CNS Embryology (5)

Question 0

What three things develop from mesoderm?

Answer 0

1. Bone
2. Skeletal muscle
3. Dermis

All derived from somites, which the mesoderm forms

Question 1

What structures are derived from endoderm?

Answer 1

Internal organs (viscera)

Question 2

What two things develop from ectoderm?

Answer 2

1. Neural structures

2. Epidermis of skin

Question 3

During what week of gestation does brain development begin?

Answer 3

3rd week of gestation

Question 4

What is the first step in the formation of the nervous system? What induces it?

Answer 4

Formation of the neural plate (thickening of the ectoderm in a rostral-caudal longitudinal band)
This is induced by the notochord

Question 5

How is the neural tube formed from the neural plate? By when is it accomplished?

Answer 5

Neural tube is formed by the end of the 3rd week when the neural folds (elevated lateral margins of the neural plate) begin to fuse.
Fusion starts centrally and moves in both rostral and caudal fashions

Question 6

By 4 weeks, how many vesicles have developed in the brain? What are they?

Answer 6

3 vesicles.

1. Prosencephalon (becomes forebrain)
2. Mesencephalon (becomes midbrain)
3. Rhombencephalon (becomes hindbrain)

Question 7

By five weeks how many vesicles are in the brain? Which?

Answer 7

5 vesicles.

1. Telencephalon
2. Diencephalon
3. Mesencephalon
4. Metencephalon
5. Myelencephalon

Question 8

The prosencephalon gives rise to what 2 vesicles?

Answer 8

Telencephalon and diencephalon

Question 9

The mesencephalon gives rise to what vesicle?

Answer 9

Mesencephalon

Question 10

The rhombencephalon gives rise to what two vesicles?

Answer 10

Metencephalon and Myelencephalon

Question 11

During which week does the neural tube close? Does anterior or posterior close 1st?

Answer 11

4th week; the anterior closes before posterior (25 vs. 27 days)

Question 12

By what week do the cerebral hemispheres begin to enlarge?

Answer 12

8th week

Question 13

What two cell types are CNS cells derived from?

Answer 13

1. Neuroblasts

2. Glioblasts

Question 14

What cell type differentiates into neuroblasts and glioblasts?

Answer 14

Ventricular zone neuroepithelial cells

Question 15

What do neuroblasts form?

Answer 15

All neurons in the CNS

Question 16

What 6 types of cells are derived from glioblasts?

Answer 16

1. Radial glial cells
2. Astrocytes
3. Oligodendrocytes
4. Ependymocytes
5. Tanycytes
6. Choroid plexus cells

Question 17

Which cells are formed before neuroblasts differentiate into neurons? Why is that order necessary?

Answer 17

Radial glial cells. Migrating neurons attach to radial glial cells and travel to their final destination; since the radial cells arrange the neurons, they need to be present before.

Question 18

When are most glial cells formed, other than radial glial cells?

Answer 18

After neuroblasts formation is complete

Question 19

During what week due Microglia invade the CNS? What enables them to do so at this point?

Answer 19

During week 3, with the formation of cerebral blood vessels

Question 20

In the embryonic neural tube, what structure separates the dorsal and ventral areas?

Answer 20

Sulcus limitans

Question 21

What type of neurons and nuclei does the alar plate in the embryonic neural tube form? What other type of neurons?

Answer 21

Sensory neurons and nuclei of the spinal cord, including dorsal root ganglia neurons.
(Alar plate is on the dorsal side of the sulcus limitans)

Question 22

What is the adult corollary to the alar plate?

Answer 22

Neurons in the dorsal sensory horn

Question 23

What types of neurons develop from the basal plate in the embryonic neural tube?

Answer 23

Motor neurons and nuclei of the spinal cord.

Question 24

Adult corollary to basal plate

Answer 24

Ventral motor horn of the spinal cord

Question 25

In the ____ month fetus, the conus medularis terminates at the end of the spinal column

Answer 25

3

Question 26

In the ____ month fetus the spinal column begins to outgrow the cord and the conus ends at S1

Answer 26

6

Question 27

In the 9 month fetus, the spinal cord ends at ____

Answer 27

L3

Question 28

What two conditions are the result of failure of the anterior neural pore to close?

Answer 28

1. Anencephaly

2. Encephalocele

Question 29

What three conditions are the result of failure of the posterior neural pore to close?

Answer 29

1. Spinal bifida
2. Meningocele
3. Myelomenigocele

Question 30

What substance can be found in mother serum or in amniocentesis that is indicative of failure of neural tube closure?

Answer 30

Alpha-fetal protein

Question 31

Failure of mesodermal cells to form bony dorsal vertebrae that surround the spinal cord

Answer 31

Spina bifida occulta (SPO)

Question 32

Why do individuals with SPO rarely develop neurological symptoms?

Answer 32

B/c the meninges and spinal cord/filum terminale are not actually involved in the defect, only the bone is affected.

Question 33

What is the difference between spina bifida aperta w/ menigocele and w/ myelomenigocele?

Answer 33

Menigocele is an outpouring containing only the meninges. Myelomenigocele contains both meninges and spinal cord/filum terminale.

Question 34

What is different about SPA from SPO clinically?

Answer 34

SPA may have severe neurological symptoms, whereas SPO usually doesn’t have any neuro symptoms

Question 35

What is the term for displacement/herniation of the cerebellar tonsils below the foramen magnum?

Answer 35

Arnold-Chiari malformation

Question 36

What is a Chiari Type II malformation?

Answer 36

Herniated cerebellar tonsils below the foramen magnum + associated cervical or occipital encephalocele