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Eye Anatomy
Retina ­ receives the
image
Full of light receptors
which are sensitive to:
Colour
Light levels
Massive blood supply is
also needed…read more

Slide 3

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How do the receptors work in the eye?
Light receptors are called rod and cone cells…read more

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Rods
Rod cells are responsible for detecting light/dark.
These cells cannot distinguish different
wavelengths of light.
Rod cells are much more plentiful than cone cells.
They contain a pigment called rhodopsin. When
light shines on this pigment, it is broken down in a
process called bleaching which creates a
generator potential that then stimulates an action
potential that is detected in the brain.
There is a 3:1 ratio of rod cells: bipolar neurone
because a threshold value has to be exceeded
before a generator potential is made in bipolar
neurone. With a 3:1 ratio this is more likely.
However, the rhodopsin is very sensitive to light,
and is therefore best in dim conditions; since in
brighter conditions it is broken down faster than it
is reformed. This is why, in dim conditions we will
see mainly in black and white…read more

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Cones
This cell has a different pigment called iodopsin.
There are 3 different types of iodopsin : sensitive to
either red, blue or green wavelengths.
Therefore we have red, green and blue cones. We
see different colours by the stimulation of different
combinations of iodopsins. E.g red and green cones
being stimulated = orange light#
Each cone has its own bipolar neurone so they do
not create generator potential when stimulated en
masse.
They only respond to high light intensity which
breaks down iodopsin. It is only then a generator
potential is produced.…read more

Slide 6

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Rods vs Cones…read more

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