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first week of human development
- day 0 fertilization in the tubes
- day 6 blastocyst formation (trophoblast/blastocoele/inner cell mass)
- day 7-10 implantation in the lining of the uterine wall
- day 8 formation of embryonic disc (bilaminar disc) of the implanted blastocyst (epiblast/dorsal columnar layer - hypoblast/ ventral cuboidal layer)
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gastrulation
- developement of the three germ layers
- occurs during the 3rd week of development
- epiblast (forms all 3 germ layers) cells migrate through the primitive streak laterally and cranially between the epiblast and hypoblast and become incorparated in the hypoblast |(polonaisien movement)
- bilaminar embryo becomes trilaminar as the ectoderm, mesoderm and endoderm form
- primitive streak closes off forming the noto chord which is a mesodermal structure that signals neuralation (primitive node at the tip)
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neuralation
- formation of the neural tube (ectodermal structure)
- occurs from 3rd-4th week
- induced by noto chord
- ectoderm thickins forming the neural plate (only above the notochord) day 17
- neural plate folds forming the neural groove day 18
- neural tube separates from ectodermal surface (leaves behind crest cells) day 20
- neural groove closes off and forms the neural tube (contains CSF) day 22
- anterior neuro pore closes day 24
- posterior neuro pore closes day 26 (both helped be vitamin b12/ folic acid)
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neural crest cells
- form:
- sensory ganglia of cranial nerves 5,7,9,10
- post ganglionic neuraons of the ANS
- Glial cells
- Schwann cells
- Satelite cells of PNS
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clinical problems
- anencephaly- failiure of anterior neuropore closure and disruption of the surrounding somites
- spina bifida- failiure of posterior neuropore closure and disruption of surrounding somites
- spina bifida occulta - large birth mark and hair where missing bone is located
- meningocele - fluid filled sace forms behind the spine
- myelomeningocele - spinal cord and cord covering protrude behind the spine
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developement of the spinal cord
- formed from caudal 1/3 of the neural tube
- 1 - migratio of neuroblast cells from ventricular zone to the mantle zone
- 2 - differentiation of neuroblast cells to neuron cell bodies in mantle zone and the differentiation of glioblast celss into neuroglial cells (astrocytes and oligodendrocytes)
- 3 - axonal growth from the neuron cells bodies out into the marginal zone
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