1.2 Development Of The NS

Question 1

What marks the onset of gastrulation?

Answer 1

The appearance of the primitive streak.

Question 2

How is the neural tube formed?

Answer 2

• gastrulation produces notochord
• notochord induces neurulation
• induction of neural plate (day 18)
• the depressed mid region is the neural groove (day 19)
• neural folds gradually approach each other in the midline and fuse = neural tube (day 21-23)

Question 3

How does neural tube fusion failure occur?

Answer 3

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

Can occur cranially or caudally.

Question 4

What does neural type fusion failure result in

• cranially
• caudally

Answer 4

Cranial = anencephaly

Caudal = spina bifida

Question 5

What is spina bifida?

Answer 5

Failure of fusion of neural tube, commonly in lumbrosacral region

Neurological deficits occur though not associated with cognitive delay. Hydrocephalus nearly always occours.

Question 6

What is rachischisis?

Answer 6

Failure of neural fold elevation

Question 7

How would you diagnose a neural tube defect?

Answer 7

• raised maternal serum a-fetoprotein
• Ultrasound
• multifactorial aetiology

Question 8

How does folic acid affect neural tube folding?

Answer 8

Reduces incidence of neural tube defects.

Question 9

How do we get the 5 anatomical divisions of the brain?

Answer 9

Cranially 3 dilations leads to 5 dilations = 5 anatomical divisions

Question 10

How does the spinal chord develop?

Answer 10

Caudally, tail = spinal chord. Comes from most of the length of the neural tube

After 3rd month, spinal chord = same length as vertebral column, therefore vertebral column grows faster.

Spinal roots must elongate because they still exit at their intervertebral foramen = get cauda equina.

Question 11

What does the

• forebrain
• midbrain
• hindbrain

Develop from during neural fold formation?

Answer 11

Forebrain = prosencephalon

Midbrain = mesencephalon

Hindbrain = rhombencephalon

After neural tube closure in the 4th week, these dilations at the cranial end become the three primary brain vesicles

Question 12

What are the 5 secondary brain vesicles and when do they form?

Answer 12

Form at week 5

The 5 secondary brain vesicles are

• Telencephalon
• diencephalon
• mesencephalon
• metencephalon
• myelencephalon

Question 13

Why must the neural tube fold upwards and how does it do it?

Answer 13

Growth and development at cranial NT exceeds available space linearly so it must fold up

• cervical flexure of spinal cord at hindbrain junction
• cephalon flexure at midbrain region

Thus the neuraxis does not remain straight

Question 14

What is the ventricular system in the developing CNS?

Answer 14

A tubular structure that persists as development proceeds

Comprised of interconnected reservoirs filled by CSF produced by cells of ventricular lining

Role: to cushion brain and spinal cord within their bony cases

Question 15

What is hydrocephalus?

Answer 15

A ventricular system abnormality

Most common in newborns suffering from spina bifida, readily treatable by use of stunt

Can occur where there is any blockage of the ventricular system e.g tumour, infection

Question 16

What is the neural crest?

Answer 16

Cells of the lateral border of the neuroectoderm tube

Become displaced and enter the mesoderm and undergo epithelial to mesenchymal transition

Form the dorsal root ganglia in an embryo

Question 17

What defects can occur as a result of neural crest migration?

Answer 17

Because migration is extensive and contributes to a wide range of structures lots of things can go wrong and its extremely vulnerable to environmental insult, especially by alcohol

Question 18

What abnormalities can occur due to neural crest migration?

Answer 18

Caused by defects of migration or morphogenetic affecting….

One structure = Hirschsprung’s disease (aganglionic megacolon)

Multiple structures = digeorge syndrome (thyroid deficiency)