Photoreceptors & Visual pigments (Photopigments)

photoreceptors

in retina

1. rods

2. cones

rods

• highly sensitive to light

• active in night vision

• no color perception

• convergence (signals from many rods carried on same neuron)

• doesn’t provide sharp image (makes general outline, fuzzy image)

cones

• not as sensitive to light

• sense color

• highly concentrated in fovea centralis

• no convergence

• provides sharp image

Visual pigments (photopigments)

• Made of retinal (absorbs light) & opsin (protein)

• Light makes retinal change shape → nerve impulse
  

• Opsin types:
  - All rods have rhodopsin
  - Each cone has 1 of 3 pigments (red, green, blue)

Colorblindness

missing one or more cone pigment

• 2 or more colors look the same

• red-green is most common type

• more common in males (x-linked recessive)

stereoscopic vision

slightly different views from each eye are combined to make a 3D image