Week 1 - Neurodevelopment

Question 1

Pre-embryonic development steps

Answer 1

1. Blastocyst formation
2. Implantation
3. Formation of bilaminar disc

Question 2

Blastocyst formation

Answer 2

1. Fertilisation
2. Cleavage
3. Morula
4. Blastocyst
5. Inner and outer cell mass

Question 3

Implantation

Answer 3

• Phase in embryonic development during which the blastocyst attaches and embeds itself into the lining of the uterus
• The trophoblast cells of the blastocyst adhere to the uterine wall, and enzymes are released to facilitate the penetration of the endometial tissue
• The outer cell mass of the blastocyst begins to rapidly divide and forms the placenta

Question 4

The two trophoblast layers

Answer 4

Once attached, the blastocyst undergoes further modifications - the trophoblast differentiates into two layers:
* Syncytiotrophoblast - invades the endometrial tissue
* Cytotrophoblast - contributes to the formation of the placenta

Question 5

Formation of the bilaminar disc

Answer 5

• Following implantation, the embryonic disc forms
• This disc is initially bilaminar, consisting of two primary cell layers - epiblast and hypoblast
  o Cells facing the amniotic cavity become the epiblast, high columnar layer of cells
  o Cells facing the blastocyst cavity become the hypoblast, small cuboidal layer of cells
• The amniotic cavity forms above the epiblast and the yolk sac cavity forms below the hypoblast

Question 6

Embryonic development steps

Answer 6

1. Gastrulation
2. Notochordal process and notochord
3. Neural plate and neural tube
4. Neural crest

Question 7

Gastrulation

Answer 7

• Begins with the formation of primitive streak
• Gastrulation - occurs along midline of epiblast as cells from epiblast move toward the primitive streak and ingress through it, creating a third layer called the mesoderm
• With the addition of the mesoderm, the bilaminar embryonic disc becomes a trilaminar embryonic disc
• Primitive streak disappears by end of week 4

Question 8

Trilaminar embryonic disc layers - formation

Answer 8

• Ectoderm - derived from epiblast
• Mesoderm - formed through gastrulation
• Endoblast - derived from hypoblast

Question 9

Trilaminar embryonic disc layers - tissues and organ systems they give rise to

Answer 9

• Ectoderm - CNS and PNS, epidermis of skin
• Mesoderm - connective tissues including blood, bone marrow, bone, cardiovascular system, reproductive and excretory organs
• Endoderm - epithelial linings of GIT, respiratory system, glands

Question 10

Notochordal process

Answer 10

• Is formed from the primitive node and primitive pit
• Is a rod-like structure which develops from the mesoderm in the midline
• Grows cranially toward prechondral plate between ectoderm and endoderm

Question 11

Prechondral plate

Answer 11

• Is a thickened region at the cranial end of notochondral process, which plays a crucial role in signalling and patterning the development of the forebrain

Question 12

Notochord

Answer 12

• Is formed from mesoderm layer
• Forms by transformation of notochodral process
  o Serves as basis for axial skeleton development
  o Induces overlying ectoderm to form neural plate

Question 13

Neuralation