Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

A BMS 381 - Developmental neurobiology > Making a map of 'things' > Flashcards

Making a map of 'things' Flashcards

1
Q

What is a map of ‘things’?

What kind of map?

A

Visual system

Spatial map - continuous information

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is a map of ‘not things’?

What kind of map?

A

Olfactory system

Discrete map - detect particular smells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What structure of the brain is the world mapped in?

A

The superior colliculus/tectum

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the difference between the superior colliculus and the tectum?

A

SC - in mammals

T - in lower vetebrates

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Where do the neurons from the different parts of the retina go to?

Why?

A

Nasal –> posterior part of tectum

Temporal —> anterior part of tectum

Because the lens flips the picture of the outside world, need to flip it back again

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Describe the stripe assay

What does it show?

A

Alternating strips of anterior and posterior tectum challenged with strips of retina from nasal to temporal

Shows:
Temporal axons avoid posterior stripes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Why do the temporal axons avoid the posterior tectum?

A

Posterior tectum makes an INHIBITORY factor that repels the temporal axons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What inhibitory factor is made by the posterior tectum that repels the inhibitory factor?

Describe them

A

Two different ephrins

MEMBRANE BOUND
NON-permissive factor

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

How are ephrins expressed in the tectum?

A

Gradient from posterior (HI) to anterior (LO)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are the receptors for ephrins?

A

Ephs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are ephs are how are they expressed in the retina and how?

A

Receptors for ephrin A2 and A5

In a counter gradient from temporal (HI) to nasal (LO)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How do you know the organisation of the axons in the tectum are due to the temporal axons avoiding a repellant factor made by the posterior tectum?

A
  • Activity is abolished in the posterior with heat treatment but NOT in the anterior
  • Posterior membrane cause growth cone collapse in vitro
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What happens in mice with ephrin A2 and A5 KO?

A

Temporal neurons project their axons to the posterior of the tectum and the topographic map is disordered

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

When KO ephrin A2 and A5 in rodents, what is unusual?

A

See a spotty distribution and see that NASAL axons are effected as well as temporal

Nasal neurons normally ignore ephrins

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Why, in the mouse, are nasal axons affected by the KO of ephrins, but in the chick/frog, they aren’t?

A

Different things occur in the mouse and other mammals compared to in the chick/frog

In the chick/frog:
- Axons initially go to where previously described (nasal - posterior, temporal - anterior)

In mice/other mammals:

  • Initial growth of ALL FIBRES through the tectum
  • Subsequent branching and synaptogenesis is what is sensitive to ephrins
  • More branching of the TEMPORAL axons towards the ANTERIOR, NASAL to POSTERIOR
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How does the branching in the mouse tectum occur?

How do temporal axons become localised to the anterior of the tectum?

A
  • Random competition between the axons for their synaptic partners (involving electrical activity)
  • Weaker synapses become eliminated

Temporal –> anterior
- Temporal have higher levels of eph receptors –> more sensitive to ephrins

  • Synapses made aren’t as good, don’t fire as well, get pruned back
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Why do temporal axons occur throughout the tectum in the mouse in a ephrin KO?

A

No competitive disadvantage, synapses are better, continue to compete throughout the tectum for synapses

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

How can electrical stimulation effect the response to guidance cues?

A

Can enhance or reverse the response to guidance cues

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What guidance cue response is enhanced using electrical stimulation?

A

Netrin

20
Q

What guidance cue response is reversed using electrical stimulation?

A

MAG

21
Q

What happens when electrically stimulate neurons in a low netrin concentration (which doesn’t normally turn growth cones)?

A

ENHANCES the response to netrin –> growth cones now turn

Causes SENSITISATION

22
Q

What happens when electrically stimulate neurons in the presence of MAG?

A

Reversal:

Turn when is initially REPULSION into ATTRACTION towards MAG

23
Q

Using the ratio of dye, what can be seen when electrical activity is applied to a neuron 10 pulses compared to 2 pulses?

A

Both have a rise in calcium but the rise after 10 pulses is more significant and sustained

24
Q

How does electrical stimulation affect cAMP?

How does this occur?

A

Increase cAMP

This increase is calcium dependant

25
Q

How does electrical stimulation of a neuron change how it responds to cues in the environment?

A

Electrical stimulation changes the CHEMICAL STATE oft eh cell

26
Q

What is refinement of axon connections dependant on?

A

ACTIVITY

27
Q

Describe the refinement of axons in the tectum of lower vertebrates (where initial map is topographic)

A
  • Initially overlap between the nasal and temporal projections
  • OVER TIME, overlapping contacts are lost and map becomes more precise

Refinement depends on ACTIVITY and COMPETITION between the axons

28
Q

What happens if block activity in the cortex?

A

Poor refinement of projections alternating between one eye or the other

Overlapping projections

29
Q

Cells that fire together..

A

…wire together

30
Q

What does the mechansim of synapse elimination involve?

A

Localised release of neurotrophic factors from 2 cells firing at the same time

31
Q

What is the neurotrophic factor released from cells firing together that strengthens their connection?

A

BDNF

32
Q

When does tectal mapping occur?

Why does this raise questions?

A

Happens before birth - before the animal encounters any light

Before encounter light - where does the electrical activity come from to? (electrical activity needed to create maps and refine axons)

33
Q

How does tectal mapping occur with no light?

How is this seen?

A

Retina become spontaneously active as axons reach the tectum
Hebbian principles already occuring?

Seen monitoring calcium levels using a dye

34
Q

What happens in the tectum if treat with TTX?

What is TTX?

A

TTX - sodium channel blocker

Blocks action potentials and therefore map refinement

35
Q

What happens in mice lacking beta2 subunit of nAChR?

What does this show?

A

Uncorrelated RGC activity
Unrefined topographic maps

Shows neural activity is required for map refinement

36
Q

What does enhanced retinal activity result in?

A

BDNF up regulation

37
Q

What does BDNF promote?

A

RGC axon branching in the tectum ONLY where the eph-ephrin interactions are low

38
Q

What does down regulation of Ephrin A5 cause?

A

Increased branching in the tectum

39
Q

What are the receptors for BDNF?

A

Trks

40
Q

How do Ephs and Trks interact?

What does the interaction between Ephs and Trks cause?

A

In a neutrophin-dependant manner

Reduced PI3K and Reduced branching

41
Q

Where are topographic maps and ephrin gradients used in the visual system

A

Tectum (superior colliculus)

MAMMALIAN RGCs

LGN

42
Q

Where does the LGN receive input from?
What does this allow?

How is this different to the tectum?

A

BOTH eyes
Allows INTEGRATION of vision

Tectum - info from ONE eye

43
Q

How are the inputs to the LGN arranged?

A

In layers

Alternative layers - alternated between the eyes

44
Q

How are the RGC axons mapped onto the LGN?

A

TOPOGRAPHICALLY using gradient of ephrins

Predetermined

45
Q

Describe the interaction between Trks and Ephrin A5 and how this is altered by Ephs (receptors)?

A

Trks and Ephrins interaction is dependant on neurotrophin

In the ABSENCE of Eph:
- Trk and ephrin A5 interation INCREASES PI3K and therefore branching

In the PRESENCE of Eph:

  • This abolishes the PI3K increase and branching
  • In CONCENTRATION DEPENDANT manner
46
Q

What is the PI3K pathway important in?

A

Branching/axon formation

A BMS 381 - Developmental neurobiology (17 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions