BMS1052 Lecture Notes - Lecture 22: Prefrontal Cortex, Growth Cone, Parahippocampal Gyrus
30 May 2018
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Week 10. Neurodevelopment
BRAIN DEVELOPMENT
• Early stages of development
o Blastula stage (7-8 days after fertilisation)
Cell division and formation of blastocyst (non-differentiated cells)
Implantation of embryo
o Gastrula stage
Ectoderm: NS and skin
Mesoderm: musculoskeletal, kidney, gonads
Endoderm: GIT, glands, lungs (organs)
o Neurula stage (week 3) – neural induction
Neural plate -> cleft = where brain and neural tube forms
o Formation of neural tube (week 4)
Neural plate (tissue from ectoderm)
Neural tube: precursor to brain and spinal cord
Notochord: secretes factors that provide position and fate information
(secretes morphogens and its concentration determines fate of cell)
Somites: blocks of mesodermal tissue on either side of neural tube that goes on
to form vertebrate/skeletal muscles/tendons
• Neural tube and neural plate formation:
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• Patterning:
o Occurs due to specific environmental conditions -> different morphogens that control
dorso-ventral or rostro-caudal axis of neural tube
• Defects in neural tube development
o Whe eural tue does’t lose properly
o Eg. spina bifida = extrusion of spinal cord and meninges -> formation of lesion
• Development of brain structure
o Occurs in first month
o Brain forms after neural tube forms -> specified into different brain regions
o Complex patterning in cortex and hippocampus
o Cortical layer 1 = sparce
o Cortical layer 4 = pyramidal neurons -> projection axons all the way to skeletal and big
toe (mainly inhibitory axons)
o Needs to establish connectivity which is extremely complex
• Process of neuronal development:
1. Proliferation (cell division)
2. Migration
3. Aggregation (form layers)
4. Differentiation (neuronal commitment)
5. Circuit formation (form connections)
6. Pruning and programmed cell death (too many connections gives information overload)
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o Eg. autism is due to lack of pruning -> iforatio oerload ad a’t proess properly
o Neurogenesis = birth of new neurons
• Neuronal proliferation – neurogenesis:
Cortical progenitor cells undergo both symmetric and asymmetric divisions
o Symmetric: can generate either two progenitor cells which predominate or two neurons
which occur later
o Asymmetric: two types -> 1 neuron and 1 glial
• Neuronal migration and aggregation:
o Inside out formation (first cells there form deepest layer)
o Radial glial cells form projections dorsal to surface of brain -> provides scaffold for
neuronal precursor to climb and form layers of cortex -> called radial migration
o Neurons are born in amniotic -> are interneurons that influence activity of projection
neurons -> oe freely aout ad do’t use radial glial ells to li to surfae -> called
tangential migration
• Neuronal differentiation and polarisation – growth
o Dendrites and axons can either be attracted or repulsed
o One pole has dendrites the other has axons
How do they know? -> concentration of actin on one side of cell that has growth cone
forms axon (guided by extracellular protein eg. BMP7 guides towards them)
o Presynaptic = axon
o Postsynaptic = cell body of cell communicating with
o Synaptogenesis: interaction between presynaptic (neurexin) and postsynaptic
(neuroligins) -> neuroligins attract neurexin
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Document Summary
Brain development: early stages of development, blastula stage (7-8 days after fertilisation) Cell division and formation of blastocyst (non-differentiated cells) Endoderm: git, glands, lungs (organs: neurula stage (week 3) neural induction. Neural plate -> cleft = where brain and neural tube forms: formation of neural tube (week 4) Neural tube: precursor to brain and spinal cord. Notochord: secretes factors that provide position and fate information (secretes morphogens and its concentration determines fate of cell) Cortical progenitor cells undergo both symmetric and asymmetric divisions: symmetric: can generate either two progenitor cells which predominate or two neurons which occur later, asymmetric: two types -> 1 neuron and 1 glial, neuronal migration and aggregation: Generation and repair: regeneration: works very well in simple organisms not mammals. If clean cut nerves, can send out chemo attractants -> attract other axons to attatch: nerve damage and regeneration. Restoration of function following nerve damage can occur by: axonogenesis (mainly peripheral nerves):
