Embryology*
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When is the pre embryonic period?
0-2.5 weeks
When is the Embryonic period?
2.5-8 weeks
When is the fetal period?
8 weeks - 9 months
what period does gastrulation and neurulation take place?
Pre embryonic period.
What is gastrulation?
When the 3rd Germ layer is established. Epiblast cells move and displace the hypoblast cells.
What are the three embryonic layers?
Ectoderm, Mesoderm, Endoderm.
What is neurulation?
It is the first major event in organogenesis. Results in the formation of the neural tube. which gives rise to the CNS. Another germ layer develops.
What is the process of neurulation?
The ectoderm thickens in the midline above the notochord (neural plate) A crease develops along the axis (neural groove). Neural folds move together. Fusing to form a neural tube. Cells on the crest if the groove are called neural crest cells.
What does gastrulation do?
It lays down the basic structural framework of the embryo and sets the stage for organogenesis. By the end of the embryonic period, all adult organ systems are recognizable.
What are neural crest cells?
They differentiate into craniofacial cartilage and bones.
How many pharyngeal arches are there in the neck region?
There are 6 pairs of pharyngeal arches in the neck region.
What does each arch have?
• Cartilage • Artery • Mesoderm component • Cranial Nerve (arch-specific) • Skeletal component.
Name the nerves of each Pharyngeal Arch.
Arch 1 = trigeminal nerve (CN V) Arch 2 = facial nerve (CN VII) Arch 3 = Glossopharyngeal nerve (CN IX) Arch 4 = vagus nerve (CN X)
Name the muscles of each pharyngeal arch.
Arch 1 = Muscles of mastication Arch 2 = Muscles of facial expression Arch 3 = Stylopharyngeus Arch 4 = Pharyngeal constrictors, soft palate & intrinsic muscles of the larynx.
Explain the development of the tongue.
The mucosa of the anterior 2/3rd of the tongue formed from lateral lingual swellings of 1st arch. Tuberculum impar of 2nd arch forms taste buds of anterior 2/3rds. The hypobranchial eminence of 3rd arch forms posts 1/3rd mucosa.