Photoreceptors

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Graduate presentation on human photoreceptors and preception of vision

  • Light and its nature have caused a lot of ink to flow during these last decades. Its dual behavior is partly explained by (1)Double-slit experiment of Thomas Young - who represents the photon’s motion as a wave - and also by (2)the Photoelectric effect in which the photon is considered as a particle. A Revolution: SALEH THEORY solves this ambiguity and this difficulty presenting a three-dimensional trajectory for the photon's motion and a new formula to calculate its energy. More information on https://youtu.be/mLtpARXuMbM
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Photoreceptors

  1. 1. Visualization and Animation of Rod and Cone Photoreceptors Presented by Bridgette C. Williams
  2. 2. Abstract <ul><li>What are the advantages to creating three-dimensional models and animations of photoreceptors? </li></ul><ul><li>How can computer graphics and animation aid in comprehension of phototransduction? </li></ul><ul><li>How does the process of phototransduction and illusory depth perception relate to visual perception? </li></ul><ul><li>How can all of this be applied to Biomedical Visualization? </li></ul>
  3. 3. Visual Perception <ul><li>What is it? </li></ul><ul><li>Depth Cues </li></ul><ul><li>Illusory Depth Perception </li></ul><ul><li>Illumination </li></ul><ul><li>Computer-generated models </li></ul>
  4. 4. Visual Perception: What is it? <ul><li>Briefly defined, it is interactivity between the viewer’s eyes, detection of light and the reflection of light on surfaces. </li></ul><ul><li>After an image is received by the retina, visual perception of the scene is assessed by the brain. </li></ul>
  5. 5. Visual Perception: Depth Cues <ul><li>Depth cues are visual clues about an object and its environment. When detected by light, these clues indicate how the object is to be perceived by the brain. </li></ul><ul><li>Perspective, texture gradients, edge interpretation, and shading are examples of depth cues that can be visually inferred by the brain. </li></ul>
  6. 6. Visual Perception: Illusory Depth Perception <ul><li>Briefly defined as imitation of depth cues so that depth can be perceived from flat images. </li></ul><ul><li>Three-dimensional computer programs are so convincing to the eye because of illusory depth perception. </li></ul>
  7. 7. Visual Perception: Illumination <ul><li>It is the phenomenon of a photon of light hitting the surface of an object. </li></ul><ul><li>In the natural world, a photon of light can interact with an object in one of three ways: absorption, reflection and transmission. </li></ul><ul><li>Absorption, reflection and transmission of a photon depends on the surface of the object. </li></ul>
  8. 8. Visual Perception: Computer-generated models <ul><li>Three-dimensional computer-generated polygonal models use illusory depth perception, depth cues, and illumination to render convincing images of objects. </li></ul><ul><li>These images are visually informative. And when they are applied, they can give an accurate interpretation of biological concepts. </li></ul>
  9. 9. Visual Pathway <ul><li>Photoreceptor morphology </li></ul><ul><li>Rhodopsin morphology </li></ul>
  10. 10. Visual Pathway: Photoreceptor Morphology <ul><li>Rod and cone cells-collectively known as photoreceptors-function to detect photons of light from the outside environment. </li></ul>
  11. 11. Visual Pathway: Photoreceptor Morphology <ul><li>The rod cell (seen at the far left) is a very light sensitive neuron needed in dim-lit monochromatic environments. The cell is slender and longer than a cone cell. It has a rod-shaped outer segment and spherule-shaped synaptic body. </li></ul><ul><li>A cone cell is not light sensitive and functions in well-lit polychromatic environments. It is broad and shorter than the rod cell. The cell has a cone-shaped outer segment and pedicle shaped synaptic terminus. </li></ul>
  12. 12. Visual Pathway:Photoreceptor Morphology <ul><li>Each neuron is comprised of four distinct regions: Outer Segment (OS), Inner Segment (IS), Outer Nuclear Layer (ONL) and Outer Plexiform Layer (OPL). </li></ul><ul><li>The OS is made of flat double lamellae disks stacked upon each other; each disk contain visual pigment proteins and other molecules needed for phototransduction. </li></ul><ul><li>Rod cell disks are separate and cone cell disks are attached to each other and the surface plasma. </li></ul>
  13. 13. Visual Pathway: Photoreceptor Morphology <ul><li>The IS has two subregions: eosinophilic ellipsoid and basophilic myoid. </li></ul><ul><li>The ellipsoid region contain the mitochondria. </li></ul><ul><li>The myoid region contain the golgi apparatus, endoplasmic reticulum, ribosome's, and microtubules. </li></ul><ul><li>The OS and IS segments are connected by cilium- a short stalk of nine microtubule filaments allowing movement of molecules between segments. </li></ul>
  14. 14. Visual Pathway: Photoreceptor Morphology <ul><li>The ONL contain an oval-shaped nucleus for each neuron. </li></ul><ul><li>The rod cell nucleus generally have an oval shape and a visible nucleolus. </li></ul><ul><li>The cone cell nucleus is also oval shaped but does not have a visible nucelolus. </li></ul>
  15. 15. Visual Pathway: Photoreceptor Morphology <ul><li>The OPL contain the synaptic terminus. </li></ul><ul><li>The synaptic terminus is a cytoplasmic expansion of axons for the rod and cone. It is specific in shape for each photoreceptor type, each containing presynaptic ribbons and sphere shaped molecules. </li></ul>
  16. 16. Visual Pathway: Rhodopsin Morphology <ul><li>Rhodopsin is a three-dimensional, integral-membrane photopigment protein that consists of a transmembrane glycoprotein and a chromophore. </li></ul><ul><li>The glycoprotein-opsin-is made of seven alpha-helices that traverse the phospholipid bilayered membrane. </li></ul>
  17. 17. Visual Pathway: Rhodopsin Morphology <ul><li>In a binding pocket between the helices 3 to 7, on the seventh helix, the chromophore-retinal- is attached to opsin. </li></ul><ul><li>Retinal is an aldehyde of Vitamin A. </li></ul><ul><li>Six interhelical loops connect the seven helices. Three loops lay on the cytoplasmic side and three lay intradiskally to the membrane. </li></ul>
  18. 18. Visual Cycle <ul><li>Visual Process </li></ul><ul><li>Phototransduction </li></ul><ul><li>Apparent Motion </li></ul>
  19. 19. Visual Cycle: Visual Process <ul><li>The visual processing pathways of images and motion begin with the eyes. </li></ul><ul><li>The primary visual processing pathway contain special cells that process motion and depth information. </li></ul><ul><li>The visual system is sensitive to motion; instinctively objects in motion captures our attention and increase visual depth perception. </li></ul>
  20. 20. Visual Cycle: Apparent Motion <ul><li>It is “the appearance of motion by rapidly showing an object in different positions on static frames” fools the brain to perceive motion from still shots played at high speeds. </li></ul><ul><li>Apparent motion is the foundation of all motion picture technology. </li></ul>
  21. 21. Visual Cycle: Phototransduction <ul><li>Working with neuroscience researchers, I reviewed current data on the phototransduction physiological process. </li></ul><ul><li>Phototransduction is the process of how light sensitive integral GPCR proteins such as rhodopsin can absorb a photon of light and convert the electrical stimulus into a chemical reaction. </li></ul><ul><li>The process results in hyperpolarization of the rod cell and sends the message to other cells that light has been detected. </li></ul>
  22. 22. Visual Cycle: Phototransduction <ul><li>In low light, 1 sodium ion (blue ball) and 1 calcium ion (gray ball) move freely in and out of the cell via cGMP gated channels. </li></ul>
  23. 23. Visual Cycle:Phototransduction <ul><li>Light enters the rod outer segment. </li></ul>
  24. 24. Visual Cycle:Phototransduction <ul><li>A photon of light hits the rhodopsin molecule. </li></ul>
  25. 25. Visual Cycle:Phototransduction <ul><li>Rhodopsin absorbs the stimuli by becoming transparent. </li></ul>
  26. 26. Visual Cycle: Phototransduction <ul><li>Rhodopsin changes to Metarhodopsin II. </li></ul>
  27. 27. Visual Cycle:Phototransduction <ul><li>Transducin detects the change in Metarhodopsin II and moves closer to the molecule. </li></ul>
  28. 28. Visual Cycle: Phototransduction <ul><li>Transducin attaches to metarhodopsin II. GDP (nucleotide) is exchanged for GTP. </li></ul>
  29. 29. Visual Cycle:Phototransduction <ul><li>The alpha subunit of transducin separates from the Beta-Gamma subunit. </li></ul>
  30. 30. Visual Cycle: Phototransduction <ul><li>The alpha subunit latches onto phosphodiesterase enzyme. </li></ul>
  31. 31. Visual Cycle: Phototransduction <ul><li>The new combination of the Phosphodiesterase enzyme and alpha subunit of Transducin hydrolyzes cGMP. </li></ul>
  32. 32. Visual Cycle:Phototransduction <ul><li>The reduced number of cGMP causes the gates to close. </li></ul>
  33. 33. How can this be applied to Biomedical Visualization?
  34. 34. How can this be applied to Biomedical Visualization?

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