Development Of The CNS

Question 1

Describe the early development of the neural tube

Answer 1

1. Proliferation of the ectoderm in the dorsal midline of the embryonic disc
2. Neural plate starts to fold and fuse does ally to form a tube - neural canal (all CNS cells)
3. At the tip = neural crest (all PNS cells)

Question 2

What are the 3 differentiations of the neuroepithelium (neural canal)?

Answer 2

1. Neuroblasts - developmental cells that turn into neurones
2. Glioblasts - these become neuroglia - astrocytes (support and protect BBB) and oligodendrocytes (central myelinating cells)
3. Ependymal cells - lining ventricles and central canal (lining of brain and central canal chord).

Question 3

What are the 3 differentiations of the neural crest cells?

Answer 3

1. Sensory neurones of dorsal root ganglia
2. Post ganglionic autonomic neurones (in periphery)
3. Schwann cells
4. Non - neuronal derivatives (eg melanocytes)

Question 4

Describe the way the neuroepithelium differentiates

Answer 4

Almost all the cells are attached to both the inner and outer membrane, cells withdrawing from outer membrane towards inner membrane, then mitosis. Daughter cells migrate from inner membrane to form neuroblasts.

Occurs across 3 layers so that one is mitosis, one is cell bodies and one is mainly axons.

Question 5

Describe the layers of the neural tube.

Answer 5

The ependymal layer surrounds the neural canal
The whole process of differentiation and migration is controlled by signalling molecules and interact with receptors of neuroblasts.

Question 6

Describe the development of spinal cord.

Answer 6

Grey matter is split into alar plate (dorsal ) and basal plate (ventral - motor), the interneurones in the alar plate become specialised to receive sensory information.

Mature spinal cord, the neural canal becomes the central canal carrying the CSF, the alar plates develop into dorsal horns and basal plates into central horns, and all surrounded by white matter

Question 7

Describe the development of the Brainstem

Answer 7

The fourth ventricle first develops and then the roof plate proliferates and dorsal part of Brainstem expands laterally. As the roof plates expand it pushes the alar plates aside and no longer dorsal to the roof plate but are actually lateral.

Question 8

Describe the development of the brain (embryo, 5 wks, 8wks, adult)

Answer 8

Dorsal view of embryo: prosenceohalon (future forebrain), mesencephalon (future midbrain), rhombocenphalon (future hindbrain)

At 5wks: forebrain (telencephalon + diencephalon), midbrain, hindbrain (pons and medulla)

At 8wks : forebrain (developing hemisphere and 3rd ventricle and lateral ventricles (drain the 3rd ventricle)), mid brain (aqueduct), hindbrain (4th ventricle and cerebellum)

Question 9

Name the 3 different flex uses in development of the brain

Answer 9

1. Cephalic
2. Pontine
3. Cervical

Question 10

Describe the development of the cerebral cortex

Answer 10

Neuroblasts are proliferating near the inner membrane, some will stay in the middle to form basal ganglia. The migration takes place via neuroblasts attaching themselves to radial glial cells. This continues to form 6 layers of the cerebral cortex, each layer has a different function.

Question 11

Explain the developmental disorders of neural tube.

Answer 11

Normal development depends on the coordinates completion if the several complex processes eg proliferation and differentiation.

1. Crainioarchisis - open brain and spinal cord
2. Anencephaly - open brain and lack of skull vault
3. Encephalocele - herniation of the meninges
4. Iniencephaly - occipital skull and spine defects with extreme retroflexion
5. Spina bifida - veterbrae not closed properly
6. Closed spinal dysraphism - deficiency of two veterbral arches = herniation of fat
7. Meningocele - perfusion of meninges filled with CSF
8. Myelomeningocele - open with spinal cord ^