Embryology of the Nervous system part 1

Question 1

What is the first indication of nervous system development?

Answer 1

Neural plate and neural groove formation in the 3rd week.

Question 2

What does the neural tube differentiate into?

Answer 2

Central nervous system

Question 3

What do neural crests cells form?

Answer 3

Forms most of the PNS and ANS

Question 4

Cranial 2/3 of the neural tube represents________________

Answer 4

Future brain

Question 5

Caudal 1/3 of the neural tube represents_________________

Answer 5

future spinal cord

Question 5

What type of cells are found in the wall of the neural tube?

Answer 5

Pseudostratified columnar neuroepithelium

Question 5

How does the central canal of the spinal cord form? Specify the weeks as well

Answer 5

Lateral walls of neural tube thicken, reducing size of
neural canal – until only a central canal of spinal cord
exists at ~ 9-10 weeks

Question 5

what develops from the neural tube caudal to the 4th somite?

Answer 5

SC

Question 5

What signalling substance is important during spinal cord development?

Answer 5

Retinoic acid signalling is essential in development of spinal cord from early patterning to neurogenesis

Question 6

Describe the marginal zone and what it forms

Answer 6

Marginal zone, containing outer part of neuroepithelial
cells forms
Eventually becomes white matter of the spinal cord
as axons grow into it from surrounding nerve cell
bodies, spinal ganglia and brain

Question 6

How do neuroblasts develop into neurons?

Answer 6

Neuroblasts become neurons as they develop cytoplasmic
processes

Question 6

What does neuroepithelium of the neural tube form? (2)

Answer 6

Ventricular zone (ependymal layer)
Gives rise to all neurons and macroglial cells
(macroglia- e.g. oligodendrocytes and astrocytes) in spinal cord

Question 6

When does glioblast formation start?

Answer 6

It starts when the neuroblast formation ceases. Then neuroepithelium will form glioblasts which will migrate to the intermediate and peripheral zone.

Question 6

How is the intermediate zone formed?

Answer 6

Dividing neuroepithelial cells in ventricular zone differentiate into primordial neurons – neuroblasts
Form an intermediate zone (mantle layer)

Question 7

What do glioblasts form?

Answer 7

Astroblasts form astrocytes
Oligodendroblasts form oligodendrocytes

Question 8

What is the order in which epedymal cells, neuroblasts and glioblasts form?

Answer 8

Neuroblasts are formed first and goes to the marginal zone, Glioblasts are formed second and goes to the I.M and Marginal zone
Ependymal cells form last and stick around in the ventricular zone

Question 9

Describe microglia

Answer 9

Scattered in white and gray matter of spinal cord
* Small cells, derived from mesenchyme

Question 10

Where do microglia originate? When do they invade the CNS?

Answer 10

Invade CNS in late foetal period, after being penetrated by
blood vessels.
* Originate in bone marrow, part of mononuclear
phagocytotic cell population

Question 11

What is the sulcus limitans?

Answer 11

Sulcus limitans – shallow, longitudinal groove, produced on each side
Separates alar plate and basal plate, plates produce longitudinal bulges

Question 12

Differentiate between alar plates and basal plates

Answer 12

Alar plates are afferent, they form dorsally
Basal plates are efferent, form anterolaterally.

Question 13

What do alar plates form? Explain

Answer 13

Cell bodies form dorsal gray columns and extend length of
spinal cord
In transverse sections these columns appear as dorsal gray horns
Neurons in columns form afferent nuclei

Question 14

As the dorsal plates enlarge, they form________________________

Answer 14

Dorsal median septum

Question 15

What do basal plates form? Explain

Answer 15

cell bodies form ventral and lateral gray columns and extend length of spinal cord
Appear as ventral and lateral gray horns in transverse sections
Axons of ventral horn cells grow out of spinal cord
Forms ventral root of spinal nerves

Question 16

Basal plates bulge ventrally on each side of the median plane, and this forms_____________ AND ______________

Answer 16

Ventral median septum
Ventral median fissure

Question 17

Explain the development of spinal ganglia (6)

Answer 17

1. Unipolar neurons in spinal ganglia (dorsal root ganglia) are derived from neural crest cells.
2. Axons were first bipolar, two processes unite.
3. Both processes have structural characteristics of axons.
4. Peripheral processes function as dendrite – conduction towards cell body
5. Peripheral processes pass in spinal nerves to sensory endings in somatic structures
6. Central processes enter spinal cord and make up dorsal root of spinal nerve

Question 18

Where do spinal meninges develop from?

Answer 18

Neural crest cells and mesenchyme (days 30-35)
Cells migrate surrounding neural tube and form primordial meninges

Question 19

How are the three meningeal layers formed?

Answer 19

External layer of these meninges thickens to form dura mater and internal layer pia arachnoid (later forms pia mater and arachnoid mater - leptomeninges).

Question 20

How is the subarachnoid space formed?

Answer 20

Fluid-filled spaces appear within leptomeninges and coalesce to form subarachnoid space

Question 21

What does the arachnoid trabeculae indicate in adults?

Answer 21

Origin of pia mater and arachnoid mater from a single layer is indicated in the adult by arachnoid
trabeculae

Question 22

When does CSF production begin?

Answer 22

5th week

Question 23

State the level at which the spinal cord terminates in fetal, neonates and adults

Answer 23

In a 24-week-old foetus, it lies at S1
* In neonates, the spinal cord terminates at L2 or L3
* In adults, spinal cord generally terminates at inferior border of L1