Flashcards in Retina Deck (65):
What fundamentally limits visual acuity?
What is visual acuity?
Ability to resolve fine detail
How do you test for visual acuity?
Recognition of letters on Snellen or LogMAR chart
How is visual acuity expressed?
VA = D'/D, where:
D' = test distance
D = distance where each letter subtends 5 min arc
At what visual acuity are you legally blind?
What is the meaning of 6/12?
Person has to be 6 m away to see what normal people see at 12 m, even though letter is bigger
What are the optical factors affecting visual acuity?
Clarity of optical media
- Corneal opacities
What is the best visual acuity at photopic levels?
What determines central vision?
Density of cones in fovea
Are there many cones outside of the fovea?
No, not many
What is the best visual acuity at scotopic levels?
Where is night vision best?
Off-centre because highest density of rods 5-15 degrees away from fovea
What are the six neuron types of the retina?
What are the synaptic layers of the retina?
Outer plexiform layer
Inner plexiform layer
What layers does light pass through before hitting the photoreceptors?
One type only
No colour vision
95% of photoreceptors
Absent from fovea
Allow colour vision
5% of photoreceptors
Densest in fovea
How is the retina wired up?
Through pathway: phtoreceptors > bipolar cells > ganglion cells
Lateral interactions > modulation
- Horizontal cells
- Amacrine cells
Which layer of the retina are horizontal cells located?
Which layer of the retina are amacrine cells located?
Which cells are the output neurons of the retina?
How many different types of bipolar cells are there?
- 1x rod bipolar cell
- 9x cone bipolar cell
What are bipolar cells important for?
From what is the input to horizontal cells?
To what is the output of horizontal cells?
What is the neurotransmitter released by horizontal cells?
How do horizontal cells respond to light?
How many types of amacrine cells are there?
Do amacrine cells have axons?
Why are amacrine cells considered mostly inhibitory?
Release glycine and GABA = inhibitory neurotransmitters
From what cells do amacrine cells receive input?
To what cells do amacrine cells send output?
Where are the cell bodies of ganglion cells located?
In ganglion cell layer
What are four types of ganglion cells?
What neurotransmitter do ganglion cells release?
Which neurons in the retina fire action potentials?
How do neurons that aren't ganglion cells transmit a signal?
Constantly releasing neurotransmitter
Shifts in amounts with changes in membrane potential
- Release more when depolarised
- Release less when hyperpolarised
How do ganglion cells respond to light?
Increase/decrease action potential firing rate
What is the receptive field?
Area of retina that when stimulated with light changes cell's membrane potential
What type of receptive field do ganglion cells have?
What is the response to light when shone in the two different parts of the receptor field?
Centre's respond to light opposite to surround's response to light
What in a photoreceptor is activated by light?
What photopigment is in a rod?
What photopigment is in a cone?
Each type has different cone-opsin
What are opsins bound to?
All-trans retinal > derivative of vitamin A
What is the response of a photopigment to light?
Retinal absorbs light > changes shape > changes shape of attached opsin
Which segment of the photoreceptor contains the pigment?
What is the response of a photoreceptor to light?
What is the neurotransmitter released by photoreceptors?
How does the amount of glutamate released change when photoreceptors respond to light?
What is happening inside the cell during the dark current in a photoreceptor?
cGMP gates Na channel > continuous influx of Na > depolarisation of cell
What happens to cGMP inside a photoreceptor in the light?
Pigment activates transducin > transducin activates PDE > breaks downk cGMP > GMP > Na channel closes > membrane hyperpolarises
What type of bipolar cells are hyperpolarised by light?
OFF bipolar cells
What type of bipolar cells are depolarised by light?
ON bipolar cells
Why do different types of bipolar cells respond differently to glutamate?
Have different types of receptors
Which receptors depolarise a bipolar cell in response to glutamate?
Which receptors hyperpolarise a bipolar cell in response to glutamate?
Which type of ganglion cells do ON bipolar cells synapse with?
ON ganglion cells
Which type of ganglion cells do OFF bipolar cells synapse with?
OFF ganglion cells
What determines the receptive field centre response?
What determines the receptive field surround response?
Inputs from horizontal cells
What cells do horizontal cells receive input from?
What cells do horizontal cells give output to?
What neurotransmitter do horizontal cells release?