Neurological Development Three

Question 1

How many stages of cortical development are there?

Answer 1

Eight

Question 2

What are the stages of cortical development?

Answer 2

1) Neural Proliferation
2) Neural Migration
3) Neural Differentiation
4) Axonal Growth
5) Dendritic Growth
6) Synaptogenesis
7) Myelination
8) Neuronal death

Question 3

When does cortical development occur?

Answer 3

Following the formation of the five vesicle stage.

Question 4

Describe the structure and vesicles involved in forebrain development:

Answer 4

The telancephalon and diancephalon from the five vesicle stage are invovled in the cortical development.

Within the structure of the telencephalon + Diancephalon lies the primitive lateral ventricles and third ventricles.

Refer to slides for pictures

Question 5

When does neural proliferation occur?

Answer 5

With the closure of the neural tube.

Question 6

what is the process of neural proliferation?

Answer 6

Cells of the telecehpalon and diancephalon lining the ventricles i.e ventricular and subventricular cells are progenitor cells which give rise to neural cells. (neuroblasts)

One mother cell gives rise to 10,000 daughter cells. (neurogenesis)

Extremely high rate of proliferation

Question 7

In simple terms what is neural migration?

Answer 7

The movement of neuroblasts formed by the progenitor cells, up radial fibres into cortical layers.

Question 8

What are the two types of neural migration?

Answer 8

Radial and Tangenital.

Question 9

What is the major cell involved in neural migration?

Answer 9

Radial glial cells

Question 10

Describe Radial neural migration:

Answer 10

With the birth of new neuroblasts in the ventricular and subventricular layers. Processes extend from the neuroblast and wrap around the radial fibre (that extends from the subventricular layer to the meninges.) It then travels up the radial fibre to the cortical plate, where marginal cells (Cajal Retzius cells) release reelin causing it to dissociated and deposit in the cortical plate. The some moves via somal translocation up the radial fibre, Actins and intermediate filaments are critical for this. (cx26 too)

Question 11

Describe cortical organisation:

Answer 11

As time proceeds the neuroblast migration increases as does the thickness of the cortical plate. There is the formation of six distinct layers. Layer 1 is most superficial while layer six is deep. However it is formed deep to superficial. Reelin release from the marginal cells instructs deposition of neuroblasts and cortical organisation

Question 12

Name the cortical layers and use an appropraite number to indicate when they were depositied.

Answer 12

i) Molecular Layer (6)
ii) External Granular Layer (5)
iii) External Pyramidal Layer (4)
iv) Internal granular layer. (3)
v) Internal pyramidal layer (2)
vi) Multiform layer (1)

White matter

Question 13

list the order of cortical formation:

Answer 13

1 Multiform Layer
2 Internal Pyramidal Layer
3 Internal Granular Layer
4 External Pyramidal Layer
5 External Granular Layer
6 Molecular Layer

Question 14

Describe the structure of the brain from the meninges to the subventricular zone

Answer 14

Meninges
Marginal Zone
Cortical Plate
Subplate
Intermediate Zone
Subventricular Zone
Ventricular Zone

Question 15

Describe tangenital migration:

Answer 15

No radial fibre but rather the cell uses a leading process that finds a target and then the cell moves forward through somal translocation (cx26, 43 and adhesins critical for this)

Question 16

What is a quote about neural function?

Answer 16

The function of a neuron is determined by its position, its position is determined by its time of birth.

Question 17

What are some problems that can occur during neural migration/ a result of?

Answer 17

Lissencephaly

Polymicroglia

Question 18

What is lissencephaly?

Answer 18

A genetic disorder that is characterized by a smooth brain/ cortex. No well defined gyrus/sulci. Genetic mutations cause this. Resulting in severe reatrdation

Question 19

What is polymicroglia?

Answer 19

Polymicroglia is the formation of many small gyri to accommodate cortex. Caused by bacterial infection, causing severe mental retardation

Question 20

What are three things that can change cortical organisation?

Answer 20

Reelin defficiency
Smoking
Cocaine

Question 21

How does reelin deficiency affect cortical formation?

Answer 21

Results in the loss of a tightly packed hippocampus, cells spread into the grey matter and have lost the ability to know when to hop off the radial fibres. Severe cortical disorganisation.

Question 22

`How does smoking and cocaine affect cortical organisation (during pregnancy)

Answer 22

Smoking causes abberant organisation, however cocaine completely stops neural migration. Once the cocaine has worn off the neuroblasts on the radial fibres start to move again but slowly, while the next layer of neural migration moves much faster, resulting in incorrect placement of neuroblasts into cortical layers thus cortical disorganisation.

Question 23

What is an important feature of migrating cells?

Answer 23

They are structurally and functionally immature

Question 24

When does cell differentiation occur?

Answer 24

Once the neuroblasts have been deposited in a cortical layer

Question 25

Describe cell differentiation

Answer 25

Once new cells reach their destination, particular genes are turned on. Leading to growth of dendrites, an axon and proteins to cope with the environment

Question 26

What are some examples of proteins to cope with various environments?

Answer 26

Developing neurons will release…… For that particular destination:

Striatum: DARP32, Meis2
Cortex: Pax6, Emx2, Dlx2, Neuropeptide Y, Parvalbumin, Calbindin

Question 27

What are the 8 stages of cortex development?

Answer 27

Cell Proliferation
Cell Migration
Cell Differentiation
Axonal Growth
Dendritic growth
Synaptogenesis
Myelonation
Neuronal death

Question 28

Where does axonal growth occur

Answer 28

At a growth cone

Question 29

Describe axonal growth.

Answer 29

Axons have specific targets and the growth cone uses chemical and electrical gradients to aid them in finding their target. They also use multiple branches.

Question 30

Where does dendritic growth occur?

Answer 30

At the growth cone

Question 31

When does dendritic growth occur?

Answer 31

Begins prenatally and continues postnatally.

Question 32

What happens during development with regards to dendritic growth?

Answer 32

Overproduction of branches leads to pruning. The remaining dendrites continue to grow and branch. (pruning removes barely used circuitry

Question 33

Describe synaptogenesis

Answer 33

Takes place as axons and dendrites grow.
One neuron can have up to 1000 synapses.
Neurotransmitter and receptors required.

Question 34

Synapses are pruned, explain more.

Answer 34

Overproliferation of synapses occurs and pruning must tame this.

Maximum number of synapses occurs at two years.
After this pruning occurs.
by 16, 50% synapses pruned.
After 40-50 10% lost per decade.

Question 35

What significance does the lateral and medial ganglionic Eminence hold?

Answer 35

They are the most proliferative during early development and therefore give rise to a lot of the brain.

Question 36

Describe the myelonation process

Answer 36

In the CNS oligodendrocytes wrap themselves around neurons axons and deposit a lipid rich myelon sheath. This decreases the energy required for a AP and increases the velocities of AP from 1ms to 50ms.

Question 37

Describe neuronal death:

Answer 37

50% of neurons created up to seven months die. Following birth.

Structure of the brain is as much as sculpting as is growth (i.e use it or loose it)

Question 38

Describe the development of the brain from gestation to post birth in terms of stages:

Answer 38

Gastrulation
Induction
Neuralation
Fusion
Visecular stage

Neural Proliferation
Neural Migration
Neural Differentiation
Axonal growth
Dendritic growth
Synaptogenesis
Myelonation
Neuron Death