Development of the CNS Flashcards
What are the precursors to the CNS and PNS
wall of neural tube (neuroepithelium) -> CNS
Neural crest -> PNS
What are the cell types that differentiate from neuroepithelium
Neuroblasts
Glioblasts
Ependymal cells
What are neuroblasts
All neurone with cell bodies (CNS)
What are glioblasts
supportive cells of the CNS, and include astrocytes +
oligodendrocytes (myelin forming cells)
What are ependymal cells
Lining ventricles and central canal
What are the layers of the neuroepithelium from inside to outside
Ependymal (developmental cells) Grey matter (migrated cells from ependymal) White matter (axons and processes of the neurons)
What are the layers of the neural tube from inside to the outside + draw
Ependymal (germinal) Floor plate Grey matter (mantle) Roof plate White matter (marginal) Neural crest (dorsal)
What controls differentiation of the neural tube cells
Signalling molecules (secreted by surrounding tissues) interact with neuroblast receptors Controls migration and axonal growth by attraction and repulsion
What does differentiation of the neural tube cells depend on
Concentration gradient and timing
Draw and label a developing spinal cord
Neurons are innermost, made up of interneurons above and motorneurons interneurons below
Neural crest cells form sensory neurons in dorsal root ganglion
Label a mature spinal cord
Central canal surrounded by the ventral and dorsal horns.
Surrounded by white matter which extends into the ventral and dorsal roots (+ dorsal ganglion)
Draw and label the developing brainstem
Fourth ventricle surrounded by the roof plate above and the sulcus limitans below. Below this lies the basal plate innermost and the alar plate
Draw and label the developing brain at 5 weeks
Telencephalon (fore) Diencephalon (fore) (mid) Pons (hind) Medulla (hind)
Draw and label the developing brain at 8 weeks
Developing hemisphere (fore) aqueduct (mid) Developing cerebellum (hind)
What are some processes involved in development
Proliferation Differentiation Migration Axon growth Synapse formation
What factors may interfere with developmental processes
Genetic mutation Environmental factors (mother's lifestyle, diet, teratogens)
What cell types differentiate form neural crest cells
Sensory neurons of dorsal root ganglia
Postganglionic autonomic neurons
Schwann cells
Non-neuronal derivatives (melanocytes)
What are the flexures seen from a lateral view on the developing brain at 4 weeks (v->D)
Cephalic flexure
Pontine flexure
Cervical flexure
Which deficiency can neural tube defects be due to
Folic acid deficiency
Describe the proliferation of neuroepithelium
Initially symmetric, then asymmetric division and differentiation
1. Cells undergo mitosis on the inner membrane after migration there
2. One of the daughter cells migrates from the basal membrane to grey matter and begins to differentiate
3. The other remains attached and proliferates to form the ependymal lining layer
4. Neuroblast - processes and axons are in the white matter
Glioblast - no axon
Describe the developing brainstem
- The fourth ventricle opens up in the brainstem so that structures in the grey matter alter their relationship with each other
- The original neural tube has a sudden proliferation into the roof plate
- Proliferation is rapid and pushes the alar plates laterally
Describe the cranial nerves in the brainstem
Cranial nerves are associated with cranial nerve nuclei, lying in the floor of the 4th ventricle . Motor nuclei are more medial, sensory are more lateral
Describe the development of the brain at 4 weeks
Most anterior tip of the neural tube Differential growth of the neural tube gives rise to 3 primary vesicles Prosencephalon -> forebrain Mesencephalon -> midbrain Rhombencephalon -> hindbrain
Describe the development of the brain at 5 weeks
Further division of the fore and hind vesicle to give rise to 5 secondary vesicles
Large anterior expansion, smaller dorsal vesicle
Anterior expansion = telencephalon (hemispheres)
Dorsal vesicle = diencephalon (thalamus + hypothalamus )
Hind brain divisions = pons + the medulla
Describe the development of the brain at 8 weeks
Hemispheres and the cerebellum start to develop
CF system starts to develop, lateral ventricles, 3rd ventricle, aqueduct, 4th ventricle
Describe the developing brain from a lateral view
Folding of the neural tube -> flexures Cephalic, pontine and cervical In the next weeks there is exaggeration 5 wks - more differentiation 8 wks - hemispheres spread back to partially hide the diencephalon
Describe the developing cortex
- Proliferating neurones in the ventricular zone attach to the processes of vertically orientated radial glial cells, with cell bodies at the inner membrane and processes that reach the outer membrane
- There are multiple waves of proliferation where the cells attach to the glia and move up.
- This continues until there is a 6 layered structure of the cortex
Describe the process of spinal cord development
- Increased proliferation of the layers.
- The space in the middle is smaller and division of the grey matter into plates. There are two alar plates dorsally, and two basal plates ventrally.
- In the alar plates, the neuroblasts develop into interneurons with sensory function.
- Some of the neurons in the basal plate will also develop into interneurons, but some will also develop into motor neurones, sending their axons out through the ventral roots to peripheral nerves.
What occurs to the neural crest tissue during spinal cord development at the same time as interneurone/motorneurone formation
The neural crest tissue on either side will develop into sensory neurons as the dorsal root ganglia.
What is the Sonic the Hedgehog molecule
Signalling molecule from the notochord which spread and induce neuroblasts to differentiate as motor neurons
What do the signalling molecules that develop from the ectoderm induce
Dorsal neuroblasts to develop into sensory cells
