68 Spinal cord development

Question 1

What are the functions of the notochord in embryonic development?

Answer 1

1. Defines the primordial longitudinal axis of the embryo and gives it some rigidity
2. Provides signals necessary for CNS and axial musculoskeletal structures
3. Contributes to the intervertebral discs

Question 2

How neural plate forms the neural tube?

Answer 2

Neural plate > Neural folds > Neural groove > Neural tube > Neural crest

Question 3

Give the major derivates of the ectoderm layer and their products.

Answer 3

1. Surface ectoderm (epidermis, hair, nails, sebaceous glands, olfactory epithelium …)
2. Neural crest ( PNS, facial cartilage, adrenal medulla….)
3. Neural tube (Brain, spinal cord, motor neurons, retina)

Question 4

Sequence of the neural tube closure.

Answer 4

• Fusion beings at day 22 in the region of 4th to 6th somite level.
• bi-directional closure: begins at 5th smite
• Anterior neural pore closes on Day25
• Posterior neural pore closes on Day 27-28
• Closure completed by the end of the 4th week

Question 5

The thickening neural plate and early neural tube become organized into a ______________ epithelium in histology.

Answer 5

pseudo-stratified

Question 6

Describe the development of the neural tube into 3 layers of the spinal cord.

Answer 6

1. Neuroepithelial cells undergo active proliferation and form the ventricular layer
2. Neuroepithelial cells differentiate into neuroblasts and form the intermediate (mantle layer)
3. Neuroblasts differentiate into neurons and send out nerve fibers to form the marginal layer.

Question 7

Events in Ventricular zone of the neural tube?

Answer 7

1. Early neural tube consists of neuroectoderm
2. First wave of proliferation and differentiation of the neuroectoderm> neuroblasts > migrate the the intermediate zone.
3. A second was of proliferation and differentiation of the neuroectoderm > glioblasts > migrate to intermediate and marginal zone
4. Neuroectoderm remains in the ventricular zone > ependymal cells

Question 8

Events in the intermediate zone of neural tube?

Answer 8

1. Intermediate zone contains neuroblasts, > dendrites + axons
2. Intermediate zone also contains glioblasts > astrocytes and oligodendrocytes
3. Intermediate zone forms the gray matter of CNS
4. Intermediate zone is divided into the ala plate (sensory functions) + basal plate (motor function)

Question 9

Events in the marginal zone of the neural tube?

Answer 9

1. With axons from neurons within intermediate zone.
2. Contains glioblasts > astrocytes and oligodendrocytes
3. Marginal zone > white matter of CNS

Question 10

Neuroblasts in the intermediate layer > a pair of ala (dorsal) plates and a pair of basal (ventral) plates. Functions?
Boundaries of the plates?

Answer 10

Ala plate: sensory areas (dorsal)

Basal plate: motor areas (ventral)

Boundary: Sulcus limitans (longitudinal groove)

Question 11

What are the roof plate and floor plates for? (2 functions)

Answer 11

• Emit important signals for neuronal differentiation.

- Also serve primarily as a pathway for nerve fibers crossing from one side to another.

Question 12

Before nerulation, the notochord secretes ______ to transform the neural plate into the floor plate?

Answer 12

Shh Sonic hedgehog

Question 13

The roof plate secretes ___________.

Answer 13

BMP (bone morphogenic protein)

Question 14

Myelination of spinal cord begins during month ____ in ventral roots.

Answer 14

4

Question 15

Which of the following about neural crest cells is false?
A. arises from lateral margins of neural folds next to surface ectroderm
B. differentiate into Schwann cells, satellite cells in PNS
C. migrate laterally and give rise to sensory ganglia (dorsal root ganglia)

Answer 15

None of the above

Question 16

How are spinal nerves formed?

Answer 16

1. Motor nerve: 4th week, arising from the basal plate > ventral nerve roots
2. Dorsal nerve roots is from the dorsal root ganglia (from neural crest cells)
3. Processes form bundles into the dorsal horns of spinal cord. Distal processes of them join ventral nerve roots > spinal nerve

Question 17

Interneuron, somatic motor neuron, preganglionic autonomic motor neuron are from?

Answer 17

Neural tube (CNS)

Question 18

Sensory neuron (DRG), postganglionic autonomic motor neuron (sympathetic and parasympathetic ganglia) are from?

Answer 18

Neural crest (PNS)

Question 19

Development of the vertebra.

Answer 19

1. Condensation of mesodermal cells adjacent to the neural tube into somites
2. Lateral portion of the somite > dermomyotome > dermis + muscles
3. Medial portion of somite > sclerotome > vertebra + ribs
4. Signalling molecules emitted from neural tube and notochord induce sclerotomal cells to migrate towards them
5. Sclerotomal cells form the vertebrae that encloses neural tube and notochord
6. Within vertebrae, notochord degenerates to form intervertebral disc.

Question 20

Neural tube defect: spina bifida meaning?

Answer 20

Non-fusion of the neural arches due to defect in closure of the neural tube.

Question 21

Spina bifida usually occurs at?

Answer 21

Anyway along body axis but most commonly in lumbosacral region.

Question 22

What is spina bifida occulta? This NTD is frequently occur in which vertebra?

Answer 22

Bony defect is covered by skin, spinal cord intact (with hair);
L5/S1 vertebra

Question 23

What is spina bifida meningocele?

Answer 23

Only a fluid-filled sac of meninges protrudes from the defect

Question 24

What is spina bifida myelomeningoceles?

Answer 24

Include the neural tissue in the fluid filled sac protruded

Question 25

What is Spina bifida with myeloschisis?

Answer 25

Area represented by flattened, plate-like mass of nervous tissue with no overlying membrane. (open spinal cord)