Retina-10

Question 1

How big is the fovea?

Answer 1

600micrometers

Question 2

Describe the fovea

Answer 2

Inner cell layers are pushed aside so light falls directly onto photoreceptors

Question 3

Describe the foveal pit

Answer 3

Only cone receptors

Question 4

At how many degrees away from the foveal pit do cones almost completely diminish?

Answer 4

10 degrees

Question 5

What is the optic disc?

Answer 5

The area where ganglion cell fibres leave the retina and form the optic nerve. there are no photoreceptors here. It is 3x bigger than the fovea and is 15 degrees more nasal.

Question 6

when looking straight ahead, objects where would fall directly onto the optic disc?

Answer 6

The periphery. but the brain compensates for this and fills in the blank

Question 7

Which segment of the photoreceptors is closest to the RPE?

Answer 7

The outer segment

Question 8

Describe the outer segment of photoreceptors

Answer 8

stacks of membrane discs which contain pigment. Rods have more discs.

Question 9

What triggers rod disc phagocytosis?

Answer 9

The morning light

Question 10

What triggers cone disc phagocytosis?

Answer 10

Night time

Question 11

What eats the discs?

Answer 11

The reticular pigment epithelium

Question 12

Describe the inner segment of photoreceptors

Answer 12

Lots of mitochondria and ribosomes for assembling opsins for the outer segment.

Question 13

What sort of transmission occurs in the OPL between photoreceptors and bipolar/horizontal cells?

Answer 13

Glutamatergic

Question 14

What photoreceptor mediates peripheral vision?

Answer 14

Rods- distributed across whole retina except fovea

Question 15

How sensitive are rods?

Answer 15

Very- can detect change in one photon of light

Question 16

What kind of vision is mediated by rods?

Answer 16

Scotopic vision- just above absolute darkness

Question 17

What kind of vision do cones mediate?

Answer 17

Photopic vision, central

Question 18

Which type of vision has a fast response to changes in illumination?

Answer 18

Photopic vision

Question 19

How many rods do we have?

Answer 19

1

Question 20

What is the maximal absorption of rods?

Answer 20

498nm

Question 21

How many cones do we have?

Answer 21

3

Question 22

What are the three cones?

Answer 22

Blue (short), green (medium) red (long)

Question 23

What is the maximum absorption of blue/short cones?

Answer 23

420nm

Question 24

What is the maximum absorption of green/medium?

Answer 24

534nm

Question 25

What is the maximal absorption of red/long?

Answer 25

564nm

Question 26

On which chromosome do mutations occur that cause colour vision deficinecy?

Answer 26

X

Question 27

What is the most common form of colour blindness?

Answer 27

Difficulty determining between red and green because medium and long wave cones produce the same pigment

Question 28

Where is pigment held?

Answer 28

Outer segment discs of photoreceptors

Question 29

What is the pigment and what is the chromophore?

Answer 29

Opsin and retinal

Question 30

What do opsin and retinal bind to form?

Answer 30

Rhodopsin

Question 31

In what form is retinal bound to opsin?

Answer 31

11-cis

Question 32

When light hits rhodopsin, what happens to retinal?

Answer 32

It isomerises and changes from 11-cis to 11-trans form

Question 33

What happens when retinal becomes 11-trans?

Answer 33

It detaches from opsin so converts rhodopsin into metarhodopsin II

Question 34

What does metarhodopsin do?

Answer 34

Activates transducin- a GTP binding protein

Question 35

What enzyme does transducin activate?

Answer 35

PDE

Question 36

What does PDE do?

Answer 36

hydrolyses cGMP bound to Na+ channels in outer segment membrane- this closes the Na+ channels

Question 37

What is the overall result of a photon of light hitting rhodopsin?

Answer 37

Closure of sodium channels in the outer segment membrane

Question 38

In the dark, are sodium channels open or closed?

Answer 38

Open

Question 39

What needs to be bound to the sodium channels for it to be open?

Answer 39

cGMP

Question 40

As well as sodium, what else can move through the channels?

Answer 40

Calcium

Question 41

Why are the photoreceptor cells so metabolically demanding?

Answer 41

Because sodium is constantly pumped back out

Question 42

In the dark, what is the resting membrane potential of the cell?

Answer 42

-40mV- more depolarised than normal because of the influx of sodium

Question 43

In light, what is the membrane potential of the cell?

Answer 43

-65mV- hyperpolarises

Question 44

What does the hyperpolarisation lead to in terms of neurotransmitter release?

Answer 44

Less glutamate release

Question 45

Describe how phototransduction has amplification

Answer 45

when one rhodopsin molecule is activated by light, 800 transducin molecules, which means 4800 cGMP molecules are hydrolysed and 200 channels close.

Question 46

How many sodium channels close for every 1 rhodopsin molecule activated?

Answer 46

200

Question 47

Where is bleached 11-trans retinal converted back to 11-cis retinal?

Answer 47

The RPE

Question 48

What are the two RPE enzymes which convert 11-trans retinol into 11-cis retinol?

Answer 48

LRAT and RPE65

Question 49

In what disease is LRAT dysfunctional?

Answer 49

Early onset macular dystrophy

Question 50

In what disease is RPE65 dysfunctional?

Answer 50

Retinitis pigmentosa

Question 51

What is the rod enzyme dysfunctional is Stargardt syndrome?

Answer 51

ABCA4

Question 52

What percentage of ganglion cells contain melanopsin?

Answer 52

3%

Question 53

What is the absorbance of melanopsin?

Answer 53

484nm

Question 54

Where do these melanopsin containing ganglion cells project to?

Answer 54

The suprachiasmic nucleus of the hypothalamus where circadian rhythms are controlled