Photoreceptors (have photosensitive layer at back of eye)
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What do they do
Respond to different Light intensities
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What is the outer segment of a rod
Rod shaped
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What used for? why
Peripheral vision as 10^9 cells per eye distributed throughout the retina
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What do they have
Good sensitive- can detect a single photon of light so are used for nigh vision
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What is there only
1 type of cell so monochromatic vision
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What is there usually
Many rods usually connected to 1 bipolar cell so poor visual acuity (ie rods are not good at resolving fine detail)
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What does outer segment of cone cell contain
photosynthetic chemicals
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What is outer segment
Cone shaped
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How many cells per eye? so?
10^6, found mainly in fovea so can only detect images in centre of retina
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What does it have
Poor sensitivity - need bright light so only work in day
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What is there
3 types of cells- red, green and blue so are responsible for colour vision
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What is each cone usually connected to
one bipolar cells good visual acuity (ability to distinguish between 2 closely spaced dots)- cones used for resolving fine detail such as reading
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Although there are far more rods than cones what do we use most of the time
Cones because they have fine discrimination and can resolve colours
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How
Constantly move our eyes is that images are focused on the same area of the retina called the fovea
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The more densely packed cone cells
the better visual acuity
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Rods=
Low LI,B&W- can't discriminate between colours, rhodopsin, low freq of AP (only freq represents intensity),summative effect
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What does summative effect do
even though low LI and low impulse therefore low freq of AP less neurotransmitter but all synapse on one
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If rods stimulated
AP fired
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What does chemical transmitter synapse with
Bipolar cells
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Relationship bw intensity of stimulus and freq
Size doesn't change, only the frequency as size of stimulus is directly proportional to freq of AP
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If 1:1 why wouldn't it work
Low light= low freq AP less NT to fire AP
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Cone?
Colour vision, works at high LI, light sensitive pigment called iodopsin, 3 different types each with a different pigment that each respond to different wavelengths of light
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If low LI
Not enough to detect light- too infrequent AP to cause impulse to be fired not enough NT
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But if High
More freq AP more NT
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Steps
High LI, inc freq of AP, Inc NT, Fire AP, connects with optic nerve
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What do rods use
Dim light, small stimulus= low freq of AP fired to optic nerve
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ratio
3 rods:1 bipolar
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what does it give and use
poor visual acuity, rhodopsin, grey vision
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What mostly used for
Night vision, provides poor visual acuity, not sensitive to colour, contains pigment rhodopsin
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What do cones use
High LI, higher freq of AP fired
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What are they sensitive to
diff wavelengths of light- diff cells (3)
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ratio
1cone:1bipolar cell
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What do they provide
Good visual acuity, contains pigment iodopsin and sensitive to colour mostly used for day vision
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