Neurulationembryo/Lectures/exam 2/06 Neurulation.pdf · Neurulation Induced by Notochord –...
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Neurulation
Readings: Chapter 5Chapter 10
P. 208-214P. 218-219 (Peripheral Nerve)p. 239-240 (Cranial Nerve)
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Neurulation
Induced by Notochord – Noggin/Chordin
Neural Plate Neural Groove Neural Tube
Regionalization – Subdivisions of the Central Nervous System (CNS)
Noggin, chordin Anterior Neural TissuesForebrain
FGF8 – Fibroblast Growth Factor 8 Posterior neural tissues, i.e. spinal cord
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Middle of third week:Neural Plate
Notochord induces overlying ectoderm neural plate –
Thickening of cell layer
Anterior Inducer: Noggin/ Chordin
Posterior Inducer: FGF-8,
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Neural Plate Neural Tube
Four Stages of Neural Tube formation:
1) Thickening of the Neural Plate
2) Establishing the contours of the Neural Plate: Cell shape changes and rearrangement of cells
3) Lateral Neural Folds elevate to form the Neural Groove – medial hinge acts as an anchor, Cell shape changes apically, expanding lateral epidermis forces elevation
4) Apposition and fusion of the Neural Folds to form the Neural Tube
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Neural Crest
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Early CNS Development
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Neural Tube Formation
Anterior Neuropore
Anterior
Central Fusion Completion – Closure of Neuropores
Posterior
Posterior Neuropore
Secondary Neurulation – Posterior to the neuropore –Mesenchymal condensation to form a rod that undergoes cavitation – secondary fusion with primary neural tube.
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Segmentation of the Neural Tube
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Segmentation of the Rhombencephalon
Neuromeres – Transient regularly spaced segments, also called Rhombomeres
7 pairs – each an isolated compartment
Alternating cell adhesive characteristics; alternating rhombomeres intermingle freely
Segmental organization gives rise to specific cranial nerves
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Specification and Position-Specific Gene
Expression
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Cephalic flexure, Cervical flexure, Pontine flexure
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Cerebrum
Thalamus CorpusCallosum
Pineal BodyHypothalamus
Midbrain Cerebellum
Pons
Medullaoblongata
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Histogenesis of CNS cells
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Cell Types
Neuroepithelium – Multipotential Stem CellBipotential Progenitor CellNeuronal vs. Glial Cell LineageNeuronal Lineage (neurofilament expression):
Bipolar neuroblast, Multipolar neuroblast, Neuron
Glial Lineage (glia fibrillary acidic protein, GFAP): Radial glia, Type-1 Astrocyte, Type-2 Astrocyte, Oligodendrocyte
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Dendrite
Cell Body
Axon
Schwann Cell
Myelin Sheath
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Spinal Cord
Central Canal – Lumen
Ventricular Zone – Cells lining the Central Canal becomes Gray matter
Intermediate Zone
Marginal Zone – neuronal cell processes; no cell bodies, becomes White matter
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6 Parts of the Spinal Cord
2 Alar Plates (Left and Right)Sulcus Limitans separates Alar
and Basal plates2 Basal Plates (Left and Right)Roof Plate connecting Alar platesFloor Plate connecting Basal platesBasal plates Motor – Ventral Horn Alar plates Sensory – Dorsal Horn
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Nerves
Motor
Sensory
AutonomicSympatheticParasympathetic
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Cranial Nerves
I – Olfactory; Telencephalon; No Ganglion; Sensory
II – Optic; Diencephalon; No Ganglion; Sensory
III – Oculomoter; Mesencephalon; Cilary Ganglion; Motor and Parasympathetic
IV – Troclear; Metencephalon; No Ganglion; Motor
V – Trigeminal (semilunar); Metencephalon, trigeminal placode; Trigeminal Ganglion; Sensory and Motor
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VI – Abducens; Metencephalon; No Ganglion; Motor
VII – Facial; Metencephalon; 4 Ganglia – Superior, Inferior (Geniculate), Sphenopalatine, Submandibular; Motor, Sensory, Parasympathetic
VIII – Vestibulocochlear; Metencephalon, 2 Ganglia –Acoustic, Vestibular; Sensory
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IX – Glossopharnygeal; Myelencephalon; 3 Ganglia –Superior, Inferior (Petrosal), Otic; Motor, Sensory, Parasympathetic
X – Vagus; Myelencephalon; 3 Ganglia – Superior, Inferior (Nodose), Vagal parasympathetic; Motor, Sensory, Parasympathetic
XI – Accessory; Myelencephalon; No Ganglia; Motor
XII – Hypoglossal; Myelencephalon; No Ganglia; Motor
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Anomalies
Defective Neural Tube ClosureSpinal Cord – RachischisisBrain – Craniochisis (lethal)
Spina Bifida – Defective closure of anterior or posterior neuropore –lacking neural arch, bulging membranous sac called a Cele, containing cerebral spinal fluid +/- neural tissues
Spina bifida occulta – Defect in Neural Arch – mildest formMeningocele – protruding dura and arachnoid tissuesMeningomyelocele – protruding spinal tissuesMeningoencephalocele – protruding brain tissuesMeningohydroencephalocele – protruding brain and ventricular
tissues
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Anomalies – Spinal Cord
Rachischisis Spina bifida occulta
Meningocele Myelomeningocele
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Spinal Abnormalities
Spina bifida
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Brain Abnormalities
microcephaly
hydrocephaly
holoprosencephaly