major early events

how is the neural tube formed from the neural plate?

• the ectoderm towards the edges thicken through a shape change in cells

• cells along the midpoint form a hinge (median hinge point-MHP) by attaching to the notocord

• the plate is now called the neural groove

• epidermis either side pushes neural groove and begins to push up

• DLHP (dorsolateral hinge point) forms and make the neural groove bend at top

• tube edges fuse together

• ectoderm grows on top

what is spina bifida

spinal cord and protective vertebrae fail to develop due to neural tube closure failure

what is exenphaly

cranial part of neural tube fails to close or fuse so brain is exposed out of the skull without a bony covering

secondary neurulation

• primary neurulation only occurs down to the lumbar (hindlimb) level

• sacral/caudal regions formed by secondary

• mesoderm not ectoderm

• mesenchymal cells form the medullary cord

• numerous cavities develop which fuse into one lumen (cavitation)

• tube fuses with primary to form one tube

how is the neural crest formed?

• neural crest cells originate at a junction between the epidermis and neural plate called the crest neuroectoderm

• closure of neural plate brings epidermis in contact with crest neuroectoderm

• this induces an EMT in crest neuroectoderm

• this causes cells to lose cell to cell connections, become migratory

• neural plate cells which break away form neural crest

• neural crest migrates along defined pathways away from neural tube

neural crest derivatives

• PNS

• pigment cells

• bone, cartialage and connective tissue in the head

PNS

• sympathetic/parasympathetic neurons/ganglia and glia

• sensory neurons/ganglia and glia in trunk

advantages of a pns

• can detect environmental change

• can detect if being attacked

• can respond to changes and attack swiftly in a coordinated manner