Embryology 2 - Neurulation, Folding, and Development of the Nervous System Flashcards
Roles of the Norochord?
- Establishes longitudinal axis and gives embryo rigidity
- Signals for MSK and CNS development
- Contributes to IV discs
What type of cells dive into primitive pit to develop notochord?
Mesenchymal cells
What forms when mesenchymal cells dive into primitive pit?
Notochordal process
When the notochordal process develops a lumen, what is it then called?
Notochordal canal
After the notochordal process approaches the prechordal plate, the floor of the notochordal process “fuses” with the endoderm and is called what?
Notochordal plate
Is there a canal present when the notochord is fully developed?
No canal present
Notochordal plate -> notochord transition starts _____ and progresses ______
Cranially; caudally
The notochord and its preceding structures are important what?
Organizers
What does the notochord not go beyond?
The prechordal plate
What does the pre-chordal plate develop into?
The oropharyngeal membrane two layer memb
What forms at the caudal aspect of the primitive streak? What is it the future site of?
Cloacal membrane two later memb. Future site of anus
Small, vascularized diverticulum (outpouching) from the caudal wall of umbilical vesicle, extending into connecting stalk
Allantois
What is the function of the allantois?
Early blood formation and bladder development
What is formed (overall) by neuralation?
Neural tube
First step of neuralation?
Notochord => neural plate
What does invagination of the neural plate form?
Neural groove with neural folds on either side
What forms when the neural folds fuse together?
Neural tube
What is the neural tube the primordium of?
CNS
When is neurulation complete?
By the end of week 4
What are the neural crest cells derivatives of?
Many structures of the PNS (mainly ganglia)
What is the intraembryonic mesoderm on either side of the notochord called?
Paraxial mesoderm
Cuboidal masses of mesoderm on wither side of the notochord, visible along the dorsolateral surface of the embryo on each side of the neural tube?
Somites
What forms somites?
Paraxial mesoderm
What do somites give rise to?
Most of the axial skeleton and associated musculature + dermis in those areas
What do the mesenchymal cells that migrate anteriorly (lateral to the notochordal process) form? What does this give rise to?
Cardiogenic mesoderm. Gives rise to embryonic heart primordia
What do the primordium of intraembryonic coelom (embryonic body cavity) appear as?
Isolates spaces in the lateral and cardiogenic mesoderm
What does the intraembryonic coelom divide the lateral mesoderm into?
Two layers:
1. Somatic layer = continuous with mesoderm covering amnion
2. Splanchnic layer = continuous with mesoderm covering umbilical vesicle
What day do the coelomic spaces form a continuous cavity?
approx. day 21
What are the three general structures that can be seen in the region of the lateral mesoderm?
- Somatopleure
- Splanchnopleure
- Intraembryonic coelom
What is somatopleure?
Somatic mesoderm and overlying ectoderm - forms the body wall
What is the splanchnopleure?
Splanchnic mesoderm and underlying intraembryonic endoderm - forms embryonic gut
What are the 3 main cavities that the intraembryonic coelom develops into in the second month?
- Pericardial cavity
- Pleural cavity
- Peritoneal cavity
When does embryonic folding begin?
End of the third week
As the embryo folds cranially ______ begin to appear
Brain vesicles
As the embryo folds laterally ____ is formed
Body wall
In cranial folding, part of the umbilical vesicle is incorporated into the embryo as what?
The foregut
What does the foregut lie between?
Brain and heart
What separates the foregut from the stomoderum?
The oropharyngeal membrane
What is the stomodeum?
The primordium of the mouth
What structure lies caudal to the heart? What does it develop into?
Septum transversum - becomes the central tendon of the diaphragm
The head fold moves the heart to the _____ surface of the embryo
Ventral
During tail folding, part of the endodermal germ layer is incorporated into the embryo as what?
The hindgut
In tail folding, the connecting stalk is now attached to the _____ surface, and the allantois is partially ________
Ventral; incorporated into the embryo
What causes lateral folding?
Rapidly growing spinal cord and somites
As the abdominal walls form, part of the endoderm germ layer is incorporated into the embryo as what?
The midgut
After lateral folding, the connection between the midgut and umbilical vesicle is narrowed to what structure?
Omphaloenteric duct
Ectoderm theme?
- CNS, PNS
- Epidermis = structure (skin, nails)
- Neural crest cells
Endoderm theme?
- Epithelial linings of most structures in the body
- Thyroid and parathyroid glands
Mesoderm theme?
- Everything else
At day 22, the cranial 2/3 of the neural tube forms the ______, and the caudal 1/3 forms the ______
brain; spinal cord
The first layer of the spinal cord that gives rise to all of the neurons and macroglia?
Ventricular zone
What does the intermediate zone of the neural tube become populated with?
Primordial neuroblasts derived from the ventricular zone
What does the outer marginal zone of the neural tube give rise to?
White matter tracts
What happens when the neuroepithelial cells cease producing neuroblasts and glioblasts?
They differentiate into ependymal cells
What do ependymal cells make?
CSF
What are formed by sites of rapid growth of the neuroepithelium?
Alar and basal plates
What separates the alar and basal plates?
Sulcus limitans
Cell bodies in the alar plates form _____
Dorsal grey horns (afferent)
Cell bodies in the basal plates form ______
Ventral and lateral grey horns
What are the unipolar neurons in the spinal ganglia derived from?
Neural crest cells
What does mesenchyme surrounding the spinal cord form?
Meninges
Derivatives of neuroepithelium?
Neurons, astrocytes, oligodendrocytes, ependyma
3 primary brain vesicles?
- Prosencephalon (forebrain)
- Mesencephalon (midbrain)
- Rhombencephalon (hindbrain)
During week 5, what does the prosencephalon partially divide into?
Telencephalon and diencephalon
During week 5, what does the rhombencephalon partially divide into?
Metencephalon and myelencephalon
As the rostral neuropore closes, what forms? What do they give rise to?
Two lateral outgrowths (optic vesicles)
Primordial retina and optic nerves
Diverticula that arise more dorsally and laterally? What do they give rise to?
Telencephalic vesicles
Primordial cerebral hemispheres