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Neuro Block > Retina > Flashcards

Flashcards in Retina Deck (28):
1

What is visual acuity?

the ability to resolve fine detail

2

What factors limit visual acuity?

neural factors
optical factors

3

How do we test visual acuity?

recognition of letters on a Snellen or LogMAR chart

4

What does 6/60 and 6/12 mean?

these individuals can see at 6m what a normal person sees at 60m = legally blind
can see at 6m what a normal person sees at 12m -> needed for driving

5

What are the optical factors affecting VA?

Pupil size
Clarity of the optical media (ie how transparent the cornea is)
Refractive errors (error in focussing of the light by the eye)

6

What is scotopic vision? what photoreceptors are most active?

low light levels (ie darkness) RODS are responsible for vision

7

What are the neural factors affecting VA?

?

8

What is photopic vision? what photoreceptors are involved?

vision under well lit conditions -due to CONES

9

What is the structure of the retina - name the 6 types of neurons involved

Layered structure with 6 types of neurons -> Ganglion cells, Bipolar cells, Horizontal cells, Amacrine Cells, Rods and Cones

10

What are the photoreceptor cells? where are they located?

Rods & Cones
Located in the last layer of the retina furtherest from the light source.

11

What are the two synaptic layers of the retina called?

Outer plexiform layer, and Inner plexiform layer

12

What do Rods do?

function in dim light & provide black and white vision. Only 1 type, Very sensitive and NOT found in the fovea

13

What do Cones do?

function in well lit conditions and are involved in the perception of colour. 3 Types (red, green, blue), less sensitive and densest in the fovea

14

Are there more rods or cones in the retina? which ones is bigger?

RODS outnumber Cones 20:1
Cones are bigger

15

What are the main layers of the retina?

GC layer, Inner plexiform layer, Inner nuclear layer, Outer plexiform layer, outer nuclear layer, Photoreceptor layer, Pigmented epithelium

16

What is the general pathway through the 6 different neuron types in the retina?

photoreceptors synapse with bipolar cells which synpase with GCs, and HC and AC create lateral interactions at each synapse (HC between Ph +BCs, and AC between BC + GCs)

17

How are bipolar cells classified?

10 different types: depending on whether they receive signals from Rods (1 type) or Cones (9 types)

18

What is the response of BCs when light falls on the retina?

OFF BCs - hyperpolarise
ON BCs - depolarise

19

How do horizontal cells function?

receive input from and provide input to photoreceptors. use GABA (inhibitory) - respond to light be HYPERPOLARISING

20

How do Amacrine cells function?

axonless cells that are important for lateral inhibition - release glycine and GABA onto bipolar and GCs

21

What is unique about the GCs?

only neuron in the retina that fires action potentials, release glutamate

22

What is the receptive field or a cell?

area of retina that when stimulated with light changes that cell's membrane potential

23

What are photopigments?

proteins that change conformation when light hits it

24

What photopigments do Rods contain?

Rhodopsin

25

What photopigments do Cones contain?

3 different kinds of cone-opsins

26

What is the role of Vit A in vision?

Vit A binds opsins (photopigments) -> essentiat for photoreceptor function

27

What happens to photoreceptors when light hits them?

respond to light with graded changes in membrane potential -> become hyperpolarised -> so they release LESS glutamate released

28

What is the mechanism by which photoreceptors become hyperpolarised in response to light?

light activates rhodopsin which leads to a siganlling pathway resulting in PDE activation which breaks down cGMP to GMP- stopping the cGMP mediated opening of the Na channel -> this stops Na+ influx into the photoreceptor -> hyperpolarized (more negative)