Session 1: Development of the Central Nervous System

Question 1

Explain how neural tube defects come about.

Answer 1

Result from a failure of the neural tube to close.

Question 2

How can the failure of the neural tube to close differ?

Answer 2

The failure can occur caudally or cranially.

Question 3

Cranial defect

Answer 3

Anencephaly

Question 4

Caudal defect

Answer 4

Spina bifida

Question 5

Explain Spina bifida

Answer 5

Failure of the neural tube to close caudally.

It can occur anywhere along the lenght of the spinal cord but is most common in the lumbosacral region.

Question 6

Complications of Spina bifida.

Answer 6

Neurological deficitis occur and almost always hydrocephalus will occur.

Cognitive delay is not common.

Question 7

What is hydrocephalus?

Answer 7

Accumulation of CSF in ventricular system.

Question 8

What are the types of spina bifida?

Answer 8

Question 9

Explain spina bifida occulta

Answer 9

The mildest form of spina bifida

Some of the outer part of the vertebrae have not fused completely.

Question 10

Explain meningocoele.

Answer 10

A meningeal cyst composing of CSF. There is no neural tissue in this cyst and only CSF.

This is still a rather mild form of spina bifida as the neural tissue is still somewhat protected.

Question 11

Explain myelomeningocoele.

Answer 11

The most severe form of spina bifida with the most severe complications. The meninges and nerves (neural tissue) protrudes out in the cyst and will be damaged.

Question 12

What is anencephaly?

Answer 12

Failure of neural tube to close cranially.

There will be absence of cranial structures and is incompatible with life.

Question 13

What is rachischisis?

Answer 13

Failure of neural fold to elevate and therefore incompatible with life.

Question 14

Diagnosis of neural tube defects.

Answer 14

Raised maternal serum alpha-fetoprotein

Ultrasound

Question 15

Prevention of neural tube defects.

Answer 15

Folic acid pre-conceptually and then for the first trimester.

This reduces incidence by 70%

Question 16

What does the neuroectoderm tube form caudally?

Answer 16

The spinal cord

Question 17

Briefly explain the development of the spinal cord.

Answer 17

At 3rd motnh the spinal cord is the same length as the vertebral column but then the vertebral column will start to grow faster and the spinal roots must elongate in order to exit their intervertbral foramen.

This forms the cauda equina.

Question 18

What does the prosencephalon (forebrain) develop into?

Answer 18

Telencephalon -> cerebral hemispheres

and

diencephalon -> thalamus

Question 19

What does the mesencephalon develop into?

Answer 19

Mesencephalon -> midbrain

Question 20

What does the rhombencephalon (hindbrain) develop into?

Answer 20

Metencephalon -> pons and cerebellum

Myelencephalon -> medulla oblongata

Question 21

Why are the flexures important?

Answer 21

Because growth and development at cranial neural tube exceeds the available space linearly so it must start to fold up.

This gives a cervical flexure and a cephalic flexure.

Question 22

Answer 22

Question 23

Why might hydrocephalus occur?

Answer 23

Can occur in spina bifida (in this case it is treated by a shunt)

Can also occur when there is obstruction of the ventricular system e.g. tumour or infection.

Most commonly in cerebral aqueduct.

Question 24

What are the alar plates of the neural tube?

Answer 24

Dorsal plates seperated from the ventral plates by sulcus limitans.

Question 25

What are the basal plates of the neural tube?

Answer 25

Ventral plates separated from the dorsal plates by sulcus limitans.

Question 26

Functions of the alar plates.

Answer 26

Sensory

Question 27

Functions of the basal plates

Answer 27

Motor

Question 28

What are the neural crests?

Answer 28

Cells of the lateral border of the neuroectoderm tube.

These will become displaced and enter the mesoderm and undergo epithelial to mesenchymal transition.

Question 29

Give examples of neural crest cell derivatives.

Answer 29

Question 30

Give an example of what neural crest cell migration is vulnerable against.

Answer 30

Alcohol

Question 31

What is Hirschsprung’s disease?

Answer 31

Aganglionic megacolon where one structure is affected in neural crest cell migration.

It is the absence of ganglions in segment of bowel.

Question 32

What is DiGeorge syndrome?

Answer 32

Thyroid deficiency, immunodeficciency secondary to thymus defect, cardiac defects and abnormal facies due to multiple structures being affected by defects of neural crest cell migration.