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NHB > Neurons > Flashcards

Neurons Flashcards

1
Q

What embryological structure gives rise to the CNS?

A

Neural tube

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2
Q

What forms the neural tube?

A

Notochord induces overlying ectoderm to form neural tissue

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3
Q

What gives rise to the PNS?

A

Neural crest

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4
Q

What is neurulation?

A

Folding of neural plate to form closed neural tube

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5
Q

Give two examples of neural tube defects

A
  1. Spina bifida

2. Anencephaly

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6
Q

What establishes cell identity along the A-P axis of the neural tube?

A

Hox genes

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7
Q

What is the Hox code?

A

Unique pattern of Hox gene expression in cells of the neural tube

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8
Q

What do Hox genes encode?

A

Transcription factor proteins that bind DNA and regulate transcription of other genes

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9
Q

What are signalling centres?

A

Act as organisers by secreting growth factors

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10
Q

What does the midbrain/hindbrain boundary (isthmus) secrete?

A

FGF8

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11
Q

What does FGF8 do?

A

Induces special fates in adjacent neural tissue dorsally

Midbrain tectum anteriorly

Cerebellum posteriorly

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12
Q

What does ventral neural tissue adjacent to isthmus generate?

A
  1. Dopamine neurons of substantia nigra

2. Cranial nerve motor neurons III + IV

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13
Q

How does the notochord induce the neural tube floorplate?

A

Secretion of Sonic hedgehog (Shh)

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14
Q

What patterns the dorsal-ventral axis of the spinal cord?

A

The floorplate of the neural tube

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15
Q

What do the highest concentrations of Shh induce?

A

Floorplate

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16
Q

What do lower concentrations of Shh induce?

A
  1. Motor neurons

2. Suppress dorsal spinal cord neuronal phenotypes

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17
Q

What is the ventricular zone?

A

Where multipotent stem cells of the neural tube divide

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18
Q

What do stem cells of the neural tube form?

A
  1. Neurons

2. Radial glia

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19
Q

What is the role of radial glia?

A

Provide a scaffold for neuroblast migration

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20
Q

What is the fate of neuronal stem cells?

A
  1. Disappear - differentiate into astrocytes

2. Persist in olfactory bulb and dentate gyrus cells of hippocampus

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21
Q

When does production of neurons cease?

A

Infancy

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22
Q

What do neural crest cells generate?

A
  1. Dorsal root ganglia
  2. Autonomic ganglia
  3. Schwann cells
  4. Adrenal medulla chromaffin cells
  5. Enteric neurons
  6. Melanocytes
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23
Q

What gives rise to head mesenchyme and skeleton?

A

Neural crest cells

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24
Q

What is a growth cone?

A

Guides axon to the right place

Navigates using actin/myosin interaction to promote cell motility

Heads forwards as long as it has a suitably adhesive substrate and is not deflected

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25
Q

What regulates growth cone progress?

A
  1. Adhesion

2. Signalling

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26
Q

What are neurotroPic factors?

A

Attractive

Promote chemotaxis of growth cone

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27
Q

What are neurotroPHic factors?

A

Nourishing

Promote survival and sprouting of neurons

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28
Q

Give two examples of diffusible/attractive factors

A
  1. Nerve growth factor (NGF)

2. Netrin

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29
Q

What is NGF?

A

Nerve growth factor

Member of neurotrophin family

30
Q

Give two examples of diffusible/repellent factors

A
  1. Semaphorins

2. Slit

31
Q

What are contact/attractive factors?

A

Cell adhesion molecules

32
Q

What do growth cone CAMs adhere to?

A
  1. Large proteins in extracellular matrix
  2. Same CAM on neighbouring cell
  3. Another CAM on neighbouring cell
33
Q

What is homophilic adhesion?

A

Growth cone CAMs adhering to same CAM on neighbouring cell

34
Q

What is heterophilic adhesion?

A

Growth cone CAMs adhering to different CAM on neighbouring cell

35
Q

What do CAMs connect to intracellularly?

A
  1. Cytoskeleton

2. Cytoplasmic signal transducers eg. tyrosine kinases

36
Q

What large proteins in extracellular matrix might CAMs adhere to?

A
  1. Laminin

2. Fibronectin

37
Q

Give three examples of contact/repellent factors

A
  1. Semaphorins
  2. Ephrins
  3. Some proteoglycans
38
Q

What attracts spinal cord axons to the floorplate?

A

Netrin

39
Q

Where do commissural axons come from?

A

Dorsal neurons

40
Q

What do the commissural axons give rise to once they decussate at the floorplate?

A

Future spinothalamic tract

41
Q

What do floorplate molecules direct growth cones to do whilst crossing?

A
  1. Turn rostrally
  2. Become insensitive to netrin
  3. Become more sensitive to inhibition so that they don’t cross back
  4. Change CAM expression
42
Q

What CAM change leads to fasciculation of commissural axons?

A

TAG-1 replaced by L1-CAM

43
Q

What causes temporal retina axons to avoid posterior tectal membranes?

A

Gradient of contact-repellent ephrin ligand

44
Q

What causes generic synapse formation?

A

Synapse-specific adhesion molecules on axons and dendrites

Recruit specific pre- and post-synaptic protein complexes

45
Q

What causes activity-dependent selection of synapses?

A
  1. Long-term potentiation

2. Long-term depression

46
Q

How can the final number of neurons be changed?

A
  1. Increased by transplanting extra limb

2. Decreased by amputation

47
Q

What is the result of loss of NGF in the embryo?

A
  1. Loss of all sympathetic neurons

2. Loss of many sensory ganglion neurons

48
Q

What is the receptor for target-derived NGF?

A

TrkA at the axon terminal

49
Q

What is the role of target-derived NGF?

A
  1. Prevents expression of target cell death programme (apoptosis)
  2. Maintains neuron survival
  3. Promotes axon sprouting
  4. Chemotactic
50
Q

What are the insulin-like neurotrophins?

A
  1. NGF
  2. BDNF
  3. NT3
  4. NT4
51
Q

What is GDNF?

A

Supports dopamine neurons of substantia nigra and some motor neurons

52
Q

What is Hebb’s rule?

A

Long term potentiation

‘Fire together, wire together’

Selection of correlated input

53
Q

Where is long term potentiation found?

A

Hippocampus

54
Q

Which receptors are involved in long-term potentiation?

A

NMDA receptors

55
Q

What occurs to the distal axon stump following crush/cut?

A

Wallerian degeneration

Both axon and myelin degenerate

56
Q

What occurs to the nerve cell body following nerve damage?

A

It survives

Reacts by re-expressing genes for axonal growth

57
Q

What condition is required for proximal stump axons to regenerate?

A

Endoneurial tube of living Schwann cells present to guide them

58
Q

What is a neuroma?

A

Local swelling that axons sprout into when the break is greater than 1cm

May produce intractable pain

59
Q

What is the maximum distance CNS axons can regenerate?

A

1mm

60
Q

Why is the mature CNS environment non-permissive for axon growth?

A
  1. ECM lacks growth-promoting molecules such as laminin
  2. Oligodendrocytes and CNS myelin express proteins that inhibit axon growth such as Nogo
  3. Astrocytes proliferate and produce growth-inhibitory chondroitin sulphate proteoglycans in brain ECM
61
Q

What is Nogo?

A

Neutralising antibody that reduces oligodendrocyte inhibition

62
Q

What is a glial scar?

A

Densely interwoven tissue formed by astrocytes following brain injury

Causes growing axons to stop

63
Q

What is NT3?

A

Neurotrophic factor for corticospinal neurons

64
Q

How does ischaemic injury, such as stroke, damage neurons?

A

Excitotoxic

Increased intracellular calcium damages/kills neurons

65
Q

What are neural stem cells?

A

Multipotent cells that divide to self-renew and produce differentiating cells with various phenotypes

66
Q

What are progenitor cells?

A

Cells that can divide but only produce cells of defined cell types

67
Q

Where are neural stem cells located in the fetal brain?

A

Ventricular and subventricular zone

68
Q

What are dentate gyrus granule cells involved in?

A
  1. Learning

2. Antidepressant drug action

69
Q

Where do new neurons for olfactory bulb come from?

A

Subventricular zone and anterior horn of lateral ventricle

70
Q

How are induced pluripotent stem cells obtained?

A

From differentiated cell types

Transfection with genes for four stem cell transcription factors

Provide patient-specific source of stem cells

NHB (17 decks)

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