the eye

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Matthias Niemeier

IntroductionVisual system provides us with unified picture of the world around us objects we see have shape and color they have position in space For us to see each of these properties neurons somewhere in the visual system must be sensitive to them Because we have two eyes we actually have two visual images in our head and somehow they must be mergedRetina extracts information about different facets of the visual imageThere are more than 100 million photoreceptors in the retina but only 1 million axons leaving the eye carrying information to the rest of the brainThe pathway serving conscious visual perception includes the LGN of the thalamus and primary visual cortex 17VI or striate cortexThe Retinofugal ProjectionNeural pathway that leaves the eye beginning with the optic nerve is often referred to as retiofugal projectionCentrifugal projection goes away from the center a corticofugal projection goes away from the cortex and the retinofugal projection goes away from the retina Ganglion cell axons pass through 3 structures before they form synapses in the brain stemOptic nerve optic chiasmoptic tractThe crossing of a fiber bundle from one side of the brain to the other is called a decussationBecause only the axons originating in the nasal retinas cross we say that a partial decussation of the reinofugal projection occurs at the optic chiasm Right and left visual hemifieldsobjects appearing to the left to the midline are in the left visual hemifield and vice versalooking straight ahead with both eyes open and then closing one eye and then the other we still can clearly see the central portion of both visual hemi fieldsregion of space called Binocular visual fieldFigure 103 left visual fieldviewed by right hemisphere controlled by nasal portion of left eye and temporal portion of right eye right visual filedviewed by left hemisphere controlled by nasal portion of right eye and temporal portion of left eyeTargets of the Optic Tract
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