L4 - Vision

Question 1

What receptor do ON bipolar cells have and what does this do?

Answer 1

mGluR6 which converts the hyper-polarisation to a depolarisation.

Question 2

What receptor do off bipolar cells have and what does this do?

Answer 2

mGlu R1 and R2 which conserve the hyperpolarization

Question 3

What are the cells in the eye which generate APs?

Answer 3

Amacrine cells and retinal ganglion cells

Question 4

How do ribbon synapses adapt to light?

Answer 4

They destabilise releasing synaptic spheres thus shortening the synapse.

Question 5

What is the function of the centre surround receptive field?

Answer 5

Emphasize edges

Question 6

What is APB and what did it show?

Answer 6

APB is. Glutamate analogue which specifically blocks mGluR6 on bipolar neurons. It was used to determine the function of on and off bipolar cells. When used it was found that an increased light response was dramatically reduced where as a decreased light response was unaffected. This disproved the separate channel model and instead suggested that horizontal cells are responsible for on/off centre receptive fields

Question 7

What’s the role of glia in the eye?

Answer 7

Provide a soft substance for neurites to grow
K homeostasis thus Elevating the signal to noise ratio
Retinal volume homeostasis
Take up glutamate

Question 8

Outline one of the responses that Müller cells have to Ca

Answer 8

Glial calcium release is triggered by light. This may lead to the release of gliotransmitters such as: glutamate, atp/Adp/adenosine, d-serine. This may lead to neuronal adaptation to elevated light levels.

Question 9

Describe midget cells

Answer 9

Account for 80% of retinal ganglion cells
Go from the ganglion cell layer of the retina to the parvocellular layers of the LGN.
Slow conduction velocity
Respond to changes in colour
Respond weakly to changes in contrast
Small dendritic trees

Question 10

Describe parasol cells

Answer 10

10% of retinal ganglion cells
Ganglion cell layer of the retina to the magnocellular layers of the LGN
Fast conduction velocity
Motion detection
Major inout for the MT cortex

Question 11

How do photoreceptors respond to a light stimulus?

Answer 11

They hyperpolarise with a graded potential

Question 12

What is the midget:parasol ratio at the fovea?

Answer 12

8:1

Question 13

What is the midget to parasol ratio at the periphery?

Answer 13

1:1

Question 14

What do ribbon synapses enable?

Answer 14

Analogue signal transfer at photoreceptors

Question 15

Where is the visual cortex located?

Answer 15

In the occipital lobe at the back of the skull

Question 16

Outline Hubel and Wiesel’s experiment

Answer 16

The demonstrated the orientation selectiveness of V1 cortical neurons using a cat and a beam of light. The beam of kig ht moved across the visual field. They found thay the neurons only fired when the line was in particular place on the retina, the activity of the neurons changed depending on the orientation of the line and sometimes the neurons only fired when the line was travelling in a certain direction.

Question 17

What are the transforms in V1?

Answer 17

Orientation, direction, spatial frequency, binocularity, on/off convergence and midget/parasol convergence.

Question 18

Outline the three models for the structure of the V1 cortex

Answer 18

The ice cube model suggests that the ocular dominance columns are arranged in a rigid cube like structure
The swirl model suggests a model similar to the ice cube however not as rigid, more bent.
The radial model

Question 19

Describe the features of v4

Answer 19

Large receptive fields
Task and intent modulated
Response can be modulated by eye movements
Not exclusively a colour area

Question 20

What is the function of the MT/V5 cotrex?

Answer 20

Integration of direction selective input - flicker, motion and depth

Question 21

What are the basic visual capacities?

Answer 21

Colour 
Brightness
Hue
Pattern
Motion
Depth

Question 22

What are the intermediate visual capacities?

Answer 22

Consistance
Selection
Recognition
Transposition
Comparison
Location

Question 23

What are the 3 qualities of colour?

Answer 23

Hue
Brightness
Saturation

Question 24

Why are there no blie cones in the central macula?

Answer 24

Blue light input is less accurate

Question 25

What is retinis pigmentosa?

Answer 25

A genetic retinal degeneration which causes a loss of rod photoreceptors leading to night blindness followed by tunnel vision

Question 26

What us cone dystrophy?

Answer 26

A genetic retinal degeneration in which there is a loss of cone cdlls leading to reduced visual acuity and loss of colour

Question 27

What is Age related macular degeneration?

Answer 27

Wet form is retinal edema
Dry form is retinal pigment epithelium loss
Caused by genetics and smoking

Question 28

What is diabetic retinopathy?

Answer 28

Vascular anomalies and retinal inflammation lead to neurodegeneration and progressive vision loss

Question 29

What happens in reactive gliosis?

Answer 29

Glial scars are made from the expression of glial fibrally protein and intermediate filaments, thus inhibiting neurite growth.

Question 30

Why is the eye an ideal research object?

Answer 30

Always have a control
Easily recorded
Local substance application
Immuno Privileged

Question 31

What is intravitreal substance application?

Answer 31

Antibody derivatives directed against VEGF are injected monthly to treat neurovascular retinal diseases