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Lecture # 21

Lecture # 21. Retinal wiring 4 /16/ 13. Wiki. Wiki how to session for last 15 minutes of class Stop me at 1:30. Rest of semester schedule. 4/18 Intro page and 3-5 refs 4 / 25 One of main pages done 5/2 Question for exam 5/9 Last class: Intro page and 3 detail pages done

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Lecture # 21

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  1. Lecture #21 Retinal wiring 4/16/13

  2. Wiki • Wiki how to session for last 15 minutes of class • Stop me at 1:30

  3. Rest of semester schedule 4/18 Intro page and 3-5 refs 4/25 One of main pages done 5/2 Question for exam 5/9Last class: Intro page and 3 detail pages done 5/16 Final

  4. Final exam Thursday May 16th 1:30-3:30

  5. Human tetrachromats

  6. A F A 530 nm 560 nm S Y T F261Y=+10 nm A269T=+14 nm A164S=+2 nm 554 nm Human red and green opsins

  7. 557 nm Human red opsins A 38% 62% 552 nm S Two variants which occur frequently in population

  8. Three M/LWS cone opsins Green MWS opsin 530 nm Red LWS opsin 557 nm Shorter red opsin 552 nm At least two genes on each X chromosome. Since females are XX they have 4 M/LWS genes which can be of 3 different types

  9. Does this matter? • Does having 3 M/LWS genes plus an SWS gene make these women tetrachromats with superior color discrimination?

  10. Previous studies used color matching • Use sliders to mix green and red to match a target yellow + red + green Just right

  11. Color matching • Tetrachromatic females perform same as trichromatic females • Caveats • Small (2-10°) fields of view • Can only add either “red” or “green”

  12. 557 nm Human red opsins A 38% 62% 552 nm S Two variants which occur frequently in population = S and A

  13. Opsin genotypes of 64 subjects for psychophysical tests

  14. Visual task - how many defined colors do you see?

  15. Visual task - how many defined colors do you see?

  16. “Normal” visual observers see 7 : ROYGBIV

  17. Visual tasks • Mark edges of all colors that you see • Count # colors

  18. Visual tasks • Mark edges of all colors that you see • Count # colors • Female Tet 10±3 • Female Tri 7.6 ±2 • Male Tri 7.3 ±2 • Male Di 5.3 ±1.5

  19. Location of color start and stop - all 15 female trichromats end start

  20. Female tetrachromat color boundaries

  21. Extra opsins • These studies suggest that unique opsins are integrated into color opponency system and used • This is similar to other senses where there are multiple receptors which change in # between species • 100-1000 olfactory genes • Why do most of us only have 3 visual pigments?

  22. Kolb 2003

  23. Wassle 2005

  24. The retina • Complex set of cells which preprocess visual information before it goes to the brain Light Kolb 2003

  25. Overall retinal responses • Response to white vs black • Total light received = luminance • Response to blue vs yellow • Response to green vs red • These three channels can describe visual perception (Young 1802)

  26. How to understand retina • Stain neurons • Distinguish by morphology • Unravel connectivity

  27. The retina = 3 layer cake • Three cellular layers Outer nuclear layer Inner nuclear layer Ganglion cell layer Kolb2003

  28. The retina = 3 layer cake • Three cellular layers • Two synaptic layers • Outer plexiform • Inner plexiform Kolb2003

  29. 6 kinds of cells 1 rod 2 cone 3 horizontal cell 4 bipolar cell 5 amacrinecell 6 ganglion cell Wassle 2005

  30. Multiple cell types in each layer with specialized functions • Outer nuclear layer • 3 types cones + rods • Inner nuclear layer • 1-4 types horizontal cells • 1 rod and 10 cone bipolar cells • 22-30 types amacrine cells • Ganglion cell layer • 20 types of ganglion cells

  31. Neurotransmitters • Glutamate is the signal from photoreceptors to bipolar cells to ganglion cells • Horizontal and amacrine cells • Excitatory and inhibitory amino acids, catecholamines, peptides and NO

  32. Rod connections – very simple • Rod spherule connects to • Horizontal cells and • Bipolar cells • Rod bipolar • Cone OFF BP Rod

  33. Rod connections • Rod spherule is junction of several cells • Rod ON bipolar cells • metabotropic GluR • Horizontal cells • ionotropicGluR - AMPA • GluR=glutamate receptor

  34. Synaptic ribbons • Only in neurons that do not generate action potentials • Photoreceptors • Bipolar cells • Ribbons have affinity for synaptic vessicles • Improves / speeds neurotransmitter release

  35. Cone connections more complex • Cone pedicle connections • Triads • ON bipolar cells (invaginating) • Horizontal cells • Connections to • OFF bipolar cells (flat) • Also have synaptic ribbons

  36. How many connections for rods and cones? Cone Rod Bipolar cell

  37. Also direct contacts between neurons • Gap junctions can provide direct feedback between : • Cone and cone • Cone and rod • 2 horizontal cells • 2 amacrine cells • May help average out noise - increase receptive field • Signal flows between many cells

  38. Light response Light Channels close Cell hyperpolarizes Glutamate output decreases Glutamate release

  39. ON and OFF bipolar cells have different glutamate receptor

  40. ON and OFF bipolar cells have different glutamate receptor

  41. Understanding retina • Electrical response to light • Cone or rod hyperpolarizes • ON bipolar depolarizes • OFF bipolar hyperpolarizes Webvision

  42. Bipolar cell response • ON bipolars go to ON ganglion cells • OFF bipolars go to OFF ganglion cells Good to read light letters on dark background Good to read dark letters on light background

  43. The retina - 3 layer cake Three cellular layers Outer plexiform layer Inner plexiform layer Kolb2003

  44. Many kinds of bipolar cells If project to upper half of Inner Plexiform Layer (IPL) - Off cells If project to lower half of IPL - On cells

  45. Many kinds of bipolar cells DB - diffuse bipolars contact many cones FMB - flat midget bipolars contact 1 cone - OFF response IMB - invaginating midget bipolars contact 1 cone - ON response BB - blue bipolars contact several S cones - ON response RB - rod bipolars contact several rods - ON response

  46. Cone connections more complex • Cone pedicle connections • Triads • ON bipolar cells (invaginating) • Horizontal cells • Connections to • OFF bipolar cells (flat) • Also have synaptic ribbons

  47. Three types of horizontal cells • HI robust dendrites but small fields • HII finer dendrites • HIII bigger than HI so bigger fields

  48. Horizontal cells wired in certain ways • HI - mostly M and L cones though to some rods or S cones in the field • HII - more S cones as well as M and L • HIII - just M and L cones

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