10: Neurulation And PNS Development

Question 1

Two important regions of ectoderm

Answer 1

Neuroectoderm, surface ectoderm

Question 2

Secondary neurulation

Answer 2

Formation of neural tube from the tail bud

Question 3

Where does secondary neurulation occur

Answer 3

Caudal to somite 31

Question 4

Where does primary neurulation end?

Answer 4

Closure of caudal neuropore at somite 31

Question 5

Secondary neurulation 5 steps

Answer 5

1. Tail bud condenses -> medullary cord
2. Medullary cord cavitates -> forms a lumen
3. Lumen of medullary cord merges with neural tube
4. NCCs arise from roof of neural tube
5. Formation of caudal somites around lateral tail bud

Question 6

Where does neural tube closure begin?

Answer 6

Several locations around the AP axis, begins at cranial regions first and moves caudally

Question 7

Neural tube defect

Answer 7

Failure at a closure site in the neural tube - caused by genetic, nutritional, and/or environmental factors

Question 8

Anencephaly/meroencephaly

Answer 8

Brain tissue open to amnionic fluid

Question 9

Encephalocele

Answer 9

Opening in neural tube, but is covered by skin (can have brain tissue in the opening)

Question 10

Craniorachischisis

Answer 10

Large portion of brain and spinal cord exposed

Question 11

Spina bifida occulta

Answer 11

Skin has closed appropriately over the neural tube defect but will typically have a tuft of hair over it

Question 12

Meningocele vs meningomyelocele

Answer 12

Meningocele: Protruding sac extending from sacral region due to absense of vertebral arch (no spinal cord involvement)
Meningomyelocele: spinal cord protrudes into meningocele sac

Question 13

Myeloschisis

Answer 13

Failure of neural tube to fuse -> open spinal cord exposed -> lower extremities deformed and nonfunctional

Question 14

What types of cells are NCCs

Answer 14

Neuroectodermal cells

Question 15

Epithelial-mesenchymal transition

Answer 15

NCCs lose cams -> gain ability to migrate/become mesenchymal

Question 16

When do NCCs migrate?

Answer 16

Before neural tube closes completely + once its all the way closed

Question 17

Nine important derivatives of NCCs

Answer 17

1. Melanocytes
2. Odontoblasts
3. Schwann cells
4. Spinal and autonomic ganglia
5. Enteric NS
6. Adrenal medulla
7. Aorta
8. Pharyngeal arches -> face and head
9. Meninges

Question 18

Two cell types that help form the meninges

Answer 18

NCCs, mesenchyme

Question 19

Five examples of neurocristopathies

Answer 19

1. Hirschsprung’s disease
2. Piebaldism
3. TCS
4. Goldenhar syndrome
5. Micrognathia

Question 20

Piebaldism

Answer 20

Melanocytes defect with characteristic pattern of non-pigmented skin

Question 21

What are both PNS and CNS derived from?

Answer 21

Neural tube

Question 22

Three components involved in PNS formation

Answer 22

NCCs, neuroectoderm, Ectodermal placodes

Question 23

When do dorsal and alar plates of the neural tube form?

Answer 23

End of 4th week

Question 24

Sulcus limitans

Answer 24

Line dividing neural tube into dorsal and ventral regions

Question 25

What does the sulcus limitans give rise to?

Answer 25

Range of cell types in the brain and spinal cord

Question 26

SHH gradient impact on neurons

Answer 26

Increased SHH -> motor neurons | Decreased SHH -> interneurons

Question 27

What does SHH activate? What does this cause formation of

Answer 27

Activates NKX2.2 + NKX6.1 -> ventral neuron formation

Question 28

BMP/TGF-B function

Answer 28

Counteract SHH -> dorsal neuron formation

Question 29

What two molecules are activated by BMP4?

Answer 29

PAX3 and PAX7

Question 30

What releases BMP4?

Answer 30

Roof plate

Question 31

What happens to the dorsal-most cells of the basal plate?

Answer 31

Become intermediolateral columns -> lateral horns

Question 32

Which type of neuron forms first typically, motor or sensory?

Answer 32

Motor first

Question 33

What area do axons exiting ventral horns pass through to form ventral roots?

Answer 33

Cranial sclerotome

Question 34

What axons join the ventral root?

Answer 34

Lateral horn axons

Question 35

when does the ANS start to develop?

Answer 35

Week 5

Question 36

What type of cells forms the preganglionic ANS cells/fibers? What cell type forms the ganglionic neuron and postganglionic fibers?

Answer 36

Preganglionic: neuroectoderm Postganglionic: NCCs

Question 37

What do NCCs form in the sympathetic ANS?

Answer 37

trunk and collateral ganglia

Question 38

What do NCCs form in the parasymp ANS?

Answer 38

Head/neck ganglia and terminal ganglia in the trunk