Development of nervous system

Question 1

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

Answer 1

Neural Plate

Question 2

What happens to the neural plate as it thickens?

Answer 2

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 3

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

Answer 3

Neural Crest

Question 4

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

Answer 4

Neural tube – CNS

Neural crest – PNS

Question 5

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

Answer 5

Neuroepithelium

Question 6

What three types of cells do neuroepithelium give rise to?

Answer 6

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 7

Are motor neurons produced from neuroepithelium?

Answer 7

Yes – although most of their axons are outside the CNS, their cell bodies are within the spinal cord

Question 8

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

Answer 8

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

Question 9

Describe the arrangement of the neuroepithelium.

Answer 9

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

Question 10

Describe the differentiation of the neuroepithelium.

Answer 10

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 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 11

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

Answer 11

Ependymal, grey matter and white matter

AKA germinal layer, mantle layer, marginal layer

Question 12

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

Answer 12

Glioblasts can migrate into the white matter

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

Question 13

What guides the process of differentiation and migration?

Answer 13

Signalling molecules

Question 14

Which factors are important with regards to signalling molecules?

Answer 14

Concentration and timing

Question 15

What can the grey matter of the neural tube be divided into?

Answer 15

Alar (interneurons) and Basal (interneurons and motor neurons) plates

Question 16

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

Answer 16

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 17

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

Answer 17

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

Question 18

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

Answer 18

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

Question 19

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

Answer 19

Cerebellum appears as outpouching from back of pons

Question 20

Name the three flexures in the developing brain.

Answer 20

Cephalic
Pontine
Cervical

Question 21

Describe the formation of the 4th ventricle.

Answer 21

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 22

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

Answer 22

Motor = medial 
Sensory = lateral 
Autonomic = in between

Question 23

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

Answer 23

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 24

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

Answer 24

Become the basal ganglia cells

Question 25

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

Answer 25

Six

Question 26

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

Answer 26

Spina Bifida (Incomplete closure of bones and membranes around spinal cord)

Question 27

What condition occurs if neural tube doesn’t close rostrally?

Answer 27

Anencephaly – Near complete absence of brain and lack of skull vault (Incompatible with life)

Question 28

What happens if there is herniation of the brain during development?

Answer 28

Results in Encephalocele (Ectopic brain substance)

Question 29

What happens if there is herniation of the meninges during development?

Answer 29

Results in Meningocele – a CSF filled protrusion through a skull or spinal defect

Question 30

What happens in the case of development of open spinal cord?

Answer 30

A Myelomeningocele – The open cord with a meningeal cyst that projects through white matter

Question 31

Where can neural stem cells be found in adults?

Answer 31

Sub-ependymal areas of brain (This is where germination level was in development)

In hippocampus (No one is sure why)

Question 32

What early structure develops into the vertebral column?

Answer 32

Notochord - A cartilaginous strip

Question 33

Where do microglia originate?

Answer 33

Systemically - enter brain early in development