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7/30/2019 Structure and Function of the Human Eye
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Structure and Function of the
Human Eye
7/30/2019 Structure and Function of the Human Eye
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Vertebrates have single-lens eyes
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 49.9
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• Sclera: a tough white layer of connectivetissue that covers all of the eyeball except
the cornea.
– Conjunctiva: external cover of the sclera— keeps the eye moist.
• Cornea: transparent covering of the front of
the eye.
– Allows for the passage of light into the
eye and functions as a fixed lens.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Parts of the Eye
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• Choroid: thin, pigmented layer lining the
interior surface of the sclera. – Prevents light rays from scattering and
distorting the image.
– Anteriorly it forms the iris. • The iris regulates the size of the pupil.
• Retina: lines the interior surface of the
choroid. – Contains photoreceptors.
• Except at the optic disk (where the optic
nerve attaches).Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
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Focusing Light
• The lens and ciliary body divide the eye intotwo cavities.
– The anterior cavity is filled with aqueoushumor produced by the ciliary body.
– The posterior cavity is filled with vitreoushumor.
– The lens, the aqueous humor, and thevitreous humor all play a role in focusing lightonto the retina.
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Focusing Light
• Accommodation isthe focusing of lightin the retina.
• Mammals focus bychanging the shapeof the lens.
• The lens is flattenedfor distant objects.
• The lens is roundedfor near objects.
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• Photoreceptors of the retina.
– rod cells - light sensitive but do not
distinguish colors.
– cone cells - not as light sensitive as rods but
provide color vision
• Most highly concentrated on the fovea – an area of
the retina that lacks rods.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Vision
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Vision
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Rhodopsin (retinal + opsin) is the visualpigment of rods.
• The absorption of light by rhodopsin initiates a
signal-transduction pathway
• Receptor potential is hyperpolization .
Fig. 49.13
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• Color reception is more complex than therhodopsin mechanism.
– Three types of cone cells each withunique photopsin (green cones, redcones, blue cones)
• Brain’s analysis of color depends on relativeresponses of each type of cone.
– Colorblindness is due to a deficiency, or absence, of one or more photopsins.
• Inherited as an X-linked trait.Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
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Vision
• Rods and Cones
synapse with
nuerons called
bipolar cells
• Bipolar cells
synapse with
galgion cells of
optic nerve