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UNT BIOL 3800 - Chapter 7: Vision
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BIOL 3800 1st Edition Lecture 11 Outline of Current Lecture I.VisionA.Anatomy of EyeII. Physical OpticsA.Physical Optics and Errors of RefractionB.NearsightednessC.HypermetropiaIII. Visible SpectrumA. Visible Spectrum for HumansIV. RetinaA. Cones and RodsCurrent LectureChapter 7: VisionI. Vision A. Anatomy of Eye1. We will emphasize on the structure of the eye which humans have we for the purposes of this class:(Fig 7-37 in book)These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.2. Anatomya. Sclera: is outside of eye that’s what you can touch. It is tough connective tissue. b. Choroid layer which is next c. Pigmented Epithelium which is really the retina and that’s where your receptors are. d. Optic Nerve - and in the lab once more you’ll probably find that spot where you cannot see anything because there are no receptors in what we call the blind spot. e. Lens and Zonula Fibers or Suspensory Ligaments the lens cannot be contracted no matter how much you try you can only allow it to contract on its own the lens is elastic at our age no longer elastic at Dr. Gross age, and so it tries to round up if you relax the tension in these fibers that’s exactly what happens when you contract ciliary muscles it really pulls the choroid layer forward relaxes the suspensory ligaments and the lens rounds up. f. Corneai. The curvature of your cornea often does more refraction than your lens but it’s fixed. So in lasik surgery that is what they do is change curvature of cornea to create different hopefully better optical situation. g. Lacrimal Glands to inside of eye that make tears. I. Physical OpticsA. Physical Optics and Errors of Refraction 1. First thing we have to know is that anytime we have a curved surface or you go from one medium to another medium (from air to glasses or air to lens for example) we have refraction or bending of the light rays.a. Refraction happens on both surfaces. So we simplify this process with this picture…b. So light gets refracted depending on the curvature. If you increase curvature you will increase refraction if you decrease the curvature you will decrease refraction and you push the focal point further and further out. 2. We have eyeballs flat ones, oblong ones, and normal ones we have the lens and we put them in the same lane, for instructional purposes, and in this diagram all the lenses should be the same. 3. So you have distant object you come in you get refracted you go to a focal point and you form an image somewhere away and if the retina happens to be there it is clean image you can see it without fuzziness.4. If however you have a very close object and everything is the same that’s then image is formed further away from the lens and the retina is in front of it and now everything is fuzzy.That happens when you’re reading a. To adjust the above situation you’d relax your suspensory ligaments by contracting your ciliary muscles. And you relax those ligaments and a young lens will start rounding up that means the focal point goes a little bit closer to the lens and that means the image is pulled onto the retina and so you can read and see things fairly clearly b. if you read too much because you have to use your ciliary muscles you get fatigue. c. So if we say its presbyopia then no matter how much you contract your ciliary muscles this lens will not round up. So the lens stays with the same curvature at that point the image goes behind retina and it’s blurry.B. Nearsightedness1. Occasionally, it could be cornea or an oblong eyeball genetically determined. So we use oblong eyeball in above picture because it’s easy to show that way. We have same lenses so consequently image is produced on same image plane. So here is the image (line in front of eyeball) and here is the retina everything is blurry how would you push that image onto the retina. 2. Only way you can push the image back onto the retina is to bring that image in so close that you get it back to being in the retina like (example A above) C. Hypermetropia1. AKA farsightedness 2. lets say we have a shortened eyeball or we have a misshapen cornea but we will stay with the eyeball again because it is easier to demonstrate. Image is behind retina when image is near so to get image in retina must allow your lens to round up by relaxing the suspensory ligaments and it rounds up if you’re young enough. II. Visible Spectrum A. Visible Spectrum for Humans1. If you look at the entire spectrum you go from gamma rays to short radio waves. So at least know that we can see from about 400 to 700 nm. Memorize this table… C. Visible spectrum for humans (pg 258) FIG 7-38----------------------------------------------------------------------------------------------------near UV violet blue green yellow red---------------------------------------------------------------------------------------------------350 400 450 500 600 650 nmIII. RetinaA. Cones and Rods(Fig 11.18)1. Chapter 11 elaborates on cones and rods 2. We have more rods than cones we need to be able to describe what happens inside. 3. Light goes through all cells of the retina then finally it gets to a cell that might be able to turn the photon into electrical or ionic currents. 4. We have horizontal cells, bipolar cells, amacrine cells, and ganglion cells5. Out of all the cells listed above ganglion cells are the only ones that have axons they are theones that go to the brain and ganglion cells are the only ones that make action potentials.6. Re Ho Bi Am Ga this may help you remember the cells in the retina. a. Receptor cells, Horizontal cells, Bipolar cells, Amacrine cells, and Ganglion cells. 7. Horizantal and Amacrine Cellsa. We are extremely good at detecting motion, for example, if you wanted to spot an ant it hard to see but as soon as it moves we can pick it up and so the horizontal cells and amacrine cells are involved in movement major thing to remember and it’s all subthreshold just EPSPs and IPSPs and really no action potential. 8. If you are a lobster, limulus, or grasshopper then if light is on, you see a depolarization if the light is off you see a repolarization, a respectable membrane potential, this is what their receptors do, this is what all other receptors do that we have learned so far. 9. If you’re a vertebrate your resting membrane potential is very low when light is on you


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