W21-L2: Retina Flashcards Preview

Matt's Block 06 - Neuro block > W21-L2: Retina > Flashcards

Flashcards in W21-L2: Retina Deck (25):
1

What is visual acuity?

Ability to resolve fine detail tested by Snellen chart

2

What do the two numbers in a snellen chart refer to?

Top number is test distance eg 6 meters, bottom number is the distance they have to be to see what a normal person would see at 6 meters

3

What is normal vision, legal blindness and the minimum acuity for driving?

6/6 is normal vision, 6/60 is legal blindless, 6/12 is minimum for driving

4

What optical factors affect visual acuity?

-Pupil size
-Clarity of optical media (eg cataracts)
-Refractive errors

5

At scotopic light what is the best visual acuity possible?

6/60

6

What are the normal neurones of the retina?

Rods, cones, Horizontal cells, Bipolar cells, amacrine cells and ganglion cells

7

What are the two synaptic layers of the retina?

-Outer plexiform layer
-Inner plexiform layer

8

Which photoreceptor is more sensitive to light, the rod or the cone?

Rod

9

Is there more cones or rods in the retina?

Rods, 100 million vs 5 million

10

Why is the vision with rods worse than cones?

Connectivity

11

What is the through pathway of the retina?

Photoreceptors--> Bipolar Cells --> Ganglion cells

12

What are the two lateral interactions that occur in the retina?

Outer retina=Horizontal cells
Inner retina= Amacrine cells (axonless)
Both inhibitory

13

Where are bipolar cells located?

Inner nuclear layer

14

What are the types of bipolar cells?

Two:
-ones that hyperpolarise when light is on the retina (off BCs)
-ones that depolarize when light is on the retina are called "on" BCs

15

What are the type of ganglion cells and what do they release?

ON, OFF, M and P and Release Glutamate

16

What is interesting about the receptor field properties of ganglion cells?

light in different parts of the receptor fields produces different rates of ganglion firing

17

What are the photopigments and what are they all attached to?

Rods contain rhodopsin
Cones contain one of three cone-opsins
All are bound to vitamin A

18

How do photoreceptors function?

-Photoreceptors are hyperpolarized by light.
-Use glutamate as their neurotransmitter.
-Respond to light with graded changes in membrane potential (not Action Potentials)

19

How does a photoreceptor function in the dark?

cGMP gates a sodium channel causing continuous influx of sodium ions which causes depolarization of the cell.

20

How does a photoreceptor function in the light?

In the light, cGMP breaks down to GMP:
-cGMP no longer gates the sodium channels
-Flow of Na ions ceases
-Cell is hyperpolarized

21

What is the process known as phototransduction?

Light activates rhodopsin
Initiates a cascade of events that ultimately leads to the closure of cGMP gated sodium channels.

Rh->Transducin->PDE->breaks down cGMP.

Closure of sodium channels>hyperpolarization

22

What creates the centre-surround response of the retina?

The way the retina is wired, which gives a central response and a surround response (horizontal cells)

23

What creates the surround response in the retina?

Horizontal cells receive input from many photoreceptors and provide output to other photoreceptors.

24

In the surround response which cells depolarize and which hyperpolarize?

Photoreceptors depolarize and ganglion cells hyperpolarizes

25

What is melanoma associated retinopathy?

Rare complication of melanoma where antibodies are produced directed against ON bipolar cells.

Decks in Matt's Block 06 - Neuro block Class (48):