2 Development of the Nervous System

Question 1

When does the notochord form?

Answer 1

When a solid core of cells from prenotochordal cells migrate from the primitive pit cephalically, acting to form the midline and driving neurulation.

Question 2

How does the neural tube form.

Answer 2

Overlying ectoderm differentiates to form the neural plate, the plate thickens and lateral edges rise up and midlines depressed to for neural groove. The lateral edges approach each other at the midline and fuse to form the neural tube.

Question 3

What is the progression of fusion of the neural folds? (I.e. where does it start and progress to?)

Answer 3

Starts in cervical region, then spreads cephalically and caudally producing neuropores anteriorly and posteriorly.

Question 4

When do the neuropores close?

Answer 4

Anterior on day 25. Posterior on day 28.

Question 5

What can defect in closure of neuropores lead to?

Answer 5

Serious neural tube defects.

Question 6

What is spina bifida?

Answer 6

Failure in the caudal neurpore fusion, normally in lumbosacral region.

Question 7

What are the effects of spina bifida?

Answer 7

Neurological deficits, (rarely mental retardation,) hydrocephalus.

Question 8

Why does hydrocephalus occur in spina bifida?

Answer 8

Lengthening of the VC causes cerebellum to be pulled into magnum foramen and cuts off CSF.

Question 9

What are the two main types of spina bifida?

Answer 9

Occulta - defect in fusion of vertebral arches.
Cystica - severe version where neural tissue and/or meninges protrude through skin to form a cyst like sac. Meningocele if only fluid-filled meninges in sac or meningomyelocele if also neural tissue in sac.

Question 10

What is anencephaly?

Answer 10

Failure of the cranial neuropore to close properly resulting in absence of brain structures, including the brain (so incompatible with life).

Question 11

What is rachischisis?

Answer 11

Neural folds do not elevate but remain as flattened mass of neural tissue.

Question 12

How are neural tube defects detected?

Answer 12

Raised serum a-fetoprotein or on USS.

Question 13

How can incidence of neural tube defects be reduced?

Answer 13

Folate intake in first trimester.

Question 14

What are the three primary brain regions in neural fold formation?

Answer 14

Forebrain (prosencephalon), midbrain (mesencephalon), and hindbrain (rhombencephalon).

Question 15

What happens to the dilations at the cranial end of the neural tube in the fourth week of development?

Answer 15

They become three primary vesicles.

Question 16

What happens to the three primary vesicles of the brain in week 5 of development?

Answer 16

5 secondary brain vesicles have formed - telencephalon, diencephalon, mesencephalon, metencephalon, and myelencephalon.

Question 17

What are the mature derivatives of the five secondary brain vesicles?

Answer 17

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

Question 18

Where is the cervical flexure of the neural tube seen?

Answer 18

At the spinal cord hindbrain junction.

Question 19

Where is the cephalic flexure of the neural tube seen?

Answer 19

At the midbrain region.

Question 20

What does the ventricular system act as in adults?

Answer 20

A reservoir of CSF to cushion the brain and spinal cord.

Question 21

What does the ventricular system develop from?

Answer 21

The neural tube lumen, persists to form 5 vesicle stage system.

Question 22

What are neural crest cells?

Answer 22

Cells of the lateral border of the neuroectoderm tube that are displaced and enter the mesoderm and undergo epithelial to mesenchymal transition.

Question 23

What is Hirschsprung’s disease?

Answer 23

Disorder of the gut which is caused by failure of the neural crest cells to migrate completely in foetal development of the intestine. The affected area of colon fails to relax, causing obstruction.