Photoreceptors Flashcards
What are photoreceptors
receptors in eye that detect light
Light Enters through pupil and amount of light entering is controlled by iris
Which part of eye contains photoreceptors
Retina
What is fovea
Area of retina where there are lots of photoreceptors cells
Nerve impulses carried from photoreceptors cells in retina to the brain by OPTIC nerve
Where does optic nerve leave eye
Blind spot - no photoreceptors here so not sensitive to light
How do photoreceptors work?
- light enters eye and hits photoreceptors and is absorbed by light sensitive optical pigments
- light bleaches pigments causing chemical change altering membrane permeability to sodium ions
- generator potential is created and if reaches threshold a nerve impulses sent along bipolar neurone
- bipolar neurones connect photoreceptors to optic nerve which takes impulse to the brain
What 2 types of photoreceptors do eyes have
Rods
Cones
Where rods found
Peripheral part of retina
Where cones found
Packed in fovea
How are rods and cones different
Contain different optical pigments making them sensitive to different wave lengths of light
Rods - black and white
Cones - colour
Word for black and white
Monochromatic
Word for coloured
Trichromatic
What are the 3 cones called
Red sensitive
Green sensitive
Blue sensitive
Stimulated in different proportions you see different colours
How can I see yellow ?
Frequency of light fall between wavelengths red and green stimulating both of these cones - converts this to seeing yellow
Sensitivity
RODS
Rods sensitive to light - they fire action potentials in dim light
Many rods join one bipolar neurone
So many weak generator potentials combine to reach threshold and trigger action potential
Sensitivity
CONES
Less sensitive than rods
Only fire action potentials in bright light
Because one cone joins one bipolar neurone so takes more light to reach threshold and trigger action potential
