2. Embryology

Question 1

What do cranial neural tube defects result in?

Answer 1

Anencephaly.

Question 2

What do caudal neural tube defects result in?

Answer 2

Spina bifida.

Question 3

What is seen neurologically in spina bifida?

Answer 3

Neurological deficits, but no cognitive delay (if untreated then can secondarily cause cognitive delay). Hydrocephalus nearly always occurs.

Question 4

What are the two types of spina bifida?

Answer 4

Meningocele - failure of the vertebral arch to form, spinal cord still within body cavity, cyst involved the meninges and CSF.
Myelomeningocele - failure fo the vertebral arch to form, spinal cord NOT within body cavity, cyst involved meninges, CSF and spinal cord.

Question 5

What is anencephaly?

Answer 5

Failure of the neural tube to close cranially leading to absence of cranial structures including the brain. Is incompatible with life.

Question 6

What is rachischisis?

Answer 6

Failure of neural fold elevation to form the neural tube. Is incompatible with life.

Question 7

How can neural tube defects be diagnosed?

Answer 7

Screening for raised maternal serum alpha-fetoprotein. USS.

Question 8

How can neural tube defects be prevented?

Answer 8

Taking folic acid pre-conceptually for 3 months and for the first trimester.

Question 9

Describe the development of the spinal cord?

Answer 9

Formed from most of the length of the neural tube. Is the same length as the vertebral column until the 3rd month, when the vertebral column then grows faster, so spinal roots elongate to still exit at their intervertebral foramen, and the cauda equina is formed.

Question 10

What are the 3 primary brain regions formed during neural fold formation which become the 3 primary brain vesicles in the 4th week?

Answer 10

Forebrain - prosencephalon.
Midbrain - mesencephalon.
Hindbrain - rhombencephalon.

Question 11

In the fifth week, the 3 primary brain vesicles form 5 secondary brain vesicles. What does the prosencephalon form and what mature derivatives does this give rise to?

Answer 11

Prosencephalon:
Telencephalon - cerebral hemispheres.
Diencephalon - thalamus.

Question 12

In the fifth week, the 3 primary brain vesicles form 5 secondary brain vesicles. What does the mesencephalon form and what mature derivatives does this give rise to?

Answer 12

Mesencephalon:

Mesencephalon - midbrain.

Question 13

In the fifth week, the 3 primary brain vesicles form 5 secondary brain vesicles. What does the rhombencephalon form and what mature derivatives does this give rise to?

Answer 13

Rhombencephalon:
Metencephalon - pons and cerebellum.
Myelencephalon - medulla oblongata.

Question 14

What does the cervical flexure form?

Answer 14

Spinal cord-hindbrain junction.

Question 15

What does the cephalic flexure form?

Answer 15

Midbrain region.

Question 16

What is the role of the ventricular system within the brian which develops as a result of the tubular structure of the developing CNS?

Answer 16

To cushion the brain and spinal cord within their bony cases.

Question 17

What part of the ventricle system of the brain develops from the telencephalon, diencephalon, mesencephalon, metencephalon and myelencephalon?

Answer 17

Telencephalon - body of the lateral ventricle.
Diencephalon - third ventricle.
Mesencephalon - cerebral aqueduct.
Metencephalon and myelencephalon - fourth ventricle

Question 18

What can a ventricular system abnormality cause?

Answer 18

Hydrocephalus - is most common in newborns with spina bifida but can occur anywhere where there is blockage of the ventricular system eg tumour or infection.

Question 19

What function does the dorsal alar plate in the neural tube form in the brain?

Answer 19

Sensory function.

Question 20

What function does the ventral basal plate in the neural tube form in the brain?

Answer 20

Motor function.

Question 21

What do neural crest cells in the lateral border of the neuroectoderm go on to form?

Answer 21

Enter the mesoderm, undergo epithelial to mesenchymal transition, and form structures of the nervous system eg sympathetic ganglion, structures of the head, neck and midline eg connective tissue and bones of the face and skull and a few other structures eg the adrenal medulla.

Question 22

Give an example of an abnormality of neural crest cell migration affecting just one structure

Answer 22

Hirschsprung’s disease - forming an aganglionic megacolon.

Question 23

Give an example of an abnormality of neural crest cell migration affecting multiple structures

Answer 23

DiGeorge syndrome - causing thyroid deficiency, immunodeficiency secondary to a thymus defect, cardiac defects and abnormal facies.