Steps in setting up the Nervous system

1. Steps in setting up the Nervous system • Induction and Patterning of a neuron-forming region • Birth and migration of neurons and glia • Specification of cell fates • Guidance of axonal growth cones to specific targets • Formation of synaptic connections • Binding of trophic factors for survival and differentiation • Competitive rearrangement of functional synapses • Continued synaptic plasticity during lifetime

2. Neuronal development • Ectoderm differentiation: Epidermis, nerve tissue, or neural crest cells? • Nerve tissue: Neuron or glial cell?

3. Neuronal development • Ectoderm differentiation: Epidermis, nerve tissue, or neural crest cells? • Nerve tissue: Neuron or glial cell?

4. Neuronal development

5. Nerve Outgrowth • Filapodia-based movements • Rely on Cytoskeleton and factors that rearrange the cytoskeleton (GTPases).

6. Types of Tissue organization in the Neural Tube

7. Spinal Cord

8. Cerebellum • Important for motor control • Purkinje fibers • BMP and Granular layer

9. Movement of Neurons • Glial cells serve as track. • Nerve Birthdays: Determine how deep in the cortex a neuron will enter.

10. Cerebrum • Similar to Cerebellum • Neocortex: subdivided into 6 layers (old cells closest to ventricular zone). • Cortex divided horizontally (approx. 40 sections). • Fate decided early on (before S phase)

11. Cortical Neurons

12. Spinal Cord

13. Motor Neuron Specification • Sonic hedgehog (Shh) secreted by floor plate.

14. Target specification of Motor neuron • As Nerves pass through the cortex, different transcriptional regulators are expressed. • Limb innervation determined by repulsion • If Lim1 is present, Eph A4 (receptor) is expressed; Eph A5 repels neuron • If no Lim1, neuropilin-2 expressed. (Axial muscles)

15. Following diffusible signals • Netrin-1 and Netrin-2 • SLIT and ROBO

16. Nerve Outgrowth • Filapodia-based movements • Rely on Cytoskeleton and factors that rearrange the cytoskeleton (GTPases).

17. Finding a place to hang out

18. Neural Crest Cells • Neurons/glial cells of sensory, sympathetic, and parasympathetic nerves • Epinephrine-producing cells of adrenal gland • Pigment containing cells • Skeletal/connective tissue of head • 4th germ layer?

19. Ventral Migration of Neural Crest

20. Neural Crest Cell specification

21. Neural Crest Regionalization • Cranial • Cartilage, bone, cranial nerves, glia, connective tissues • Cardiac • Melanocytes, neurons, cartilage, musculo-connective tissue wall of large arteries • Trunk • Dorsal root ganglia, sympathetic ganglia, adrenal medulla, nerve clusters around aorta • Vagal and Sacral • Parasympathetic ganglia of gut

22. Trunk Neural Crest Cells: Migration • Dorso-lateral inhibited • At first, between somites, but Semaphorin-3F causes movement through somites.

23. Further migration • Cells that stop in sclerotome- dorsal root ganglia • Cells past sclerotome-lack wnt and neurotropin receptors- parasympathetic and sympathetic nerves. • BMPs from aorta convert cells to sympathetic and adrenal lineage • Glucocorticoids- adrenomedullary cells. • Neural crest cells committed to path early, but differentiate to determine final location.

24. Cranial Neural Crest • Head is most anatomically sophisticated portion of vertebrate body. • Mainly composed of neural crest cells

25. Cranial Neural Crest: Bone Formation

26. Neural Crest and neurocranium • Viscerocranium (jaws, pharyngeal arches) well established as being of Neural crest origin…neurocranium controversial origin

27. The Face reflects the brain!

28. Cardiac Neural Crest

29. Cranial placodes