Embryo Topic 4

Question 1

Neural induction hinge points

Answer 1

1. Median hinge point forms - columnar cells adopt triangular morphology
2. Lateral hinge point forms by a similar mechanism - probably from signaling from nearby mesoderm
3. As neural folds close, neural crest delaminates and migrates away
4. Closure happens first in middle of the tube and then zips rostrally and caudally

Question 2

Neurlation

Answer 2

Folding and closing of the neural plate. Folding and closure of the neural tube occurs first in the cervical region. The neural tube then “zips” up toward the head and toward the tail, leaving two openings which are the anterior and posterior neuropores.

Question 3

Anencephaly

Answer 3

When the anterior neuropore fails to close. The baby’s brain and skull don’t fully develop.

Question 4

Spina bifida

Answer 4

When the posterior neuropore fails to close. The baby’s spinal cord doesn’t fully close.

Question 5

Proliferation of progenitor cells

Answer 5

The progenitors migrate to apical portion undergo either equal or unequal mitosis.
- Equal = generates two progenitors that migrate back to ELM to undergo another round of DNA replication
- Unequal = generates a progenitor and cell that will differentiate into a neuron

Question 6

4 plates of developing neural tube

Answer 6

• Roof plate: signaling center (BMPs and Wnts)
• Alar plate: sensory
• Basal plate: motor
• Floor plate: signaling center (Shh)
  The dorsalventral patterning in the neural tube is mediated by Shh from the floorplate and BMPs and Wnts from the roofplate.

Question 7

What are the four sections of the neural crest?

Answer 7

Cranial, Vagal, Trunk, and Sacral

Question 8

Trunk Crest pathways

Answer 8

There are three pathways of neural crest cells.
1. Ventral pathway (sympathoadrenal lineage)
2. Ventrolateral pathway (sensory cells in dorsal root ganglion)
3. Dorsolateral pathway (melanocytes)

Question 9

Trunk Crest generations of SNS

Answer 9

The SNS arises from neural crest cells. The sympathetic nervous system is the more excited nervous system. They migrate along the ventral stream and BMPs from the aorta play further instructive role to specify bi-potential progenitors. The sympathetic ganglion neurons are induced by the presence of FGF and NGF. The adrenal chromaffin cells are induced by glucocorticoids in the adrenal gland.

Question 10

PNS generation

Answer 10

Derived from the cranial, vagal, and lumbosacral crest

Question 11

Circumpharyngeal Neural Crest: vagal crest

Answer 11

Migrate caudal to 6th arch and then become associated with wall of fore-, mid-, and proximal hindgut. The signals that guide them toward the gut include downregulated expression of Robo and a Slit-2 receptor. Hand2 influences differentiation into cholingeric phenotype neurons.

Question 12

Vagal crest inervation

Answer 12

innervate gut wall from foregut to proximal 2/3 of transverse colon in hindgut

Question 13

Sacral crest innervation

Answer 13

innervate hindgut wall from distal 1/3 of transverse colon to rectum

Question 14

Cranial crest: signaling center

Answer 14

• Dorsoventral patterning by the floor (Shh) and roof (Wnts and BMPs) plates.
• Antero-posterior patterning by the isthmic organizer (FGF-8 at the midbrain-hindbrain boundary)

Question 15

Pre-rhombomeric

Answer 15

forehead, maxilla, and mandible as well as ganglia associated with occulomotor and trigeminal nerves

Question 16

Major divisions of the developing brain (know how to label too)

Answer 16

3 parts: Prosen-, Mesen-, and Rhombencephalon
5 parts: Prosencephalon divides into telen- and diencephalon, rhomboencephalon divids into met- and myelencephalon

Question 17

Epidermis development

Answer 17

The skin of the embryo consists of simple cuboidal epithelium…the surface ectoderm. The surface ectoderm cells proliferate and form a layer of squamous epithelium, the periderm, and basal germinative layer. The peridermal cells continually undergo keratinization and desquamation and are replaced by cells arising from the basal layer. Replacement of peridermal cells continue until it disapears and the stratum corneum is formed. This layer becomes the stratum germinativum. Melanoblast turn to melanocytes in the basal layer.

Question 18

Layers of the epidermis

Answer 18

Stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, stratum germinativum, and melanocytes.

Question 19

Hair follicle development

“Hairy Babies Have Super Soft Dreams and Magical Moments.”

Hairy = Hair bud forms from epidermis.
Babies = Bulb forms at the base of the hair.
Have = Hair shaft grows through the epidermis.
Super = Sheath (root sheath) forms around the hair.
Soft = Sebaceous gland develops.
Dreams = Dermal root sheath forms from mesenchyme.
Magical = Muscle (arrector pili) forms.
Moments = Melanocytes give the hair color.

Answer 19

Hair development begins in the 3rd month but becomes visible by the 20th week.

1. Hair bud formation: The epidermis proliferates to form a hair bud that grows into the dermis.
2. Hair bulb: The bottom of the hair bud becomes cup-shaped, forming the hair bulb, which is invaginated by the mesenchymal hair papilla.
3. Hair shaft: The central epithelial cells of the hair bulb form the hair shaft, which grows through the epidermis and protrudes above the skin.
4. Root sheath: Peripheral cells of the bulb form the epithelial root sheath.
5. Sebaceous gland: The root sheath forms a sebaceous gland bud.
6. Dermal root sheath: Surrounding mesenchyme differentiates into the dermal root sheath.
7. Arrector pili muscle: The surrounding mesenchyme also forms the arrector pili muscle.
8. Melanocytes: Melanoblasts migrate into the hair bulb and differentiate into melanocytes, giving the hair color.