Lecture12 6 13

1,408 views

Published on

Published in: Technology, Health & Medicine
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
1,408
On SlideShare
0
From Embeds
0
Number of Embeds
8
Actions
Shares
0
Downloads
27
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

Lecture12 6 13

  1. 1. Accessory Structures of the Eye Figure 17–3
  2. 2. Neural Tunic (Retina) Figure 17–4c
  3. 3. Retina • Rods, cones are types of photoreceptors Figure 17–6
  4. 4. Rods • Highly sensitive to light, do not discriminate colors • Rods dominate peripheral areas of retina • Provide low-resolution black–and–white vision in dimly lit environments Cones • Sensitive to colored light • Densely clustered in fovea • Provide high–resolution color vision in brightly lit environments
  5. 5. Photoreceptor Figure 17–13a
  6. 6. • Rods and cones synapse with neurons called bipolar cells • Bipolar cells then synapse with neurons called ganglion cells Figure 17–6a
  7. 7. Horizontal Cells • Where receptors synapse with bipolar cells Amacrine Cells • Where bipolar cells synapse with ganglion cells • Both facilitate or inhibit communication between photoreceptors and ganglion cells • Alter sensitivity of retina
  8. 8. Optic Disc • Circular region just medial to fovea • Origin of optic nerve Figure 17–6b, c
  9. 9. Blind Spot Figure 17–7
  10. 10. Visual Pigments • Where light absorption occurs • Derivatives of rhodopsin (opsin plus retinal) • Retinal: synthesized from vitamin A Figure 17–13b
  11. 11. Phototransduction 1) Photon strikes retinal portion of rhodopsin 2) Opsin is activated: – Goes from 11-cis form to 11-trans form 3) Opsin activates transducin (G protein), then activates phosphodiesterase (PDE) 4) Cyclic-GMP (cGMP) levels decline; gated sodium channels close 5) Dark current is reduced; neurotransmitter release declines
  12. 12. In dark, photoreceptors are activated (stimulated) Dark Current In light, photoreceptors are inactivated (inhibited) Figure 17–14
  13. 13. Bleaching • Rhodopsin molecule breaks down into retinal and opsin Figure 17–15
  14. 14. Dark-Adapted State • Pupil dilates • Most pigments can be activated • A single photon can be detected Light-Adapted State • Pupil constricts • Bleaching of visual pigments occurs • “Blinding” when go from dark to light room
  15. 15. Pupillary Muscle Reflexes Figure 17–5
  16. 16. Color Sensitivity • Integration of information from red, green, and blue cones • All wavelengths reflected off an object looks white Figure 17–16
  17. 17. Color Blindness • Inability to detect certain colors Figure 17–17
  18. 18. Visual Pathway • Begins at photoreceptors • Ends at visual cortex of cerebral hemispheres • Message crosses 2 synapses before goes toward brain: –photoreceptor --> bipolar cell –bipolar cell --> ganglion cell (sensory neuron) “processing in retina”
  19. 19. Convergence • Each ganglion cell receives input from many photoreceptors • Therefore, Receptive field of ganglion cell is monitored by many photoreceptors
  20. 20. M Cells • ganglion cells that monitor rods • Provide information about: –general form of object –motion –shadows in dim lighting P Cells • ganglion cells that monitor cones • Provide information about: –edges –fine detail –color
  21. 21. Visual Pathway 1. Axons from ganglion cells converge on optic disc 2. Penetrate wall of eye 3. Proceed toward diencephalon as optic nerve (II) 4. 2 optic nerves (1 for each eye) reach diencephalons at optic chiasm Figure 17–19
  22. 22. Optic Tracts 5. Axons from both eyes projecting from optic chiasm to lateral geniculi Optic Radiations 6. Bundles of projection fibers from lateral geniculates to visual cortex
  23. 23. Visual Cortex 7. Info from right or left fields of vision arrive at visual cortex of opposite occipital lobe: – left half arrives at right occipital lobe – right half arrives at left occipital lobe
  24. 24. Depth Perception • By comparing relative positions of objects between left–eye and right–eye images But, at great distances: - Previous familiarity - Occlusion - Perspective - Motion parallax - Shadows and light Figure 17–19

×