L11-19

Question 1

which cell leaves the eye?

Answer 1

Retinal Ganglion cells

Question 2

Where are the photoreceptors?

Answer 2

in the retina

Question 3

where does the optic nerve cross?

Answer 3

the Optic Chiasm

Question 4

where is the Lateral Geniculate Nucleus (LGN)?

Answer 4

Thalamus

Question 5

where does LGN project to?

Answer 5

layer 4 V1

Question 6

What is the LGN segregated besed on?

Answer 6

segregated by eye of origin

Question 7

where does the secondary visual pathway run?

Answer 7

Superior colliculus->pulvinar nucleus in thalamus->V1

Question 8

explain the layout of the retina

Answer 8

BACK TO FRONT:
Photoreceptor
(amacrine cell)
Bipolar cell
(horizontal cell)
RGC

Question 9

which part of the retina has the highest visual acuity? and why?

Answer 9

Fovea

highest density of cone receptors

Question 10

how much of V1 does the fovea represent

Answer 10

> 50%

Question 11

what are saccades?

Answer 11

tiny, very fast eye movements that scan the environment to get the entire visual field in the centre of your vision

Question 12

Describe the journey of light in the eye

Answer 12

• Light enters through the cornea (transparent outer membrane)
• passes through lens and vitreous
• forms an image on the retina
• reaches the photoreceptor

Question 13

how many and what are segments of the photoreceptor

Answer 13

2 segments
Inner segment: cell body and nucleus
outer segment- stacks of membranes (the famous bits)

Question 14

how many types of rods are there?

Answer 14

1 : black and white

Question 15

How many types of cones are there?

Answer 15

3:
Short (S) Blue
Medium (M) Green
Long (L) Red

Question 16

ratio of rods to cones

Answer 16

100 million: 5 million

Question 17

what is the Resting potential of photoreceptors?

Answer 17

-40mV- depolarised at rest- off response glutamate released, Na+ channels activated

Question 18

what happens to photoreceptors when light hits them

Answer 18

Hyperpolarisation proportional to stimulus. reduced glutamate release.

Question 19

what is the difference between the two classes of bipolar cells?

Answer 19

reaction to glutamate:
off bipolar cells: glutamate gated cation channels gives classical EPSP from Na+ influx. excitatory receptor. in light reduced glu release: stop firing
On bipolar cells: GPCR inhibitory receptor. in dark reduced glu release, less inhibition; fires more

Question 20

horizontal cells

Answer 20

gabaergic
responsible for lateral inhibition
release gaba onto photoreceptors inverting the synapse

Question 21

what is a receptive field?

Answer 21

area of the retina that has a change in membrane potential when stimulated.

Question 22

explain RGC receptive fields

Answer 22

synapses of bipolar and horizontal cells in retina are arranged so RGC have opposing surround concentric receptive fields

Question 23

explain centre surround receptive fields for o+ O-

Answer 23

eg. light centre dark surround.
centre:
light hits photoreceptor-> cone depolarises-> reduced glu release->on bipolar cells depolarise and release glu-> excites RGC

surround
no light hits-> horizontal cells not activated no inhibition

if light hits surround:
horizontal cells hyperpolarise->reduced GABA release-> central photoreceptor depolarisation->increased glu release->bipolar cells hyperpolarise-> RGC inhibited

Question 24

what are the types of RGC and their relative abundence

Answer 24

Midget ganglion cells- 80%
Parasol ganglion cells- 10%
Koniocellular ganglion cells- 10%

Question 25

what is the function of Midget GCs

Answer 25

static stimuli
detail and colour
luminance sensitive and colour sensitive

Question 26

what is the function of parasol cells

Answer 26

motion and change

luminance sensitive

Question 27

what is responsible for focusing light on retina

Answer 27

refractive indices of different media- cornea, lens, vitreous

Question 28

what is responsible for most of the refraction seen

Answer 28

cornea 75%

lens 25%