chapter 2: brain development
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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) - PowerPoint PPT PresentationTRANSCRIPT
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Chapter 2: Brain DevelopmentTJHSST Neuroscience Society
Prepared by Usnish Majumdar
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Development
• First neurons must be created (differentiated cells)
• Neurons must then migrate• Axon-dendrite migration and connection
occurs
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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
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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
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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
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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
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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.
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Connections
• Axons travel long distances until they find dendrites
• In the case of a motor neuron, axon may travel from spinal cord to foot
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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
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Cervical
Thoracic
Lumbar
Sacral
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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
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Critical Periods
• Important period when nervous system must obtain certain critical experiences.
• “use it or lose it”• Enriched environments bolster brain
development
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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 …
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Quiz: 5 minutes, 15 Questions