8. Neurulation and Neural Crest

Question 1

When are the Central Nervous System and Neural Crest cells developing?

Answer 1

Week 3

Question 2

How does the notochord induce the neural plate?

Answer 2

Release of Sonic Hedgehog

Question 3

What are the steps of Neurulation?

(Try to describe it to yourself)

Answer 3

Notocord releases Sonic Hedgehog

Neural Plate is induced

Neural Plate folds inward to form the Neural Fold, and then the Neural Groove

The the Neural Groove pinches off to become the Neural Tube, and the Neural Crest pinches off to float above it.

The Neural Crest cells migrate away.

Question 4

After Neurulation, what three types of Ectoderm are we left with?

Answer 4

1. Neural Ectoderm

(Neural Plate → Folds → Tube)

2. Surface Ectoderm

The Ectoderm that is left on top after the neural ectoderm enters the mesoderm layer

3. Neural Crest

Question 5

What is the clinical significance of the number of somites in an embryo?

Answer 5

You can tell how old the embryo is with ultrasound by counting the number of somites.

Question 6

On what day does the Rostral Neural Pore close?

Answer 6

Day 25

Question 7

On what day does the Caudal Neuropore close?

Answer 7

Day 28

Question 8

What is Primary vs Secondary Neurulation?

Answer 8

Primary Neurulation is the complete formation (and closure) of the Neural Tube for the Brain, Cervical, Thoracic, and Lumbar regions.

Secondary Neurulation is the fusion of the Caudal Eminance with the Caudal Neuropore (gives rise to the sacral and coccygeal regions of the spinal cord)

Question 9

What regions of the embryo primarily have the Neural Crest cells present?

Answer 9

Cranial and Trunk Regions

Question 10

What type of neurons do the Neural Crest cells give rise to?

Answer 10

Sensory neurons

Question 11

What specific structures do Neural Crest cells give rise to?

(Just an overview)

Answer 11

Dorsal Root Ganglia (sensory)

Sensory Cranial Nerves (5,7,9,10)

Autonomic Ganglia

Schwann Cells (neurilemma) / Satellite cells

Pia / Arachnoid mater

Melanocytes

Cromaffin Cells of Adrenal Glands

Bone and Cartilage of the Face

Aortic arches

Enamel and Dentin of the Teeth

Question 12

What do we call diseases related to the Neural Crest?

Answer 12

Neurocrisopathies

Question 13

What is Hirschsprung’s Disease?

Answer 13

A Neurocristopathy where an infant can develop Megacolon

(no autonomic innervation to the colon)

Question 14

What is the common cause for all forms of Spina Bifida?

Answer 14

Failure of the Caudal Neural Pore to close at the appropriate time

Question 15

List the defining characteristics for

Spina Bifida Occulta

Answer 15

Spina Bifida Occulta

Incomplete formation of the vertebral lamina and a gap where the spinus process should be.

Caudal Neural Pore closed too slowly

Common (10% of the population)

Hair on lower back sometimes

Question 16

List the defining characteristics for

Meningocele

Answer 16

Meningocele

Caudal Neural pore closed WAY too slowly, so there are no vertebral arches, and the meninges and CSF protrude into the back.

Patient may or may not have deficit.

Question 17

List the defining characteristics for

Meningomyelocele

Answer 17

Meningomyelocele

Spinal cord exists intact, but is located out in a CSF filled cyst.

Patients do have defects

Question 18

List the defining characteristics for

Myelocele

Answer 18

Myelocele

There is no cyst here, but the spinal cord presents open on the back.

Patients do have motor and sensory deficits.

Question 19

What might increased levels of Alpha-Fetoprotien in a pregnant woman indicate?

Answer 19

Either a Meningocele / Meningomyelocele / Meylocele

or Anencephaly.

Note: Spina Bifida Occulta is not an “open” neural tube defect, and will not show increased alpha-fetoprotien as the other three will.

Question 20

What nutrient can prevent Neural Tube defects?

Answer 20

Folate

Question 21

What embryological mistake can cause anencephaly?

What are the results?

Answer 21

Failure of the Rostral Neural Tube to close

Lack of a neocortex, risk for infection. Results in death shortly after birth.

Question 22

Besides Anencephaly, what other two defects we talked about can arise from a failure of the Rostral Neural Pore to close?

Answer 22

Encephalocele with Brain tissue

Depending on the severity, can cause neurological defects.

Encephalocele without Brain tissue

Patients can be normal.

Question 23

What gives rise to the Meninges?

What is it made of?

Answer 23

The Meninx Primitiva

Mesoderm - specifically Pariaxial Mesoderm (Sclerotome)

AND

Neural Crest Cells

Question 24

What two cell populations come from the Meninx Primitiva?

What are they made of, and what do they make?

Answer 24

1. Pachymeninx

Mesoderm (Scleratome) portion of the Meninx Primitiva. Makes the Dura Mater

2. Leptomeninges

Neural Crest portion of the Meninx Primitiva. Makes the Arachnoid Mater and the Pia Mater.