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Chapter 2: Brain Development

Chapter 2: Brain Development. TJHSST Neuroscience Society Prepared by Usnish Majumdar. Development. First neurons must be created (differentiated cells) Neurons must then migrate Axon-dendrite migration and connection occurs. 3 Layers of Embryo. Ectoderm (“ ecto ” latin = outside)

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Chapter 2: Brain Development

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  1. Chapter 2: Brain Development TJHSST Neuroscience Society Prepared by UsnishMajumdar

  2. Development • First neurons must be created (differentiated cells) • Neurons must then migrate • Axon-dendrite migration and connection occurs

  3. 3 Layers of Embryo • Ectoderm (“ecto” latin = outside) • Skin • Neural Tissue • Mesoderm (“middle” latin = middle) • Endoderm (“endo” latin = within) http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/Bio%20102/Bio%20102%20lectures/Animal%20Diversity/Protostomes/Lophotrochozoans/Image7.gif

  4. Neural Tube • Formed 3-4 weeks after conception • Two parallel ridges form from ectoderm tissue • Hollow • Forms spinal cord and Brain http://scienceblogs.com/retrospectacle/2007/06/neurological_defect_spotlight.php

  5. Cell Differentiation • Most embryonic cells are pluripotent stem cells • A variety of chemicals signal cells to turn into specialized cells • Ectodermal cells are inhibited by molecules, signalling a development into neural cells and not skin cells • After neural cell determination: • Sonic hedgehog – protein secreted from mesoderm • Higher concentration = glial cell • Lower concentration = motor neuron • Even lower concentration = interneuron

  6. More Cell Differentiation (Yes, this is important) • Signals help determine the specific neurotransmitters that can be used by a neuron • If neurons are cultured by themselves = norepinephrine • Cultured with cardiac tissue = acetylcholine • Based on different genes turning off and on

  7. Neuronal Migration in The Brain • Neurons produced in center of tube, migrate outward • Ventricular zone -> Marginal zone • Migration prominent in cortex • Mechanisms • Neurons migrate along fibers to destination • inhibitory interneurons migrate tangentially • External forces that can disrupt proper neuronal migration: • Alcohol, Cocaine, Radiation, etc.

  8. Connections • Axons travel long distances until they find dendrites • In the case of a motor neuron, axon may travel from spinal cord to foot

  9. Axon Growth • Controlled by Growth Cone • Contains receptors for certain signaling proteins • Signaling proteins (actually classes of proteins) • Netrin • Semaphorins • Ephrins • Possible effects • Move forward • Stop • Recoil • Change Direction • Axon meets Dendrite and forms synapse • Additional molecules help with target recognition • Last process is the wrapping of axon in myelin

  10. Cervical Thoracic Lumbar Sacral

  11. Paring Back • Neural network is ‘pruned’ to create a more efficient and accurate system (too many connections at first) • Apoptosis: programmed cell-death • AP Biology: regulated by several proteins • Neuron doesn’t receive enough trophic factor to deter these proteins, it dies • Each trophic factor supports a specific group of neurons • Ex: nerve growth factor = sensory neuron survival

  12. Critical Periods • Important period when nervous system must obtain certain critical experiences. • “use it or lose it” • Enriched environments bolster brain development

  13. Development Continues • Even in your late teens, your brain is still maturing. • Frontal lobe is last to become connected with myelinated axons • Judgement, insight, and impulse control • …college students …

  14. Quiz: 5 minutes, 15 Questions

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