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Flashcards in AF - Mechanisms of circuit formation Deck (43)
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1
Q

How many connections are in the brain?

A

10^14

2
Q

What was Weiss’s hypothesis about the connectivity in adults?

A
  • Random connections and diffuse neuronal outgrowth occurs to all targets
  • Followed by elimination of non-functional connections
  • Activity of the neuron reinforces connection
3
Q

When did Weiss state his hypothesis?

A

1928

4
Q

What was Sperry’s hypothesis about the connectivity in adults?

A

CHEMOAFFINITY HYPOTHESIS

  • Directed and specific axon outgrowth occurs through axons, following “individual identification tags” carried by “cells and fibres” of the embryo
  • Chemicals are followed by growth cones
5
Q

When did Sperry state his hypothesis?

A

1939

6
Q

What is the superior colliculus termed in the Xenopus?

A

The tectum

7
Q

When an object is seen, what happens as the image passes through the lens?

A

It is flipped, so that on the retina, the image is upside-down and back to front

8
Q

How is the upside-down image on the retina flipped the correct way again?

A

The connections from the retina are organised so that:

  • The axons from the nasal side of the retina (more ANTERIOR) go to the POSTERIOR of the tectum
  • The axons from the temporal side of the retina (more POSTERIOR) for the ANTERIOR of the tectum
  • There is a graduation of axons, corresponding topological mapping of the retina in the tectum, forming a fine map
9
Q

What was the experiment done by Sperry to show that his hypothesis was correct?

A
  • Cut optic nerve and removed temporal part of the retina (so that ONLY nasal axons can grow back)
  • The regrowing nasal axons grew through but ignored the territory of the temporal axons
  • He also ablated the edges of both the nasal and temporal neurons retina, only leaving the central retina
  • Neurons grew back
  • Shows that the mapping of the retinal ganglion in the tectum was graded
10
Q

What would happen to the nasal neurons in Sperry’s experiment, if Weiss was correct?

A

The nasal neurons would grow everywhere and then be ‘pruned’ back

11
Q

What did Sperry’s experiments show and not show evidence for?

A
  • Neuron growth during axon regeneration

- Not what happens in the developing embyro

12
Q

In regards to axon outgrowth, what happens in the embryo?

A
  • Patterns of axon outgrowth which is highly organised. reproducible and stereotyped
  • In the mouse, drosophila, zebrafish and human
13
Q

What experiment was done to test if a specific neuron knew where to grow?

What was the control for this experiment?

A
  • Reverse part of the spinal cord between T7-LS3 and see if the axons still know where to grown
  • The motor axons still knew where to find their way to their muscle targets
  • Showing that axons navigate to their targets and different neurons know where to send their axons

Control: Taking out this part of the spinal cord and putting it back in the same way

14
Q

What are guidance cues?

A

Factors in the environment of a neuron which axons use to find their correct targets

15
Q

What is a growth cone?

A

The growing tip of the axon which senses guidance cues in the environment

16
Q

Who proposed the growth cone?

A

Cajal

17
Q

Why were insects used to identify the location of guidance cues?

A
  • Relatively simple nervous system
  • Easy to observe and manipulate
  • Can ablate the cells using lasers (in grasshoppers)
18
Q

What did Corey Goodman discover?

A

In the grasshopper, identified almost every neuron in the embryonic nerve cord and draw a map of axon projections

19
Q

How are development pathways in embryos the same?

A

s

20
Q

Where can guidance cues be found?

A

s

21
Q

What happens when a growth cone encounters an axon?

A

s

22
Q

What is the ‘labelled pathway hypothesis’?

A

s

23
Q

Where are subplate neurons found and what neurons do they provide scaffold for?

How is this proved?

A

s

24
Q

What do pioneer neurons supply for follower neurons and how?

A

s

25
Q

How do the pioneer axons find their way to the target in an apparently ‘featureless’ environment?

A

s

26
Q

What are the characteristics of pioneer axon pathways?

What do their growth cones do?

A

s

27
Q

In the grasshopper limb, what happens to the Ti1 (pioneer) growth cone?

A

s

28
Q

What happens in the grass hopper limb when Cx1 cell is ablated?

A

s

29
Q

Where is Cx1 present in the grasshopper limb?

A

s

30
Q

Does Cx1 have any obvious morphological features?

A

s

31
Q

What happens when ‘stepping stones’ or ‘guidepost cells’ are ablated?

A

s

32
Q

Where do the molecular differences in the environment come from, which guide pioneer axons to the correct place?

A

s

33
Q

What pathways do axon tracts in the forebrain do?

A

s

34
Q

What defines particular regions of the brain?

A

s

35
Q

What pathways do axon tracts in the hindbrain do?

A

s

36
Q

How is the hindbrain compartmentalised?

A

s

37
Q

What pathways do axon tracts in the spinal cord do?

A

s

38
Q

What are the 4 forces of axon guidance and describe them?

A

s

39
Q

Where are axon cues located?

A

s

40
Q

in the grasshopper limb, what suggests that axon guidance cues can be attractive?

A

s

41
Q

In the grasshopper limb, what suggests that axon guidance cues can be repulsive?

A

s

42
Q

What type of guidance is used by guidepost cells and how?

A

s

43
Q

How does contact attaction/repulsion occur?

A

s