Photoreceptors in the eye

• The retina lines the interior surface of the choroid- contains photoreceptors
• The blind spot is where the optic nerve is
• The fovea contains a particularly high number of cone cells
• Two types of photoreceptors

  • Rod cells
  • Cone cells
• Rod cells

  • Monochromatic
  • Very sensitive: can operate on very little light
• Cone cells

  • Trichromatic
  • Needs a lot of light, will not work in low light
  • Provides more detail
• Rod cells detect black, grey and white
• Rod cells all contain the photoreceptor rhodopsin
• Rhodopsin gets broken down when light hits it, the break down is what starts the generator potential
• rod cells are connected in groups of up to 100 to a single bipolar neurone 
• Rod cells have low visual acuity, low detail, provide a general picture
• Rod cells are highly sensitive (useful in low light)
• The highest concentration of rod cells are found in the periphery of the retina (outside fovea and optic blind spot)
• Cone cells detect coloured light
• There are three forms of cone cells

  1. Blue light sensing cells
  2. Red light sensing cells
  3. Green light sensing cells
• Cone cells have high visual acuity as each cone cell is connected to one bipolar neurone
• Cone cells have low sensitivity (only useful in high light)
• Cone cells have the highest concentration in the fovea
• Rod cells and cone cells

  A) Direction of light rays

  B) Retina

  C) Rod cells

  D) Cone cells

  E) Bipolar neurones

  F) To optic nerve

  G) Bipolar neurons

  H) Single bipolar neuron