24-hr Chick

9. Formation of the Neural Tube Secondary Neurulation Occurs beyond the caudal neuropore lumbar and tail region Exclusive mechanism for fish Starts with formation of medullary cord Cavitation of cord to form hollow tube

11. Differentiation of Neural Tube Major morphological changes: differentiation of brain vesicles and spinal cord Differentiation of neural tube cells Development of peripheral nervous system

13. Differentiation of Brain Vesicles Anterior neural tube bulges: 3 primary vesicles:

14. Then further differentiation into 5 secondary vesicles:

16. Differentiation of the Neural Tube Neural tube must maintain dorsal-ventral polarity Sensory neurons- dorsal Motor neurons- ventral Accomplished by �inductive cascades� Dorsal: BMPs from epidermis?Roof plate cells in neural tube?TGF-B cascade?Cell differentiation Ventral: Sonic hedgehog from notochord and retinoic acid from somites?Floor plate cells of neural tube?shh gradient?Cell differentiation

18. Differentiation of the Neural Tube Histological changes Neural tube initially a single layer of cells: germinal epithelium Cells are called neural stem cells Neurons Glial Cells: Myelin sheath

28. Development of Peripheral Nervous System Divisions: Autonomic NS Sympathetic vs. Parasympathetic Somatic NS Anatomy Sensory Neurons Enter dorsal part of spinal cord Soma located outside of cord?Dorsal ganglia Form Dorsal Root of Spinal Nerve Motor Neurons Soma in ventral gray matter Somatic NS: Neurons run directly from SC to muscle Autonomic: 2 Neurons Sympathetic: Ganglia near SC Parasympathetic: Ganglia near or in or near organ

30. Development of Peripheral Nervous System Anatomy Spinal Nerves:Spinal Cord Sensory fibers of somatic nervous system: Dorsal root Preganglionic neurons of sympathetic system: Ventral root Motor fibers of somatic nervous system: Ventral root Cranial Nerves: Brain stem Sensory fibers of somatic nervous system: Dorsal root Preganglionic neurons of parasympathetic system: Ventral root Motor fibers of somatic nervous system: Ventral root

33. Origin of PNS Cells From neural tube: All motor neurons of somatic nervous system Preganglionic neurons of autonomic system From neural crest: Sensory nerves and associated ganglia Postganglionic neurons of autonomic system

36. Neural Crest Cells Induced by organizing cells of notochord Main functional groups: Cranial neural crest: Bones and connective tissue of face Tooth primordia Thymus, parathyroid, thyroid glands Sensory cranial neurons Parasympathetic ganglia and nerves Parts of the heart (cardiac neural crest)

37. Neural Crest Cells Main functional groups: Trunk neural crest: Melanocytes Sensory neurons Sympathetic ganglia and nerves Medulla of adrenal glands

40. Neural Crest Cells Migration: Epithelial to mesenchyme transition Migrational pathways are established by juxtacrine signals: Fibronection, laminin in ECM + integrins Ephrin proteins: Restrict movement Contact inhibition Use of existing structures Migration ceases when these signals are reversed

42. Neural Crest Cells Differentiation: Largely based on location along neural tube and their migration route:

43. Neural Crest Cells Differentiation: Migration routes along trunk: Ventral pathway: cells move through anterior portion of somite toward ventral side of embryo Cells become: sensory neurons, sympathetic ganglia, medulla of adrenal gland Dorsolateral pathway: cells move between epidermis and somite Cells become: melanocytes Basic organization of the PNS is established by the migratory pathways of the neural crest cells

45. Neural Crest Cells Differentiation: How do they know what to become? Most cells are pleuripotent- fate determined by position Paracrine factors play a role Example: Endothelin-3 and Wnt Some exceptions: only NC cells from head make bone Individual cells may differentiate early in migration

46. Differentiation of Neurons Within nerve tube: Dorsal? Interneurons Ventral? Motor neurons

47. Differentiation of Neurons Motor neurons: Tissues they innervate depends on: Anterior-posterior location along the nerve tube When the cells were �born�

49. Axonal Pathways

50. Establishing pathways and connections: Pathway selection Target selection Address selection Axonal Pathways

51. Pathway Selection Pathway axon takes influenced by extracellular matrix and cells encountered: signals by both paracrine and juxtacrine factors: Cell adhesion and contact guidance: Haptotaxis Growth cone repulsion Ephrin and semaphorin proteins Labeled Pathways Hypothesis: Pioneer Neurons Diffusible molecules Axonal Pathways

52. Target Selection: Neurotrophins on target cells (muscle or another neuron) Address selection: constructing the synapse Axonal Pathways