Development of the Nervous System Flashcards Preview

MD1 Neuroscience > Development of the Nervous System > Flashcards

Flashcards in Development of the Nervous System Deck (89):
1

What are the main steps in the development of the nervous system?

Neural induction
Neurulation
Morphogenesis and patterning of neural tube
Neurogenesis
Neuronal migration
Axon growth and pathfinding, and dendritic arborisation
Synaptogenesis
Gliogenesis/myelination

2

Define neural induction

Assigning neural potential to region of early embryo

3

Define neurulation

Forming rudimentary nervous system

4

Define neurogenesis

Production of neurons and glia from precursor cells

5

Define neuronal migration

Neurons move from sites of production to positions in mature brain
Makes space for new neurons

6

Define synaptogenesis

Making and refining synaptic connections

7

In what stages of nervous system development does apoptosis occur?

Neurogenesis
Neuronal migration
Axon growth and pathfinding, and dendritic arborisation
Synaptogenesis
Gliogenesis/myelination

8

Which part of the embryo acquires a neural fate?

Region of dorsal embryonic ectoderm = neural plate

9

What forms from the neural plate?

Entire CNS

10

What happens to the rest of the ectoderm?

Acquires epidermal fate

11

What determines epidermal fate?

Local bone morphogenetic protein (BMP) signalling

12

What is the organiser region of the neural plate, and what does it do?

Intermediate marginal zone
Cells underneath programmed to secrete inhibitors that stop cells above from becoming epidermis - block BMP signal

13

What is a neurula?

An embryo that has undergone neural induction
Happens at 3 weeks

14

What is neurulation?

Formation of the neural tube

15

How is the neural tube formed?

Neural plate cells become more columnar
Elevation of neural folds
Neural folds fuse in dorsal midline
Neural tube pinches off from epidermis
Occurs all the way along the embryo

16

What is the inside of the neural tube, and what does it contain?

Ventricle
Contains fluid

17

In which direction does the neural tube zip up?

Bidirectionally from initial point of closure

18

Where are the two points of closure of the neural tube?

Hindbrain-cervical boundary
Forebrain-midbrain boundary

19

What causes neural tube defects?

Failure of neural fold formation or closure

20

What doesn't close in spina bifida?

Caudal neuropore

21

What doesn't close in anencephaly?

Cranial neuropore

22

What is the role of folate thought to be?

Enhancing cellular competency

23

Where do neural crest cells develop?

At neural plate margin

24

When do neural crest cells migrate?

When dorsal margins of tube fuse

25

Where do neural crest cells migrate?

From dorsal to ventral side

26

What do neural crest cells give rise to?

Dorsal root ganglia
Sympathetic ganglia
Adrenal medulla
Enteric NS ganglia
Melanocytes
Schwann cells
Cartilage and bone of face and jaw

27

What happens after the neural tube closes?

Primary and secondary brain vesicles form

28

Describe the primary and secondary brain vesicles

Wall = neuroepithelium
Fluid-filled central cavity = ventricular system

29

What are the three vesicles that form at the rostral end of the neural tube?

Prosencephalon = forebrain
Mesencephalon = midbrain
Rhombencephalon = hindbrain

30

What does the prosencephalon split into?

Telencephalon
Diencephalon

31

What does the rhombencephalon split into?

Metencephalon
Myelencephalon

32

What does the telencephalon give rise to?

Olfactory bulb
Cerebral cortex
Hippocampus
Striatum/basal ganglia

33

What does the optic vesicle give rise to?

Retina

34

What does the diencephalon give rise to?

Thalamus
Hypothalamus

35

What does the mesencephalon give rise to?

Midbrain

36

What does the metencephalon give rise to?

Pons
Cerebellum

37

What does the myelencephalon give rise to?

Medulla

38

What provides the different positional cues for specifying cell fate?

Gradients of morphogens from patterning centres or organising regions

39

What induces the roof plate?

Overlying ectoderm

40

What does the roof plate secrete?

Dorsalising morphogens

41

What induces the floor plate?

Underlying notochord

42

What does the floor plate secrete?

Ventralising morphogen

43

What cell types are derived because of the roof plate?

Interneurons
Oligodendrocytes

44

What cell types are derived because of the floor plate?

Motor neurons

45

How many layers does the neuroepithelial lining of the brain vesicles have?

1

46

Why do the neuroepithelial cells in the vesicles appear multi-layered?

Nucleus develops at ventral end
Cell extends processes dorsally
Nucleus moves up and down processes with different phases of cell cycle
Called interkinetic nuclear migration

47

Where are neuroepithelial cells and what do they give rise to?

In ventricular zone
Self-replicate
Give rise to radial glia

48

Where are radial glia and what do they give rise to?

In ventricular zone
Self-replicate, and give rise to intermediate progenitors and astrocytes = asymmetrical cell divisions

49

Where are the intermediate progenitors and what do they give rise to

In sub-ventricular zone
Give rise to neurons

50

What are radial glial cells?

Neural stem cells

51

What are symmetric divisions?

Produce two identical daughter cells
Expand neuroepithelial progenitor pool early
Give rise to two neurons late

52

What are asymmetric divisions?

Produce two different daughter cells
Radial glia divide and produce a radial glial cell and a differentiated neuron

53

What is the structural role of radial glia?

Provide scaffold for radial migration of neuron progeny

54

Where do the neuronal progeny of radial glia migrate to?

Away from ventricular zone towards pial surface of brain

55

What is the order of cortical layer formation?

Earliest form preplate
Preplate splits into marginal zone and subplate when first wave of cortical plate neurons arrive
Neurons of cortical plate assemble into layers II-VI in inside-out way
- Deepest layers first

56

Where are the stem cells of the adult brain?

At ventricle

57

What do stem cells of the adult brain produce?

Neurons for olfactory bulb

58

Where are cortical interneurons produced?

Basal forebrain

59

Along what do olfactory bulb neuroblasts migrate?

Rostral migratory stream

60

Where do cerebellar granule cell precursors originate>

Rhombic lip

61

What are some neuronal migration disorders?

Schizencephaly = clefts in brain
Lissencephaly = smooth brain
Agyria = lack of folds
pachygyria = thick folds
Polymicrogyria/microgyria = many/small folds
Neuronal heterotopia = other place, including band heterotopia = double cortex
Agenesis of corpus callosum
Agenesis of cranial nerves

62

What are some symptoms of neuronal migration disorders?

Vary
Poor muscle tone and motor function
Seizures
Developmental delay and impaired cognitive development
Failure to grow and thrive, and difficulties with feeding
Smaller than normal head

63

How is grey matter heterotopia formed?

Neurons fail to migrate from ventricle, or migrate halfway to cortical plate

64

What is the result of grey matter heterotopia?

Disorganised patches or bands of misplaced neurons

65

What is band heterotopia caused by?

DCX mutation on X chromosome

66

What happens in band heterotopia?

Neurons that fail to migrate accumulate below layer of white matter

67

How does a cobblestone cortex occur?

Neurons overshoot cortical plate and reside in layer I

68

Are neurogenesis and gliogenesis controlled by the same transcriptional programs?

No
They also inhibit each other

69

What occurs first: neurogenesis or gliogenesis?

Neurogenesis

70

What proportion of neurons are pyramidal?

80%

71

What do pyramidal neurons do?

Excitatory long-range projection neurons
Axons project to other cortical hemisphere or sub-cortical targets like spinal cord

72

What proportion of neurons are interneurons?

20%

73

What do interneurons do?

Mainly locally-projecting inhibitory neurons
Modulate cortical excitatory output

74

How does the dendritic arbor develop?

Basic plan genetically specified
Growth and branching influenced by environmental factors
- Local signals
- Contact-dependent
- Diffusible cues
- Active synapses

75

How do dendrites and axons grow?

Repulsion of outgrowing axon
Attraction of apical dendrite
Elongation/retraction and branching of apical/basal dendrites
Activity-dependent spine stabilisation

76

What controls the extent of the dendritic arbor?

Growth factors

77

Where does axon growth happen?

At the very motile tip of the neurite = growth cone

78

What do actin filaments do in growth cones?

Regulate shape and directed growth of growth cone

79

Where are these actin filaments in the growth cone?

Filopodia

80

What do microtubules do in the growth cone?

Provide structural support to axon shaft
Essential for axon extension
Help push growth cone forward

81

When do microtubules grow in?

After actin filaments stabilise

82

What sort of environmental guidance cues steer growth cones?

Gradient of long-range repellent and attraction
Contact adhesion and repulsion
Growth cone senses and integrates signals

83

What is the corpus callosum?

Largest fibre tract in brain
Formed by axons projecting to opposite hemisphere

84

What do axon guidance defects result in?

Complete or partial failure of corpus callosum to form

85

What are the symptoms of agenesis of the corpus callosum?

Variable severity
Sensory and motor deficits including:
- Vision impairments
- Low muscle tone
- Poor muscle coordination
- Delays in motor milestones
Cognitive disabilities; eg in:
- Complex problem solving
- Missing subtle social cues

86

When do gyri and sulci start to develop?

Seven months of gestation

87

What processes in brain development continue or happen after birth?

Axonal and dendritic outgrowth
Synapse formation
Myelination

88

What is the relative rate of development of excitatory and inhibitory synapses?

Excitatory synapses peak a lot earlier than inhibitory synapses develop

89

What does refinement of of synapses involve?

Connections originally overproduced
Performance improved by adjusting number, boundaries, and strength of connections through competitive process
Eg: poly- to mono-innervation at developing neuromuscular junction

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