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MSK Exam I > Neurulation And Development Of The PNS > Flashcards

Neurulation And Development Of The PNS Flashcards

1
Q

What is ectoderm?

A

Neuroectoderm + surface ectoderm

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2
Q

What significant event happens at the beginning of week 3?

A

Notochord induces neuroectoderm to form the neural plate

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3
Q

What is neurulation?

A

Process by which the notochord and neuroectoderm are made physically and functionally distinct (formation of the neural tube)

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4
Q

What is primary neurulation?

A

Formation of general embryonic ectoderm into a neural plate -> lateral folding of the neural plate creates neural folds and a neural groove -> NT is formed by fusion of the neural folds and outer ectoderm

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5
Q

Where does neurulation start?

A

At the 5th somite

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6
Q

Gastrulation ends with what?

A

Formation of the tail bud (caudal eminence)

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7
Q

Primarily neurulation is complete with what?

A

Closure of caudal neuropore at somite 31 but the NT extends caudally into sacral and coccygeal regions

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8
Q

What is secondary neurulation?

A

Formation of the NT from the tail bud

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9
Q

What develops from the tail bud?

A

Caudal most NT, neural crest cells and somites

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10
Q

Describe secondary neurulation

A

Tail bud cells condense into a solid mass known as the medullary cord —> medullary cord cavitates forming a lumen —> merges with central canal of NT

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11
Q

What do NCC arise from?

A

The roof of the NT and are migratory

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12
Q

What happens when the lateral tail bud cells segments?

A

They form caudal somites

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13
Q

What does the caudal notochord grow into?

A

The sacral, coccygeal and tail regions

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14
Q

What are neural crest cells?

A

Neuroectodermal cells positioned along dorsal neural folds bilaterally along the entire cranial caudal NT

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15
Q

What process do NCC undergo?

A

Epithelial mesenchymal transition (EMT)

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16
Q

What happens to NCC when they undergo EMT?

A

Lose contacts and become migratory
Migrate ventrally from their dorsal positions along the length of the embryo
Give rise to numerous derivatives

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17
Q

List some NCC derivatives

A

Melanocytes, odontoblasts, Schwann cells
Spinal and autonomic ganglia
Enteric NS
Suprarenal (adrenal) medulla

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18
Q

What are neurocristopathies?

A

Defects in NCC

Ex. Goldenhar syndrome, micrognathia, TCS, Hirschsprung disease and piebaldism

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19
Q

What is Goldenhar syndrome (hemifacial macrosomia)?

A

A type of neurocristopathy characterized by incomplete development of the eyes, ears and nose on one side of the body

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20
Q

What is micrognathia?

A

A type of neurocristopathy in which a child has a very small jaw

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21
Q

What is TCS or mandibulofacial dystosis?

A

A type of neurocristopathy characterized by incomplete development of bones and tissue of the face

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22
Q

What is Hirschsprung disease?

A

A type of neurocristopathy that causes mega colon leading to difficulty passing a stool

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23
Q

What is piebaldism?

A

A type of neurocristopathy in which a person develops unpigmented or white patches of skin or hair
Due to a lack in melanocytes/NCC

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24
Q

What do the meninges develop from?

A

NCC and mesenchyme between 20-35 days

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25
Q

NCC and mesenchyme migrate and surround the NT to form what?

A

The primordial meninges (meninx primitiva)

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26
Q

What does the primitive meninx differentiate into?

A

The ectomeninx and endomeninx at approximately 34-48 days of development

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27
Q

What occurs between 45-60 days of development in regards to the ectomeninx of the meninges?

A

Becomes more compact and forms spaces for future venous sinuses (allows blood to drain from the CNS)

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28
Q

What occurs between 45-60 days of development in regards to the endomeninx of the meninges?

A

Becomes more reticulated and subarachnoid space/cisterns appear

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29
Q

The spinal ectomeninx dissociates from the vertebral bodies and gives rise to what?

A

The spinal epidural space which is essential for epidurals

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30
Q

True or false: Neural tube closure does not occur simulatanously with the length of the NT

A

True - cranial regions are more advanced than caudal regions (still undergoing gastrulation)

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31
Q

What is the result of the NT closure not occurring simultaneously with the length of the NT?

A

Results in the formation of the cranial and caudal neuropores

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32
Q

Where is NT closure initiated?

A

At several locations along the AP axis

33
Q

What are some examples of cranial neural tube defects?

A

Anencephaly, encephalocele, meroencephaly and cranioraschischisis
Due to the anterior neuropore failing to close

34
Q

What is anencephaly?

A

A cranial NTD characterized by absence of a major portion of the brain, skull, or scalp

35
Q

What is encephalocele?

A

A cranial NTD that can be with or without brain tissue
Characterized by a sac-like protrusion or projection of the brain and the membranes that cover it through an opening in the skull

36
Q

What is meroencephaly?

A

A cranial NTD that is a rare form of anencephaly characterized by malformed cranial bones leaving brain tissue open to amniotic fluid and stopping brain development

37
Q

What is cranioachischisis?

A

A cranial NTD in which the entire brain and spinal cord remain open

38
Q

What are the biggest factors causing NTDs?

A

Genetic, nutritional (especially folic acid intake) and environmental

39
Q

What are examples of spinal NTDs?

A

All a type of spina bifida including spina bifida occulta, meningomyelocele, meningocele and myeloschisis
Due to the posterior neuropore failing to close

40
Q

What is spina bifida occulta?

A

A type of spinal NTD in which the neural arch does not fuse

Characterized by a tuft of hair on the back and sx include back pain

41
Q

What is meningomyelocele?

A

A type of spinal NTD that involves protrusion of the meninges and spinal cord but remain covered

42
Q

What is meningocele?

A

A type of spinal NTD that involves protrusion of the meninges without spinal cord involvement (Tx = surgery)

43
Q

What is myeloschisis?

A

A type of spinal NTD (most severe) in which the meninges and spinal cord protrude
Nervous tissue is completely bare/uncovered

44
Q

What is the ventricular zone of the NT?

A

Stem cells positioned closest to the lumen of the tube
Cells divide and migrate
Will become ependyma

45
Q

What is the mantle/intermediate zone of the NT?

A

Migrating cells that undergo differentiation into neurons and/or glia
Extend axons away from the lumen toward the outer surface while cell bodies stay put
Becomes the gray matter

46
Q

What is the marginal zone of the NT?

A

Lacks neuronal cell bodies but contains axon bundles that will eventually be myelinated
Forms the white matter

47
Q

Which cell types arise from neuroectoderm during differentiation of the NT zones?

A

A polar neuroblast -> neuron
Glioblast -> macroglia or oligodendrocytes
Ependyma

48
Q

What significant event occurs at the end of the 4th week of development?

A

Mantle layer of the NT reorganizes into an alar (dorsal) plate and a basal (ventral) plate which are divided into these regions by the sulcus limitans

49
Q

What structure dorsally connects the right and left alar plates?

A

Roof plate

50
Q

What structure connects the left and right basal plates?

A

Connected ventrally by a floor plate

51
Q

True or false: alar and basal plates extend the entire length of the SC

A

True - then undergo differentiation due to signaling from roof and floor plates

52
Q

What is the nervous tissue composed of once the NT closes?

A

Germinal neuroepithelium that spans the full width of the NT from lumen/canal to outer surface and will give rise to a range of cell types in the brain and SC

53
Q

How does increased SHH concentrations direct neuron identity?

A

Induces motor neuron development

54
Q

How do decreased SHH concentrations direct neuron identity?

A

Multiple interneurons are induced

55
Q

Shh activates what downstream targets and for what type of neuron formation?

A

Shh activates Nkx2.2 and Nkx6.1 for ventral neuron formation

56
Q

What is the function of BMP/TGF-beta signaling?

A

Counteracts Shh gradient

57
Q

What does BMP4 activate?

A

Pax3 and pax7 which are responsible for induction of dorsal associated neurons

58
Q

Which type of neurons form first: motor or sensory?

A

Motor neurons form before sensory neurons

59
Q

What are interomedial columns?

A

The most dorsal cells of the basal plate that undergo segregation to form the interomedial columns —> eventually form the lateral horns

60
Q

What is T1-L3?

A

Visceral MNs of sympathetic division (ANS)

61
Q

What is S2-S4?

A

Visceral MNs of parasympathetic division (ANS)

62
Q

CNS derivatives form from what structure?

A

The neural tube

63
Q

What does the PNS develop from?

A

The neural tube including NCC, neuroectoderm and ectodermal placodes

64
Q

The PNS includes what type of neurons?

A

Sensory and motor (somatic and visceral) neurons of the head, trunk and extremities

65
Q

What do NCC and ectodermal placodes form in the PNS?

A

Sensory ganglia of the head

66
Q

What do neural crest cells alone form in the PNS?

A

Form sensory neurons on DRG, Schwann cells and ENS (trunk)

67
Q

Describe formation of the ventral root and the lateral horn

A

Axons exiting ventral horn pass through cranial sclerotome —> form ventral root —> ventral root then joined by axons from the lateral horn

68
Q

Describe the formation of the DRG and dorsal horn

A

Neural crest cells form the DRG sensory neurons —> axons then extend from the DRG —> dorsal horn is formed

69
Q

What is the two chain pathway of the ANS?

A

1st preganglionic neuron and fibers

2nd ganglionic neuron and postganglionic fibers

70
Q

When does development of the ANS occur?

A

During the 5th week

71
Q

What are preganglionic fibers of the ANS derived from?

A

Neuroectoderm

72
Q

What are ganglionic neurons of the ANS derived from?

A

Neural crest cells

73
Q

Describe the sympathetic division ganglia of the ANS

A

Trunk and collateral ganglia

74
Q

Describe ganglia of the parasympathetic division of the ANS

A

CN ganglia in the head and neck

Terminal ganglia in the trunk

75
Q

When does the anterior neuropore close?

A

Day 24

76
Q

When does the posterior neuropore close?

A

Day 26/27

77
Q

What does the ectomeninx form in the adult?

A

Dura mater

78
Q

What does the endomeninx form in the adult?

A

Arachnoid and pia mater

79
Q

Which nervous system cell is the only one derived from mesenchyme?

A

Microglial cells

MSK Exam I (34 decks)

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