Session 1 - Embryrology of the CNS

Question 1

Why is the nervous system so suspect to damage during its development?

Answer 1

• Due to the sheer length of time it takes to develop

Question 2

How is the notocord formed?

Answer 2

When a solid core of pre-notochordal derived cells migrates from the primitive pit cephalically

Question 3

What three things does formation of the notocord drive?

Answer 3

Formation of

• Midline
• The axial skeleton
• The neural tube

Question 4

What is neurulation?

Answer 4

Process whereby the neural plate forms the neural tube

Question 5

How is neurulation initiated?

Answer 5

When the overlying ectoderm differentiates to form the neural plate;

Question 6

How does the neural plate form the neural tube?

Answer 6

It thickens and its lateral edges rise up, while the midline depresses (forming the neural groove).
The lateral edges approach each other at the midline to form the neural tube.

Question 7

Where does fusion of the neural plate to form the neural tube begin, and in what direction does it proceed?

Answer 7

Begins in the cervical region and proceeds in the cranial and caudal directions.

Question 8

What are neuropores?

Answer 8

Openings in the two ends of the neural tube.

Question 9

What does a defect in fusion of neural tube form?

Answer 9

Neural tube defects

Question 10

What does failure of the neural tube to close caudally cause?

Answer 10

Spina bifida

Question 11

Failure to close crainially?

Answer 11

Anecephaly

Question 12

Define spina bifida

Answer 12

Failure of caudal fusion of the neural tube

Question 13

Where does spina bifida usually occur?

Answer 13

In the lumbosacral region

Question 14

What deficits are usually associated with spina biffida?

Answer 14

• Neurological deficits

- Hydrocephalus

Question 15

Why does hydrocephalus occur in spina bifida?

Answer 15

Lengthening of vertebral column causes the cerebellum to be pulled into the magnum foramen, cutting of the CSF

Question 16

What are the two main types of spina bifida?

Answer 16

Spina bifida occulta

Spina bifida cystica

Question 17

What is spina bifida occulta?

Answer 17

A defect in the vertebral arches whereby there is a lack of fusion of the vertebral arches. Cyst formation in the subarachnoid space, but no herniation of spinal cord

Question 18

What is spina biffida cystica?

Answer 18

A severe NTD where neural tissue and/or meninges protrude through the skin to form a cyst like sac.

Question 19

What is a meningocele?

Answer 19

If only fluid-filled meninges are in the sac in spina bifida cystica

Question 20

What is a meningomyelocele?

Answer 20

If neural tissue AND menignes are in the cyst in spina bifida cystica

Question 21

How does anencephaly occur?

Answer 21

failure of the cranial neuropore to close properly, resulting in an absence of brain structures, including the brain, so is incompatible with life.

Question 22

What is rachischisis

Answer 22

• Rachischisis occurs when the neural folds do not elevate but remain as a flattened mass of neural tissue. Vertebrae do not fuse, leaving the neural tube exposed.

Question 23

Give two ways neural tube defects can be detected?

Answer 23

Through raised serum α-fetoprotein or on USS

Question 24

How can NTD be prevented?

Answer 24

Increased folic acid intake before and during the first trimester has been known to reduce incidence by 70%.

Question 25

How does the spinal cord change during development

Answer 25

At three months spinal cord is same length as the vertebral column, but in an adult is much shorter

Question 26

Where does the spinal cord end in the adult?

Answer 26

L1/L2

Question 27

Where are lumbar punctures usually taken?

Answer 27

L3/L4

Question 28

What is the area of the spine called where lumbar punctures take place?

Answer 28

Cauda equina

Question 29

What are the three primary brain regions during neural fold formation?

Answer 29

- forebrain (prosencephalon) - midbrain (mesencephalon) - hindbrain (rhombencephalom).

Question 30

What are the five secondary brain vesicles known as?

Answer 30

telencephalon, diencephalon, mesencephalon, metencephalon, myelencephalon.

Question 31

What two secondary brain vesicles does the prosencephalon form?

Answer 31

Telencephalon | Dieencephalon

Question 32

What secondary brain vesicles does the mesencephalon form?

Answer 32

Mesencephalhon

Question 33

What does the rhombencephalon form?

Answer 33

Metencephalon and myelencephalon

Question 34

Give the adult brain equivalents for these developmental pre-cursors Telencephalon

Answer 34

Cerebral hemisphere

Question 35

Give the adult brain equivalents for these developmental pre-cursors Diencephalon

Answer 35

Thalamus

Question 36

Give the adult brain equivalents for these developmental pre-cursors Mesencephalon

Answer 36

Midbrain

Question 37

Give the adult brain equivalents for these developmental pre-cursors Metencephalon

Answer 37

Pons & Cerebellum

Question 38

Give the adult brain equivalents for these developmental pre-cursors Myelencephalon

Answer 38

Medulla Oblongata

Question 39

Why does the brain form flexures?

Answer 39

Because the cranial end of the neural tube undergoes such rapid enlargement

Question 40

Where are the two flexures of the brain?

Answer 40

Cervical flexure at the spinal cord hindbrain junction and a cephalic flexure at the meidbrain region

Question 41

What is the ventricular system of the brain?

Answer 41

Acts as a reservoir of CSF, cushioning the brain and spinal cord within their bony cases

Question 42

What are two reasons for the formation of hydrocephalus?

Answer 42

Can result if there is blockage of the ventricular system or impaired absorption of CSF fluid

Question 43

What are the three layers of the neural tube, from inside to out?

Answer 43

- Neuroepithelial layer - Intermediate layer (neuroblasts) - Marginal layer (processes)

Question 44

Where do neural crest cells come from?

Answer 44

Cells of the lateral border of the neuroectoderm tube become displaced and enter the mesoderm and undergo epithelial to mesenchymal transition.

Question 45

What is the role of neural crest cells?

Answer 45

They have an input in a large number of different structures’ development, such as adrenal medulla, Schwann cells, or C cells of the thyroid gland.

Question 46

Why do neural crest cells mess people up so often?

Answer 46

Their migration is particularly sensitive to environmental and genetic insult

Question 47

Outline a disease of neural crest cells

Answer 47

Hirschsprung’s Disease Hirschsprung’s Disease (or congenital aganglionic megacolon) is a disorder of the gut which is caused by the failure of the neural crest cells to migrate completely during fetal development of the intestine. The affected segment of the colon fails to relax, causing an obstruction.