Development of Nervous System Flashcards
What is gastrulation
- Conversion of bilaminar embryo into trilaminar embryo
- Migration of superficial epiblast cells (totipotent) interiorly creates a third layer
What are the steps involved in gastrulation
- Epiblast cells migrate to primitive streak, form longitudinal axis
- Cells push through primitive groove and form mesoderm
- Mesoderm spreads between epipvastic and hypoblastic layers of embryonic disc
- Areas where embryonic mesoderm cells are absent form cloacal and oral membrane
What is organogenesis
- Formation of body organs and organ systems
- Endoderm, mesoderm and ectoderm
What does the endoderm form
- Inner layer from hypoblast
- GI tract / associated glands
- Lungs
- Urinary tract / mucosae
- Thyroid cells
- Pancreatic cells
What does the mesoderm form
- Middle layer, somites paired mesodermal blocks
- Muscles
- Bones
- Circulatory system
- Tubule cells of kidney
What does the ectoderm form
- Outer layer, from epiblast
- Neurulation causes differentiation to brain and spinal cord
- NS
- Skin / epidermis
- Hair
What are the phases of neurodevelopment (4)
- Neural plate formation and induction (delineation of ectoderm cells)
- Neural proliferation, migration and aggregation
- Axon growth and synapse formation
- Cell death and synapse rearrangement
What occurs in neurulation (2)
- Neural plate develops neural folds to form neural tube
- Bending: 3 hinge points, median hinge point (over pre-chordal plate) and paired dorsolateral hinges
- Folding: Rotation of plate around hinge points, elevation (folding MHP) and conversion (folding DLHP)
What are the steps in neural tube formation (neurulation)
- Cells migrate cranially from primitive node to form notochord
- Notochord induces ectodermal cells to elevate and thicken, forming neural plate
- Folds fuse to to elevation of hinge points and form neural tube (closes from middle outwards) with neural crest above
- PNS develops from neural crest
- Placodes give rise to ears and nose
What is BMP signalling
- Bone morphogenetic proteins
- Potent epidermalising agent
- Inhibition is required for neural crest induction and signalling
- Initially BMP promotes formation of non-neural ectoderm
- Inhibition is required to establish primitive neural tissue (neuroectoderm)
What is Wnt signalling
- Secreted signalling proteins
- Promote cell cycle progression in stem and progenitor cells
- Associated with BMP signal activation in dorsal spinal cord
What is a neural tube defect
- Failure of neural tube to close (1 in 500)
- Tube closes from the middle and extends anteriors / posteriorly
What are examples of neural tube defects
- Anencephaly (defect in anterior closure)
- Spina bifida (defect in posterior closure, leg weakness, orthopaedic abnormalities, paralysis)
Why is folate important in pregnancy
- Folate is a water soluble vitamin that is present in food (green leafy vegetables)
- Important in the synthesis of DNA, DNA repair and methylation of DNA
- Prevents NTD births among most women who have previously had NTD affected births
- Folate supplements of 0.4-5 mg per day suggested
What occurs during neural proliferation, migration and differentiation (2)
- Proliferation: Swellings of anterior brain become forebrain, midbrain and hindbrain, daughter cells become fixed
- Migration: Slow movement guided by radial glia, soma and immature axons, aggregation occurs once complete
- Differentiation: Cells location determines differentiation (function / precise connections), active
