Retina Flashcards
How many neurons in the retinal structure?
6
What is the functional pathway?
Photoreceptors
Bipolar cells
Ganglion Cells
which two pathways do photoreceptors signal in the retina?
the ON and OFF pathyways due to glutamate receptor on BCs
Visual acuity is best for which type of Photoreceptor? why?
cone vision b/c low convergence of pathway
what 2 things limit visual acuity?
- neural foctors
2. optical factors
3 big optical factors
- pupil size
- clarity of optical media (eg. cataracts)
- refractive errors/blur (myopia)
how far away from fovea to get Visual acuity loss?
5 minutes of arc away
what is photopic light level?
bright
what is scotopic light levels?
darker
where and what do you see best in scotopic light levels?
5-15degrees with your Rods
what are the six neurons in the retina?
Rods cones Horizontal cells Bipolar Cells Amacrine Cells Ganglon cells
Rods vs. Cones re: sensitivity
rods more sensitive
Rods vs. Cones re: how many types?
Rods: one type
Cones: 3 types
Rods vs. Cones number of cells?
Rods: 100 million
Cones: 5 million
what one thing do you need for good visual acuity?
small closely packed detectors
why are rods visual acuity not as good as cones?
connectivity
light on photoreceptors BCs causes what two things?
OFF: hyperpolarization
ON: depolarization
what are the two cells that deal with lateral interactions?
Horizontal cells
amacrine cells
Horizontal cells does what? how?
inhibit via GABA causing hyperpolarization
what is the ‘through’ pathway?
Ph>BC>GC
Amacrine cells does what? how?
Axonless Cells and inhibitory via glycine/GABA
Ganglion cells are the only cells that do what?
fire action potential
rest are graded potential
Ganglion cells are where? do what? how?
main output of retina
depolarize via glutamate
fire action potentials
what is a receptive field property?
GCs have a concentric-surround receptive field. they act as comparators not just a detector
Photopigments for rods vs. cones? bind to?
Rods: Rhodopsin
Cones: Cone-opsins
Both bind to Vitamin A
Photoreceptors depolarized by light? which NT?
Nope, hyperpolarized via glutamate
Photoreceptors fire action potentials?
Nope. graded changes in membrane potential
How do you get graded membrane potential in dark and light?
- Dark: cGMP gates a Na+ channel: continuous influx = depolarization
- light: cGMP breaks down: no Na+ influx =hyperpolarization
What are the steps in photo transduction?
- light activates rhodopsin
- cascade close cGMP Na+ channels
- Rh>transducin>phosphodiesterase>break cGMP
- hyperpolarization
How do ON and OFF Bipolar Cells interact?
Both are activated simultaneously
what is the centre-surround?
centre: through pathway
surround: determined via input to horizontal cells and their output to photoreceptors
horizontal cells release?
GABA
what is the surround in centre-surround?
surround: action of horizontal cells on the central group of photoreceptors, determined by the wiring
What is melanoma associated retinopathy? how Rx?
Antibodies against ON bipolar cells
Rx: oral prednisolone
