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Chapter 17, part 2

Chapter 17, part 2. The Special Senses. retina. Retina contains rods and cones Cones densely packed at fovea (center of the macula lutea) Retinal pathway Photoreceptors to bipolar cells to ganglion cells, to the brain via the optic nerve

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Chapter 17, part 2

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  1. Chapter 17, part 2 The Special Senses

  2. retina • Retina contains rods and cones • Cones densely packed at fovea (center of the macula lutea) • Retinal pathway • Photoreceptors to bipolar cells to ganglion cells, to the brain via the optic nerve • Axons of ganglion cells converge at blind spot (optic disc) • Horizontal cells and amacrine cells modify the signal passed along the retinal neurons

  3. Figure 17.6 The Organization of the Retina Figure 17.6a

  4. Figure 17.6 The Organization of the Retina Figure 17.6b, c

  5. Eye anatomy • Ciliary body and lens divide the anterior cavity of the eye into posterior (vitreous) cavity and anterior cavity • Anterior cavity further divided • anterior chamber in front of eye • posterior chamber between the iris and the lens

  6. Figure 17.8 The Circulation of Aqueous Humor Figure 17.8

  7. Fluids in the eye • Aqueous humor circulates within the eye • diffuses through the walls of anterior chamber • passes through canal of Schlemm • re-enters circulation • Vitreous humor fills the posterior cavity. • Not recycled – permanent fluid

  8. Lens • Posterior to the cornea and forms anterior boundary of posterior cavity • Posterior cavity contains vitreous humor • Lens helps focus • Light is refracted as it passes through lens • Accommodation is the process by which the lens adjusts to focus images • Normal visual acuity is 20/20

  9. Figure 17.9 Image Formation Figure 17.9

  10. Figure 17.10 Accommodation Figure 17.10

  11. Figure 17.11 Visual Abnormalities Figure 17.11

  12. Visual physiology • Rods – respond to almost any photon • Cones – specific ranges of specificity

  13. Figure 17.13 Rods and Cones Figure 17.13

  14. Photoreceptor structure • Outer segment with membranous discs • Narrow stalk connecting outer segment to inner segment • Light absorption occurs in the visual pigments • Derivatives of rhodopsin

  15. Figure 17.14 Photoreception Animation: Photoreception PLAY Figure 17.14a, b

  16. Figure 17.14 Photoreception Figure 17.14c, d

  17. Figure 17.15 Bleaching and Regeneration of Visual Pigments Figure 17.15

  18. Color sensitivity • Integration of information from red, blue and green cones • Colorblindness is the inability to detect certain colors

  19. retinal adaptation • Dark adapted – most visual pigments are fully receptive to stimulation • Light adapted – pupil constricts and pigments bleached.

  20. the visual pathway • Large M-cells monitor rods • Smaller more numerous P cells monitor cones

  21. Figure 17.18 Convergence and Ganglion Cell Function Figure 17.18

  22. Seeing in stereo • Vision from the field of view transfers from one side to the other while in transit • Depth perception is obtained by comparing relative positions of objects from the two eyes

  23. Figure 17.19 The Visual Pathways Figure 17.19

  24. Visual circadian rhythm • Input to suprachiasmic nucleus affects the function of the brainstem • Circadian rhythm ties to day-night cycle, and affects metabolic rates

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