Photoreceptors

• What are photoreceptors?


  Light receptors in the eye
• Light enters the eye through where?

  the pupil
• The amount of light that enters the pupil is controlled by what?

  The muscles of the iris
• Where and what are light rays focused by?

  Focused by the LENS onto the RETINA
• What does the retina line?


  the inside of the eye
• What does the retina contain?


  Photoreceptor cells - these detect light
• What is the fovea?


  An area of the retina where there are LOTS OF PHOTORECEPTORS
• Where are nerve impulses from the PHOTORECEPTOR CELLS carried?


  From the retina to the brain by the OPTIC NERVE which is a bundle of neurones
• What is the blind spot?


  Where the optic nerve leaves the eye is called the blind spot
• Describe the blind spot?


  There are not any photoreceptor cells , so it is NOT SENSITIVE TO LIGHT
• What is light absorbed by?

  • Light enters eye, hits the PHOTORECEPTORS and is absorbed by LIGHT-SENSITIVE OPTICAL PIGMENTS
  • Light BLEACHES the pigments, causing a chemical change & altering the membrane permeability to sodium ions
  • A generator potential is created and if it reaches the threshold, a nerve impulse is sent along a bipolar neurone
• What do bipolar neurones do?


  Connect photoreceptors to the optic nerve, which takes impulses to the BRAIN
• How does light get to the photoreceptor?


  Light passes straight through the optic nerve and bipolar neurone to get to the photoreceptor
• What are the 2 types of PHOTORECEPTOR found in the human eye?


  rods and cones
• Where are rods mainly found?


  In the peripheral parts of the retina
• Where are cones found?


  Found packed together in the fovea
• What do rods and cones contain?


  Different optical pigments making them sensitive to different wavelengths of light ~
• Details about rods?

  Rods only give info in black and white (monochromatic vision)
• Details about cones?

  Give information in colour (trichromatic vision)
• How many types of cones ?


  3
• What does each different type of cone contain?

  A different optical pigment - red-sensitive, green-sensitive and blue-sensitive

  • when stimulated in different proportions you see different colours