topic 9.7 - detection of light by mammals Flashcards
1
Q
structure of the human retina
A
- ganglion cell
- bipolar neurons
- photoreceptors - rods & cones
- synapse
- optic nerve fibre
- pigment epithellum
2
Q
what do rods and cones do
A
- they provide information needed for the brain to produce images
- they respond to different intensities of light giving effective vision in different conditions
3
Q
cone cells
A
- responsible for great visual acuity in bright light
- contain the pigment iodopsin
3 type/colours - next card
4
Q
rod cells
A
- more important at low light levels (grey scale)
- very sensitve to light
- contain pigment rhodopsin
- low acuity
5
Q
where are rod cells located
A
- evenly distributed around periphery
- NOT in central fovea
6
Q
where are cone cells located
A
central fovea
7
Q
what is acuity
A
the level of detail seen
8
Q
why do rod cells have low acuity
A
- due to the number of cells connected to a bipolar neurone
- brain would not be able to tell which of the three rod cells have received light
9
Q
why do cone cells have low sensitivity
A
- due to the iodopsin
- iodopsin is less sensitive to light than rhodopsin
- one cone cell affects one bipolar neuron
10
Q
interpretation of vision in the brain
A
- electrical signals are sent from photoreceptors to bipolar cells to ganglion cells
- they then travel along the optic nerve to the visual cortex of the brian
- brain interprets these signals allowing us to perceive attributes of light such as colout & intensity
11
Q
how does rhodopsin initiate action potential
A
- break down of rhodopsin - when rod cells absorb light - release opsin and retinal
- this causes Na+ channels to close
- Na+ continues to be pumped out of the cell
- inside of cell becomes more negative as positive ions are pumped out
- hyperpolarisation results which stops inhibitory neurotransmitter release
- this allows the bipolar neuron to stimulate the sensory nerve fibre to depoalrise
11
Q
rod cells in response to dark
A
- sodium ions diffuse into rod through open channels
- sodium ions actively pumped out of rod cell
- leakage of Na+ back into the cell causes partial depolarisation to -40mV
- this allows secretion of a neurotransmitter whcih inhibits depolarisation of the bipolar neuron
- hence no info is transmitted to the brain
12
Q
what is rhodopsin made of
A
opsin and retinal
