SDL-4 Neuroembryology (1) Flashcards
What does the ectoderm become?
Skin, sweat glands, hair, teeth, eye & ear, and pituitary
What does the mesoderm become?
Most organs, connective tissue, DURA MATER
What does the endoderm become?
Epithelial linings (GI, lung, bladder), parenchyma of 4 throat structures (Tonsils, Thyroid, paraThyroid, Thymus), liver and pancreas
Describe primary neuralation.
Induction of the ectoderm to form the neural plate until ectoderm fusion over neural tube
What genes are important in primary neurulation?
- Sonic hedggehog (Shh)
- FGF8
- BMP4
- TGFb
What is formed in primary neurulation?
C1-S2 segments
What are some defects associated with primary neurulation?
Craniorachischisis totalis, anencephaly, myeloschisis, encephalocele, myelomeningocele
What is Sonic hedgehog (Shh)?
- Protein that induces overlying ectoderm to differentiate into neuroectoderm,
- Signals for cell differentiation into VENTRAL spinal cord
- Basal plate under influence of Shh
- Opposes BMP gradient (promotes dorsoventral differntiation)
What is Bone Morphogenic Protein (BMP)?
- Protein that signals for cell differentiation into DORSAL spinal cord
- Alar plate under influence of BMPs
- Opposes Shh gradient (promotes dorsoventral differntiation)
What are Homeobox genes (Hox genes)?
- A set of genes that are variably expressed at different levels of the spinal cord and determines head-to-toe development
- Important for anterior-posterior axis development and secondary neurulation
What is the cause of Craniorachischisis totalis?
- Complete failure of neurulation - exposed tissue dies.
- Incompatible with life
What is the cause of Myeloschisis?
Posterior neuropore not closed, neural plate caudal to NECK is open
What is the cause of Myelomeningocele?
Partial failure of posterior neuropore closure
What is dysjunction?
Separation of neural tube from surface ectoderm
Describe neural crest cells.
Transition from epithelial to mesenchymal, migrating away from neuroectoderm to mesoderm
What do neural crest cells become?
Nerve ganglia, autonomic ganglia, meninges, PNS glial/schwann cells (and connective tissues, melanocytes, & thyroid)
Describe secondary neurulation.
Mesenchymal cells around “posterior” neural tube (caudal mass region) form a tube and fuses with neural tube
What is formed in secondary neurulation?
S3-Coccyx innervations
What are some defects associated with secondary neurulation?
Diastematomyelia, tethered spinal cord, caudal regression syndrome
What is Tethered spinal cord?
Fixed caudal end of spinal cord (filum terminale anchors spinal cord, rendering it inflexible)
What is Diastematomyelia?
Split spinal cord due to persistence of neuroenteric canal
What is Caudal Regression Syndrome?
Sacral hypoplasia/hypoplasic femurs
What is Spina Bifida Meningocele?
Fluid-filled sac of meninges protrudes outwards
Neurological symptoms present
Spina Bifida Myelomeningocele (neural tissue included in fluid filled sac)
What is Spina Bifida Cystica?
Meninges or neural tissues protrude outwards