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Development of Neural Circuits

Development of Neural Circuits. Lecture 4. Stages of Cellular Activity. 6 distinct stages 1. Neurogenesis 2. Cell migration 3. Differentiation 4. Synaptogenesis 5. Neuronal cell death 6. Synaptic rearrangement ~. Neurogenesis. Precursors (stem) cells Neural tube’s ventricular zone

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Development of Neural Circuits

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  1. Development of Neural Circuits Lecture 4

  2. Stages of Cellular Activity • 6 distinct stages 1. Neurogenesis 2. Cell migration 3. Differentiation 4. Synaptogenesis 5. Neuronal cell death 6. Synaptic rearrangement ~

  3. Neurogenesis • Precursors (stem) cells • Neural tube’s ventricular zone • Induction signals • Asymmetrical mitosis •  another stem cell • Can divide again •  neuroblast • Cannot divide • Neuroblasts  neurons & glia ~

  4. Neuronal Migration • Neural crest  PNS • Guided by cell adhesion molecules (CAMs) • Neural tube  CNS • along radial glia • later: along other neurons ~

  5. Cell Migration • Long-distance migration • Along radial glia • Tangentially to other brain areas • Cerebellar neuroblasts • Mesoencephalon  • Rhombencephalon ~

  6. Differentiation • Into specific neuron & glia types • Cell-autonomous • Genetic instructions • Cell-to-cell interactions • Induction signals • Critical periods ~

  7. Construction of Circuits • Linkage of neurons in different regions • Growth of axon from origin to target • Formation of appropriate synapses • Cell-to-cell signaling • Tropic factors • Trophic factors ~

  8. Axon Guidance • Axonal growth cone • Filopodia • Decision points • Decussate or not • Chemical cues • Ligands/receptors ~ • Non-diffusable cues • CAMs • Tropic & trophic • Diffusable chemical signals • Attraction • netrins • Repulsion • Semaphorins ~

  9. Synaptogenesis • Superior cervical ganglion (PNS) •  eyes •  ear blood vessels • After axons reach target • Establish synapse • Retract & regrow • Do not form synapse ~

  10. Synaptogenesis • Neurotropic factors • Ephrins & cadherins • Specificity  ligand/receptor types • Neurotrophic factors (neurotrophins) • After synapse formation • Cell-to-cell signals • Nerve growth factor (NGF) •  neurite growth ~

  11. Apoptosis • Neuronal cell death • programmed cell death • 20-80% of neurons in a region • lack of neurotrophic factors • Wrong or no connection • neurons wither & die ~

  12. Synaptic Rearrangement • Competition • elimination of synapses • formation of new synapses • Activity-dependent • Neurotransmitter release • Losing axon retracts • May strengthen synapse at other targets • Winner  synapses at target ~

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