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The retina
photoreceptors and
neurones supplying
the optic nerve
Two main types of
photoreceptors: rods
and cones…read more

Slide 4

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Contains a visual pigment called
Rhodopsin is made up of opsin and
Not very tightly packed together and
several synapse with the same neurone
Very sensitive to low light levels
Provides monochromatic vision
Used for peripheral vision…read more

Slide 5

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How the rods work
When light hits rhodopsin, cis-
retinal is converted into trans-
retinal. The rhodopsin breaks up
into opsin and retinal ­
Sodium (Na) ion channels close
A generator potential is set up in
the rod
If the threshold is reached, an
action potential is set up in the
bipolar cell
A nerve impulse is sent along the
optic nerve to the brain.…read more

Slide 6

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Visual pigment called iodopsin
Three types of iodopsin, each sensitive
to one primary colour of light ­ colour
Only one cone to each bipolar cell -
good resolution
Found mainly in the fovea…read more

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