Development of the Nervous System PDF

Development of the central and peripheral nervous system Chapter 10: Hytell, 2010 Signaling proteins 1. BMP4 from surface ectoderm 2. Sonic hedgehog (Shh) from notochord 3. Hepatic Nuclear Factor- 3β Cells from the developing Notochord 4. Noggin 5. Cordin Signaling proteins...

Development of the central and peripheral nervous system Chapter 10: Hytell, 2010 Signaling proteins 1. BMP4 from surface ectoderm 2. Sonic hedgehog (Shh) from notochord 3. Hepatic Nuclear Factor- 3β Cells from the developing Notochord 4. Noggin 5. Cordin Signaling proteins This signaling protein prevents the dorsal ectoderm 1. BMP4 from surface ectoderm from forming neural tissue. 2. Sonic hedgehog (Shh) from notochord 3. Hepatic Nuclear Factor- 3β Cells from the developing Notochord 4. Noggin 5. Cordin Signaling proteins 1. BMP4 from surface ectoderm This protein functions as a chemical signal that is 2. Sonic hedgehog (Shh) from notochord essential for embryonic development. 3. Hepatic Nuclear Factor- 3β 4. Noggin 5. Cordin Signaling proteins 1. BMP4 from surface ectoderm 2. Sonic hedgehog (Shh) from notochord 3. Hepatic Nuclear Factor- 3β 4. Noggin These two molecules are potent neural inducers that block the inhibitory influence of BMP4 and 5. Cordin thus allow the ectoderm dorsal to the notochord to form neural tissue. Neural tube and neurogenesis Fig. 10-1: Formation of the neural tube and the neural crests. The boxed areas in A–C are enlarged to the right (modified after Rüsse and Sinowatz, 1998). A: 1: Notochord; 2: Surface ectoderm: B: 1: Notochord; 2: Surface ectoderm; 3: Neural groove; 4: Neural plate. C: 1: Notochord; 2: Epithelium of the neural groove; numerous mitoses occur in the neural epithelium; 3: Neural groove; 4: Neural crest; D: 1: Notochord; 2: Surface ectoderm; 3: Neural tube; 4: Neural crest, which at this stage is still a continuous sheet of cells. E: 1: Notochord; 2: Surface ectoderm; 3: Neural tube; 4 Neural crests, which are segmented into groups of cells giving rise to different cell types. HE: Ependymal cells; VZ; Ventricular zone; MZ: Marginal zone. Courtesy Sinowatz and Rüsse (2007). Neuroblast formation Neuroblast formation Cell lineages of CNS Cell lineages of CNS Cell lineages of CNS Nerve cells (development of the axon and dendrites)  Glial cells Not all glial cells of the spinal cord originate from the neuroepithelium. Microglial cells, which appear in the second half of fetal development, are highly phagocytotic cells derived from the mesoderm. Review Development of the spinal cord Ependyma Ventricular system Development of the spinal cord Ependyma Ventricular system  Ependyma Development of the spinal cord Ventricular system Fig. 10-6: Four successive stages in the development of the spinal cord. A and B: 1: Neuroepithelium; 2: Central canal; 3: Notochord; 4: Surface ectoderm; 5: Basal plate; 6: Roof plate; 7: Floor plate; 8: Marginal zone; 9: Spinal ganglion; 10: Dorsal (sensory) horn; 11: Spinal nerve. C: 1: Neuroepithelium; 2: Central canal; 3: Notochord; 4: Surface ectoderm; 5: Basal plate; 6: Alar plate; 7 and 8: Intermediate horn; 9: Marginal zone; 10: Roof plate; 11: Floor plate; 12: Spinal ganglion; 13: Dorsal root; 14: Spinal nerve; D: 1: Ependyma; 2: Central canal; 3: Dorsal (sensory) horn; 4: Intermediate horn; 5: Ventral (motor) horn; 6: Dorsal (sensory) root; 7: Spinal nerve. 7′: Ventral (motor) root; 8: Septum dorsale; 9: Median fissure; 10: White matter; 11: Spinal ganglion. Courtesy Sinowatz and Rüsse (2007). Development of the spinal cord Ependyma Ventricular system Development of the spinal cord As the spinal cord matures, the intermediate layer becomes the greymatter, where the cell bodies of the neurons are located. As the neuroblasts continue to develop axons and dendrites, a peripheral marginal layer (marginal zone) is formed. It contains neural processes but not neural cell bodies and later forms the white matter of the spinal cord.  Basal plates Development of the spinal cord Alar plates Basal plates: General somatic efferent nerve fibers and visceral efferent nerve fibers. Alar plates: General somatic afferent nerves, special visceral afferent nerves, general visceral afferent nerves Development of the spinal cord Basal plates Alar plates Development of the spinal cord Spinal cord  Neural crest cells > sensory or spinal ganglia (dorsal Dorsal root root ganglia) > ganglia cells (sensory ganglia, general visceral efferent ganglia of the sympathetic and parasympathetic system), Schwann cells, ganglia and melanocytes, odontoblasts, and mesenchyme of the pharyngeal arches. spinal Neuroblasts of the spinal ganglia develop two nerves processes, which soon unite in a T- shaped fashion (pseudo-unipolar neurons). Dorsal root ganglia and spinal nerves Neural crest cells > sensory or spinal ganglia (dorsal root ganglia) > ganglia cells (sensory ganglia, general visceral efferent ganglia of the sympathetic and parasympathetic system), Schwann cells, melanocytes, odontoblasts, and mesenchyme of the pharyngeal arches. Neuroblasts of the spinal ganglia develop two processes, which soon unite in a T- shaped fashion (pseudo-unipolar neurons). Dorsal root ganglia and spinal nerves The centrally growing processes enter the dorsal portion of the neural tube and constitute the afferent dorsal root of the spinal cord. In the spinal cord, they either form synapses with afferent dorsal horn interneurons or ascend through the marginal layers to one of the higher brain centres. The peripherally growing processes join the fibres of the ventral root to form the trunk of the spinal nerve through which they eventually terminate in sensory receptors. Development of the brain Development of the brain Development of the brain (SUPPLEMENT SLIDE) Development of the brain Development of the brain Development of the brain Development of the brain Brain flexures  Brain flexures Flexures: 1. Midbrain/cephalic (4) 2. Cervical (5) 3. Pontine (arrow) Differential growth of the five secondary brain vesicles (telencephalon, diencephalon, mesencephalon, metencephalon and myelencephalon) gives rise to flexures Rhombencephalon (hindbrain) Myelencephalon Fourth ventricle and choroid plexus Rhombencephalon: Myelencephalon  C: Day 120. 1: Pons; 2: Medulla oblongata; 3: Trigeminal ganglion; 3′: Nucleus sensibilis pontinus n.trigemini; 3′′: Nucleus tractus mesencephali; Rhombencephalon: 3′′′: Nucleus tractus spinalis n. trigemini; 4: Velum medulare rostrale; 5: Velum medullare caudale; 6: Fissura postculminata; 7:Fissura Metencephalon postpyramidalis; 8: Pyramis, 9: Uvula; 10: Fissura uvulonodularis; 11: Lobus flocculonodularis. Courtesy Sinowatz and Rüsse (2007).  Each basal plate of the metencephalon contains three groups of motor neurons: (1) the medial general somatic efferent group, which forms the nucleus of the abducens (VI) nerve; (2) the intermediate special visceral efferent group, Rhombencephalon: which gives rise to the nuclei of the trigeminal (V) and facial (VII) nerves, innervating the musculature Metencephalon of the first and second pharyngeal arches; (3) the lateral general visceral efferent group giving rise to the nucleus of the facial (VII) nerve, supplying the mandibular and sublingual glands. Some alar plate neurons migrate ventrally to form the pontine nuclei. Mesencephalon (midbrain) Ventral to the aqueduct the basal plates form the tegmentum which contains the efferent nuclei of the: ✓oculomotor (III; general somatic efferent and general visceral efferent) ✓trochlear (IV; general somatic efferent) nerves. Their axons supply most of the extrinsic muscles that move the eyeball. A relatively small special visceral efferent nucleus, the Edinger- Westphal nucleus, innervates the pupillary sphincter muscle of the eye through the oculomotor nerve (III). Prosencephalon (forebrain) Forebrain: ✓The hypothalamic masses, originally paired, later fuse to form a single structure that becomes a master regulatory centre. ✓It differentiates into a number of nuclear areas controlling basic homeostatic functions such as sleep, body temperature, hunger, fluid and electrolyte balance, emotional behaviour, and activity of the pituitary. ✓Paired subthalamic nuclei, the mamillary bodies, can be seen as distinct protuberances on the midventral surface of the hypothalamus. Forebrain: Telencephalon  ✓Consist of cranial and spinal nerves ✓Nerve fibers: Peripheral a. afferent/efferent b. somatic/visceral Nervous ✓Visceral efferent pathway: System a. preganglionic neuron b. postganglionic neuron ✓Schwann cells Meninges