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What are the
receptors in the eye?
o They are called light receptors.
o Found in the retina of the eye.
o There 2 main types of receptors:
rod cell & cone cell.
o It is sensitive to colour and light.
o Its main purpose is to detect
different light intensities & send
nerves impulse to the brain.
o Both cells act as transducers by
converting the light energy into
electrical energy of nerve
impulse.…read more

Slide 3

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Rod Cells-produce black/white picture
o Rod cells are the most numerous type of
receptor in the eye, with around 120
million in each eye.
o Multiple rod cells can join to one sensory
neurone, via one bipolar neurone. This
has two implications:
1. Rod cells can only detect very low
intensities of light that is why they
can't distinguish different wavelengths
of light and therefore producing black
and white picture.
o They contain a pigment called
Rhodopsin. When light shines on the
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.
2. Rod cells have poor visual acuity. As
many rod cells share the same sensory
neurone, the brain will receive an
impulse along that neurone, but it
doesn't know which specific rod cell was
stimulated by a photon coming from a
certain object. Therefore, the brain is
limited in its resolution of objects from
rod cells. (i.e. cannot distinguish
between 2 separate sources, so 2 dots
can only be seen as 1 blob.)…read more

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Cone Cells-produce colour picture
o Cone cells aren't as common as rod
cells, with around 6 million. most of the
cone cells are concentrated at the centre
of the back of the eye.
o Each cone cell is joined onto a
sensory neurone, via its own bipolar
neurone, this has two implications (not
mixed with rod cell):
o Cone cells can only detect high
intensity levels of light. They contain
a pigment called Iodopsin, the pigment
is broken down when light shines on it
and is capable to produce a large
enough generator potential to exceed
the threshold value for an action
potential down the sensory neurone.
o There are 3 different types of
iodopsin : sensitive to either red, blue
or green wavelengths.
o Cone cells have high visual acuity,
because only one cone cell stimulates
one sensory neurone, the brain knows
more precisely where photons are
coming from, just by the number of
impulses it receives from certain
neurones. This means that cone cells
offer greater resolution of objects. (can
distinguish between the 2 sources, so 2
dots can be seen separately)…read more

Slide 5

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Rod cell Cone cell
Rod shaped Cone shaped
More in retina Less in retina
Distribution ­ more at the Distribution ­ fewer at the
periphery of the retina, absent periphery of the retina,
at the fovea concentrated at the fovea
Give poor visual acuity Give good visual acuity
Sensitive to low light intensity Sensitive to high light intensity
Produce black and white picture Produce colour picture…read more


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