Development of the Nervous System Flashcards

1
Q

What germ layer is the nervous system derived from

A

The ectoderm specifically the neural plate
- The neural tube → CNS
- The neural crest → PNS and ANS (cranial, spinal and autonomic ganglia)

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2
Q

What are the 3 main parts of the nervous system

A
  • The central nervous system (brain and spinal cord)
  • The peripheral nervous system (neurons outside the CNS, nerves connecting CNS to peripheral structures)
  • The autonomic nervous system (parts in both CNS and PNS, neurons that innervate the smooth and cardiac muscles and glandular epithelium)
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3
Q

What structures induce the ectoderm to differentiate

A
  • The notochord and the paraxial mesenchyme to the neural plate
  • with the members of the TGF-ß family, Shh and BMPs
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4
Q

What regions are established by the signalling molecules?

A
  • BMPs establishes the sensory regions (info from brain → sensory nerves, afferent)
  • Shh establishes the motor regions (info from the motor nerves → brain, efferent)
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5
Q

Explain the gradient between Shh and BMP on the dorsoventral place of the neural tube

A
  • The notochord and the floor plate of the neural tube secretes high levels of shh
  • The dorsoventral concentration of Shh is higher on the floor plate and lower on the roof plate (ventral-to-dorsal)
  • a member of the TGF-ß family (BMPs) is highly secreted on the roof plate in the opposing gradient of Shh (dorsal-to-ventral)
  • Together, they determine dorsoventral cell fates
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6
Q

Explain the development of the nervous system

A
  • The neural tube is formed in the 3rd week & completed by the end of the 4th week (neurulation)
  • The anterior neuropore closes on day 25 and the posterior neuropore closes on day 27
  • The walls of the neural tube forms the brain and spinal cord
  • The neural canal forms the ventricular system of the brain and the central canal of the spinal cord
  • The neuroepithelial cells grow and the lumen decreases
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7
Q

What 3 types of cells do the neuroepithelial cells produce

A
  • Neuroblasts which become neurons
  • Glioblasts which become macroglia (oligodendrocytes and astrocytes)
  • cells next to the neural canal become the ependymal cells
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8
Q

Explain the differentiation of the neuroepithelial cells

A
  • the walls of the neural tube differentiates into the ventricular, intermediate and the outer marginal layer
  • The ependymal cells stay in the ventricular layer
  • The neuroblasts and glioblasts differentiate in the intermediate layer
  • The marginal zone is the outer parts of the neurons and glial cells
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9
Q

Explain the development of the spinal cord

A
  • The neural tube caudal to the 4th pair of somites becomes the spinal cord
  • The lateral walls of the neural tube thickens which reduces the size of the canal to be really small at 9-10 weeks
  • The roof and floor plates are thin with the sulcus limitans separating the lateral wall wall to a alar (dorsal) and basal (ventral) plate
  • Alar plate becomes the dorsal horn of grey matter, neuron cell bodies in the intermediate layer, marginal layer = white matter and it has sensory neurons growing into it (afferent fxn)
  • Basal plate becomes the lateral and ventral horns of the grey matter, the neurons grow out of the ventral horn → roots of spinal nerve, it also has motor neurons growing out of it (efferent fxn)
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10
Q

Explain the development of the spinal ganglia

A
  • The neural crest cells form the unipolar neurons in the spinal ganglia and the dorsal root ganglia
  • The axons of cells in the ganglia are first bipolar then they unite with the unipolar neurons in a T-shaped fashion
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11
Q

What is the dorsal root ganglia

A
  • They are the cell bodies of sensory neurons
  • They are peripheral processes in the spinal nerves
  • This is the unit of affarent fxn as the central processes enter here to get to the dorsal horn of grey matter
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12
Q

Explain the differentiation of the spinal nerve

A

The spinal nerve divides into the:
- Dorsal primary ramy which innervates the limbs, vertebral joints & skin of the back
- Ventral primary ramy which in innervates the limbs and ventral body wall

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13
Q

Explain the development of the spinal meninges

A
  • The mesenchyme surrounding the neural tube condenses → primordial meninx (meninges)
  • The external layer of the meninges forms the dura mater
  • The internal layer of the meninges (derived from neural crest cells)forms the pia-arachnoid mater also known as the (leptomeninges)
  • The cerebrospinal fluid (CSF) beings to form in the 5th week
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14
Q

Explain the positional changes of the spinal cord

A
  • The vertebral column grows faster than the spinal cord making its position in it change
  • The spinal cord lies at higher levels in the vertebral column making it end in the L1 position in adults
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15
Q

myelination of nerve fibers

A
  • It begins in the late fetal period and continues during the 1st yr after birth
  • in the PNS, myelin is formed by the Schwann cells but in the CNS, myelin is formed by the oligodendrocytes
  • tracks become fxnal when myelinated
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