Neurological Development Three Flashcards
How many stages of cortical development are there?
Eight
What are the stages of cortical development?
1) Neural Proliferation
2) Neural Migration
3) Neural Differentiation
4) Axonal Growth
5) Dendritic Growth
6) Synaptogenesis
7) Myelination
8) Neuronal death
When does cortical development occur?
Following the formation of the five vesicle stage.
Describe the structure and vesicles involved in forebrain development:
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
When does neural proliferation occur?
With the closure of the neural tube.
what is the process of neural proliferation?
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
In simple terms what is neural migration?
The movement of neuroblasts formed by the progenitor cells, up radial fibres into cortical layers.
What are the two types of neural migration?
Radial and Tangenital.
What is the major cell involved in neural migration?
Radial glial cells
Describe Radial neural migration:
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)
Describe cortical organisation:
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
Name the cortical layers and use an appropraite number to indicate when they were depositied.
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
list the order of cortical formation:
1 Multiform Layer 2 Internal Pyramidal Layer 3 Internal Granular Layer 4 External Pyramidal Layer 5 External Granular Layer 6 Molecular Layer
Describe the structure of the brain from the meninges to the subventricular zone
Meninges Marginal Zone Cortical Plate Subplate Intermediate Zone Subventricular Zone Ventricular Zone
Describe tangenital migration:
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)
What is a quote about neural function?
The function of a neuron is determined by its position, its position is determined by its time of birth.
What are some problems that can occur during neural migration/ a result of?
Lissencephaly
Polymicroglia
What is lissencephaly?
A genetic disorder that is characterized by a smooth brain/ cortex. No well defined gyrus/sulci. Genetic mutations cause this. Resulting in severe reatrdation
What is polymicroglia?
Polymicroglia is the formation of many small gyri to accommodate cortex. Caused by bacterial infection, causing severe mental retardation
What are three things that can change cortical organisation?
Reelin defficiency
Smoking
Cocaine
How does reelin deficiency affect cortical formation?
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.
`How does smoking and cocaine affect cortical organisation (during pregnancy)
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.
What is an important feature of migrating cells?
They are structurally and functionally immature
When does cell differentiation occur?
Once the neuroblasts have been deposited in a cortical layer
Describe cell differentiation
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
What are some examples of proteins to cope with various environments?
Developing neurons will release…… For that particular destination:
Striatum: DARP32, Meis2
Cortex: Pax6, Emx2, Dlx2, Neuropeptide Y, Parvalbumin, Calbindin
What are the 8 stages of cortex development?
Cell Proliferation Cell Migration Cell Differentiation Axonal Growth Dendritic growth Synaptogenesis Myelonation Neuronal death
Where does axonal growth occur
At a growth cone
Describe axonal growth.
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.
Where does dendritic growth occur?
At the growth cone
When does dendritic growth occur?
Begins prenatally and continues postnatally.
What happens during development with regards to dendritic growth?
Overproduction of branches leads to pruning. The remaining dendrites continue to grow and branch. (pruning removes barely used circuitry
Describe synaptogenesis
Takes place as axons and dendrites grow.
One neuron can have up to 1000 synapses.
Neurotransmitter and receptors required.
Synapses are pruned, explain more.
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.
What significance does the lateral and medial ganglionic Eminence hold?
They are the most proliferative during early development and therefore give rise to a lot of the brain.
Describe the myelonation process
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.
Describe neuronal death:
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)
Describe the development of the brain from gestation to post birth in terms of stages:
Gastrulation Induction Neuralation Fusion Visecular stage
Neural Proliferation Neural Migration Neural Differentiation Axonal growth Dendritic growth Synaptogenesis Myelonation Neuron Death
