2007 Sensory Physiology

Rods

• more photopigment
  (~10⁸ rhodopsins/outer segment)
• single pigment type = rhodopsin
  • spectral sensitivity falls between blue and green cones
• high sensitivity (single photon)
  • saturate in daylight
• smaller dynamic range
• lower temporal resolution
  • slow response
  • signal integration
• poor spatial resolution
  • not in fovea
  • respond to scattered light
  • high degree of convergence onto bipolar cells

S&G Figure 10.34

S&G Figure 10.30

Cones

• less photopigment
• 3 pigment types (L cones = red, S=blue, M=green)
  • absorbance of the pigments overlap, so that different colours will produce different patterns of cone activity
• lower sensitivity (multiple photons)
  • saturate only in intense light
  • larger dynamic range
• high temporal resolution
  • faster response
  • less signal integration
• good spatial resolution
  • concentrated in fovea
  • respond best to narrow axes of light path
  • low degree of convergence onto bipolar cells