Neurulation Flashcards
How is the CNS closed tube formed?
Ectoderm along the dorsal surface folds inwards, driven by local cell shape changes along three stripes. Instructions from notochord/ inward push due to cell proliferation leads to sealed ectoderm and neural tube formation
How does spinal bifida occur?
When sealing of neural tube and separation from the ectoderm fails; paralysis, bad for maturation of spine, vertebrae cannot form
What is anencephaly?
Inside of the brain is open to back of head so stops brain growth/ upper brain missing (incompatible for post-natal life)- sealing has not occurred
How is spinal bifida and anencephaly a public health issue?
Common when deprived of folic acid (green vegetables and fruit)- needed for DNA synthesis
How does fetus- in-fetu occur?
Slightly delayed twin is caught inside closing folds of the neural tube
How is segmentation obvious in the human body?
Shingles (grief/stress) strips where each nerve serves form sensory ganglia
When is segmentation first seen in the developing embryo?
Mesoderm each side of the midline divides into somites (precursors of vertebrae)- head to tail
How does the embryo use neurulation differences to create more internal differences?
Notochord releases signalling molecule SHH up to floorplate, different concentrations cause different proteins to be synthesised/ signals from neighbour can pattern a tissue
How does signals from the neural tube cause differentiation of tissues?
High concentration of SHH and low concentration of other protein= bone, varying concentrations of short/long/ different protein types causes different tissue to form (early organogenesis)
What are neural crest cells?
Dorsal cells that leave neural tube and diffuse/ move to create new tissue such as facial tissues
How is the position of features determined and how might this create abnormalities?
Centreline of face where two neural crest streams meet from back of head- if ventral walls haven’t sealed properly/ fetus in fetu occurs then neural crest streams in different places
How does a cleft palate occur?
The lateral and median palatal shelf do not fuse together properly so secondary palate has connection to nasal cavity
