Neurology 1 - CNS development Flashcards
Describe the early development of the nervous system
- Ectoderm of the trilaminar disk thickens forming the neural plate
- Neural plate folds to form the neural groove, which fuses to form the neural tube, the walls of this have the neuroepithelium
- Begins with neural plate, ectoderm, endoderm and mesoderm
- The neural crest lies just outside the neural tube
What does the neuroepithelium of the neural tube develop into?
- Neuroblasts (all neurones with cell bodies in CNS)
- Glioblasts (astrocytes and oligodendrocytes)
- Ependymal cells (lining ventricles and central canal)
What do the neural crest cells develop into?
- Sensory neurones of dorsal root ganglia
- Postganglionic autonomic neurones
- Schwann cells
- Non-neuronal derivatives (eg. melanocytes)
Describe the formation of the layers of the neuroepithelium
- Ependymal cells (developmental cells) remain at the inner membrane, and undergo proliferation (germinal layer)
- Neuroblasts migrate to the grey matter layer (mantle layer, in the middle)
- Their axons form the outer white matter layer (marginal layer)
- Glioblasts migrate to both the grey and white matter layers
Describe the development of the spinal cord
- Basal plate in at the ventral grey matter is where the motor neurones develop, form the ventral horns
- Alar plate develops from the dorsal grey matter where the sensory neurones develop, form the dorsal horns
- Dorsal horns bring information in
- Ventral horns take information out
tissue
Describe the structure of the brain at 4 weeks
- Neural tube develops by forming vesicles and folding
- Brain develops from the anterior end of the neural tube into three primary vesicles (future forebrain, future midbrain and future hindbrain).
Describe the development of the brainstem
- Early development is tubular like the spinal cord
- Lateral proliferation of the roof plate enlarges the neural canal to form the 4th ventricle (in the middle)
- This results in a change in the relationship of the basal and alar plates – basal plates (motor) now lie medially and alar (sensory) plates lie laterally
- This dictates the pattern of cranial nerve nuclei in the brainstem
Describe the development of the cerebral cortex
- This results from migration of neuroblasts, formed from neuroepithelium, towards the pial surface along radial glia
- Successive waves of migration form the cortical layers
How can understanding of development lead to treatment of neurological disorders?
- Use of stem cells (from hippocampus) to replace neurons lost in old age
- Use of axonal guidance to induce regeneration
What does the neuroepithelium form?
CNS
What controls differentiation in the nervous system?
- Signalling molecules, secreted by surrounding tissues at specific times, interact with receptors on neuroblasts
- Control migration and axonal growth by attraction and repulsion
- Depends on concentration gradient and timing
List the causes of developmental disorders
- Genetic mutation and environmental factors
- Mothers lifestyle, diet, teratogens (agents known to interfere with normal developmental process - axonal growth, proliferation.ect)
- Largely due to problems in the third trimester
- Folic acid can prevent these disorders
What is ancephaly?
Open brain - anterior portion of the neural tube forms no cerebral vesicles so there is no brain deleopment.
What is spina bifida occulta?
Not visible, some of the vertebrae are not completely closed around the vertebral column
Describe the layers of the neural tube
- Germinal layer in the centre
- Grey matter mantle layer (middle)
- White matter around the outside (marginal layer)
- The floor plate is ventral
- The roof plate is dorsal
Describe the structure of the brain at 5 weeks term
- The prosencephalon divides to the telenchepalon and diencephalon
- The hindbrain develops into the pons and medulla
- This forms 5 secondary vesicles
Describe the structure of the brain at 8 weeks term
- At 8 weeks the hemispheres develop alongside the lateral ventricles, which drain into the third ventricle (middle).
- The aquaduct develops which drains into the 4th ventricle in the hindbrain.
- The cerebellum starts to develop
Describe the process that happens in the developing cortex
- In the ventricular zone of the telencephalon, radial glial cells (neuroblasts from neuroepithelium) form a scaffolding from the ventricle to the pial surface
- Successive waves of migration form the layers of the cortex
Explain the term neural crest cells
- A temporary group of cells that arise from the ectoderm cell layer, which are outside the neural tube
- Gives rise to the PNS
Describe the development of the flexures of the brain
- At 4 weeks, there are two flexures folding the neural tuble inwards
- At 8 weeks folding becomes more exaggerated
- Three flexures are creates - cephalic flexure (between 1st and 2nd vesicles) Pontine flexure (between 2nd and 3rd vesicles) and cervical flexure (between 3rd vesicles and spinal)
