the special senses vision - 3
DESCRIPTION
The Special Senses Vision - 3. Professor A.M.A Abdel Gader MD, PhD, FRCP (Lond., Edin), FRSH (London) Professor of Physiology, College of Medicine & King Khalid University Hospital Riyadh, Saudi Arabia. C o l o r (Ph o to pic) V i s i o n ‘Young - Helmholtz theory’ - PowerPoint PPT PresentationTRANSCRIPT
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The Special SensesVision - 3
Professor A.M.A Abdel GaderMD, PhD, FRCP (Lond., Edin), FRSH (London)
Professor of Physiology, College of Medicine &King Khalid University Hospital
Riyadh, Saudi Arabia
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Color (Photopic) Vision‘Young - Helmholtz theory’‘The Trichromatic theory’
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History of color visionNewton (1704) used a prism to show thatsunlight was composed of light with allcolors in the rainbow. He defined it as the
spectrum.
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History of color vision
Primary colors:
723-647 575-492 492-450
Thomas Young 1807:primary colors: when mixed >>>
white or any other color
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Mixing colors
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Photopic vision (CONES)
Helmholtz ..1860:The three primary colors are
perceived by three photoreceptor pigments (with
broad absorption curves)
White light is produced by mixing three colours
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Cone wavelength ranges
S M L
Wavelength (nm)
Rela
tive a
bso
rpti
on
400 500 600 700
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Photopic vision (CONES)
Cone pigments: three kinds
565 535 440
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Photopic visionYoung Helmholtz theory
Color vision is subserved bythree types of cones, each containing a
photoreceptor pigment most sensitive to one primary color
1. Cones (contain red-sensitive pigment)2. Cones (contain green-sensitive
pigment) 3. Cones (contain blue-sensitive pigment)
in the fovea centralis
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Cone wavelength ranges
S M L
Wavelength (nm)
Rela
tive a
bso
rpti
on
400 500 600 700
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Color Blindness
Weakness or total blindness in detecting a primary color:
Definitions:1. Trichromats: see the 3 1ry colors
2. Dichromats: blind to one 1ry color
3. Monochromats: have color pigment
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Color Blindness –cont.
•Prot …… Red•Deuter …. Green•Trit …… Blue•Anamoly …weakness
•Protanamoly •Deuteranamoly Trichromats•Tritanamoly
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Color Blindness –cont.
•Anamoly …weakness•Anopia …. Total loss
•Protanopia •Deuteranopia Dichromats•Tritanopia
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Trichromatic/dichromatic color
vision
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Color Blindness –cont.
•Prevalence:males ………….8%females …. 0.4%
Inheritance: sex-linked due abnormal gene in the X
chromosome
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Electrophysiology of Vision
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Light
Change in photopigment
Metarhodopsin II
Activation of transducin
Activation of phophodiesterase
Decrease IC cyclic GMP
Closure of Na channels
Hyperpolarization of receptorAction potential in optic nerve fibres
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Photoreception
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Figure 17.15
Bleaching and Regeneration of Visual Pigments
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Electrophysiology of Vision
Electric recording in Retinal cells:•Bipolar cells: Hyper- & Depolarization
•Horizental cells: Hyper- & Depolarization
•Amacrine cells: Depolarizing potential
•Ganglion cells:Depolarizing potential
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