12- Gastrulation, neurulation and somitogenesis Flashcards
When does Neurulation begin?
beginning of third week
Neurulation at beginning of week 3
Development of the neural plate
notochord induces ectoderm to form neuroectoderm / neural plate
Neurulation Day 19
Neural plate will give rise to the CNS and neural crest cells
Neural plate lengthens and lateral edges elevate to form neural groove
Neurulation Day 20
Neural folds form by individual cell shape changes
Somites begin to form
Neurulation Day 22, 23
Neural folds zip/fuse cranially and caudally
Neural tube open at cranial (cranial neuropore) and caudal end (caudal neuropore)
When does the cranial neuropore close?
Day 25
When does the caudal neuropore close?
day 28
Anencephaly
failure of the cranial neuropore to close between day 23-25.
Usually only brainstem present, little to no cerebrum develops
Poor prognosis, most die before birth. Some have lived to 3 years old
Encephalocele
Failure of the neuropore to close between days 23-25
can affect the anterior or posterior skull
Depending on severity. Reconstructive surgery can be used and patient can live normal life.
spina bifida
Failure of caudal neuropore to close between days 22-28.
different types depending on severity of anomaly
2 major types of cells in embryos
epithelial cells
Mesenchymal cells
Epithelial cells in embryos
Epithelial tissues; cells tightly connected to one another; form tubes or sheets
mesenchymal cells
connective tissue; loosely connected to one another. Form matrices and can migrate and act independently
Epithelial to mesenchymal transition (EMT)
cells lose polarity and cell-to-cell adhesions to become invasive and migratory multipotent cells able to differentiate into a variety of cell types.
Mesenchymal to epithelial transition (MET)
cells transition from migratory and multipotent to sheets or tubes of polarized cells that form tight junctions.
Neural crest cell migration
Neural crest cells come together then undergo EMT and migrate all over the body.
- sensory ganglia or cranial and spinal nerves
- Autonomics (lots of type of ganglia)
- Schwann cells
- Meninges
- Connective tissue/ bone of face and skull
- Dermis, vascular smooth muscle of the face and skull
- Odontoblasts
- parafollicular cells of the thyroid gland
- Chromatin cells of the adrenal medulla
- Conotruncal septum of the heart
- Melanocytes
Which types of autonomic ganglia are derived from neural crest cells?
all peripheral parasympathetic and sympathetic ganglia; sympathetic chain ganglia, prevertebral sympathetic ganglia; parasympathetic ganglia
Segmentation
Early mesoderm forms bilateral messnchymal tissue on notochord –> called segmental plate
– forms cranial to caudal
Primitive streak regressing and nueral folds gather, segmental plate mesenchyme differentiates to “whorls” of cells called somitomeres
Outer part undergo MET while inner remain mesenchymal. Anterior and posterior epithelial fissures are formed creating a segment or somite.
somites form cranial to caudal along both sides of NEURAL TUBE
What happens to the ventral side of the somite?
undergoes EMT to form Sclerotome which forms vertebrae and ribs
*Dorsal region become dermomyotome (remains epithelial)
What happens to cells at medial and lateral ends of dermomyotomes?
Undergo EMT and migrate ventral to the dermatome (middle of the dermomyotome ) to form myotome.
What happens to medial and lateral myotome cells?
Medial become primaxial muscles (back and intercostal mm)
Lateral cells with parietal lateral plate mesoderm will become abaxial muscles (body wall and limb mm)
primaxial vs abaxial
Primaxial is near neural tube
Abaxial is by lateral plate
Lateral somitic frontier
crossed by myotome cells that leave the somite for the parietal lateral plate mesoderm to designate the abaxial domain.
Those around the neural tube will designate the primatial domain.
What does the lateral plate mesoderm split into?
Dorsal (parietal/somatic) layer
Ventral (splanchnic/visceral) layer
