Anatomy of visual sys

Question 1

What’s the term for crossing chiasm or not?

Answer 1

Ipsilateral: doesn’t cross chiasm.
Contralateral: crosses chiasm.

Question 2

What is the common property of animals with frontal eyes? What group is the exception?

Answer 2

They eat meat, they are hunters. Primates are the exception.

Question 3

What’s the name of the area in frontal eye animals that only one eye sees?

Answer 3

Nasal crescent.

Question 4

What regions in the frontal eye animal eye are ipsi/contralateral?

Answer 4

Ipsi: fovea to temporal edge.
Contra: fovea to nasal edge.

Question 5

What does the chiasm in a frontal eye animal do?

Answer 5

Partial decussation.

Question 6

What regions of what eyes cross?

Answer 6

The nasal region of the contralateral eye crosses with the temporal region of the ipsilateral eye.

Question 7

What eyes do axons in the optic track come from? What percent of the VF do they cover?

Answer 7

Axons come from both eyes, cover half the VF.

Question 8

Compare the decussation and what part of VF ends up where in human vs mouse.

Answer 8

Mouse: almost complete decussation. Everything in one side of VF ends up in contralateral hemi.
Human: partial decussation. Everything in half of VF ends up in a contralateral hemi.

Question 9

What percent of axons on optic nerve terminate where. What does the exception do?

Answer 9

90% at LGN. Most of rest at SC, some at hypothalamus. The exception is neurons that regulate eye movement.

Question 10

How many layers does LGN have? What are they named?

Answer 10

6 primary layers. Magnocellular&Parvocellular. 6 Koniocellular layers in between. goes like kMkMkPkPkPkP

Question 11

How many of what layer in LGN receives input from what eye and what ganglion?

Answer 11

1 magno for ipsi eye, one for contra. 2 parvo per eye similarly. M gang->magno, P gang->parvo. Small bistratified blue-on gang->konio. K layers receive from the eye ventral to them.

Question 12

What makes K layer different from M/P genetically?

Answer 12

They express 3 genes that the others don’t.

Question 13

Explain retionotopic organization of LGN (cat). Where do they receive input from? What do they contain?

Answer 13

Two big layers. A,A1. Magno C, Parvo C1,C2. A,A1 are for separate eyes, mixture of X/Y ganglion. C from W cells.

Question 14

What do you observe in cat LGN when you drive electrode in normal to surface?

Answer 14

All cells you encounter get input from same degree of visual field.

Question 15

Explain how you observe topographic projection in monkey retina->LGN->V1

Answer 15

Ablate a bit of V1. When animal dies, take out LGN. Some cells are paler. Line of projection spans all layers. These all send axons to ablated area in V1. This area receives from a specific area in retina on contralateral eye.

Question 16

Explain mouse LGN lamination.

Answer 16

No obvious lamination. Hidden lamination can be observed by looking at type specific termination of ganglion cells.

Question 17

What layer receives from what ganglion in cat?

Answer 17

K:W
P:X
M:Y

Question 18

Do cats have color vision? What type of ganglion cell explains this?

Answer 18

Barely. The only chromatically tuned cell is a blue-on ganglion cell.

Question 19

Where do axons from the LGN go?

Answer 19

Optic radiation. Some avoid it and go to pretectum. Some go to SC. V1.

Question 20

What paths do axons reach V1 from LGN?

Answer 20

Straight, and through temporal lobe.

Question 21

What is the loop of meyer?

Answer 21

Axons go from lateralmost LGN to temporal lobe.

Question 22

What part of LGN goes to V1 how? Where in V1 do they end?

Answer 22

Medial LGN straight. Lateral LGN thru loop of meyer. Loop: lower calcarine fissure. Straight: upper calcarine fissure.

Question 23

What is the name for axons that don’t go thru loop of meyer?

Answer 23

Retrolenticular.

Question 24

What’s the point of loop of meyer? How does this relate to organization of LGN?

Answer 24

Lateral LGN = upper visual field. (loop)

Medial LGN = lower VF (straight)

Question 25

What happens when you lose one eye?

Answer 25

Blindness in that eye, duh. WW BB

Question 26

What happens when you cut the chiasm?

Answer 26

You only see fovea-temporal in both eyes. BW WB

bitemporal hemianopsia.

Question 27

What happens when you cut the optic tract after chiasm? [right]

Answer 27

Contralateral half of VF gone. BW BW

Left homonymous hemianopsia

Question 28

What happens when you cut Meyer’s loop? [right]

Answer 28

Contralateral upper quarter of VF gone. Left Superior quadrantanopsia

Question 29

What happens when you cut the striate cortex? [right]

Answer 29

Contralateral half of VF gone, fovea remains. Fovea is in superior cerebellum. Left Homonymous hemianopsia with macular sparing.

Question 30

Explain a natural condition for bitemporal hemianopsia

Answer 30

Pituitary gland tumor.

Question 31

Explain gordon holmes’s theory of foveal representation in V1.

Answer 31

Upside down, right to left. Mapped visual field loss based on brain damage. 1/3 of occipital lobe of fovea.

Question 32

How did modern imaging show what percent of V1 is fovea?

Answer 32

fMRI studies with observing an expanding ring shows that half of V1 is dedicated to the fovea.

Question 33

How many degrees is our VF? How many degrees is the fovea?

Answer 33

2deg fovea, 160 deg VF.

Question 34

Explain ganglion cell density in retina. How much movement away from fovea in mm and deg causes what factor of ganglion cell density loss?

Answer 34

14mm away from fovea (50deg) causes 1/10. Or 1000. idk.

Question 35

What magnification factor cortex per degree do fovea cells have?

Answer 35

magnification factor of 1000.

Question 36

What happens when you think of fovea in V1 not in terms of cortex per degree but cortex per ganglion cell?

Answer 36

Wassle calculatied that per ganglion cell, there is no magnification. Just more ganglion cells.

Question 37

What’s a better measure of magnification? Whose study?

Answer 37

Cowey and Azzopardi. they put traver into V1, watch it go to LGN then retina. You inject to different places and see how many ganglions. For every sq mm of cortex, 3-6 times more ganglion in fovea than elswehere.

Question 38

Is increasing # of photoreceptors and ganglion cells in fovea sufficient for acuity?

Answer 38

It’s necessary but not sufficient. We need more visual cortex circuitry in fovea.

Question 39

Where does SC send axons to and what does this achieve?

Answer 39

Pulvinar complex in thalamus. Directs attention to visual targets.

Question 40

What happens when you drive an electrode in fovea representation in SC and stimulate? What does this tell us about SC?

Answer 40

You get a movement of eyes toward fovea. SC is sensory and motor.

Question 41

Obscure: What’s the accessory optic system?

Answer 41

3 nuclei, lateral/medial/dorsal terminal. Axons from contralateral retina. Innervate SC and premotor neurons. Cause microsaccades that correct for directional drift that stabilizes image on retina.

Question 42

Does the brain talk to the retina?

Answer 42

Yes. In humans a retinopetal axon exists. Releases serotonin. Function unknown.