Session 1.2 - Development of Nervous system 1

Question 1

Describe how the notochord is formed

Answer 1

Prenotochordal cells migrate from primitive pit and form the midline and drive neurulation.

Neurulation initated by overlying ectoderm that differentiates to form neural plate - this tickens and its lateral edges rise up and the midline depresses to form a neurla groove. These edges then meet and fuse, forming a neural tube.

Question 2

Describe the fusion of the neural tube. How can it lead to neural tube defects?

Answer 2

Neural tube fuses in a cephalic to caudal manner, producing anterior and posterior neuropores. These neuropores close on day 25 and 28 for anterior and posterior respectively. Any defects in closure can cause NTDs.

Question 3

Describe how spina bifida occurs.

Answer 3

Failure of posterior neuropore to fuse.

Question 4

What are the 2 main types of spina bifida? Briefly describe them.

Answer 4

Spina bifida occulta - Defect in vertebral arches resulting in lack of fusion of the vertebral arches

Spina bifida cystica - more severe. neural tissue and/or meninges protrude through skin to form a cyst. If only fluid filled meninges in sac = meningocele. If neural tissue also in sac = meningomyelocele

Question 5

What is anencephaly and how does it occur?

Answer 5

Failure of anterior neuropore to close resultingin absence of brain. Incompatible with life

Question 6

What is rachischisis?

Answer 6

Posterior neuropore fails to close resulting in vertebrae of spine being unfully formed, leaving the spinal cord exposed

Question 7

How can neural tube defects be detected before birth?

Answer 7

Raised serum alpha-fetoprotein in mother or on USS

Question 8

Why does the spinal cord roots have to stretch to exit the correct spinal level?

Answer 8

Up to 3 months During development the spinal cord is the same length of the vertebral column, and exits the column at the same level. However, after this point the vertebral column grows faster and so the spinal roots must elongate to exit their original IV foramina

Question 9

What are the derivatives of the telencephalon and the diencephalon?

Answer 9

Telencephalon - cerebral hemisphere

diencephalon - thalamus

Question 10

What are the derivatives of the mesencephalon?

Answer 10

Midbrain

Question 11

What are the derivatives of the metencephalon?

Answer 11

pons and cerebellum

Question 12

What are the derivatives of the myelencephalon?

Answer 12

medulla oblongata

Question 13

Why does the brain have so many folds? Where do the 2 flexures of the spinal cord occur?

Answer 13

The cranial end of the neural tube rapidly enlarges and exceeds the available space, and therefore begins to fold up.

Cephalic flexure occurs at midbrain region. Caudal flexure occurs at spinal cord hindbrain junction

Question 14

What is the ventricular system in the adult brain? From what does it develop?

Answer 14

Acts as a reservoir of CSF within the brain, cushioning the brain and spinal cord.

Develops from the neural tube lumen.

Question 15

Label the ventricles of the nervous system

Answer 15

Question 16

What cells produce CSF in the ventricular system?

Answer 16

cells of ventricular lining

Question 17

What happens to the neural crest cells at the lateral border of the neuroectoderm tube? Why are these cells vulnerable?

Answer 17

Become displaced and enter mesoderm and transition to mesenchymal cells. They input into a number of different structures such as adrenal medulla, schwann cells, or c cells of thyroid.

Vulnerable to environmental insults esp. alcohol

Question 18

What is hirschprungs disease?

Answer 18

Disorder of the gut which is due to failure of neural crest cells to migrate completely. Affected part of colon fails to relax causing obstruction.