Notes 3 - Neurodevelopment 19:23 Neurodevelopment,...

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Neurodevelopment 19:23 Neurodevelopment, Disorders of Development The Three Prenatal Stages: Overview Days 1-6 post-fertilization o Cellular division ~16 cells day 3 (somewhat slow) ~200 cells day 6 (division picks up) o Zygote travels to uterus and implants in the wall Has to move form the fallopian tube where it is fertilized to the uterus ~1/5 th  of one millimeter on day 14, size after 2 weeks From gestational day (when pregnancy started) 15/week 3 through week 8 o Embryonic period  o For humans pre-natal development spans about 38 weeks in total Gestational week 9-38 o Fetal period Development in the Embryonic Stage ~21 days (week 3) o so far we’ve had a blastocyst in the first couple of weeks, and then around  this time it flattens and becomes a disc, then the disc folds in on itself folding over of the ectoderm (the back cells) over which becomes the  spinal cord
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creates a hole within itself, becomes the central canal of the spinal  cord o 1.  Neural plate  forms o 2. Folds close around the  neural groove o 3. Closes around the  neural tube Reason we have two sides to our nervous system is this folding, a left  and right part o o Rapid changes during embryonic stage 33 days, flat fold over organism starts to curve around o
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37 days, a lot of fill in of cells, there is a good deal of celluluar proliferation,  stuff is going where it needs to go o rudimentary vital organs o not a lot of brain, the folded over hemispheres are there but there is still  unfilled early skin/membrane without a lot of cells in it o 57 days, much more cells filled in so there is an actual structure o Phases of Neurodevelopment
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“Progenitor” cells in the ventricular zone (inner cell layer closest to the ‘hole’)  of the neural tube o happens in two phases: o 1. Symmetrical division  a “progenitor” cell (that makes other cells) undergoes symmetrical  division initially – it produces two of itself, multiplying until the  ventricular zone becomes very thick, stockpiled with unspecialized  cells o 2. Asymmetrical division Around 7 weeks, we enter a new phase where the progenitor cells  aren’t just multiplying into the same, “asymmetrical division” They’re multiplying and producing a neuron Radial glial cells o Has a cell body in the ventricular zone (think of it as an axon structurally,  though it doesn’t release neurotransmitters), ends of axon reach up to  most outer layer (layer of pia) and forms a structure o Radial glia radiate from the ventricular zone, provide ladders for neurons  to crawl up Cajal-Retzius (C-R cells) o Near radial glia terminal ends
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