Neurulation and the neural crest Flashcards
What is the CNS and what part of the embryo forms it?
- CNS = brain and spinal cord
- formed from the neural tube
What is the PNS and what part of the embryo forms it?
- PNS = sensory, enteric, sympathetic and parasympathetic
- formed from the neural crest
What does the neural tube form from?
- neural tube forms from the ectodermal layer
Where is the neural crest born?
- the neural crest is born in the dorsal part of the neural tube
Apart form the neural tube what does the ectoderm also form?
- the epidermis
What is the definition of neurulation?
- the process by which the neural tube forms from the ectodermal layer
How does the ectoderm from?
- formed from the cells that remain in the epiblast during gastrulation
What are the 4 basic steps of neurulation?
- shaping and folding (sleep)
- elevation (eat)
- convergence (cook)
- closure (chicken)
What happens during stage 1 - shaping and folding?
- shaping - the ectoderm layer thickens towards the edge by changes in shape of cells
- folding - cells along the midline form a hinge (median hinge point MHP) by attaching to the notochord
- the plate is now called the neural groove
What happens at stage 2 - elevation?
- ectoderm on either side of the neural groove pushes towards the centre causing the centre to deepen and edges to lift up
What happens at stage 3 - convergence?
- the dorsolateral hinge point (DLHP) forms which makes the neural groove bend at the top
What happens at stage 4 - closure?
- the edge of the neural tube fuse
- the ectoderm grows over the top
- once the tube is fully closed a layer of tissue fully grows over the top, that layer is now called the epidermis
Closure of the neural tube is initiated in how many different places?
- 5 different places so not craniocaudal progression
What happens if there is failure to close caudal neural tube?
- spina bifida
What happens if there is failure to close the cranial neural tube?
- exencephaly
Why is folic acid important during embryonic development?
- a lack of folic acid will cause incomplete and incorrect closure of the neural tube
what results from primary neurulation?
- the cranial neural tube is formed
- the neural plate elevated then folds to from tube
- only occurs down to lumbar level
How are the sacral/caudal regions formed?
- formed by secondary neurulation
How is the medullary chord formed?
- medullary chord formed when mesenchymal cells form a solid rod
- mesenchymal cells = stem cells that form from the mesoderm
How does a lumen from in the medullary chord?
- numerous cavities within the medullary chord eventually fuse together to from one lumen known as cavitation
Where do the neural crest cells originate from?
- originate at the junction of the epidermis and neural plate - crest neuroectoderm
What does the neural plate closure do?
- brings the epidermis in contact with the crest neuroectoderm
What happens when the epidermis contacts the crest neuroectoderm?
- this induces an epithelial to mesenchymal transition within the crest neuroectoderm
what forms the neural crest?
- neural plate cells that break away from the neural pate
How does the neural crest migrate?
- migrates along defined pathways away from neural tube
What are the neural crest derivatives?
- PNS
- pigment cells
- bone, cartilage, and connective tissue - only in the head
What is the sympathetic/parasympathetic system?
- both part of the ANS
- flow of information from the CNS to the periphery
- control gut motility, blood vessel diameter, bladder control, energy release/storage (glucose)
- basis of fight or flight / rest and digest responses
- sympathetic uses energy
- parasympathetic - conserves energy
What is the sensory nervous system?
- sensory neurons “sense” the environment and send info via the spinal cord
- flow of information from the periphery to CNS
What are the advantages to the peripheral nervous system?
- can detect changes in the environment
- can detect if being attacked
- can respond to changes and attack swiftly and in co-ordinated manner
