Development of the nervous system

Question 1

Describe the formation of the neural tube. (8)

Answer 1

Gastrulation produces the notochord which induces neurulation to cause ectoderm to differentiate into neuroectoderm.
The neural plate forms, and the edges thicken to form the neural groove.
The neural folds grow together and fuse, first in the middle, creating the cranial and caudal neuropores.

Question 2

Describe three defects that can occur as a result of the failure to form the neural tube properly. (7)

Answer 2

Anencephaly - absence of brain in head due to cranial neuropore abnormality.
Spina bifida - caudal neuropore abnormality.
Rachishisis - failure of cranial folds to elevate causing a splayed neural tube with no derivatives.

Question 3

Describe how you would detect a neural tube defect of a foetus. (2)

Answer 3

20 week anomaly scan.

Raised alpha fetoprotein in the mother - indicates any open defect.

Question 4

Describe one factor that a mother can change to reduce the chances of her baby being born with a neural tube defect. (2)

Answer 4

Folic acid supplements for 3 months post-conception and in the first trimester.

Question 5

Describe the two types of spina bifida. (2)

Answer 5

whether the spinal cord is within the cyst (more serious) or not.

Question 6

Describe the pathophysiology of spina bifida. (4)

Answer 6

Most commonly occurs a cyst forms due to a missing vertebral arch, often in the limbo-sacral region, associated with neurological deficits but not cognitive delay (unless untreated hydrocephalus occurs).

Question 7

What is the derivative of the lumen of the neural tube? (1)

Answer 7

The ventricular system.

Question 8

Describe the formation of the cauda equina. (4)

Answer 8

At month 3, the cord and the vertebral column are the same length, but after this the column grows faster than the cord, meaning the spinal nerves are stretched and the cauda equina is formed.

Question 9

What is the medullary pyramid and where is it? (2)

Answer 9

The bottom of the spinal cord, and at L3.

Question 10

Describe the primary brain vesicles as seen at week 4. (3)

Answer 10

Forebrain - prosencephalon
Midbrain - mesencephalon
Hindbrain - rhomencephalon

Question 11

Describe the secondary brain vesicles as seen at week 5 and their root primary vesicles. (7)

Answer 11

Prosencephalon - telencephalon + diencephalon
Mesencephalon stays the same.
Rhombencephalon - metencephalon + myelencephalon.

Question 12

Describe the derivatives of the secondary brain vesicles. (11)

Answer 12

Telencephalon - cerebral hemispheres
Diencephalon - thalamus 
Mesencephalon - midbrain 
Metencephalon - pons and cerebellum
Myelencephalon - medulla.

Question 13

Describe the anatomical directions of the head. (4)

Answer 13

Through the nose - rostral
Down the cord - caudal
Anterior - ventral
Posterior - dorsal

Question 14

Describe the flexures of the brain during development and explain why they occur. (3)

Answer 14

The cervical flexure occurs on the spinal cord - rhombencephalon juncture.
The cephalic flexure occurs in the mesencephalon region.
They occur because the cranial end of the neural tube exceeds the space available linearly.

Question 15

Describe the relationship between the secondary brain vesicles and the ventricular system. (5)

Answer 15

Lateral ventricles - telencephalon
3rd ventricle - diencephalon
Cerebral aqueduct - mesencephalon
4th ventricle - metencephalon and myelencephalon

Question 16

Describe neural crest cells. (5)

Answer 16

Cells from the roof plate enter the mesoderm and become mesenchymal, giving rise to ganglion (sympathetic, pre-aortic, enteric, dorsal root) and the adrenal gland. They are vulnerable to environmental damage eg DiGeorge Syndrome.