Neurulation and PNS formation Flashcards
What is Neurulation?
Folding process in vertebrate embryo;
Neural plate -> neural tube
What is the new ectoderm comprised of?
Neuroectoderm and surface ectoderm
What does the notochord cause to form in the neuroectoderm?
Neural plate in week 3
What do you need the notochord for?
Neurulation and nervous system development
What happens in primary neurulation?
Neural plate –> Neural folds –> Neural tube
Where does neurulation start?
5th somite
What is the neural groove?
Center of neural plate right above the notochord that holds in place so the neural folds can fold
What happens when the neural folds enlarge and fold up?
They eventually fuse and pinch off to form neural tube
What are the lateral most cells from the neural plate called?
Neural crest cells ;
They fuse as well in between the surface ectoderm and neural tube and will eventually migrate away
What layer of the primary germ layers forms the neural tube?
Ectoderm
What and where are the 2 neural pores?
Cranial neuropore and caudal neuropore - last things to close
Neural tube closes around what?
Up and around the head and down to the 31st somite
What marks the end of primary neurulation?
Closure of cranial and caudal neuropores
What marks the end of gastrulation?
Formation of tail bud (caudal eminence)
What is secondary neurulation?
Formation of neural tube from tail bud
Describe what happens during secondary neurulation
Tail bud cells condense into medullary cord
Medullary cord cavitates and creates a lumen
The medullary cord then merges with the central canal of the neural tube
What are neural crest cells?
Neuroectodermal cells along dorsal side of neural folds that run along entire cranial-caudal neural tube
Where do the neural crest cells go?
Migrate VENTRALLY using EMT and give rise to many derivatives
List some things neural crest cells create
Create jaw, pulmonary trunk and pigment cells
Abnormalities in NCC are called
Neurocristopathies
What develops the meninges?
NCC and mesenchyme that migrate and surround neural tube to form meninx primitiva
20-35 days
What does the meninx primitiva create?
Ectomeninx and endomeninx
What then happens to the ectomeninx?
It forms spaces for venous sinuses and then dissociates to create the epidural space
The ectomeninx ultimately becomes
The dura matter
What then happens to the endomeninx?
It reticulates and subarachnoid space appears
The endomeninx ultimately becomes
The arachnoid and pia matter
Does the neural tube close simultaneously down from cranial to caudal?
NO
What can neural tube defects be attributed to?
Nutritional aspect; folic acid deficit
Anencephaly/meroencephaly
No closure at anterior head so brain is open
Encephalocele
Back of head protrusion; with or without brain tissue
Craniorachischisis
No closure at anterior head all the way to thoracic region
The PNS develops from
Neural tube, NCC, Neuroectoderm
Ventral and dorsal regions of neural tube are separated by
Sulcus limitans
Ventricular zone of neural tube
Stem cells that divide and migrate
Intermediate zone of neural tube
Differentiate into neurons and glia
Marginal zone of neural tube
Axons that will eventually be myelinated
1st cells that come out of neuroblasts
Neurons
2nd cells that come out of neural tube
Glioblasts that form Macroglia
Regions of the growing neural tube
Roof and floor plate, alar and basal plate, sulcus limitans
What does the sulcus limitans do?
Separate afferent signals and efferent signals
Alar plate
Dorsal (posterior) that produces sensory neurons
Basal plate
Ventral (anterior) that produces motor neurons
What is needed for motor neuron identity?
increased SHH that activates NKX2.2 and NKX6.1 genes for anterior motor neuron formation
What is needed for sensory neuron identity?
BMP/TGF-beta that activates PAX3 and PAX7 to create posterior sensory association neurons
Where does the lateral horn stem from?
Dorsal side of the basal plate that forms the intermediolateral cell columns
What does the lateral horn produce?
Visceral motor neurons due to coming from basal plate (motor neurons) – smooth muscle ANS
Preganglionic cells from
Neuroectoderm
Ganglionic cells from
NCC
List some neurocristopathies
Piebaldism, micrognathia, hirshspung disease, mandibulofacial dystosis, goldenhar syndrome
