Development Of Spinal Cord

Question 0

Formation of marginal layer? Second stage of development

Answer 0

Axons sprout from the cell bodies of the mantle layer grow out further to give rise to marginal layer.
These have no cell bodies and have fatty myelin sheaths wrapped around the axon (produced by oligodendrocytes in CNS, schwann cells in PNS)
This marginal layer becomes what we call the white matter.

Question 1

How is the mantle layer formed? First stage of development

Answer 1

Neuroepithelial cells that surround the canal of neural tube undergo first wave of differentiation to produce young neurones that project outwards to form a second layer of cell bodies, the mantle layer.
This is what will eventually become grey matter

Question 2

What does second wave of differentiation form?

Answer 2

Glioblasts which differentiate in glia of CNS to provide metabolic and structural support.
This includes astrocytes and oligodendrocytes.

Question 3

What does the third wave of differentiation produce?

Answer 3

Ependymal cells that line ventricles and central canal to produce CSF.

Question 4

Formation of 4 plates.

Answer 4

At end of 4th week the mantle layer organises itself into 4 plates;

• 2 ventral/basal plates (motor neurones that innervate voluntary muscles)
• 2 dorsal/alar plates (association neurones which synapse w sensory neurones from DRG)

These Re separated by sulcus limitans groove.

Question 5

Where and what is small intermediate horn?

Answer 5

A group of neurones accumulates between dorsal and ventral horns.
Contains neurones of sympathetic portion of ANS.
Present only at T1-12 and upper lumbar levels.

Question 6

When does the spinal cord extend entire length of embryo?

Answer 6

By the 3rd month.
Ends at L3 but the dural sac ends at S2. Therefore the extensions of the pia mater below L3 are filum terminal and nerve fibers form the cauda equina.

Question 7

Sonic hedgehog protein Shh

Answer 7

Protein secreted by mesodermal tissue lying beneath the developing spinal cord.
Marks directly adjacent neural cells to become specialized glial cells.
Cells far away from the SHH are exposed less so become motor neurones that control muscles.
Cells at even lower concentrations become interneurones.

Question 8

Where is shh most found

Answer 8

Highest concentration at ventral part of neural tube

Gradient

Question 9

Where does the Shh bind

Answer 9

Binds to a receptor encoded by the patched (PTCH1) ligand