9.7 detection of light by mammals Flashcards

1
Q

what are the two types of photoreceptors in the retina?

A

rods and cones

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2
Q

what is the fovea?

A

area of the retina containing only cones, region of highest visual activity

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3
Q

which photoreceptor has their own sensory neurones?

A

cones

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4
Q

what is the visual pigment in rods?

A

rhodopsin

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5
Q

what is rhodopsin made up of?

A

opsin and retinal

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6
Q

what happens when a photon of light hits a rhodopsin molecule?

A

rhodopsin is bleached and breaks down into opsin and retinal

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7
Q

what happenes to rods in dim light?

A

1- rhodpsin breaks down to retinal+opsin
2- opsin, acting as an enzyme, closes the Na+ channels in the outer segment so there is no facilitated diffusion
3- Na+ is actively pumped out making the inside more negative
4- neurone is now hyperpolarised
5- causing the bipolar neurone to become depolarised
6- bipolar neurones release neurotransmitter to the ganglion cells and an action potential is initiated

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8
Q

what happened to rod cells in the dark?

A

1- retinol+opsin reform rhodopsin
2- Na+ channels are open so Na+ can diffuse back into the outer segment
3- Na+ actively pumped out of the inner segment using ATP which maintains the concentration gradient between the outer and inner segments
4- inner segment slightly depolarises
5- neurotransmitter glutamate is released binding to the bipolar cell
6- bipolar cell is not depolarised and therefore there is no action potential initiated in ganglion cells

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9
Q

what happens when light hits cones?

A

1- iodopsin is broken down but needs more light than rhodopsin so colours are not easily distinguished in dim light
2- each type of cone has it’s own iodopsin

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