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©2009 Mark Tuttle Development of the CNS – Dr. Yeasting - Ectoderm o Neuroepithelium Becomes central portion of nervous system All the cells which have their cell bodies within central portion of nervous system, EXCEPT MICROGLIAL CELL Don’t come in at all until invasion of vasculature i.e. they come in with mesodermal ingrowths Take up residency within neural tube, and take up phagocyticic function Is multipotential Differentiate into: o Glial cells (almost all) Oligodendrocytes Astrocytes Fibrous o Stronger, have intracellular fibers within them o Are more supportive o Found largely within tract areas Protoplasmic o Help line blood brain barrier Radial (temporary) Ependymal cells o Line central canal and ventricles o Helps produce CSF! o Extend from luminal surface to pial surface o Neural cells (almost all) EXCEPT mesencephalic nucleus of CN V These are thought to be neural crest cells that didn’t separate away like other primary sensory neurons did, but instead got embedded in mesencephalon o Transition tissue Neural crest Primary sensory neurons Postganglionic autonomic neurons o Including adrenal medulla Melanocytes Schwann cells ©2009 Mark Tuttle - - - - - In head/neck region, gives rise to CT structures, especially supportive tissues o Ex. Cartilage and bone More caudally, does NOT give rise to CT elements, but gives rise to the other stuff listed above Mesoderm o Somites Axial skeleton o Intermediate Genital system o Lateral plate Digestive system Body wall Endoderm Notocord o Not only a skeletal element (nucleus pulposis) o Strong controller, inducer, regulator Does NOT activate ectoderm to become neuroepithelium o Will elaborate o Diffuse in embryonic mass, help create 3-4 dimensional matrix, signaling where cells are within embryonic body Procordal plate (cranial to the notochord) o Around the oropharyngeal membrane o Sends out many signal molecules and is responsible in the short run to help control development of cranial regions whereas the notochord is responsible to help develop non-cranial portions of body o When you get into neck region, there is a “border” where it transitions from procordal/notochord control o Possible do develop a fetus with perfectly good body, but messed up cranium because procordal plate had a problem Spinal cord & lower brainstem have a similar (not exactly the same) structure, but once you get above that: diencephalon & telencephalon, the organization changes o Reason: notochord controls development up to the junction between midbrain/diencephalon o Above this level, it is under control of procordal plate Neural plate: o cells here assume a columnar epithelial configuration o elsewhere, regular ectoderm, are cuboidal o There is a transition tissue between regular ectoderm and neural plate Neural crest! o Undergoes folding process, and gives rise to neural groove ©2009 Mark Tuttle - - Margins of the plate begin to rise up Changing from relatively flat structure to a trench (if you will) As the neural groove forms, the neural crest which was at the margin, is now brought closer together, sealed off with [roof plate]? Regular ectoderm is brought closer together Neural groove ultimately closes on its dorsal aspect and gives rise to neural tube As this closure occurs, neural crest cells migrate downward and ultimately lie lateral to neural tube Now, neuroepithelium comprises the neural tube Fusion of the tube usually begins in region that usually becomes the neck region, and “zippers” both ways, cranially and caudally As neural groove is closing, ultimately the ends of the neural tube will still be open (openings = neural pores) Ultimately cranial/caudal neural pores will ultimately close. Day 24 for cranial, day 26 for caudal α-fetal protein is produced by neural crest area Does not normally get out of embryonic system But if there is a defect and it escapes via neural pores or some other hole within neural tube, α fetal protein builds up in amniotic fluid and gets into maternal circulation This is often tested in pregnancy If found positive, further testing is necessary to see if there are neural tube defects Not much can be done, but can forewarn parents-to-be Adjacent to the neural tube are developing somites o Develops into Base of skull Vertebral column Musculature of axial skeleton, limbs pharyngeal arches Part of CT of dermis o Partially controlled by neural tube o Also reciprocally influences development within neural tube Tissue surrounding somites will migrate upward and fill in region around neural tube Timing is important o If delayed closure of neural tube, tissue surrounding it (somites) tissue may no longer “be in the mood” to migrate since it’s on its own timer o Differential growth and differential tensions can pull ectoderm apart, even pull open the neural tube (Myeloschisis = open tube) o If you have some tissue migrating, but not really enough to make a full vertebral column Spina bifida ©2009 Mark Tuttle - - Neural arch is not complete Can get protrusion of tissue through here of vesicle Meningocele Meningomyelocele (not only meninges, also neural tube – myelon – spinal cord) Dorsal vertebral column defect o Lack of portion of neural arch: lamina, spinous process, or more extreme: non closure – neural tube is not closed and is continuous with surface epithelium o Under modern circumstances, closed defects (spina bifida cystic with meningocele) can live productive lives o Open defect, however, no way of closing it. Infection sets in very quickly, and child dies of overwhelming infection of nervous system Sides of neural crest o Becomes DRG o - Development of neuroepithelium In inactive stages of mitotic cycle, developing neural cells out toward periphery In mitotic phase, they are down toward lumen Mostly, running from luminal to pial surface See a migration of nucleus within cell, not whole cell Luminal aspect is the generative aspect o Combine concept of development (luminal to pial) with radial cells Radial cells are important in areas of nervous system that are stratified Ex. cerebral cortex. Neurons proliferating near luminal surface Neuroblasts round up and migrate up radial glial cells nd o 2 wave migrates up and goes through existing layer to reach outer surface o In neocortical layer, (six layers), occurs several times This probably also happens in allocortex, but not as many times o Develop into cortical column All cells in a given column migrated in a proliferative zone out to the pia and are organized in a “family” o Oldest neurons are the innermost (layer 6), because subsequent layers LEAPFROG older layers - Neural tube o Neural tube gets stratified o In early neural tube, there are 3 major zones Neuroepithelium (ventricular zone) right next to lumen Proliferative, reserve cell zone ©2009 Mark Tuttle - Mantle zone (intermediate): Cells which have migrated toward periphery Develop processes, spread throughout nervous system Becomes the “Honda H” of the spinal cord – grey matter Marginal zone: on periphery where processes of Mantle zone cells develop Becomes white matter of spinal cord o Ventral/Dorsal afferent/efferent organization develops Develops because of signaling factors Mantle Notocord, ventrally, realeases SHH which signals that this area is ventral and should develop efferent neurons (basal plate) o Highest concentration of SHH yields lower motor neurons (send axons out of CNS to innervate skeletal muscle) o Adjacent to them (slightly lower concentration) develop into other motor neurons, gamma and beta Dorsally, signaling factors, including bone morphogenic factors, PAX genes signal this as dorsal, should develop afferent neurons (alar plate?) o Most dorsally, highest exposure to PAX/morphogenic factors develop into 2nd order relay afferent neurons Intermediate zone develops in between these two zones Sulcus limitans o Medial sulcus is in middle o Neural crest cells o Origin of neuroepithelium Notocord does NOT activate ectoderm to develop into neuroepithelium Instead, signaling molecules from notochord influence neural tube Releases chordin and noggin, released into intercellular space o Interact with bone morphogenic proteins and other transforming growth factors and prevent them from making their way to the ectoderm o Thus, this ectoderm is then free to differentiate into neuroepithelium o THUS, neuroepithelium is really the default tissue of ectoderm, but it usually is acted on by bone morphogenic/other transforming growth factors to develop into neuroepithelium IGNORE OBJECTIVE #14 Disorders of Neural crest cell o Congenittal megacolon o Waldberug’ White forlock Related to neural crest cells, both bigment within regular hair cells and ear hair cells because it usually helps generate endolymph there ©2009 Mark Tuttle - - - - - Results in deafness o Albinism Melanocytes – neural crest o Feto Chromatosis Excess adrenaline etc because of o Neuro fibratosis Combination of problems of dermis and neural supportive tissue o DeGeorge syndrome Gets more into CT elements BVs, septation of the aorta Differential growth of spinal cord o Spinal cord initiall is down low o Spinal cord grows slower than vertebral column o DRGs and nerves stay put and elongate to form cauda equine Divisions o Telencephalon o Diencephalon o Mesencephalon o Rhombencephalon Metencephalon Cerebellum Pons Myelencephalon Medulla Nerves grow out and try to make contact with peripheral tissues o If they indeed make contact, they become mature nerves o If they only make it to for example a muscle which is already innervated, they die off Ex. Basal plate (ventral area) This explains differential gray matter in different sections of spinal cord Folding of embryo o Neural tube gets bent as head forms o Caudal to notochord No more basal plate (motor neurons) o Develop mesencephalic flexure -> main brain flexure o Develop Rhombencephalic flexure o Develop cervical flexure o All balance out Cerebellum formation o Thin tissue layer between ventricle in 4th ventricle Just Epyndyma Tila choroidia forms median aperture madidiga Also forms lateral apertures of luschka ©2009 Mark Tuttle o - - Granular cells Granular cells on surface Cell body migrates inward Become parallel processes which interact with purkinje cells o Deep nuclei are a later migration from ventricular zone Ex. Dentate nucleus o NOT complete at birth Brainstem o Under control of homeobox genes (also control pharyngeal arches nearby) Determine structure of pharyngeal arches and neurons which go into pharyngeal arches o Basal plate Separates into CN nuclei CN III, VI, XII Special visceral efferent (skeletal mm of pharyngeal origin) V, VII, IX, X (nucleaus ambiguous) General visceral efferent (preganglionic parasympathetic) Edinger westval Salivatory Dorsal motor nucleus of vagus o Alar plate Special visceral afferent Solitary nucleus o VII, IX, X Vestibular cochlear o VIII General somatic V Reticular nuclei Not just neurons that receive info from primary sensory neurons, but ALSO all the interneurons Diencephelon/telecephalon which were initially separate, fuse o Telencephalon Basal ganglia Medial temporal lobe “older” areas of cortex Cortex Processes leaving/entering cortex, cut through the nuclear groups and create striatum, separate – and create: Caudate nucleus Putamen ©2009 Mark Tuttle Held together by three commissures Anterior Hippocampal Corpus callosum All start out in the area known as the lamina terminalis o Was the anterior aspect of the neural tube o Anterior wall of the third ventricle Oldest commisure is the anterior commissure o Connects largely olfactory areas Hippocampal commissure connects the two hippocampal formations o They were initially very anterior, but migrated posteriorly Corpus callosum o Starts in close proximity to lamina terminalis o Begins to knit together frontal lobe structures and then progressive posteriorly, knitting together structures as it goes o Of these areas, corpus callosum is the most common area for problem Tissue between corpus callosum and fornix gets stretched out and becomes septum pellucidum Ventricles Choroid outside Tila choroidia inside BVs of pial origin invaginate into tila choroidia o Becomes choroid plexus o Creates component of CSF o Choroid epithelium is the main filter determining what gets out into CSF o Presence of healthy astrocytes induces blood brain barrier to develop o If you don’t have astrocytes, you don’t get a blood-brain barrier Not just development, also postnatal life o In tila choroidia, there are no astrocytes, do not get blood brain barrier Disorders o Blockage within ventricular system Get hydrocephalus Should not really see this in developed countries Can put a shunt in here to correct this Head growth Mostly occurs after birth ©2009 Mark Tuttle Resistive pressure of uterus is removed when baby is born head can now grow