Midterm 2: Vision

Question 1

Why is Paper 2 an exploratory paper?

Answer 1

project started because they were looking at expression of various [some big class of molecules] that they knew were expressed in different retinal ganglion cell types

Question 2

What is JAM-B?

Answer 2

labels a specific type of RGC – these cells were very evenly distributed within retina

Question 3

What is the Cre/Lox system? How does it work?

Answer 3

system for selective deletion of genes and labeling of cells – often used to knock out genes only in a specific subset of cells within the animal

• enzyme Cre catalyzes recombination between DNA sequences called LoxP sites, and cut out region of DNA between those two sites
• if the chunk of DNA being removed has stop codon, then it will couple a promoter with marker gene, then you will get expression of the marker only in cells that express Cre
• create mouse that has Cre expressed under control of JAM-B promoter

Question 4

What do ON-centre ganglion cells respond to?

Answer 4

• increase in light in centre of receptive field (+)
• decrease in light in surround (-)

Question 5

What do OFF-centre ganglion cells respond to?

Answer 5

• decrease in light in centre of receptive field (-)
• increase in light in surround (+)

Question 6

What features can the visual system encode?

Answer 6

• size
• colour
• shape
• contrast
• texture
• intensity (brightness)
• location
• motion direction
• motion speed
• rotation
• depth
• recognition

Question 7

What does the lens do?

Answer 7

focuses light on retina

Question 8

What does the pupil do?

Answer 8

increase/decrease amount of light that goes through

Question 9

What does the iris do?

Answer 9

increase/decrease amount of light that goes through

Question 10

What is protanopia?

Answer 10

missing long (red) cone – cannot detect redness, red and green look very similar

Question 11

What is luminance?

Answer 11

light intensity

Question 12

What is scotopic vision? Are rods and/or cones active?

Answer 12

at very lowest levels of light

• only rods are active – b/c they are more sensitive
  below cone threshold

Question 13

What is mesopic vision? Are rods and/or cones active?

Answer 13

some ability to detect colours b/c cones are activated above this threshold – but it’s not great

Question 14

What is photopic vision? Are rods and/or cones active?

Answer 14

indoor levels of light

• rods are saturate ∴ not giving much information
• relying much more heavily on cones ∴ have better colour vision