Neurobiology
Brain development & corticogenesis
Development of the Nervous System
1. Neural Induction
2. Polarity and Segmentation
3. Neurogenesis and Migration
4. Determination and Differentiation
5. Axon Growth and Guidance
6. Target Selection
7. Naturally occurring neuron death
8. Synapse Formation and Function
9. Refinement of Synaptic Connections
Neural induction
The blastocyst develops into a gastrula (primary germ
layers, serve as primitive tissues from which all body organs
will derive) with three primary germ layers - ectoderm,
endoderm, and mesoderm.
The neurulation process
The neural tube is transformed
into the primitive structures that
will later develop into the
central nervous system
The notochord induces the
formation of the central nervous
system (CNS) by signalling the
ectoderm germ layer above it to form the thick and flat neural plate. The neural
plate folds in upon itself to form the neural tube, which will later differentiate into the
spinal cord and the brain, eventually forming the central nervous system
Notochord – rod of mesodermal cells that serves as axial support
Polarity and segmentation
1
,There are many more things influencing this
segmentation. Intrinsic mechanism cause
different genes to be transcribed in different
places.
Neurogenesis and migration
The overall length of the progenitor cell cycle
increases during embryogenesis.
Radial migration in the cortex
There are many human malformations due to
migration defects.
Determination and differentiation
When a neural progenitor left in its normal
environment turns into a particular type of neuron.
An intrinsically determined progenitor′s fate is
unchanged by transplantation to a different
environment.
A progenitor whose fate is determined
extrinsically and so is changed by transplantation
to a different environment.
Axon growth and guidance
2
, The Growth Cone
• Extension and retraction of filopodia
• Cytoskeletal-dependent
• Adhesion of filipodia - allows growth cone to pull the cell
• Filipodia find path
Axonal projections are dependant on
attractors and repulsons
4 major families
• Netrins
• Slits
• Semaphorins
• Ephrins
A sensory neuron turns toward a pipette that is ejecting nerve
growth factor (NGF) and thus producing a diffusible gradient.
Each time the pipette is moved, the axon reorients its growth.
Target selection
Conceptual stages of targeting
1. Defasciculation
2. branching and inhibition
3. axon guidance gradient
4. find topographic correct layer
5. target right cells
Naturally occurring neuron death
Five sources that influence neuron survival →
A comparison between apoptosis and necrosis
Apoptosis: shrinkage, nuclear matter
condensed, forming crescent- shaped
figures.
Necrosis: mitochondria stop functioning >
no osmotic balance. Swelling, autolysis,
and finally bursts open.
3
Brain development & corticogenesis
Development of the Nervous System
1. Neural Induction
2. Polarity and Segmentation
3. Neurogenesis and Migration
4. Determination and Differentiation
5. Axon Growth and Guidance
6. Target Selection
7. Naturally occurring neuron death
8. Synapse Formation and Function
9. Refinement of Synaptic Connections
Neural induction
The blastocyst develops into a gastrula (primary germ
layers, serve as primitive tissues from which all body organs
will derive) with three primary germ layers - ectoderm,
endoderm, and mesoderm.
The neurulation process
The neural tube is transformed
into the primitive structures that
will later develop into the
central nervous system
The notochord induces the
formation of the central nervous
system (CNS) by signalling the
ectoderm germ layer above it to form the thick and flat neural plate. The neural
plate folds in upon itself to form the neural tube, which will later differentiate into the
spinal cord and the brain, eventually forming the central nervous system
Notochord – rod of mesodermal cells that serves as axial support
Polarity and segmentation
1
,There are many more things influencing this
segmentation. Intrinsic mechanism cause
different genes to be transcribed in different
places.
Neurogenesis and migration
The overall length of the progenitor cell cycle
increases during embryogenesis.
Radial migration in the cortex
There are many human malformations due to
migration defects.
Determination and differentiation
When a neural progenitor left in its normal
environment turns into a particular type of neuron.
An intrinsically determined progenitor′s fate is
unchanged by transplantation to a different
environment.
A progenitor whose fate is determined
extrinsically and so is changed by transplantation
to a different environment.
Axon growth and guidance
2
, The Growth Cone
• Extension and retraction of filopodia
• Cytoskeletal-dependent
• Adhesion of filipodia - allows growth cone to pull the cell
• Filipodia find path
Axonal projections are dependant on
attractors and repulsons
4 major families
• Netrins
• Slits
• Semaphorins
• Ephrins
A sensory neuron turns toward a pipette that is ejecting nerve
growth factor (NGF) and thus producing a diffusible gradient.
Each time the pipette is moved, the axon reorients its growth.
Target selection
Conceptual stages of targeting
1. Defasciculation
2. branching and inhibition
3. axon guidance gradient
4. find topographic correct layer
5. target right cells
Naturally occurring neuron death
Five sources that influence neuron survival →
A comparison between apoptosis and necrosis
Apoptosis: shrinkage, nuclear matter
condensed, forming crescent- shaped
figures.
Necrosis: mitochondria stop functioning >
no osmotic balance. Swelling, autolysis,
and finally bursts open.
3
