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56 Cards in this Set

  • Front
  • Back
What is neural induction?
Specification of a region of the ectoderm which will form the neural plate on the dorsal surface of the embryo.
When does the development of the nervous system begins in an embryo?
At the end of the gastrula stage of embryogenesis with embryo having 3 layers of germ cells surrounding a primitive gut.(3rd week of embryonic dev.)
What forms the skin and the nervous system?
Outer layer-ectoderm
What is the name of the critical event during neurulation?
Neural induction.
How does neurulation begin?
When a sheet of ectodermal cells(neural plate) on dorsal surface transformed into specialized tissue from which entire Nervous system develops.
Neural induction is an interaction between ectoderm and underlying mesoderm.
What is the notochord?
Distinct cylinder of mesodermal cells which extends along midline of embryo.
What does the notochord underlie?
Portion of plate which will eventually become midbrain,hindbrain and spinal cord.
Prechordal mesoderm gives rise to
What are the candidate molecules for induction of forebrain structures?
How does differentiation of subset of cells in the ectoderm into neural precursors occur?
Inductive signals sent from mesoderm to ectoderm.
How is neural tube formed?
Neural plate buckles at midline--->edges of plate elevate and fuse at dorsal midline.
Neural tube separates from overlying ectoderm.
What does the neural tube give rise to?
All cells of CNS-brain & spinal cord.
From where does the PNS arise?
Neural crest cells.(also give melanocytes of skin)
What are neural crest cells?
Transient structure that arises from dorso-lateral margins of closing neural tube.
Neural crest cells migrate away from dorsal neural tube.
True.(epithelial-mesenchymal transition occurs and neural crest cells migrate extensively throughout body.
What kind of cells do neural crest cells differentiate into?
Spinal(sensory),autonomic ganglia,Schwann cells and melanocytes.
Name one disorder of closure of spinal cord.
Spina Bifida
What factor is important in neural tube closure?
Folic acid.
As soon as neural tube closes,where does the formation of neurons and neuroglia occur?
Rapid cell division in ventricular zone-inner surface of neural tube.
In general,precursor cells can produce both neurons and glia.
What determines specific fate of a neuron?
Birthdate and environment.
Neuronal tumours are rare.
True.Most tumours are from glial cells.
At the time of closure of neural tube,there is more than one layer of columnar epithelial cells.
False.(Only 1 single layer of columnar epithelial cells-neuroepithelium)
Neurons migrate along radial glia ,away from ventricular zone.
Give a brief summary of neurogenesis and gliogenesis.
-neuroepithelial cells extend processes which span entire wall of neural tube.
-Cell nucleus migrate up process towards outer marginal zone where replication occurs.
-Nucleus migrates back to ventricular surface,retracts its processes and divides to produce 2 daughter cells.
What happens to both daughter cells early on in the process of cell genesis?
They remain in mitotic cycle.
What process marks the birthdate and fate of a cell?
After severeal divisions,a precursor cell will lose its ability to divide and will begin to migrate away from germinal zone to appropriate position in dev. NS
Most progenitor cells are likely to unipotent.
False.Most likely to be multipotent-producing glia and neurons.
Where is the intermediate zone located?(formed as neural tube expands)
Between ventricular and upper marginal zones.
What happens during 4th-5th weeks of human embryonic dev. as a result of cells migration?
Formation of 3 distinct swelling s or vesicles at rostral end of tube,in regions of future brain.
What does the forebrain vesicle give rise to?
Cerebral hemispheres and diencephalon.
Midbrain vesicle gives rise to
Adult midbrain.
Hindbrain vesicle gives rise to
Pons, medulla and cerebellum.
What is lissencephaly?
Smooth brain due to failure of cell migration.
What causes agenesis of corpus callosum>
Abnormal migration.
Neuronal heterotopias occur due to
Displacement due to abnormal migration.
What is microcephaly?
Small brain due to proliferation defects.
Radial glia turn to astrocytes eventually.
Exposure to alcohol could affect
Migration to superficial layers of cortex/ premature dismantling of radial glia.
From where do immature,post-mitotic neurons migrate to their definitive location in dev. NS?
From germinal zone.
What is radial glia?
Group of specialized supporting cells which form a scaffold along which immature neurons migrate.
What is reelin?
EC matric protein secreted by transient Cajal-Retzius cells located in the marginal zone of cerebral cortex(and hippocampus and cerebellum)
What does reelin do?
Arrests progress of neurons along radial glia.
What happens when a neuron stop progressing along radial glia?
Neuron leaves glial fibre take up definitive position within a cellular layer or nucleus.
Which layer forms first?
Layer 6
How is the formation of layers in cerebral cortex?
Inside-out(layer6,then layers 5-2)
How is migration in dev. neocortex?
Mainly RADIAL ,although some neurons undergo tangential migration from ganglionic eminences to reach destination(interneurons from subventricular proliferative zone)
On what does regional diff. of cerebral cortex seem to depend on?
Afferent input & intrinsic patterns of cell diff.
Cerebral cortex is
2-4 mm thick
Cortical plate is associated with
Beginning of cortex.
Layer 5 is found on top of layer 6.
Layer 1 is the original marginal zone with no cells really.
When are most neurons formed?
Between 10-18 wks of gestation.
Lissencephaly can result in
Mental retardation.(abnormal migration----> improper lamination)