Development of the CNS

Question 1

What are the layers for the development of the CNS? Draw this.

Answer 1

See diagram. endoderm, mesoderm + notocord, ectoderm (neural plate)

Question 2

What happens to the ectoderm in the embryonic disk around 3 weeks?

Answer 2

There is proliferation of the ectoderm in the dorsal midline called the neural plate

Question 3

What happens to the neural plate?

Answer 3

The neural plate folds together. When the neural folds come together it forms the neural canal. On the tips of the neural folds you get a bunch of cells called the neural crest. The neural crest separates from the neural tube.

Question 4

What are the two independent sources of nervous tissue?

Answer 4

Neural tube - CNS cells

Neural crest - PNS cells

Question 5

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

Answer 5

Neuroeptithelium

Question 6

What are the different cell types that come from the neuroepithelium?

Answer 6

Neuroblasts - precursor to all cells have cell bodies in the CNS
Glioblasts - precursor to neuroglia (astrocytes and oligodendroytes)
Ependymal - line the ventricles, central canal and neural tube. Inner layer of the neural tube

Question 7

Where do motor neurones originate from in terms of the cell types derived from the neuroepithelium?

Answer 7

They are neuroblasts. They have cell bodies in the CNS even though most of their axons are in the PNS

Question 8

What are the different cell types that come from the neural crest?

Answer 8

Sensory neurones of the dorsal root ganglia and cranial ganglia
Postganglionic autonomic neurones
Schwann cells
Non-neuronal derivatives e.g melanocytes

Question 9

Describe the cellular organisation of the neuroepithelium

Answer 9

The cells are attached to both the inner and outer membranes

Question 10

Describe the differentiation of the neuroepithlieum

Answer 10

See diagram. Neuroblasts.
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

Glioblasts have a similar pattern of differentiation and migration to neuroblasts but glioblasts can migrate into white matter as well. Remember glioblasts are support neuronal cells

Question 11

What are the layers formed from the differentiation of the neural epithelium?

Answer 11

Ependymal Layer - Layer by the inner membrane - where mitosis occurs - germinal layer
Grey Matter - Layer of cell bodies - mantle layer
White Matter - Layer of axons - marginal layer

This is the beginning of the difference between grey and white matter. Grey matter = cell bodies White matter = axons

Question 12

What do glioblasts develop?

Answer 12

Processes NOT axons

Question 13

What are the roof and floor plate?

Answer 13

These show the most dorsal and ventral parts of the canal

Question 14

What is the process of differentiation and migration controlled by?

Answer 14

Signalling molecules that are secreted from the tissues surrounding the neural tube or by cells within the tube.
They interact with receptors on neuroblasts controlling migration and axonal growth by attraction and repulsion.
Depends on the concentration gradient and timing. Higher concentration when the signalling molecules are close to the source

See notes - Dorso-ventral patterning

Question 15

Draw the layers of the neural tube in cross section

Answer 15

Draw diagram

Question 16

During later stages of development what the grey matter split into?

Answer 16

Alar plate - dorsal; INTERNEURONES specialised to receive sensory information coming from the dorsal root ganglia (neuronal crest)
Basal plate - ventral; Some INTERNEURONES mainly developing MOTOR NEURONES

These terms are only used for the embryonic nervous system - neural tube

Question 17

What do the different parts of the neural tube develop into? (The mature spinal cord)

Answer 17

Neural canal –> central canal - carries CSF
Alar plate –> dorsal horn
Basal plate –> ventral horn

The whole spinal cord is surrounded by a thick layer of white matter

Question 18

How does the brain stem develop?

Answer 18

See notes. 4th Ventricle, Roof plate, Alar plates,

Question 19

Draw the structure of the brain at 4 weeks and label the sections

Answer 19

See diagram

Question 20

What are the primary vesicles of the anterior neural tube that will form the brain?

Answer 20

Prosencephalon - Future forebrain - divides into two
Mesencephalon - Future midbrain
Rhombencephalon - Future hindbrain - divides into two

Question 21

What do the primary vesicles divide into to form the secondary vesicles?

Answer 21

Telencephalon
Diencephalon
Mesencephalon - stays the same 
Pons
Medulla

Separation of the vesicles happens at 5 weeks

Question 22

What happens at 8 weeks of brain development?

Answer 22

See diagram. Ventricles

Question 23

What are the flexures of the three vesicles?

Answer 23

Cephalic flexure - By 8 weeks the telencephalon has got so big its started to move back and cover the diencephalon
Pontine flexure
Cervical flexure

Question 24

What is the organisation of matter in the brain?

Answer 24

White matter inside and grey matter outside

This occurs due to the migration of neurones from the inner membrane where they proliferate along radial glial cells.

Question 25

How is the basal ganglia formed?

Answer 25

From neurones migrating and stopping in the middle

Question 26

Describe the orientation of radial glial cells

Answer 26

They have their cell bodies anchored in the inner membrane and have a single long process that extend out to the outer membrane.

Question 27

How many layers are there in the cerebral cortex?

Answer 27

6 layers - wave of proliferation and migration. Each layer has different types of cells with different functions and different connections

Question 28

Developmental disorders of the nervous system

Answer 28

Normal development depends on the coordinated completion of several complex processes (e.g. proliferation, differentiation, migration, axon growth and synapse formation)

Genetic mutation and environmental factors such as the mother’s lifestyle, diet and teratogens can interfere with these processes

See slide 27

• Craniorachischisis
• Anencephaly
• Encephalocele
• Iniencephaly
• Spina bifida occulta
• Closed spinal dysraphism
• Meningocele
• Myelomeningocele