12- Gastrulation, neurulation and somitogenesis

Question 1

When does Neurulation begin?

Answer 1

beginning of third week

Question 2

Neurulation at beginning of week 3

Answer 2

Development of the neural plate

notochord induces ectoderm to form neuroectoderm / neural plate

Question 3

Neurulation Day 19

Answer 3

Neural plate will give rise to the CNS and neural crest cells

Neural plate lengthens and lateral edges elevate to form neural groove

Question 4

Neurulation Day 20

Answer 4

Neural folds form by individual cell shape changes

Somites begin to form

Question 5

Neurulation Day 22, 23

Answer 5

Neural folds zip/fuse cranially and caudally

Neural tube open at cranial (cranial neuropore) and caudal end (caudal neuropore)

Question 6

When does the cranial neuropore close?

Answer 6

Day 25

Question 7

When does the caudal neuropore close?

Answer 7

day 28

Question 8

Anencephaly

Answer 8

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

Question 9

Encephalocele

Answer 9

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.

Question 10

spina bifida

Answer 10

Failure of caudal neuropore to close between days 22-28.

different types depending on severity of anomaly

Question 11

2 major types of cells in embryos

Answer 11

epithelial cells

Mesenchymal cells

Question 12

Epithelial cells in embryos

Answer 12

Epithelial tissues; cells tightly connected to one another; form tubes or sheets

Question 13

mesenchymal cells

Answer 13

connective tissue; loosely connected to one another. Form matrices and can migrate and act independently

Question 14

Epithelial to mesenchymal transition (EMT)

Answer 14

cells lose polarity and cell-to-cell adhesions to become invasive and migratory multipotent cells able to differentiate into a variety of cell types.

Question 15

Mesenchymal to epithelial transition (MET)

Answer 15

cells transition from migratory and multipotent to sheets or tubes of polarized cells that form tight junctions.

Question 16

Neural crest cell migration

Answer 16

Neural crest cells come together then undergo EMT and migrate all over the body.

1. sensory ganglia or cranial and spinal nerves
2. Autonomics (lots of type of ganglia)
3. Schwann cells
4. Meninges
5. Connective tissue/ bone of face and skull
6. Dermis, vascular smooth muscle of the face and skull
7. Odontoblasts
8. parafollicular cells of the thyroid gland
9. Chromatin cells of the adrenal medulla
10. Conotruncal septum of the heart
11. Melanocytes

Question 17

Which types of autonomic ganglia are derived from neural crest cells?

Answer 17

all peripheral parasympathetic and sympathetic ganglia; sympathetic chain ganglia, prevertebral sympathetic ganglia; parasympathetic ganglia

Question 18

Segmentation

Answer 18

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

Question 19

What happens to the ventral side of the somite?

Answer 19

undergoes EMT to form Sclerotome which forms vertebrae and ribs

*Dorsal region become dermomyotome (remains epithelial)

Question 20

What happens to cells at medial and lateral ends of dermomyotomes?

Answer 20

Undergo EMT and migrate ventral to the dermatome (middle of the dermomyotome ) to form myotome.

Question 21

What happens to medial and lateral myotome cells?

Answer 21

Medial become primaxial muscles (back and intercostal mm)

Lateral cells with parietal lateral plate mesoderm will become abaxial muscles (body wall and limb mm)

Question 22

primaxial vs abaxial

Answer 22

Primaxial is near neural tube

Abaxial is by lateral plate

Question 23

Lateral somitic frontier

Answer 23

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.

Question 24

What does the lateral plate mesoderm split into?

Answer 24

Dorsal (parietal/somatic) layer

Ventral (splanchnic/visceral) layer

Question 25

What does the dorsal (parietal/somatic) layer differentiate into?

Answer 25

sternum, dermis of the body wall, parietal pleura and peritoneum, and bones/connective tissues of the limbs

Question 26

What doe the ventral (splanchnic/visceral) layer differentiate into?

Answer 26

the walls of the gut tube (with endoderm), visceral pleura/peritoneum, cardiac muscle, and lung/tracheal cartilages and connective tissues.

Question 27

gastroschesis happens when defect in what tissue?

Answer 27

lateral parietal plate

Question 28

Head mesoderm

Answer 28

from the anteriormost paraxial mesoderm

Does not form somites.

Goes on to form skeleton, muscles, and connective tissues of the face and skull with help from neural crest