1. Development of nervous system

Question 1

What is the nave given to the dorsal medial proliferation of the ectoderm?

Answer 1

Neural plate

Question 2

What happens to neural plate as it thickens?

Answer 2

Folds up the sides and eventually two neural folds join to form a neural canal

Question 3

What is the name given to the cells at the tip of the neural fold that are excluded during fusion?

Answer 3

Neural crest

Question 4

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

Answer 4

CNS - neural tube

PNS - neural crest

Question 5

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

Answer 5

Neuroepithelium

Question 6

What’s either side of the neural canal?

Answer 6

Mesodermal somites

Question 7

What three types of cells do neuroepithelium give rise to?

Answer 7

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

Question 8

What is the notochord?

Answer 8

mesodormal in origin

below the neural canal from a transverse plane

Question 9

Are motor neurons produced from neuroepithelium?

Answer 9

Yes – 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 neurons of dorsal root ganglia and cranial ganglia
Autonomic post-ganglionic neurons
Schwann cells
Non-neuronal cells e.g. melanocytes

Question 11

Describe the arrangement of the neuroepithelium.

Answer 11

Neuroepithelium has an inner layer and an outer layer
Most cells are connected to both the inner and outer layer but the nuclei are at different positions
Nuclei tend to be further away form the inner layer (own observation)

Question 12

Describe the differentiation of the neuroepithelium.

Answer 12

Firstly, you get cells withdrawing away from the outer membrane towards the inner membrane where it undergoes mitosis
One of the daughter cells will remain attached to the inner membrane (ependymal layer) 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 (white matter), cell bodies within grey matter
Three layers are formed

Question 13

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

Answer 13

Ependymal, grey matter and white matter

AKA germinal layer, mantle layer, marginal layer

Question 14

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

Answer 14

Glioblasts can migrate into the white matter

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

Question 15

What guides the process of differentiation and migration?

Answer 15

Signalling molecules secreted by surrounding tissue interact with receptors on neuroblasts.
Concentration and timing important
Control migration and axonal growth by attraction and repulsion

Question 16

What can the grey matter of the neural tube be divided into and what neurons do they contain?

Answer 16

Alar plates (dorsal) - interneurons 
Basal plates  (ventral) - interneurons and motor neurons

Question 17

Which structures around the neural tube release signalling molecules and what effect do they have on the cells in the neural tube?

Answer 17

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 18

Around 4 weeks, you get differentiation of the wall of the anterior neural tube to form three primary vesicles. Name these primary vesicles.

Answer 18

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

Question 19

What is dorsal root ganglion?

Answer 19

a cluster of neurons, posterior

contains cell bodies of sensory neurons

Question 20

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

Answer 20

The first and third vesicles divide in two
Prosencephalon - telencephalon + diencephalon
Rhombencephalon - pons + medulla

Question 21

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

Answer 21

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

Question 22

Name the three flexures in the developing brain.

Answer 22

Cephalic
Pontine
Cervical
From distal to proximal relative to trunk

Question 23

Describe the formation of the 4th ventricle.

Answer 23

In the neural tube in the region that will become the brainstem, the roof plate rapidly proliferates and 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 24

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

Answer 24

Motor = medial
Sensory = lateral
Autonomic = in between

Question 25

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

Answer 25

Sulcus limitans

Question 26

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

Answer 26

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

Question 27

What happens to neuroblasts that stay in the middle of the cortex?

Answer 27

Become basal ganglia

Question 28

How many layers in cerebral cortex?

Answer 28

6

Question 29

What can folic acid deficiency in pregnancy lead to?

Answer 29

Spina bifida

Question 30

Describe visible neural tube defects

Answer 30

Craniorachischsis (open brain + spinal cord)
anancephaly(open brain no vault)
encephalocele(herniation of brain meninges)
iniencephaly( occipital skull and spine defects with extreme retroflexion of the head)