S1) Embryology of the Nervous System Flashcards

1
Q

Describe the five steps involved in the formation of the neural tube in early embryonic development

A

Gastrulation produces the notochord

Notochord induces neurulation

Neurulation induces the neural plate

⇒ Elevation of lateral edges of neural plate

⇒ Neural folds gradually approach each other in the midline and fuse, producing the neural tube

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2
Q

What is the role of the notochord during neurulation?

A

The notochord directs the conversion of the overlying ectoderm to neurectoderm

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3
Q

What is a neuropore?

A

A neuropore is a region corresponding to the opening of the embryonic neural tube in the anterior/posterior portion of the developing prosencephalon

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4
Q

Defects in closure of the neuropores underlie serious and common birth defects of the nervous system.

What are neural tube defects?

A
  • Neural tube defects are defects which result from failure of the neutral tube to close
  • Failure can occur caudally or cranially
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5
Q

What are the results of the following:

  • Cranial neural tube defect
  • Caudal neural tube defect
A
  • Cranial neural tube defect results in anencephaly
  • Caudal neural tube defect results in spina bifida
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6
Q

What is spina bifida?

A
  • Spina bifida is a type of neural tube defect occurring when the vertebrae don’t form properly around part of the baby’s spinal cord
  • It arises from the failure of neural tube closure caudally
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7
Q

Spina bifida can occur anywhere along the length of the spine.

What is the most common location?

A

Spina bifida most commonly occurs in lumbosacral region

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8
Q

What is anencephaly?

A

- Anencephaly is a neural tube defect resulting in the absence of cranial structures, including the brain

  • It results from the failure of neural tube closure cranially and is incompatible with life
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9
Q

What is rachischisis?

A

Rachischisis is a neural tube defect occuring due to the failure of neural fold elevation

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10
Q

How can one diagnose a neural tube defect?

A
  • Raised maternal serum α-fetoprotein
  • USS
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11
Q

How can a neural tube defect be prevented?

A

Folic acid pre-conceptually (3 month) and for the first trimester reduces incidence by 70%

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12
Q

Most of the length of the neural tube gives rise to the spinal cord.

In four steps, explain how the cauda equina forms

A

⇒ A 3 months, the spinal cord is the same length as the vertebral column

⇒ Thereafter, the vertebral column grows faster

⇒ The spinal roots must elongate in order to exit at their intervertebral foramen

Cauda equina is formed

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13
Q

During neural fold formation three primary brain regions can be distinguished.

Identify these primary brain vesicles

A
  • Embryonic forebrain (prosencephalon)
  • Embryonic midbrain (mesencephalon)
  • Embryonic hindbrain (rhombencephalon)
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14
Q

At 5 weeks of development, the three primary brain vesicles become five secondary brain vesicles.

Identify these

A
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15
Q

Identify the mature derivatives of the following secondary brain vesicles:

  • Telencephalon
  • Diencephalon
  • Mesencephalon
  • Metencephalon
  • Myelencephalon
A
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16
Q

How are flexures formed in the embryological development of the nervous system?

A

Growth & development at the cranial neural tube exceeds available space linearly, so it must fold up to form flexures

17
Q

Which two flexures are formed in the embryological development of the nervous system?

A
  • Cervical flexure
  • Cephalic flexure
18
Q

Where are the cervical and cephalic flexures located respectively?

A
  • Cervical flexure – hindbrain junction
  • Cephalic flexure – midbrain region
19
Q

What is the role of the ventricular system?

A

The ventricular system cushions the brain & spinal cord within their bony cases

20
Q

Compare and contrast the ventricular system in development and adults

A
  • In development, it is a tubular structure of the developing CNS persisting as development proceeds
  • In the adult, it is comprised of interconnected “reservoirs” filled by CSF, produced by cells of ventricular lining
21
Q

Relate the secondary brain vesicles to their corresponding ventricle in the ventricular system

A
  • Telencephalon → lateral ventricle
  • Diencephalon → third ventricle
  • Mesencephalon → cerebral aqueduct
  • Metencephalon & myelencephalon → fourth ventricle
22
Q

What is hydrocephalus?

A
  • Hydrocephalus is a condition characterised by excessive accumulation of fluid in the brain
  • Is is most common in newborns with spina bifida occur due to a blockage of the ventricular system e.g. tumour, infection
23
Q

How can hydrocephalus be treated?

A

Hydrocephalus is readily treatable by use of shunt

24
Q

Explain the early organisation of the neural tube by describing its three layers

A
  • Inner: neuroepithelial layer
  • Intermediate: mantle layer (neuroblasts)
  • Outer: marginal layer (processes)
25
What is the function of the roof and floor plates of the neural tube?
Roof & floor plates regulate **dorsal & ventral patterning**
26
Describe the modality of the alar and basal plates respectively
- Alar plate = **sensory** - Basal plate = **motor**
27
Describe the location and function of neural crest
- **Location**: cells of the lateral border of the neuroectoderm tube - **Function**: become displaced and enter the mesoderm and undergo epithelial to mesenchymal transition
28
Identify 8 neural crest derivatives in the nervous system
- Cranial nerve ganglia - Spinal root ganglia - Sympathetic ganglia (chain & pre-aortic) - Parasympathetic ganglia - Schwann cells - Glial cells - Leptomeninges (arachnoid & pia) - Connective tissue & bones of the face & skull
29
Identify 3 neural crest derivatives in the head, neck and midline
- Odontoblasts - Dermis (face & neck) - C cells of the thyroid gland
30
Identify 3 miscellaneous neural crest derivatives
- Conotruncal septum (heart) - Melanocytes - Adrenal medulla