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MSK 1!!! > Neurulation & Development of PNS > Flashcards

Neurulation & Development of PNS Flashcards

1
Q

what induces neurulation?

A

notochord (sitting in the mesoderm, below ectoderm)

starts at week 3

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2
Q

what is primary neurulation?

A

process of forming neural plate, then neural folds, then a neural tube

occurs in the part of the ectoderm directly on top of the notochord (the rest becomes surface ectoderm)

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3
Q

what is the neural groove?

A

anchors the neural plate (sits right along the center of it)

remains throughout all of neurulation

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4
Q

what days does primary neurulation occur during?

A

days 17-20

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5
Q

what direction does primary neurulation occur in?

A

starts in the cervical region

moves up over then head and down towards the lumbar region at the same time (like a zipper going in both directions)

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6
Q

what are the different layers that form during primary neurulation? (3)

A
  1. both sides of the neural plate meet - pinch off and form the neural tube
  2. neural crest cells (lateral to the groove) - both sides meet in the middle - pinch off and form neural crest cells (between surface ectoderm and mesoderm)
  3. surface ectoderm on both sides meet (most superiorly) and form a whole surface ectoderm layer
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7
Q

what signals the end of primary neurulation?

A

ends when the caudal neuropore closes (around somite 31)

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8
Q

what is secondary neurulation?

A

formation of neural tube in the sacral/cocygeal segments from the tail bud - eventually merges with the caudal neuropore

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9
Q

where does the tail bud come from?

A

forms during gastrulation

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10
Q

what are the steps that cause the tail bud to form into the neural tube?

A
  1. tail bud condenses to form the medullary cord (a solid mass)
  2. medullary cord caviate (forms a lumen)
  3. this lumen merges with the central canal of the neural tube
  4. lateral segments of the tail bud become somites
  5. neural crest cells form and migrate
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11
Q

how does the location of neural crest cells change during neurulation?

A

start lateral on the neural plate- end up dorsal to the neural tube

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12
Q

what transition do neural crest cells under go?

A

epithelial to mesenchymal transition (become migratory)

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13
Q

how do neural crest cells migrate?

A

migrate ventrally

can migrate before the neural tube closes or after then neural tube closes

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14
Q

what are important neural crest cell derivatives?

A

neural crest cells named by region: cranial, cardiac, trunk, sacral

  1. cranial - chin formation
  2. cardiac - septa between aorta and pulmonary trunk
  3. melanocytes, odontoblast, Schwann cells, ganglia, enteric nervous system, adrenal medulla
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15
Q

what are neurocristopathies? (3 examples)

A

group of diseases (effect depends on which neural crest cells are affected )

eg; head/neck -goldenhar syndrome, micrognathia, TCS

trunk - Hirschsprung (impacted megacolon)

melanocytes - piebaldism

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16
Q

what days does the first round of meninges formation occur during?

A

days 25-30

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17
Q

what do meninges develop from?

A

neural crest cells and mesenchyme

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18
Q

what is the mininx primordial?

A

primordial meninges - original layer of neural crest cells/mesenchyme that migrate around the spinal cord

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19
Q

what happens to the primitive mininx during days 34-48

A

splits into the ectomeninx and endomeninx

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20
Q

what does the ectomeninx form?

A

dura matter

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21
Q

what does the endomeninx form?

A

arachnoid/pia matter

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22
Q

what role do the vertebra play in meninges development?

A

vertebra form at the same time as the neural tube

neural crest cells migrate towards the vertebra, then mix with mesenchyme

eventually form circular structure around the closed neural tube

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23
Q

what changes does the ectomeninx undergo during days 45-60

A

the ectomeninx becomes compact and forms a dural Venus sinus

in the spinal region– it disassociates from the vertebral bodies in order to form the epidural space

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24
Q

what is the dural Venus sinus

A

drains cranial blood (formed by the ectomeninx)

25
Q

what happens to the endomeninx during days 45-60

A

the endomeninx becomes reticulated (forms a meshwork)

the subarachnoid space forms (arachnoid matter still keeps its connection to Pia matter)

26
Q

which part of the neural tube closes first?

A

closure occurs at various points along the neural tube

cranial closure is more advanced than caudal closure

27
Q

what forms when the neural tube closes?

A

cranial and caudal neural pores form

28
Q

what is necessary during pregnancy in order to prevent neural tube defects?

A

folic acid

29
Q

what are some examples of cranial neural tube deficiencies?

A

anencephaly/microencephaly (brain tissue open to amniotic fluid)
encephalocele
craniorachichisis (extends into the thoracic region)

30
Q

what is spina bifida occulta?

A

spinal neural tube defect

can be asymptomatic

vertebral arch does not form (but it is still covered by skin)

sx: skin pigment, hair tuft over section, dimple in sacral region (dermal sinus)

31
Q

what is meningocele?

A

spinal neural tube defect

no vertebral arch forms, some meninges are involved (spinal cord is not involved)

sx: protruding sac

32
Q

what is meningomyelocele?

A

spinal neural tube defect

similar to meningocele but spinal cord is involved as well (protrusion of sac and spinal cord)

33
Q

what is myeloschesis?

A

spinal neural tube defect

no lateral vertebral structures form

meninges and spinal cord are exposed
neural tube is not closed`

34
Q

what is the sulcus limitans?

A

divides dorsal and ventral portions of the neural tube

extends from 4th somite to caudal region

35
Q

what are the zones of the neural tube?

A

go laterally - from central canal out

ventricular zone
intermediate zone
marginal zone

36
Q

what is found in the ventricular zone of the neural tube?

A

stem cells that undergo mitosis - grow and divide and then move to the intermediate zone as neuroblasts

37
Q

what is found in the intermediate zone?

A

neuroblast cells that differentiate into:

  1. neurons (initial wave of growth of the spinal cord)
  2. glioblast (after enough neurons are made) - differentiate into macroglia (astrocytes/oligodendrocytes) or ependymal (needed for CSF)
38
Q

what is found in the marginal zone?

A

where white matter is formed

39
Q

how is the spinal cord organized?

how are these all organized : roof plate, floor plate, alar plate, basal plate, sulcus limitans, notochord

A

roof plate- centrally on the dorsal side

alar plate - 2, one on each side - forms dorsal region

sulcus limitans - separate alar and basal plates

basal plate - 2, one on each side - forms ventral side

floor plate - centrally on the ventral side

notochord - adjacent to floor plate

40
Q

which plates of the spinal plate have growth?

A

roof/floor - no growth (connect both alar plates and both basal plates together )

alar/basal plates- growth (establish sensory/motor processing)

41
Q

what does sonic hedge hog do in the neural tube?

A

causes neuron differentiation

increased SHH induces motor neuron differentiation

42
Q

how is the SHH gradient established? what is the effect of it?

A

ventral side has increased levels (closer to notochord) , dorsal side has decreased levels

ventral neurons differentiate into motor neurons
dorsal neurons differentiate into interneurons

43
Q

what type of neurons form first? motor or sensory?

A

motor neurons

closer to notochord

44
Q

where is BMP/TGFB released from?

A

roof plate

45
Q

where is SHH released from?

A

notochord

46
Q

what counters the effects of SHH?

A

BMP/TGF B (released from the opposite side of spinal cord - gradient runs in the opposite direction of SHH)

47
Q

what does BMP 4 do?

A

activate PAX 3/ PAX 7 (help process sensory from DRG)

48
Q

where are the lateral horns located?

A

intermediolateral column

most dorsal portions of the basal plate (closest to the sulcus limitans)

49
Q

where do SNS and PSNS motor neurons originate? (which spinal segments)

A

SNS: T1-L3
PSNS: S2-S4

50
Q

what fibers are in the spinal nerve?

A

sensory and motor mixed

51
Q

what fibers are in the spinal roots?

A

motor or sensory only

anterior - motor only
posterior - sensory only

52
Q

what fibers are in the rami?

A

mixed motor and sensory (based on location they are traveling to)

53
Q

what is the process of somatic motor neuron formation?

A

occurs first
starts In the ventral horn

passes through cranial sclerotome and forms the ventral root (anterior root) and goes out to the target musculature

54
Q

what are pioneer fibers?

A

the first somatic motor neurons that begin extending - spontaneously start forming

55
Q

what is the process of the autonomic nervous system formation?

A

fibers arise in the lateral horn - follow the same ventral (anterior) root that already exists (from somatic motor neuron formation)

2 chain pathway - leaves ventral root to synapse on synaptic chain–> then hops back on spinal nerve to go out to the body

56
Q

what gives rise to preganglionic neurons of the ANS ?

A

neuroectoderm

57
Q

what gives rise to post ganglionic neurons of the ANS ?

A

neural crest cells

58
Q

what is the process of sensory neuron formation?

A

starts in the DRG (outside the spinal cord)

extends in 2 direction - towards the spinal cord dorsal horn and outwards using the ventral root

meets the dorsal root at the spinal nerve and goes out to the body

MSK 1!!! (10 decks)

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