Development of mesoderm and neural crest cells

Question 1

What is a zygote?

Answer 1

Sperm and egg fuse together during fertilisation

Question 2

What is cleavage?

Answer 2

Cells of zygote split without growing:

• 2 cells = blastomere
• 4 cells
• 8 cells
• 16 cells

Question 3

What is a morula

Answer 3

16 cells mass resembling a mulberry

Question 4

What happens after a morula is formed?

Answer 4

Form an outer cell mass - trophoblasts

Form an inner cell mass - embryoblasts

Embryoblasts clump together at one end, leaving a fluid filled cavity called a blastoceal. When this process ozzurs, the zygote forms a blastocyst

Question 5

What stage comes after cleavage?

Answer 5

Blastulation

Question 6

What processes occurs in blastulation?

Answer 6

• Zona pelucida disintegrates
• Inner cell mass of embryoblasts forms a cavity inside it called an amniotic cavity
• Embryoblasts closest to blastocyst differentiate and become hypoblasts
• Embryoblasts above hypoblast cells differentiate to form epiblasts

Question 7

What is gastrulation?

Answer 7

• Formation of primitive streak marks gastrulation (site in epiblast layer start to migrate inside the bilaminar disk)
• Cells differentiate even more

Question 8

What is a trilaminar disk?

Answer 8

• These are the 3 germ layers
  
  • Ectoderm
  • Mesoderm
  • Endoderm

Question 9

What occurs in neuralation?

Answer 9

• Further differentiation of cells occurs
  
  • In centre of mesoderm, a notochord forms (forms some of intervertebral disks)
  • Notochord induces a change in the ectoderm above it = thickening of the ectoderm to form the neural plate
    
    • Neural plate cells dive into the mesoderm and form a tube = neural tube
    • Cells from the neural tube break off and go into the mesoderm = neural crest cells – differentiate into special tissues

Question 10

What is the blastoceal also known as?

Answer 10

primary yolk sac

Question 11

What do embryoblasts form?

Answer 11

Embryo proper

Question 12

What is the function of trophoblasts?

Answer 12

Form placenta and are associated with implantation

Question 13

When is the bilaminar disk formed?

Answer 13

After 8 days of gestation

Question 14

When is the trilaminar disk formed?

Answer 14

After the third week of development

Question 15

Label this image

Answer 15

Question 16

Label this image

Answer 16

Question 17

What are neural crest cells?

Answer 17

• As the neural tube forms, a group of
cells separate from the
neuroectoderm (ectoderm destined
to form neural tissues).

• These cells have the capacity to
migrate and differentiate extensively
within the developing embryo, and
they are the basis for such
structures as the spinal sensory
ganglia, sympathetic neurones,
Schwann cells, pigment cells, and
meninges

Question 18

What is thought to be critical for inducing the neural crest cascade?

Answer 18

bone morphogenetic proteins, Wnt (wingless homologue in
vertebrates), and fibroblast growth factor signalling pathways are

Question 19

What do neural crest cells in he head region do?

Answer 19

In additionto assisting in the formation of the cranial sensory ganglia, they also
differentiate to form most of the connective tissue of the head.

Question 20

How is embryonic connective tissue in the head different to that in other parts of the body?

Answer 20

Embryonic connective tissue elsewhere is derived from mesoderm and
is known as mesenchyme, whereas in the head it is known as
ectomesenchyme, reflecting its origin from neuroectoderm

Question 21

Why is the correct migration of neural crest cells important in dentistry?

Answer 21

In a dental context the proper migration of neural crest cells is essential
for the development of the face and the teeth.

• In Treacher Collins syndrome, for example, full facial development does
not occur because the neural crest cells fail to migrate properly to the
facial region.

• All the tissues of the tooth (except enamel and perhaps some cementum) and its supporting apparatus are derived directly from neural crest cells, and their depletion prevents proper dental development.