1 - Development of the NS

Question 1

Describe the early development of the CNS (spinal chord)

Answer 1

• first you get proliferation of the ectoderm (in the dorsal midline of the embryonic disk) - this forms the neural plate
• as it thickens, the neural plate folds
• the 2 neural folds fuse and form a tube

Question 2

What is the name given to the proliferation of the ectoderm in the dorsal midline?

Answer 2

Neural plate

Question 3

What happens to the neural plate as it thickens?

Answer 3

It folds up the sides and eventually the two neural folds fuse to form a tube
The space in the middle is the neural canal

Question 4

What is neural canal?

Answer 4

the space in the middle of the neural tube

Question 5

What are the neural crests?

Answer 5

little bunches of cells at the tips of the neural fold (they separate from the neural folds and doesn’t take part in fusion)

Question 6

Which cells do the neural tube and neural crest cells give rise to?

Answer 6

Neural tube – all cells of the CNS

Neural crest – all cells of the PNS

Question 7

What is the name given to the wall of the neural tube?

Answer 7

Neuroepithelium

Question 8

What three types of cells do neuroepithelium give rise to?

Answer 8

Neuroblasts – all cells with cell bodies in the CNS (precursors for neurones)
Glioblasts – these become neuroglia (astrocytes + oligodendrocytes)
Ependymal cells – line the ventricles and the central canal

Question 9

Are motor neurons produced from neuroepithelium?

Answer 9

Yes – (included with neoblasts) although most of their axons are outside the CNS, their cell bodies are within the spinal cord

Question 10

State four cell types that neural crest cells can differentiate into.

Answer 10

• Sensory neurones of dorsal root ganglia and cranial ganglia
• (Autonomic) post-ganglionic neurones
• Schwann cells
• Non-neuronal cells e.g. melanocytes

Question 11

What is contained in grey and white matter?

Answer 11

grey matter - neuronal cell bodies (and dendrites)

white matter - (tracts) myelinated axons

Question 12

Describe the differentiation of the neuroepithelium.

Answer 12

• cells withdraw (away from the outer membrane towards the inner membrane) and undergo mitosis
• one daughter cell will remain attached to the inner membrane and the other daughter cell will move away from the inner membrane and become a neuroblast
• the neuroblast will develop processes and one will become the axon
• these axons are directed away from the inner membrane
• three layers are formed

Question 13

What are the three layers formed by the differentiation of the neuroepithelium?

Answer 13

Ependymal (layer by the inner membrane where mitosis is occurring)
grey matter (cell bodies)
white matter (axons)

Question 14

How does the arrangement of grey and white matter differ in the brain and spinal chord?

Answer 14

In the brain, the cortex (outer layer) is grey matter and white matter lies underneath the cortex.
In the spinal chord, the grey matter is on the inside and the white matter in on the outside

Question 15

Glioblasts show a similar pattern of differentiation to neuroblasts. State one difference.

Answer 15

Glioblasts can migrate into the white matter

NOTE: glioblasts do not develop axons (but they do develop processes)

Question 16

What are the layers of the neural tube? Give the embryological name for these layers swell

Answer 16

Inner ependymal layer (germinal layer)
Grey matter (mantle layer)
White matter (marginal layer)

Question 17

What guides the process of differentiation and migration (of the neuroepithelium)?

Answer 17

Signalling molecules (from the notochord)

they bind to receptors on neoblasts

Question 18

Which factors are important with regards to signalling molecules? Why?

Answer 18

Concentration - the concentration gradient determines the direction of the signalling molecules
Timing - the signalling molecules need to bind to the correct receptors on the neurones

Question 19

Later in development, what can the grey matter of the neural tube be divided into?

Answer 19

Alar plates (dorsal)
basal plates (ventral)

Question 20

Which types of neurons do the alar plate and basal plate give rise to?

Answer 20

Alar plate – interneurons

Basal plate – interneurons and motor neurones (it has motor function)

Question 21

What is the arrangement of the mature spinal chord?

Answer 21

• the neural canal has become the central canal carrying CSF (surrounded by ependymal cells)
• the alar plates have become the dorsal horns
• the basal plates have become the ventral horns
• the whole spinal chord is surrounded by a thick layer of white matter

Question 22

Which structures around the neural tube release signalling molecules and what effect do they have on the cells in the neural tube (to form the dorsal-ventral patterning)?

Answer 22

Notochord and ectoderm

Notochord releases signalling molecules that induce the cells nearest to it to differentiate into motor neurons
Ectoderm produces signalling molecules that inhibit the cells nearest to it from differentiating into motor neurons

Question 23

At approx 4 weeks, there is differentiation of the wall of the anterior neural tube to form three primary vesicles. Name these primary vesicles.

Answer 23

Prosencephalon – future forebrain
Mesencephalon – future midbrain
Rhombencephalon – future hindbrain

Question 24

Describe the changes that occur to these three vesicles in the week or so following their formation.

Answer 24

The first and third vesicles divide in two:
Prosencephalon —–> telencephalon + diencephalon
Rhombencephalon —–> pons + medulla

Question 25

What important structure begins to appear quite late in development (around 8 weeks) and where does it appear from?

Answer 25

Cerebellum – appears as an out pouching from the back of the pons

Question 26

Name the three flexures in the developing brain (folding)

Answer 26

Cephalic (head flexure)
Pontine (pons)
Cervical (base of the skull)

NOTE: they are named based on their position

Question 27

Describe the formation of the 4th ventricle (and the brainstem)

Answer 27

(in the neural tube at the region that will become the brainstem) the roof plate rapidly proliferates
this causes the alar plates to split apart so that they are lateral to the roof plate
The space left from the proliferation of the roof plate will become the 4th ventricle

Question 28

Describe the arrangement of motor, sensory and autonomic cranial nuclei within the brainstem.

motor = basal plate (ventral)

Answer 28

Motor = medial
Sensory = lateral
Autonomic = in between

Question 29

What structure divides the motor nuclei from the sensory nuclei in the brainstem?

Answer 29

Sulcus limitans

Question 30

How do neuroblasts migrate from the inner membrane to the outer membrane in the brain?

Answer 30

They attach themselves to radial glial cells and climb up them towards the outer membrane

(Radial glial cells have their cell bodies anchored to the inner membrane and have a single long process to the outer membrane)
There will be a wave of proliferation near the inner membrane then a wave of migration towards the outer membrane, this continues until 6 layers have formed.

Question 31

What happens to neuroblasts that stay in the middle of the cortex (and do not migrate)?

Answer 31

They become the basal ganglia

Question 32

How many layers of cells are there within the cerebral cortex?

Answer 32

6

Question 33

What can a deficiency of folic acid in pregnancy lead to?

Answer 33

Spina bifida