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Phase 2 4. Neurology > Development of the CNS > Flashcards

Development of the CNS Flashcards

1
Q

What is neurulation?

A

Formation of the neural tube

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2
Q

When does neurulation occur?

A

during the third week of development

along with gastrulation during formation of trilaminar disc

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3
Q

Which germ layer gives rise to the central and peripheral nervous systems?

A

The ectoderm

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4
Q

Where does the notochord form from?

A

From the primitive node in the opposite direction of the primitive streak

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5
Q

What relationship does the notochord have with the ectoderm?

A

Inductive

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6
Q

What are the stages of development of the notochord?

A
  • tube extension
  • axial process
  • notochordal process
  • notochord
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7
Q

What germ layer is the notochord derived from?

A

The mesoderm

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8
Q

What does the notochord induce the ectoderm to do, once formed?

A

To thicken and form the neural plate

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9
Q

What cells make up the neural plate?

A

Neuroectoderm

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10
Q

What is formation of the neural plate a process of?

A

neurulation

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11
Q

What is the first thing to happen to the neural plate after formation?

A

The plate lengthens and the lateral edges elevate forming the neural folds

The depressed midregion forms the neural groove

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12
Q

How is the neural tube formed?

A

When the neural folds approach each other in the midline and fuse

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13
Q

What happens to the shape of the cells during neurulation?

A

The cells become more columnar in appearance

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14
Q

Which factors effect the bending of the neural plate?

A

> Intrinsic

  • cytoskeleton
  • stage of cell cycle

> Extrinsic
- adhesion points

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15
Q

Which hinge-points are present during neural plate bending?

A

The middle aspect becomes known as the medP) once the lateral edges begin to rise up

Dorsal-lateral hinge-points form in the dorsal lateral regions

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16
Q

What changes in the cells facilitate the tube formation in neurulation?

A

The cells at the hinge points become wedge-shaped and allow convergence

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17
Q

What are the four stages in neural tube formation?

A
  • shaping and folding
  • elevation
  • convergence
  • closure
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18
Q

What needs to be inhibited to allow for induction of the neural plate?

A

BMP-4

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19
Q

What needs to be promoted to allow for induction of the neural plate?

A

FGF

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20
Q

What does Chordin do?

A

Also acts to inhibit BMP-4

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21
Q

What does Noggin do?

A

Also acts to inhibit BMP-4

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22
Q

What cell adhesion molecule is expressed to regulate the formation of the neural tube?

A

Switching from E-cadherin to N-cadherin

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23
Q

What does N-cadherin do?

A

helps with the joining of the neural folds by allowing the teo ends of the folds to recognise each other.
also prevents fusion of the newly formed neural tube to the overlying ectoderm

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24
Q

What are the neural crest cells?

A

Temporary group of cells that are highly migratory

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25
Q

List the neural crest cell derivatives

A

These neural crest cells are destined to form the melanocytes in the skin and the hair follicles

Neural crest cells also go on to form dorsal root ganglia.
The cells can migrate in a ventral pathway through the anterior half of the somite and they form sensory ganglia, sympathetic neurons, Schwann cells, or adrenal medulla cells

The neural crest cells also migrate from the cranial end of the embryo before the neural tube is fully fused and contribute to the cranio-facial skeleton as well as neurons for the cranial ganglia, glia and melanocytes in this region

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26
Q

How does the neural tube fuse?

A

From the middle, and proceeds in cephalic and caudal directions simultaneously

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27
Q

What are the open ends of the tube called?

A

Anterior and posterior neuropores

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28
Q

What do the anterior and posterior neuropores connect with?

A

The overlying amniotic cavity

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29
Q

When does the anterior neuropore close?

A

By day 25

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30
Q

When does the posterior neuropore close?

A

By day 27

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31
Q

Which cells are found in the walls of the neural tube?

A

The walls of the newly closed neural tube consist of neuroepithelial cells, which extend over the entire thickness of the neural tube.

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32
Q

Describe the histology of the neural tube

A

Thick pseudostratified epithelium

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33
Q

What cells doe the neuroepithelial cells give rise to?

A

neuroblasts

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34
Q

What are the features of neuroblasts?

A

Large round nuclei

Pale nucleoplasm and dark stained nucleoli

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35
Q

What are neuroblasts?

A

Primitive nerve cells

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36
Q

What do the neuroblasts form?

A

The mantle layer and marginal layer of the spinal cord

37
Q

What is the mantle layer of the spinal cord?

A

The zone around the neural epithelial layer that will go on to form the grey matter of the spinal cord

38
Q

What is the marginal layer?

A

The outer layer of neuroblasts, consisting of nerve fibers emerging from the mantle layer

As a result of myelination, this will go on to be white matter

39
Q

What happens to the neural tube after neuroblast formation?

A

Differentiation of the neural tube wall in the ventral and dorsal aspects

40
Q

What are the basal plates?

A

The ventral aspect thickening of the neural tube wall

41
Q

What is derived from the basal plates?

A

The motor area of the spinal cord

42
Q

What are the alar plates?

A

The dorsal aspect thickening of the neural tube wall

43
Q

What is derived from the alar plates?

A

The sensory area of the spinal cord

44
Q

What is the sulcus limitans?

A

A longitudinal groove marking the boundary between the basal and alar plates

45
Q

What is the dorsal mid-line plate called?

A

The roof plate

46
Q

What is the ventral mid-line plate called?

A

The floor plate

47
Q

What is the function of the floor and roof plates?

A

Serve primarily as pathways for nerve fibers to cross from one side of the spinal cord to the other

Do not contain neuroblasts

48
Q

What is the function of the floor and roof plates?

A

Serve primarily as pathways for nerve fibers to cross from one side of the spinal cord to the other

Do not contain neuroblasts

49
Q

What structure develops in addition to the dorsal and ventral horns?

A

The intermediate horn

50
Q

What is the intermediate horn responsible for?

A

Contains sympathetic neurons from the ANS

51
Q

Which regions is the intermediate horn found?

A

The thoracic and upper lumbar regions of the spinal cord

52
Q

What structures develop following the development of dorsal and ventral horns?

A

The ventral fissure and the dorsal median septum

53
Q

When do motor nerve fibers first appear?

A

Week 4

54
Q

Where do motor nerve fibers arise from?

A

The nerve cell bodies present in the basal plate of the ventral horn

55
Q

What are ventral nerve roots?

A

The outgrowing motor axon fibers that collect into bundles and extend into the periphery

56
Q

Where are the nerve cell bodies of the sensory fibers found?

A

In the dorsal root ganglia

57
Q

Where do the dorsal root ganglia arise from?

A

The neural crest cells that have migrated to this area

58
Q

Where do the nerve fibers found in the dorsal horn stem from?

A

The processes are formed within the dorsal root ganglion and form bundles that grow into the dorsal horn

59
Q

Where do the peripheral sensory nerve fibers stem from?

A

The processes are formed within the dorsal root ganglion and form bundles that protrude out to the periphery

60
Q

What fibers are found in spinal nerves?

A

Sensory and motor

61
Q

How many brain vesicles are present at week 3?

A

3

62
Q

What are the three primary brain vesicles?

A

Forebrain - prosencephalon
Midbrain - mesencephalon
Hindbrain - rhomencephalon

63
Q

What are the derivatives of the prosencephalon?

A

Forebrain

  • Telencephalon = cerebrum
  • Diencephalon = eye, thalamus, hypothalamus and epithalamus
64
Q

What are the derivatives of the mesencephalon?

A

Midbrain

65
Q

What are the derivatives of the rhombencephalon?

A

Hindbrain

  • Metencephalon = pons, cerebellum
  • myelencephalon = medulla oblongata
66
Q

How many brain vesicles are present at week 5?

A

5 secondary vesicles

67
Q

What are the 5 secondary vesicles?

A
  • telencephalon
  • diencephalon
  • mesencephalon
  • metencephalon
  • myelencephalon
68
Q

Which cells form the meninges?

A

The meninges develop from the mesenchymal cells and neural crest cells

69
Q

During what time period does the meninges form?

A

day 20-35

70
Q

How is the dura mater formed?

A

The mesenchymal cells and neural crest cells migrate to surround the tube forming an external layer that forms a membrane called the dura mater

71
Q

How is the arachnoid mater formed?

A

The neural crest cells migrate to surround the tube forming an internal layer that forms the arachnoid mater

ONLY FORMED FROM NEURAL CREST CELLS

72
Q

How is the pia mater formed?

A

The neural crest cells migrate to surround the tube forming an internal layer that forms the pia mater

ONLY FORMED FROM NEURAL CREST CELLS

73
Q

How is the subarachnoid space formed?

A

When the small spaces fill with CSF and coalesce to form larger spaces

74
Q

Where is CSF made?

A

Produces in the choroid plexus in the brain ventricles

75
Q

Where does the choroid plexus form?

A

Where the pia mater and the ependyma come into direct contact
- mainly in the roof of the 4th ventricle

76
Q

Which disorders result from the failure or incomplete closure of the neural tube?

A
  • anencephaly

- spina bifida

77
Q

What is anencephaly?

A
  • failure of closure in the anterior neuropore
78
Q

What is spina bifida?

A
  • failure in closure of the posterior neuropore
79
Q

How may neural tube defects be prevented?

A
  • folic acid supplementation
80
Q

What are the different forms of spina bifida?

A
  • spina bifida occulta
  • meningocele
  • myelomeningocele
81
Q

Describe spina bifida occulta

A
  • mildest form
  • the outer part of the vertebrae is not completely closed
  • no protrusion of the spinal cord
  • sometimes the only indication is a small tuft of hair or dimple
82
Q

Describe meningocele

A
  • least common form of spina bifida
  • vertebrae form normally
  • the meninges protrude through gaps of the vertebrae
83
Q

Describe myelomeningocele

A
  • most serious form
  • whole are involved in te lesion has a flattened plate like mass of nervous tissue
  • no overlying protective membrane protruding from the spinal cord
  • associated nerves at the site of the lesion are damaged or do not form properly => loss of sensation or paralysis
  • the more cranial the defect the more serious loss of function will be
84
Q

What is hydrocephalus?

A
  • water on the brain
  • associated with spina bifida
  • large head shape
  • cerebral anomaly
  • raised pressure
85
Q

What is anencephaly?

A

an absence of a major portion of the skull and scalp

Normally the telencephalon structures that fail to form when this condition is present
- The cerebral hemispheres do not develop
Normally not compatible with life longer than a few hours after birth

86
Q

How is hydrocephalus treated?

A

relief of intracranial CSF pressure by shunting fluid

87
Q

What is spina bifida cystica

A

meningocele

88
Q

How does raised ICP occur in spina bifida cystica?

A

CSF builds up in head due to obstruction of the foramen magnum by the cerebellum

  • CSF gets trapped
  • = raised ICP

Phase 2 4. Neurology (29 decks)

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