Light detection
 
 
Photoreceptors (retina) <ul><li>Connected to nerve-endings from optic nerve </li></ul><ul><li>Nerve conveys impulses to br...
Question: <ul><li>Have you experienced occasions when you are not able to see for a short period of time? </li></ul><ul><l...
Rods <ul><li>Contain  visual purple </li></ul><ul><li>Pigment concerned with vision in  dim light </li></ul><ul><li>Light ...
Cones <ul><li>Less sensitive to light  </li></ul><ul><li>Inefficient in dim light </li></ul><ul><li>Concerned with  bright...
 
 
<ul><li>yellow spot  </li></ul><ul><li>where images are normally focused </li></ul><ul><li>highest conc. of cones </li></u...
Fovea centralis <ul><li>yellow spot </li></ul><ul><li>where images are normally focused </li></ul><ul><li>only contains co...
Blind spot <ul><li>found immediately over optic nerve where it enters the eye </li></ul><ul><li>has  no photoreceptors  (n...
Vision
Formation of image on retina http:// www.bausch.com/us/vision/teens/illusions/eyeworks.jsp
Image formed on retina <ul><li>Inverted (upside down) </li></ul><ul><li>Reversed (back to front) </li></ul><ul><li>Diminis...
 
What are the similarities between the eye and a camera?
Processing by brain <ul><li>Impulses produced by light falling on the rods and cones are transmitted via the optic nerves ...
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Chapter 14 The Human Eye Lesson 2 - Light Detection

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Chapter 14 The Human Eye Lesson 2 - Light Detection

  1. 1. Light detection
  2. 4. Photoreceptors (retina) <ul><li>Connected to nerve-endings from optic nerve </li></ul><ul><li>Nerve conveys impulses to brain when stimulated </li></ul><ul><li>2 kinds: </li></ul><ul><li>Rods </li></ul><ul><li>Cones </li></ul>
  3. 5. Question: <ul><li>Have you experienced occasions when you are not able to see for a short period of time? </li></ul><ul><li>When does this situation normally take place? </li></ul>
  4. 6. Rods <ul><li>Contain visual purple </li></ul><ul><li>Pigment concerned with vision in dim light </li></ul><ul><li>Light detection by visual purple by bleaching </li></ul><ul><li>From bright  dark place unable to distinguish objects for a while (because takes time for visual purple to reform) </li></ul><ul><li>Requires vitamin A (deficiency  night-blindness) </li></ul>
  5. 7. Cones <ul><li>Less sensitive to light </li></ul><ul><li>Inefficient in dim light </li></ul><ul><li>Concerned with bright light and c o l o u r vision </li></ul><ul><li>3 types: (each contain a different pigment) </li></ul><ul><li>Red </li></ul><ul><li>Blue </li></ul><ul><li>Green </li></ul><ul><li>Pigments absorb light of different wavelengths </li></ul><ul><li>Taken together, cones allow us to see spectrum of colours </li></ul>
  6. 10. <ul><li>yellow spot </li></ul><ul><li>where images are normally focused </li></ul><ul><li>highest conc. of cones </li></ul><ul><li>vision sharpest in bright light </li></ul><ul><li>No photoreceptors (not light sensitive) </li></ul><ul><li>blind spot formation </li></ul>
  7. 11. Fovea centralis <ul><li>yellow spot </li></ul><ul><li>where images are normally focused </li></ul><ul><li>only contains cones </li></ul><ul><li>concentration of cones highest at this point </li></ul><ul><li>Therefore vision is sharpest in bright light when images are focused onto the yellow spot </li></ul>
  8. 12. Blind spot <ul><li>found immediately over optic nerve where it enters the eye </li></ul><ul><li>has no photoreceptors (not sensitive to light) </li></ul>Blind spot
  9. 13. Vision
  10. 14. Formation of image on retina http:// www.bausch.com/us/vision/teens/illusions/eyeworks.jsp
  11. 15. Image formed on retina <ul><li>Inverted (upside down) </li></ul><ul><li>Reversed (back to front) </li></ul><ul><li>Diminished (smaller in size than the object being observed) </li></ul>
  12. 17. What are the similarities between the eye and a camera?
  13. 18. Processing by brain <ul><li>Impulses produced by light falling on the rods and cones are transmitted via the optic nerves to rear of cerebrum </li></ul><ul><li>Brain interprets these impulses so we see the object the right way up and the right size </li></ul>

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