06 Formation and derivates of the neural crest and placode ectoderm

Question 1

What are the differences between Ectodermal placode cells and neural crest cells ?

Answer 1

1. Placode
   - Cranial, lateral and epithelial thickenings
   - May form vesicles
2. Neural crest cells
   - Caudal, medial, epithelo-mesenchymal transition

Question 2

The elevated neural folds formed during neurulation contain _______ (which cells?)
-> What will they undergo next?

Answer 2

neural crest cells along most of the neural axis
-> these cells undergo epithelial-mesenchymal transition to acquire the migratory characteristics of crest cells.

Question 3

The elevated neural folds formed during neurulation contain neural crest cells along most of the neural axis; these cells undergo epithelial-mesenchymal transition to acquire the migratory characteristics of crest cells.
-> How about other cells?

Answer 3

Other cells which originate in the neural folds but remain within the ectoderm after neurulation.
-> These areas of neuroepithelium are called ectodermal placodes.
-> Ectodermal placodes develop between the 10- and 30-somite stage at the rostral border between the neural plate and surface ectoderm.

Question 4

What are the 2 non-neurogenic placodes?

Answer 4

Hypophyseal placode
Lens placode

Question 5

What are the 4 neurogenic placodes?

Answer 5

1. Olfactory placodes
2. Trigeminal placodes
3. Otic placodes
4. Epibranchial placodes

Question 6

What are the characteristics of neural crest and ganglionic crest cells?

Answer 6

• The neural crest is a transient and multipotent cell population at the edge of the neural plate in vertebrates.
• Mediodorsal cells immigrate laterally to invade spinal ganglia.
  => He named them „ganglionic crest” cells.

Question 7

What are the 4 divisions of placodes?

Answer 7

1. Cranial part (caudal forebrain until the 6th rhombomere)
2. Vagal part (between somites 1-7)
3. Truncal part (between somites 8-28)
4. Lumbosacral part (caudal to somite 28)

Question 8

1. Cranial part (caudal forebrain until the 6th rhombomere)
   - What are Divisions of the neural crest – contribution to the skull?

Answer 8

• Rhombomeres 1, 2, (3)– ‘trigeminal migratory stream’ – into 1st branchial (pharyngeal) arch
• Rhombomeres (3), 4, (5) – ‘hyoid migratory stream’ – into 2nd branchial (pharyngeal) arch
• Rhombomeres (5), 6, 7, 8 – ‘post-otic migratory stream’ – into 3rd - 6th branchial (pharyngeal) arches
• Mesomere – into 1st branchial (pharyngeal) arch, also rostrally, surrounding the forebrain: ethmoid, sphenoid, frontal, maxilla etc.
• Ectomesenchyme: bones, cartilage, conn. tissue, vessels (* 2 of 3 auditory ossicles, jaw (Meckel’s cartilage)- skull… „new head”)

Question 9

Cranial part (caudal forebrain until the 6th rhombomere)
- What are Non-neural derivatives – ecto-mesenchyme?

Answer 9

• Certain bones of the skull: frontal, parietal, squama of temporal, nasal, vomer, palatine, maxilla, mandible
• Meninges, choroid and sclera of eye
• Odontoblasts of the teeth
• Glandular connective tissue (lacrimal, nasal, labial, palatine, oral, salivary, thyroid, parathyroid, thymus)
• Connective tissue of the head (melanocytes, cartilages, ligaments, tendons)
• Cono-truncal septum (tunica media of the outflow tract of the heart and great vessels)

Question 10

1. Cranial part (caudal forebrain until the 6th rhombomere)
   -. What are neural derivatives of neural crest?

Answer 10

1. General sensory ganglia (general somatosensory modality):
   - trigeminal ggl. (partly)
   - sup ggl. (IX.)
   - sup ggl. (X.)
2. Autonomic ganglia (general visceromotor modality):
   - ciliary ggl. (III.)
   - pterygopalatine ggl. (VII.)
   - submandibular ggl. (VII.)
   - otic ggl. (IX.)

Question 11

Divisions of the neural crest of vagal part?

Answer 11

1. aorticopulmonary septum
2. parasympathetic innervation of the gut - (enteric nervous system)

Question 12

Divisions of the neural crest of truncal part

Answer 12

a) dorsal migratory pathway – melanocytes in skin and hair follicles
b) ventrolateral migratory pathway – sensory ggl, satellite cells, Schwann cells
c) ventromedial migratory pathway – sympathetic neurons, glia chromaffin cells of adrenal medulla

Question 13

Divisions of Lumbosacral part (caudal to somite 28) of the neural crest

Answer 13

1. hypogastric plexuses – parasympathetic ganglia (enteric nervous system)
2. sympathetic ganglia and nerves