the Retina from the back of the eye through the orbit, reaching the base of the brain near the pituitary gland.
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What is the purpose of the Macula?
It is part of the Retina used for central vision and is distinguished by the relative absence of large blood vessels.
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What is the Fovea?
A dark spot, 2mm in diameter and marks the center of the retina.
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What is the focal distance?
The distance from the refractive surface to the point where parallel raye converge
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What does the Focal distance depend on?
The curvature of the cornea, a tighter curve means there is a shorter focal distance.
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What does the Lens do?
Is involved in forming crisp images of objects that are located closer than 9m from the eye.
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How does the Pupillary light reflex work?
It uses connections between the Retina and the brain stem neurons which control the muscles that constrics the pupils, changing their size, dependent on the amount of light that needs to be let into the eye.
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What cells are used in Retinal Processing?
Horizontal and Amacrine cells
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What does the Horizontal cell do in Retinal Processing?
It takes input from photoreceptors and projects neurites laterally, influencing the surrounding areas.
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What does the Amacrine cell do in Retinal Processing?
It takes input from bipolar cells, projecting laterally to ganglion cells, bipolar cells and other amacrine cells
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What are photoreceptors?
Are cells which have light as their stimulus, they are called rods and cone cells.
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What cellular organization does the Retina have?
Laminar Organization, where the cells are organzied in layers.
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Give the Laminar Organization of the Retina, in order.
Ganglion cell layer, inner plexiform layer, inner nuclear layer, outer plexiform layer, outer nuclear layer, photoreceptor outerpigment, pigmented epithelium
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What is the structure of the Photoreceptors?
An outer segment, inner segment, cell body and synaptic terminal. Rods are long and cylindrical, Cones are shorter and taper to a point
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Where are the photopigments located in photoreceptors?
In the outer segment along disk membranes. Called rhodopsin and absorbs light triggering changes in membrane potential.
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What does bleaching of Rodopsin cause?
It stimulates a G protein transducin which activates phospodiesterase which breaks down cGMP that causes Na+ channels to close which causes hyperpolarization.
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What wavelengths of light are Cone cells best suited for?
Blue, green and red
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What is Dark adaptation?
The transition from using all-cone daytime vision to using all-rod night time vision
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What is Light adaptation?
The reversal of changes in the retina that accompany dark adaptation.
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Which neurotransmitter is used by photoreceptors?
Glutamate
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How do OFF bipolar cells work?
They mediate depolarizing EPSPs from Na+ influx, using Glutamate-gated channels.
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How do ON bipolar cells work?
They use G protein coupled receptors which respond to Glutamate, hyperpolarizing.
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How is the Optic chiasm created?
When the optic nerve exit the left and right eye at the optic disks.
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What is decussation?
The crossing of fiber bundles from one side of the brain to the other.
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What is the Right Visual Hemisfield?
Any object appearing to the right of the midline
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What is the Binocular Visual Hemisfield?
The region of space viewed by both retinas.
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What does the Optic tract synapse with?
The Lateral Geniculate Nucleus (LGN)
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What does the LGN project to?
The Primary Visual Cortex
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How many layers does the LGN have?
6
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Name the layers of the LGN
Magnocellular, Parvocellular, Koniocellular
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What are simple cells?
Cortical neurons that receive a converging input from 3 or more LGN cells with receptive fields aligned along one axis.
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What are complex cells?
Cells that have ON/OFF receptive fields responding to stimuli throughout.
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What is the Magnocellular pathway?
M type ganglion cells project to magnocellular layer of LGN, then projecting to IVC alpha of striate cortex, then projecting to IVB.
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What is the Magnocellular pathway involved in?
The analysis of object motion and the guidance of motor actions.
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What is the Parvo-Interblob pathway?
P type Ganglion cells project to Parvocellular layers in LGN, then project to IVC beta of stirate cortex which projects to layers II and III interblob regions
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What is the Parvo-Interblob pathway involved in?
The analysis of fine object shape.
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What is the Blob pathway?
nonM and nonP cells project to koniocellular layers of LGN, projecting to cytochrome oxidase blobs in layers II and III
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What is the Blob pathway involved in?
The analysis of object colour.
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What does the Dorsal Stream and Ventral Stream do?
Dorsal Stream analyses the visual motion and control of action. Ventral stream deals with visual perception and object recognition.
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Card 2

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allows light to enter the eye, reaching the Retina

Card 3

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Card 4

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What is the purpose of the Cornea?

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Card 5

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What is the purpose of the Scleara?

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