07 Flashcards

1
Q

T/F: albino cats don’t have STEREO OR BINOCULAR FUSION

-WHY?!

A

TRUE! So all siamese cats are strabismic albinos! Albinism in warm parts of body

-Normally, R LGN processes info from L VF. In albino cats, R LGN processes ALL INFO from L EYE - because ALL FIBERS CROSS IN ALBINOS; not only the nasal ones!

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2
Q

Because almost all retinal fibers CROSS in albinos, there is effectively NO (ipsi/contra) LGN

-implications?

A

IPSI LGN - non-existent

-LGN receives all wiring from CONTRA eye –> entire visual field from contra eye is projected - NO binocularity possible!

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3
Q

How are albinos still able to function relatively well, even though they don’t have binocular fusion or stereopsis?

-when do all of these changes occur?

A

Fibers crossing corpus callosum (were supposed to die if normal) actually send out massive INHIBITORY signals –> acts as a SUPPRESSION mechanism.

Result: each side only responds to one half of the visual field - just like in nml cats!

  • half the cortex is thus always inhibited, but it’s better than being unable to localize objects in VF
  • PRENATALLY
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4
Q

Four findings that you’d expect to find in an albino patient:

A
  • reduced vision (20/80-20/200)
    • 2’ to reduced foveal pit, reduced rod-free zone/cone density
  • reduced stereo
  • strabismus
  • nystagmus (opposing signals)
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5
Q

T/F: vision can be 20/20 in an albino.

-how is this possible?

A

True

-most albinos have cone densities close to normal!

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6
Q

What will the nerve do in FISH/AMPHIBIA if:

  • it gets cut:
  • it gets crushed:
  • it gets cut and the eye is inverted:
  • the optic tectum is partially removed:
A
  • cut: quick atrophy, then regrowth to exact position
  • crushed: edema/inflamm, then regrowth to same connections
  • cut/inverted eye: ON has no idea - regrows to identical old position
  • tectum: entering axons reorganize to occupy what’s left
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7
Q

What happens if you implant a third eye in a frog?

A

It will send its extra ON to one of the optic tectums (which were receiving individual L and R fibers to each respective tectum)

-whichever tectum gets the fibers develops ocular dominance columns as seen in mammals

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8
Q

What happens if you cut the optic nerve of a mammal (cat)?

A

it does NOT regrow.

it MAY sprout axons to the abandoned optic nerve - note the flexibility

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9
Q

What’s the key factor if sprouting is to happen 2’ to a cut optic nerve (or enucleated eye) in a cat?

-How long after the nerve has been cut/eye enucleated IN HUMANS would it be before ganglion cell sprouting would cease? (ie, when is the START of the critical period in humans)?

A

TIMING!!! sprouting to abandoned LGN only likely to happen w/i 30 days of life (beginning of critical period in cats)

7 months - start critical period, so NO more sprouting can occur - must be some other mechanism to describe amblyopia!

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10
Q

What kind of drugs exist that may lead to retention of the dendritic tree after the ON is cut?

A

BDNF - brain-derived neural growth factor

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