L4 - Vision overview

Question 1

What are the 3 types of stimuli recognised by the visual system? (3)

Answer 1

-Food
-Predator
-Mate

Question 2

What is the processing level organisation in the visual system?

Answer 2

-Positive feedforward
-Negative feedback
-Negative feedforward

Question 3

What part of the visual system sends information to the brain?

Answer 3

Optic nerve

Question 4

What is the main function of the retina

Answer 4

Image acquisition

Question 5

What part of the brain preprocesses visual information

Answer 5

Lateral geniculate nucleus (LGN)

Question 6

Where does main processing of visual information happen in the brain?

Answer 6

Visual cortex

Question 7

What part of the brain does the right hemifield activate?

Answer 7

Left brain (and vice versa)

Question 8

What are the two main visual pathways in the cortex? (2)
and what do they do? (2)
and where are they found (2)

Answer 8

Ventral - “what” (V1,V2 and V4) - Inferior temporal
Dorsal - “where” - Posterior parietal

Question 9

What dos the pupil do?

Answer 9

Pupil regulate the amount of light that falls on the retina

Question 10

What does the lens do?

Answer 10

Lens focuses image on the fovea

Question 11

What does the Fovea do?

Answer 11

Fovea is a part of the retina with highest visual acuity

Question 12

What part of eye does light travel through?
Which cells does light go through?

Answer 12

-The retina
-Light can’t travel through most of retina only Muller cells

Question 13

What do the 5 layers of the retina consist of?

Answer 13

3 layers of neutrons
2 layers of synapses

Question 14

What cells are ‘feedforward neurones’? (3)

Answer 14

-Photoreceptors
-Bipolar cells
-Ganglion cells

(Photoreceptors signal with bipolar cells which signal with ganglion cells)
(Glutamate expressed in the bipolar cells activate the ganglion cells)

Question 15

What cells are ‘feedback neurones’? (2)

Answer 15

Horizontal cells
Amacrine cells

Question 16

What are the two layers of synapses known as? (2)
What are they made up of? (2)

Answer 16

Inner and Outer plexiform layers

Outer plexiform layer consist of synapses between photoreceptors, bipolar cells and horizontal cells

Inner plexiform layer contains synapses between bipolar cells, amacrine cells and ganglion cells

Question 17

What do Amacrine cells express? and do? (2)

Answer 17

-Amacrine cells express GABA
-They send information back and forward and directly inhibit the ganglion cells

Question 18

Where do bipolar and horizontal cells receive input from?
Where do ganglion and marine cells receive input from?

Answer 18

Bipolar and horizontal cells receive input from photoreceptors in the outer plexiform layer (OPL)

Ganglion cells and amacrine cells receive input from bipolar cells (and ganglion cells from amacrine cells) in the inner plexiform layer (IPL)

Question 19

What are the two types of photoreceptor in the retina? (2)
When are they active? (2)

Answer 19

-Rod and cone cells
-Rods are active at dim light and cones are active at bright

Question 20

Where does phototransduction happen in rod and cone cells?
How does this work?

Answer 20

-The outer segment
-cGMP activates specific ion channel to cause hyperporlarisation/depolarisation

Question 21

What is the phototransduction mechanism?

Answer 21

-ON bipolar cells depolarise when light goes on and OFF bipolar cells hyper-polarise
-Photoreceptor hyper-polarise in response to light
-Less glutamate the less its active
-Some cells have different response and their membrane potential increases

Question 21

What is the phototransduction mechanism? (2)

Answer 21

-ON bipolar cells depolarise when light goes on and OFF bipolar cells hyper-polarise
-Photoreceptor hyper-polarise in response to light

Less glutamate the less its active
Some cells have different response and their membrane potential increases

Question 22

What is released by rod and cone cells in the dark?

Answer 22

Constant release of glutamate in darkness
(less released during activation by light)

Question 23

How does the mechanism of On cell activation differ from photoreceptors? (3)

Answer 23

-ON cells express mGluR instead of AMPAR to signal a cascade, using a G protein cascade

-G-protein (Go), not the same as in photoreceptor cascade

-Removal of cGMP is not required for ion channel closure
Various candidates:
TRPM1: expressed in ON but not OFF cells
Nyctalopin, proteoglycan required for light and glutamate responses in ON cells

Question 24

What gene is required in response for ON channels?

Answer 24

TMPR1

Question 25

What is the mechanism of ON cell activation? (4)

Answer 25

-Flashes of light leads to activation of bipolar cells
-Axons of ON bipolar cells and dendrites of ON ganglion and amacrine cells are located in the same sub-laminae in the inner plexiform layer
-ON and OFF cells project into different parts of the plexiform layer
-There are different types of ganglion dendrites

Question 26

Where are the axons of ON bipolar cells and dendrites of ON ganglion and amacrine cells located?

Answer 26

In the same sublaminae in the IPL (inner plexiform layer)

Question 27

When will retinal ganglion cells fire APs?

Answer 27

When specific areas of the retina are illuminated
(centre surround receptive field) - centre normally cell body

Question 28

What do different parts of the receptive field do when stimulated? (2)
Bipolar and ganglion cells have centre surrounded organisation

Answer 28

Spot (centre) - depolarisation
Annulus (surrounding ) - hyperopolarisation