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The Special Senses Vision - 3

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’

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The Special Senses Vision - 3

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  1. The Special SensesVision - 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

  2. Color (Photopic)Vision ‘Young - Helmholtz theory’ ‘The Trichromatic theory’

  3. History of color vision Newton (1704) used a prism to show that sunlight was composed of light with all colors in the rainbow. He defined it as the spectrum.

  4. History ofcolorvision Primary colors: 723-647 575-492 492-450 Thomas Young 1807: primary colors: when mixed >>> white or any other color

  5. Mixing colors

  6. Photopicvision (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

  7. Cone wavelength ranges S M L Relative absorption 700 400 500 600 Wavelength (nm)

  8. Photopicvision (CONES) Cone pigments: three kinds 565 535 440

  9. PhotopicvisionYoung Helmholtz theory Color vision is subserved by three types of cones, each containing a photoreceptor pigment most sensitive to one primary color • Cones (contain red-sensitive pigment) • Cones (contain green-sensitive pigment) • Cones (contain blue-sensitive pigment) in the fovea centralis

  10. Cone wavelength ranges S M L Relative absorption 700 400 500 600 Wavelength (nm)

  11. Color Blindness Weakness or total blindness in detecting a primary color: Definitions: • Trichromats: see the 3 1ry colors • Dichromats: blind to one 1ry color • Monochromats: have color pigment

  12. Color Blindness –cont. • Prot …… Red • Deuter …. Green • Trit …… Blue • Anamoly …weakness • Protanamoly • Deuteranamoly Trichromats • Tritanamoly

  13. Color Blindness –cont. • Anamoly …weakness • Anopia …. Total loss • Protanopia • Deuteranopia Dichromats • Tritanopia

  14. Trichromatic/dichromatic color vision

  15. Color Blindness –cont. • Prevalence: males ………….8% females …. 0.4% Inheritance: sex-linked due abnormal gene in the X chromosome

  16. Electrophysiology of Vision

  17. Light Change in photopigment Metarhodopsin II Activation of transducin Activation of phophodiesterase Decrease IC cyclic GMP Closure of Na channels Hyperpolarization of receptor Action potential in optic nerve fibres

  18. Photoreception

  19. Bleaching and Regeneration of Visual Pigments Figure 17.15

  20. 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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