Ch 5 outline - 5.1 Maturation of the vertebrate brain The...

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5.1 Maturation of the vertebrate brain The human central nervous system begins to form when the embryo is about two weeks old. Dorsal surface thickens and neural tube forms Develops into spinal cord/brain Avg human brain weighs 350 grams at birth Growth and development of neurons Proliferation – production of new cells Processes in development of neurons – proliferation, migration, differentiation, myelination, synaptogenesis. Migrate – move Differentiate – forms axon and dendrites Myelination – glia produce insulating fatty sheats that accelerate transmission in vertebrate axons. Synaptogenesis – formation of synapses. (continues throughout life) Stem cells – cells that haven’t specialized into a particular type of cell yet Chemical pathfinding by axons Paul weiss grafted extra leg to salamander and waited for axons to grow into it. Came up with idea that each muscle received many signals but responded to only one
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Specificity of axon connections Weiss was incorrect Roger sperry found that in cutting optic nerves of newts, where new synapse formed, newt regained normal vision. Chemical gradients Humans have 30000 genes Growing axons follow a path of cell-surface molecules Axons with lowest concentration of TOPdv protein connect to tectal cells with lowest concentration. Ones with greatest concentration connect tectal cells with highest concentration of that chemical Competition among axons as a general principle When axons initially reach their targets, each forms synapses onto many cells
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Ch 5 outline - 5.1 Maturation of the vertebrate brain The...

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