Lecture 9: Embryology

Question 1

What is gastrulation?

Answer 1

Formation of the Trilaminar Disc form the epiblast

Question 2

Which embryological layer forms the Ns?

Answer 2

Ectoderm

Question 3

How does CNS formation begin?

Answer 3

Ectoderm thickens just anterior to the primitive node (signals from primitive node trigger this) forming the Neural Plate

At the start of week 3

Then the edges thicken and move up to form neural folds

Question 4

How is the neural tube formed?

Answer 4

Neural Folds migrate towards eachother, fusing at the midline. This starts at the middle (Around day 18) and works its way out to the ends.

It initially stays open at the ends (Neuropores) so the CNS is in contact with the amniotic fluid

Question 5

When do the ends of the neural tube close?

Answer 5

Anterior (Cranial/Rostral) neuropore closes ~25 days

Posterior (Caudal) Neuropore closes ~27 days

Question 6

When do the brain vesicles begin developing?

Answer 6

When the anterior neuropore closes around day 25

Question 7

At which somite level does the brain form?

Answer 7

Above the 4th somite pair is brain and below that is Spinal cord & PNS

Question 8

When do the various brain vesicles form?

Answer 8

3 primary vesicles form in week 4:

• Prosencephalon
• Mesencephalon
• Rhombencephalon

5 Secondary Vesicles form in week 5:

• Telencephalon
• Diencephalon
• Mesencephalon
• Metencephalon
• Myelencephalon

Question 9

The brain has 3 flexures during embryology, what are they?

Answer 9

• Cephalic flexure (3rd week)
• Cervical Flexure (4th Week)
• Pontine Flexure (5th week)

Question 10

Where is the cephalic flexure found?

Answer 10

Cephalic between the mesencephalon (midbrain) and rhombencephalon (Hindbrain)

Question 11

Where is the cervical flexure found?

Answer 11

Between Hindbrain & Spinal Cord

Question 12

Where is the pontine flexure found?

Answer 12

In the hindbrain between the metencephalon & Myelencephalon

Question 13

What structures do each of the secondary vesicles become?

Answer 13

Telencephalon - Cerebrum, hippocampus & Basal Ganglia

Diencephalon - Thalmus, hypothalamus, pituitary & pineal glands

Mesencephalon - Midbrain

Metencephalon - Cerebellum, pons

Myelencephalon - Medulla

Question 14

What ventricles form from which vesicles?

Answer 14

Telencephalon - Lateral
Diencephalon - 3rd
Mesencephalon - Cerebral Aqueduct
Rhombencephalon - 4th

Question 15

When does CSF production begin?

Answer 15

5th week

Question 16

Describe the inner surface of the neural tube?

Answer 16

Pseudostratified Neuroepithelial cells

Question 17

How are neurons, glia, ependymal cells formed?

Answer 17

Neuroepithelial cells differentiate into neurons and Glial cells
(Except Microglia which from mesenchymal cells)

After they finish dividing the last neuroepithelial cells form ependymal cells

Question 18

What are neural crest cells and what do they do?

Answer 18

Cells from the tip of the neural folds.

They migrate around the neural tube forming:

• Pigment cells
• DRG
• Autonomic ganglia
• Adrenal Medulla

Question 19

Specifically how do neural crest cells form the DRG and associated spinal nerves?

Answer 19

The crest cell itself form the DRG and give off two processes:

• Peripheral Process extends into the body
• Central Process extends into the dorsal root & horn

Question 20

How does the cauda equina form?

Answer 20

Basically during development the spinal cord reaches all the way to the coccyx, there the dura attaches and the sacral spinal nerves attach to their levels

Then the column and dura outgrow the cord.

Cord is elongated within the dural sac forming the cauda equina

This happens between month 3 and birth