Difference between revisions of "Ectoderm"

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==Some Recent Findings==
 
==Some Recent Findings==
  
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=Ectoderm Development=
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<div style="background:#F5FFFA; border: 1px solid #CEF2E0; padding: 1em; margin: auto; width: 90%; float:left;"><div style="margin:0;background-color:#cef2e0;font-family:sans-serif;font-size:120%;font-weight:bold;border:1px solid #a3bfb1;text-align:left;color:#000;padding-left:0.4em;padding-top:0.2em;padding-bottom:0.2em;">Lecture Notice - Mark Hill</div>This online lecture page will contain the content required when attending the lecture. Currently this page is only a template and will be updated before the lecture (this notice removed when completed). Final lecture pages can also be printed out using the "printable version" lefthand menu.</div>
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== Introduction ==
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{|
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| <wikiflv width="240" height="240" autostart="true" repeat="true">Neuraltube_001.flv|File:Neuraltube_001_icon.jpg</wikiflv>
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| This animation shows early neural development from week 3 onward. The whole early embryo development (dorsolateral view) is shown, yolk sac to left.
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This lecture will cover the early development of the ectoderm layer of the trilaminar embryo. Note that we will be returning later to discuss neural (central nervous system; brain and spinal cord) and neural crest (peripheral nervous system; sensory and sympathetic ganglia).
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Epidermis (integumentary, skin contribution) development will be briefly mentioned due to its ectoderm origin, but will also be covered later in the current course.
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|}
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{|
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| [[Image:Stage10 neural sm.jpg|400px]]
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| [[Image:Stage10 SEM1.jpg|300px]]
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|}
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=Ectoderm Development=
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[[Image:Stage10 neural sm.jpg|400px|right]]
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[[Image:Stage10 SEM1.jpg|300px|right]]
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== Introduction ==
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This lecture will cover the early development of the ectoderm layer of the trilaminar embryo. Note that we will be returning later to discuss neural (central nervous system; brain and spinal cord) and neural crest (peripheral nervous system; sensory and sympathetic ganglia). Epidermis (integumentary, skin contribution) development will be briefly mentioned due to its ectoderm origin, but will also be covered later in the current course.
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==Lecture Objectives==
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* Understanding of events during the third and fourth week of development
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* Understanding the process of notochord formation
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* Understanding the process of early neural development
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* Brief understanding of neural crest formation
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* Brief understanding of epidermis formation
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* Understanding of the adult components derived from ectoderm
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* Brief understanding of early neural abnormalities
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==Textbook References==
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* Human Embryology (3rd ed.) Chapter 5 p107-125
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* The Developing Human: Clinically Oriented Embryology (6th ed.)
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Other textbooks
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* Moore and Persaud Chapter 18 p451-489
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* Essentials of Human Embryology Larson Chapter 5 p69-79
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* Before We Are Born (5th ed.) Moore and Persaud Chapter 19 p423-458
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== Development Overview ==
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==Notochord==
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* forms initially as the Axial Process, a hollow tube which extends from the primitive pit , cranially to the oral membrane
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* the axial process then allow transient communication between the amnion and the yolk sac through the neuroenteric canal.
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* the axial process then merges with the Endodermal layer to form the Notochordal Plate.
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* the notochordal plate then rises back into the Mesodermal layer as a solid column of cells which is the Notochord.
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==Ectoderm==
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* 2 parts
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* midline neural plate
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** columnar
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* lateral surface ectoderm
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** cuboidal
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** sensory placodes
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** epidermis of skin, hair, glands, anterior pituitary, teeth enamel
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==Neural Plate==
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[[Image:Neuralplate cartoon.png|right]]
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[[Image:Stage11 SEM1.jpg|thumb|Stage 11 neural groove to tube]]
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{| border='0px'
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|-
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| <wikiflv width="316" height="500" autoplay="true">Neuralplate_001.flv|File:Neuralplate_001 icon.jpg</wikiflv>
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| Development of the [[N#neural plate|neural plate]] region at the embryonic disc stage.
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Dorsal view of the embryonic disc from the amniotic cavity side showing the ectoderm with the central region developing into the [[N#neural plate|neural plate]].
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The [[N#neural plate|neural plate]] extends from buccopharyngeal membrane to primitive node and forms above the notochord and paraxial mesoderm.The neuroectodermal cells form a broad brain plate and narrower spinal cord region.
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Three specific regions medial to lateral can also be identified: midline region [[F#floor plate|floor plate]], neural plate, edge of neural plate [[N#neural crest|neural crest]]
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* '''blue''' - [[N#neural plate|neural plate]] region
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* '''white and black midline strip''' - [[P#primitive streak|primitive streak]] ending in [[P#primitive node|primitive node]]
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* '''white''' - [[E#ectoderm|ectoderm]] forming the epithelium of the skin
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* '''upper circular region''' - [[B#buccopharyngeal membrane|buccopharyngeal membrane]]
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* '''lower circular region''' -  [[C#cloacal membrane|cloacal membrane]]
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:[[Media:Neuralplate_001.mov|Quicktime version]]
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|-
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|}
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* extends from buccopharyngeal membrane to primitive node
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* forms above notochord and paraxial mesoderm
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* neuroectodermal cells
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** broad brain plate
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** narrower spinal cord
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* 3 components form: floor plate, neural plate, neural crest
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'''Neural Determination'''- neuronal populations are specified before plate folds
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* signals from notochord and mesoderm - secrete noggin, chordin,follistatin
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** all factors bind BMP-4 an inhibitor of neuralation
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** bone morphogenic protein acts through membrane receptor
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* lateral inhibition generates at spinal cord level 3 strips of cells
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* expression of delta inhibits nearby cells, which express notch receptor, from becoming neurons
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* Delta-Notch inetraction- generates Neural strips
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==Neural Groove==
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{| border='0px'
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|-
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| <wikiflv width="480" height="480" autostart="true">Neuraltube_001.flv|File:Neuraltube_001 icon.jpg</wikiflv>
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| valign="top" |This animation of early neural development from week 3 onward shows the [[N#neural groove|neural groove]] fusing to form the [[N#neural tube|neural tube]].
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'''View''' - Dorsolateral of the whole early embryo and yolk sac. Cranial (head) to top and caudal (tail) to bottom. Yolk sac is shown to the left.
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Beginning with the  [[N#neural groove|neural groove]] initially fusing at the level of the 4th somite to form the  [[N#neural tube|neural tube]] and closing in both directions to leave 2 openings or neuropores: a [[C#cranial_neuropore|cranial neuropore]] (anterior neuropore) and a [[C#caudal_neuropore|caudal neuropore]] (posterior neuropore).
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The animation also shows as the embryo grows and folds it increases in size relative to the initial yolk sac. Note also the increasing number of somites over time.
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|-
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|}
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* forms in the midline of the neural plate (day 18-19)
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* either side of which are the neural folds which continues to deepen until about week 4
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* neural folds begins to fuse, beginning at 4th somite level
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==Neural Tube==
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[[Image:Stage12 SEM3.jpg|thumb|Stage 12 caudal neuropore]]
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* the neural tube forms the brain and spinal cord
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* fusion of neural groove extends rostrally and caudally
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* begins at the level of 4th somite
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* closes neural groove "zips up" in some species.
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** humans appear to close at multiple points along the tube.
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* leaves 2 openings at either end - '''Neuropores'''
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** cranial neuropore closes before caudal
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Failure for the neural tube to close correctly or completely results in a '''neural tube defect'''.
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==Secondary Neuralation==
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{| border='0px'
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|-
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| <wikiflv width="316" height="300" autostart="true" position="left">Secondary_neurulation_01.flv|File:Secondary_neurulation_01 icon.jpg</wikiflv>
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| valign="top" |This animation shows the early developmental process often described as secondary neurulation.
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<font color=orangered>'''Red - site of secondary neurulation'''</font> | <font color=deepskyblue>'''Blue - neural tube'''</font>
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* caudal end of neural tube formed by secondary neuralation
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* develops from primitive streak region
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* solid cord canalized by extension of neural canal
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* mesodermal caudal eminence
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:'''Links:''' [[Media:Secondary neurulation 01.mov|Quicktime version]] | [[Neural System Development]]
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|-
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|}
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==Neural Crest==
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[http://embryology.med.unsw.edu.au/Notes/ncrest.htm Neural Crest Notes]
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* a population of cells at the edge of the neural plate that lie dorsally when the neural tube fuses
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** dorsal to the neural tube, as a pair of streaks
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** pluripotential, forms many different types of cells
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** cells migrate throughout the embryo
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** studied by quail-chick chimeras
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** transplanted quail cells have obvious nucleoli compared with chicken
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===Neural Crest Derivitives===
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* dorsal root ganglia
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* autonomic ganglia
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* adrenal medulla
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* drg sheath cells, glia
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* pia-arachnoid sheath
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* skin melanocytes
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* connective tissue of cardiac outflow
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* thyroid parafollicular cells
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* craniofacial skeleton
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* teeth odontoblasts
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==Early Brain Structure==
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==Primary Vesicles==
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[[Image:CNS primary vesicles.jpg]]
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* rostral neural tube forms 3 primary brain vesicles (week 4)
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* 3 primary vesicles: '''prosencephalon''' (forebrain), '''mesencephalon''' (midbrain), '''rhombencephalon''' (hindbrain)
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==Secondary Vesicles==
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[[Image:CNS secondary vesicles.jpg]]
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From the 3 primary vesicles developing to form 5 secondary vesicles
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* prosencephalon- '''telencephalon''' (endbrain, forms cerebral hemispheres), '''diencephalon''' (betweenbrain, forms optic outgrowth)
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* '''mesencephalon'''
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* rhombencephalon- '''metencephalon''' (behindbrain), '''myelencephalon''' (medullabrain)
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==Ventricles==
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[[Image:Csf_cartoon2.jpg|thumb|CNS ventricles]]
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MH - this will be covered in detail in later neural development
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* cavity within tube will form the contiguious space of the ventricules of the brain and central canal of spinal cord
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* this space is filled initially with amniotic fluid, later with CerebroSpinal Fluid (CSF)
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* CSF is secreted by a modified vascular structure, the '''chorioid plexus''', lying within the ventricles
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** (More? [[http://embryology.med.unsw.edu.au/Notes/neuron6.htm Notes Chorioid Plexus])
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==Brain Flexures==
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Rapid growth folds the neural tube forming 3 brain flexures
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* '''cervical flexure''' - between brain stem and spinal cord
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* '''midbrain flexure''' - pushes mesencephalon upwards
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* '''pontine flexure''' - generates 4th ventricle
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==Neural Layers==
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[[Image:Stage22 HPA1L.jpg|thumb|Stage 22 developing head cross section]]
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[[Image:Stage22 HPA2L.jpg|thumb|Stage 22 developing cortex]]
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[[Image:Neuron_cartoon.jpg|thumb|Neuron and supporting glial cells]]
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* neural stem cells lie in the layer closest to the ventricular space, the '''ventricular layer'''
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** this layer generates both neuroblasts and glioblasts
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'''Neuroblasts''' - neurons arise first as neuroblasts and migrate along radial gial, their migration stops at cortical plate.
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'''Glioblasts''' - glia arise later as glioblasts
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Both neurons and glia undergo a complex process of growth, differentiation and interaction over a long developmental time period.
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==Spinal Cord Axes==
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Identified by experimental manipulation of interactions.
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* Initial experiments looked at how isolated tissues may influence the development of the spinal cord.
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* Repositionining of specific tissues both in vivo and in vitro
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* specific markers of or alteration of differentiation. '''Notocord Induction'''
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===Ventral Axis===
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[[Image:Sonic_hedgehog_expression.jpg|thumb|Notochord secreting sonic hedgehog]]
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* Sonic Hedgehog (SHH) - notochord secretes sonic hedgehog
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* Gene expression studies (ISH) showed shh gene expression occured in a subset of inducing tissues
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* has a patterning role elsewhere (limb, sclerotome, lung)
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* 2 signaling activities acting (locally and at a distance) Ventral- Sonic Hedgehog
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* Binds to cell surface receptor patched
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* without shh, patched (Ptc) binds smoothened (Smo)
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* with shh shh-Ptc releases Smo activating G protein pathway '''Gene Diseases'''
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* shh Human mutation- holoprosencephaly 3
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** characteristic faces of the severe form of HPE which included a single fused eye (cyclopia) and a nose-like structure (proboscis) above the eye
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** Downstream targets of Sonic hedgehog signalling:
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*** transcription factors like Gli3 (responsible for Greigs polycephalosyndactyly in humans)
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*** d Hoxd13 (responsible for polysyndactyly)
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===Dorsal Axis===
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* Dorsalin - ectoderm secretes a growth factor shown to controls patterning in embryonic mesoderm (frog)
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** Transforming Growth factor beta, (TGF b), related factors BMP-2, BMP-4, BMP-7, radar (flies related protein determines dorsoventral)
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** homology search of vertebrate library identified protein of same family.
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** dorsalin-1 (dsl-1) (Basler, Cell 73, p687, 1993) Dorsalin-1
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** From overlying ectoderm
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** Naming comes from the obvious reason that it promotes the differentiation of neural crest cells.
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** Also signal for dorsal signal of neural tube.
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** Inhibits the differentiation of motoneurons.
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** Implication is that dsl-1 and shh act antagonistically, or competitively to establish d-v axis of neural tube.
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===Rostro-Caudal Axis===
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* Brain rostro-caudal axis is generated by differential expression of Hox genes (transcriptional activators)
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** corresponding to genetic order on chromosome. (Wilkinson, Nature, 341, p405, 1989) Hox Genes
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** Stands for '''H'''omeob'''ox''' domain Genes
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** A family of transcription factors
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** Discovered in flies and conserved between all species. [../OtherEmb/fly.htm#antennapedia antennapedia]
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** Expressed in sequence along the embryo rostro-caudal axis.
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** Regulate many other aspects of development.
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** 180aa region binds DNA and regulate gene expression
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** large family of genes organized and expressed in sequence on the chromosome
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** Nkx-2.2 first detected at 1 somite stage
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** Lim hox gene expressed at spinal cord level
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==Ectodermal Placodes==
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* Specialized ectodermal "patches" in the head region
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* Contribute sensory structures - otic placode (otocyst), nasal placode, lens placode
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* Contribute teeth
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== Human Neuralation - Early Stages ==
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The stages below refer to specific Carneigie stages of development.
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* '''stage 8 '''(about 18 postovulatory days) neural groove and folds are first seen
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* '''stage 9''' the three main divisions of the brain, which are not cerebral vesicles, can be distinguished while the neural groove is still completely open. [http://embryology.med.unsw.edu.au/wwwhuman/Stages/stage9sem.htm Stage 9 SEM]
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* '''stage 10''' (two days later) neural folds begin to fuse near the junction between brain and spinal cord, when neural crest cells are arising mainly from the neural ectoderm [http://embryology.med.unsw.edu.au/wwwhuman/Stages/stage10sem.htm Stage 10 SEM]
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* '''stage 11''' (about 24 days) the rostral (or cephalic) neuropore closes within a few hours; closure is bidirectional, it takes place from the dorsal and terminal lips and may occur in several areas simultaneously. The two lips, however, behave differently. [http://embryology.med.unsw.edu.au/wwwhuman/Stages/stage11sem.htm Stage 11 SEM]
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* '''stage 12''' (about 26 days) The caudal neuropore takes a day to close [http://embryology.med.unsw.edu.au/wwwhuman/Stages/stage12sem.htm Stage 12 SEM]
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* the level of final closure is approximately at future somitic pair 31
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* corresponds to the level of sacral vertebra 2
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* '''stage 13''' (4 weeks) the neural tube is normally completely closed [http://embryology.med.unsw.edu.au/wwwhuman/Stages/stage13sem.htm Stage 13 SEM]
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'''Secondary neurulation''' begins at stage 12 - is the differentiation of the caudal part of the neural tube from the caudal eminence (or end-bud) without the intermediate phase of a neural plate.
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(Stage text modified from: Neurulation in the normal human embryo.&nbsp;O'Rahilly R, Muller F Ciba Found Symp 1994;181:70-82)
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==Abnormalities==
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See also [http://embryology.med.unsw.edu.au/Notes/neuron2.htm Neural Abnormalities]
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[[Image:Abnormal81-92-neuron.png|thumb|Australian Birth Statistics]]
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[[Image:Neural_tube_defect_meningomyelocele.jpg|thumb|Neural tube defect - Meningomyelocele]]
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===Neural Tube Defects (NTD)===
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Failure of neural tube closure either incorrectly or incomplete
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* '''Dysraphism''' is the term often used to describe the defective fusion of the neural folds. The position and degree of failure of fusion will result in either embryonic death or a range of different neural defects. The way (mode) in which the human neural tube fuses has been a source of contention. In humans, fusion appears to initiate at multiple sites but the mode is different from that found in many animal species used in developmental studies.
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* severity dependent upon level within the tube and degree of failure
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* caudal failure - spina bifida cranial failure - anancephaly
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===Maternal Diet===
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Found that supplementation of maternal diet with folate reduces incidence of NTDs (More? [http://embryology.med.unsw.edu.au/Defect/page5e.htm Folic Acid and Neural Tube Defects])
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* A randomised controlled trial conducted by the Medical Research Council of the United Kingdom demonstrated a 72% reduction in risk of recurrence by periconceptional (ie before and after conception) folic acid supplementation (4mg daily).
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* Women who have one infant with a neural tube defect have a significantly increased risk of recurrence (40-50 per thousand compared with 2 per thousand for all births)
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[[Image:USA spina bifida rates.jpg|300px|USA spina bifida rates]] [[Image:USA anencephaly rates.jpg|300px|USA anencephaly rates]]
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In the U.S.A. the Food and Drug Administration in 1996 authorized that all enriched cereal grain products be fortified with folic acid, with optional fortification beginning in March 1996 and mandatory fortification in January 1998. The data in the above graphs show the subsequent changes in anencephaly and spina bifida rate over that period.
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===Holoprosencephaly===
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Holoprosencephaly (HPE) is developmental abnormality where the forebrain does not divide into the two separate hemispheres and ventricles.
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===Critical Periods of Human Development===
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Exposure to teratogens during these "critical periods" results in specific abnormalities. [http://embryology.med.unsw.edu.au/Medicine/images/hcriticaldev.gif Critical Periods]
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* most systems are susceptible during embryonic development (first trimester)
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* the earlier the exposure the more severe the effects
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* each system has a different critical period
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* longest critical periods
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** longest developing systems (neural, genital)
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** complicated developmental origins (sensory systems)
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==UNSW Embryology Neural Links==
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* [http://embryology.med.unsw.edu.au/Science/ANAT2341lecture05.htm Neural Lecture 5 2008]
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* [http://embryology.med.unsw.edu.au/Notes/neuron.htm Neural Notes] | [http://embryology.med.unsw.edu.au/Notes/neuron3.htm Stage 13/14] | [http://embryology.med.unsw.edu.au/Notes/neuron4.htm Stage 22] | [http://embryology.med.unsw.edu.au/Notes/neuron5.htm#high%20power Stage 22 Brain] | [http://embryology.med.unsw.edu.au/Notes/neuron5a.htm Stage 22 Spinal Cord] | [http://embryology.med.unsw.edu.au/Notes/neuron6.htm Ventricular System] | [http://embryology.med.unsw.edu.au/Notes/neuron6a.htm Cerebrospinal Fluid] | [http://embryology.med.unsw.edu.au/Notes/neuron4a.htm Week 10] | [http://embryology.med.unsw.edu.au/Notes/neuron8.htm Fetal] | [http://embryology.med.unsw.edu.au/Notes/neuron7.htm Gliogenesis] | [http://embryology.med.unsw.edu.au/Notes/neuron_pain.htm Pain] | [http://embryology.med.unsw.edu.au/Notes/neuron11.htm Molecular]
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* Abnormalities - [http://embryology.med.unsw.edu.au/Notes/neuron2.htm Abnormalities] | [http://embryology.med.unsw.edu.au/Defect/page5e.htm Folic Acid and Neural Tube Defects] | [http://embryology.med.unsw.edu.au/Medicine/images/hcriticaldev.gif Critical Periods]
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* Postnatal - [http://embryology.med.unsw.edu.au/Child/page7.htm Postnatal Neural] | [http://embryology.med.unsw.edu.au/Child/page7a.htm Neural Assessment]
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* [http://embryology.med.unsw.edu.au/Notes/ncrest.htm Neural Crest Notes] | [http://embryology.med.unsw.edu.au/Notes/ncrest2.htm Abnormalities][http://embryology.med.unsw.edu.au/Notes/ncrest3.htm Stage 13/14] | [http://embryology.med.unsw.edu.au/Notes/ncrest4.htm Stage 22] | [http://embryology.med.unsw.edu.au/Notes/ncrest5.htm Stage 22 high power] | [http://embryology.med.unsw.edu.au/Notes/ncrest6.htm Generation] | [http://embryology.med.unsw.edu.au/Notes/ncrest7.htm Migration] | [http://embryology.med.unsw.edu.au/Notes/ncrest8.htm Peripheral Ganglia] | [http://embryology.med.unsw.edu.au/Notes/ncrest9.htm GIT Enteric] | [http://embryology.med.unsw.edu.au/Notes/ncrest12.htm Heart] | [http://embryology.med.unsw.edu.au/Notes/ncrest10.htm Molecular] | [http://embryology.med.unsw.edu.au/Notes/ncrestlink.htm Web Links]
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* [http://embryology.med.unsw.edu.au/wwwhuman/Stages/Stagesem.htm|Carnegie Stages - scanning electron micrographs]
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* [http://embryology.med.unsw.edu.au/sysnote.htm System Notes]
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* [http://embryology.med.unsw.edu.au/week/weekbyweek.htm Development Timeline]
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== Internet Links ==
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* '''Embryo Images'''  [http://www.med.unc.edu/embryo_images/unit-bdyfm/bdyfm_htms/bdyfmtoc.htm Early Cell Populations and Establishment of Body Form] |  [http://www.med.unc.edu/embryo_images/unit-nervous/nerv_htms/nervtoc.htm Nervous System Development]
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* '''Society for Neuroscience''' [http://web.sfn.org/content/Publications/BrainFacts/index.html http://web.sfn.org/content/Publications/BrainFacts/index.html Brain Facts]
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* '''Anatomy of the Human Body''' [http://www.bartleby.com/107/7.html The Neural Groove and Tube]
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* '''Environmental Health Perspectives''' [http://www.ehponline.org/members/2000/suppl-3/511-533rice/rice-full.html Critical Periods of Vulnerability for the Developing Nervous System: Evidence from Humans and Animal Models] | [http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1637807 PMC: 1637807] | [http://www.ncbi.nlm.nih.gov/pubmed/10852851 PMID: 10852851]
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* '''Journal''' [http://www.neuraldevelopment.com/Neural Development]
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== References ==
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===Textbooks===
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* '''The Developing Human: Clinically Oriented Embryology''' (8th Edition) by Keith L. Moore and T.V.N Persaud - Mesoderm Ch15,16: p405-423, 426-430 Body Cavities Ch9: p174-184
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* '''Larsen’s Human Embryology''' by GC. Schoenwolf, SB. Bleyl, PR. Brauer and PH. Francis-West -  Mesoderm Ch11 p311-339 Body Cavities Ch6 p127-146
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Additional Textbooks
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* Before We Are Born (5th ed.) Moore and Persaud Ch16,17: p379-397, 399-405
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* Essentials of Human Embryology Larson Ch11 p207-228
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* Human Embryology Fitzgerald and Fitzgerald Body Cavities Ch5 p29-32, Ch7 p47,48
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* Human Embryology and Developmental Biology ?Carlson Ch9,10: p173-193, 209-222 Body Cavities Ch5 p29-32, Ch7 p47,48
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===Online Textbooks===
 +
* '''Developmental Biology''' by Gilbert, Scott F. Sunderland (MA): Sinauer Associates, Inc.; c2000 [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=dbio.section.3455 Paraxial Mesoderm: The Somites and Their Derivatives]
 +
* '''Molecular Biology of the Cell''' 4th ed. Alberts, Bruce; Johnson, Alexander; Lewis, Julian; Raff, Martin; Roberts, Keith; Walter, Peter New York and London: Garland Science; c2002 -  [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=mboc4.figgrp.3943 Figure 21-78. Somite formation in the chick embryo]
 +
 +
* '''Madame Curie Bioscience Database''' Chapters taken from the Madame Curie Bioscience Database (formerly, Eurekah Bioscience Database) Eurekah.com and Landes Bioscience and Springer Science+Business Media; c2009 [http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=eurekah&part=A16427 Patterning the Vertebrate Neural Plate by Wnt Signaling] |  [http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=eurekah&part=A55523 Neural Crest Delamination and Migration]
 +
 +
===Search ===
 +
 +
* '''Bookshelf'''  [http://www.ncbi.nlm.nih.gov/sites/entrez?db=Books&cmd=search&term=ectoderm ectoderm] | [http://www.ncbi.nlm.nih.gov/sites/entrez?db=Books&cmd=search&term=neural_plate neural plate] | [http://www.ncbi.nlm.nih.gov/sites/entrez?db=Books&cmd=search&term=neural_tube neural tube] | [http://www.ncbi.nlm.nih.gov/sites/entrez?db=Books&cmd=search&term=neural_crest neural crest]
 +
 +
* '''Pubmed''' [http://www.ncbi.nlm.nih.gov/sites/gquery?itool=toolbar&cmd=search&term=ectoderm ectoderm] | [http://www.ncbi.nlm.nih.gov/sites/gquery?itool=toolbar&cmd=search&term=neural_plate neural plate]
 +
 +
===Reviews===
 +
* Temporal dynamics of patterning by morphogen gradients. Kutejova E, Briscoe J, Kicheva A. Curr Opin Genet Dev. 2009 Jul 9. [http://www.ncbi.nlm.nih.gov/pubmed/19596567 PMID: 19596567]
 +
 +
* The Hedgehog, TGF-beta/BMP and Wnt families of morphogens in axon guidance. Charron F, Tessier-Lavigne M. Adv Exp Med Biol. 2007;621:116-33. Review.
 +
[http://www.ncbi.nlm.nih.gov/pubmed/18269215 PMID: 18269215]
 +
 +
* Novel brain wiring functions for classical morphogens: a role as graded positional cues in axon guidance. Charron F, Tessier-Lavigne M. Development. 2005 May;132(10):2251-62. Review.
 +
[http://www.ncbi.nlm.nih.gov/pubmed/15857918 PMID: 15857918] | [http://dev.biologists.org/cgi/content/full/132/10/2251 Development Link]
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==Movies==
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{| border='0px'
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|-
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| [[File:Neuralplate_001 icon.jpg|90px|link=Development Animation - Neural Plate]]
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| [[File:Neuraltube_001 icon.jpg|90px|link=Development Animation - Neural Tube]]
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|
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|-
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| [[Development Animation - Neural Plate|Neural Plate]]
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| [[Development Animation - Neural Tube|Neural Tube]]
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|
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|-
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|}
  
 
== References ==
 
== References ==
Line 27: Line 412:
 
'''Search Pubmed:''' [http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&cmd=search&term=Ectoderm Ectoderm]
 
'''Search Pubmed:''' [http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&cmd=search&term=Ectoderm Ectoderm]
  
 +
==Take the Quiz==
 +
<quiz display=simple>
 +
 +
{Ectoderm refers only to the neural plate region of the trilaminar embryo
 +
|type="()"}
 +
- true
 +
+ false
 +
|| The entire layer of the trilaminar embryo is the '''ectoderm''' (meaning outer layer), the neural plate is only the central portion of this layer.
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{The central nervous system forms in the sequence:
 +
|type="()"}
 +
- norochord to neural plate to neural tube
 +
- neural tube to neural plate to neural groove
 +
+ neural plate to neural groove to neural tube
 +
- neural plate to neural crest to neural zone
 +
||The sequence '''neural plate to neural groove to neural tube''' represents the gradual folding of a flat surface sheet of ectodermal cells into a closed tube isolated from the embryo surface. The '''notochord''' is part of the mesoderm and regulates the initial overlying differentiation process. The '''neural crest''' are a population at the edge of the neural plate that do not get incorporated into the neural tube. I think I made up '''neural zone'''.
 +
 +
{The neural plate is narrower at the caudal (tail) end and therefore closes earlier than the broad cranial (head) end.
 +
|type="()"}
 +
- true
 +
+ false
 +
|| The caudal or posterior neuropore closes after the cranial or anterior neuropore.
 +
 +
 +
{The correct sequence from cranial to caudal of the secondary brain vesicles is:
 +
|type="()"}
 +
- prosencephalon, mesencephalon, metencephalon, myelencephalon, rhombencephalon
 +
- telencephalon, diencephalon, metencephalon, mesencephalon, myelencephalon
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+ telencephalon, diencephalon, mesencephalon, metencephalon, myelencephalon
 +
- prosencephalon, diencephalon, mesencephalon, myelencephalon, metencephalon
 +
||The '''prosencephalon''' and '''rhombencephalon''' are primary brain vesicles. The others are distractors using your lack of understanding of what the terms mean.
  
 +
</quiz>
 
{{Template:Glossary}}
 
{{Template:Glossary}}
  
 
{{Template:Footer}}
 
{{Template:Footer}}
  
[[Category:Ectoderm]] [[Category:Neural]] [[Category:Neural Crest]] [[Category:Integumentary]]
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[[Category:Ectoderm]] [[Category:Neural]] [[Category:Neural Crest]] [[Category:Integumentary]] [[Category:Week 3]] [[Category:Week 4]]

Revision as of 10:44, 10 August 2010

Notice - Mark Hill
This page will contain the content required when attending the lecture. Currently this page is only a template placeholder and will be updated (this notice removed when completed).

Introduction

The trilaminar embryo

The top layer of the early trilaminar embryo germ layers (ectoderm, mesoderm and endoderm) formed by gastrulation.

Ectoderm Links: Ectoderm, Early Neural, Neural Crest | Lecture 2009 | Category:Ectoderm

Some Recent Findings

Ectoderm Development

Lecture Notice - Mark Hill
This online lecture page will contain the content required when attending the lecture. Currently this page is only a template and will be updated before the lecture (this notice removed when completed). Final lecture pages can also be printed out using the "printable version" lefthand menu.

Introduction

File:Neuraltube_001_icon.jpg</wikiflv> This animation shows early neural development from week 3 onward. The whole early embryo development (dorsolateral view) is shown, yolk sac to left.


This lecture will cover the early development of the ectoderm layer of the trilaminar embryo. Note that we will be returning later to discuss neural (central nervous system; brain and spinal cord) and neural crest (peripheral nervous system; sensory and sympathetic ganglia).

Epidermis (integumentary, skin contribution) development will be briefly mentioned due to its ectoderm origin, but will also be covered later in the current course.



Stage10 neural sm.jpg Stage10 SEM1.jpg

Ectoderm Development

Stage10 neural sm.jpg
Stage10 SEM1.jpg

Introduction

This lecture will cover the early development of the ectoderm layer of the trilaminar embryo. Note that we will be returning later to discuss neural (central nervous system; brain and spinal cord) and neural crest (peripheral nervous system; sensory and sympathetic ganglia). Epidermis (integumentary, skin contribution) development will be briefly mentioned due to its ectoderm origin, but will also be covered later in the current course.

Lecture Objectives

  • Understanding of events during the third and fourth week of development
  • Understanding the process of notochord formation
  • Understanding the process of early neural development
  • Brief understanding of neural crest formation
  • Brief understanding of epidermis formation
  • Understanding of the adult components derived from ectoderm
  • Brief understanding of early neural abnormalities

Textbook References

  • Human Embryology (3rd ed.) Chapter 5 p107-125
  • The Developing Human: Clinically Oriented Embryology (6th ed.)

Other textbooks

  • Moore and Persaud Chapter 18 p451-489
  • Essentials of Human Embryology Larson Chapter 5 p69-79
  • Before We Are Born (5th ed.) Moore and Persaud Chapter 19 p423-458

Development Overview

Notochord

  • forms initially as the Axial Process, a hollow tube which extends from the primitive pit , cranially to the oral membrane
  • the axial process then allow transient communication between the amnion and the yolk sac through the neuroenteric canal.
  • the axial process then merges with the Endodermal layer to form the Notochordal Plate.
  • the notochordal plate then rises back into the Mesodermal layer as a solid column of cells which is the Notochord.

Ectoderm

  • 2 parts
  • midline neural plate
    • columnar
  • lateral surface ectoderm
    • cuboidal
    • sensory placodes
    • epidermis of skin, hair, glands, anterior pituitary, teeth enamel

Neural Plate

Neuralplate cartoon.png
File:Stage11 SEM1.jpg
Stage 11 neural groove to tube
File:Neuralplate_001 icon.jpg</wikiflv> Development of the neural plate region at the embryonic disc stage.

Dorsal view of the embryonic disc from the amniotic cavity side showing the ectoderm with the central region developing into the neural plate.

The neural plate extends from buccopharyngeal membrane to primitive node and forms above the notochord and paraxial mesoderm.The neuroectodermal cells form a broad brain plate and narrower spinal cord region.

Three specific regions medial to lateral can also be identified: midline region floor plate, neural plate, edge of neural plate neural crest



Quicktime version
  • extends from buccopharyngeal membrane to primitive node
  • forms above notochord and paraxial mesoderm
  • neuroectodermal cells
    • broad brain plate
    • narrower spinal cord
  • 3 components form: floor plate, neural plate, neural crest

Neural Determination- neuronal populations are specified before plate folds

  • signals from notochord and mesoderm - secrete noggin, chordin,follistatin
    • all factors bind BMP-4 an inhibitor of neuralation
    • bone morphogenic protein acts through membrane receptor
  • lateral inhibition generates at spinal cord level 3 strips of cells
  • expression of delta inhibits nearby cells, which express notch receptor, from becoming neurons
  • Delta-Notch inetraction- generates Neural strips

Neural Groove

File:Neuraltube_001 icon.jpg</wikiflv> This animation of early neural development from week 3 onward shows the neural groove fusing to form the neural tube.

View - Dorsolateral of the whole early embryo and yolk sac. Cranial (head) to top and caudal (tail) to bottom. Yolk sac is shown to the left.

Beginning with the neural groove initially fusing at the level of the 4th somite to form the neural tube and closing in both directions to leave 2 openings or neuropores: a cranial neuropore (anterior neuropore) and a caudal neuropore (posterior neuropore).

The animation also shows as the embryo grows and folds it increases in size relative to the initial yolk sac. Note also the increasing number of somites over time.

  • forms in the midline of the neural plate (day 18-19)
  • either side of which are the neural folds which continues to deepen until about week 4
  • neural folds begins to fuse, beginning at 4th somite level

Neural Tube

Stage 12 caudal neuropore
  • the neural tube forms the brain and spinal cord
  • fusion of neural groove extends rostrally and caudally
  • begins at the level of 4th somite
  • closes neural groove "zips up" in some species.
    • humans appear to close at multiple points along the tube.
  • leaves 2 openings at either end - Neuropores
    • cranial neuropore closes before caudal

Failure for the neural tube to close correctly or completely results in a neural tube defect.

Secondary Neuralation

File:Secondary_neurulation_01 icon.jpg</wikiflv> This animation shows the early developmental process often described as secondary neurulation.

Red - site of secondary neurulation | Blue - neural tube

  • caudal end of neural tube formed by secondary neuralation
  • develops from primitive streak region
  • solid cord canalized by extension of neural canal
  • mesodermal caudal eminence
Links: Quicktime version | Neural System Development


Neural Crest

Neural Crest Notes

  • a population of cells at the edge of the neural plate that lie dorsally when the neural tube fuses
    • dorsal to the neural tube, as a pair of streaks
    • pluripotential, forms many different types of cells
    • cells migrate throughout the embryo
    • studied by quail-chick chimeras
    • transplanted quail cells have obvious nucleoli compared with chicken

Neural Crest Derivitives

  • dorsal root ganglia
  • autonomic ganglia
  • adrenal medulla
  • drg sheath cells, glia
  • pia-arachnoid sheath
  • skin melanocytes
  • connective tissue of cardiac outflow
  • thyroid parafollicular cells
  • craniofacial skeleton
  • teeth odontoblasts

Early Brain Structure

Primary Vesicles

CNS primary vesicles.jpg

  • rostral neural tube forms 3 primary brain vesicles (week 4)
  • 3 primary vesicles: prosencephalon (forebrain), mesencephalon (midbrain), rhombencephalon (hindbrain)

Secondary Vesicles

CNS secondary vesicles.jpg

From the 3 primary vesicles developing to form 5 secondary vesicles

  • prosencephalon- telencephalon (endbrain, forms cerebral hemispheres), diencephalon (betweenbrain, forms optic outgrowth)
  • mesencephalon
  • rhombencephalon- metencephalon (behindbrain), myelencephalon (medullabrain)

Ventricles

CNS ventricles

MH - this will be covered in detail in later neural development

  • cavity within tube will form the contiguious space of the ventricules of the brain and central canal of spinal cord
  • this space is filled initially with amniotic fluid, later with CerebroSpinal Fluid (CSF)
  • CSF is secreted by a modified vascular structure, the chorioid plexus, lying within the ventricles

Brain Flexures

Rapid growth folds the neural tube forming 3 brain flexures

  • cervical flexure - between brain stem and spinal cord
  • midbrain flexure - pushes mesencephalon upwards
  • pontine flexure - generates 4th ventricle

Neural Layers

Stage 22 developing head cross section
Stage 22 developing cortex
Neuron and supporting glial cells
  • neural stem cells lie in the layer closest to the ventricular space, the ventricular layer
    • this layer generates both neuroblasts and glioblasts

Neuroblasts - neurons arise first as neuroblasts and migrate along radial gial, their migration stops at cortical plate. Glioblasts - glia arise later as glioblasts

Both neurons and glia undergo a complex process of growth, differentiation and interaction over a long developmental time period.

Spinal Cord Axes

Identified by experimental manipulation of interactions.

  • Initial experiments looked at how isolated tissues may influence the development of the spinal cord.
  • Repositionining of specific tissues both in vivo and in vitro
  • specific markers of or alteration of differentiation. Notocord Induction

Ventral Axis

Notochord secreting sonic hedgehog
  • Sonic Hedgehog (SHH) - notochord secretes sonic hedgehog
  • Gene expression studies (ISH) showed shh gene expression occured in a subset of inducing tissues
  • has a patterning role elsewhere (limb, sclerotome, lung)
  • 2 signaling activities acting (locally and at a distance) Ventral- Sonic Hedgehog
  • Binds to cell surface receptor patched
  • without shh, patched (Ptc) binds smoothened (Smo)
  • with shh shh-Ptc releases Smo activating G protein pathway Gene Diseases
  • shh Human mutation- holoprosencephaly 3
    • characteristic faces of the severe form of HPE which included a single fused eye (cyclopia) and a nose-like structure (proboscis) above the eye
    • Downstream targets of Sonic hedgehog signalling:
      • transcription factors like Gli3 (responsible for Greigs polycephalosyndactyly in humans)
      • d Hoxd13 (responsible for polysyndactyly)

Dorsal Axis

  • Dorsalin - ectoderm secretes a growth factor shown to controls patterning in embryonic mesoderm (frog)
    • Transforming Growth factor beta, (TGF b), related factors BMP-2, BMP-4, BMP-7, radar (flies related protein determines dorsoventral)
    • homology search of vertebrate library identified protein of same family.
    • dorsalin-1 (dsl-1) (Basler, Cell 73, p687, 1993) Dorsalin-1
    • From overlying ectoderm
    • Naming comes from the obvious reason that it promotes the differentiation of neural crest cells.
    • Also signal for dorsal signal of neural tube.
    • Inhibits the differentiation of motoneurons.
    • Implication is that dsl-1 and shh act antagonistically, or competitively to establish d-v axis of neural tube.

Rostro-Caudal Axis

  • Brain rostro-caudal axis is generated by differential expression of Hox genes (transcriptional activators)
    • corresponding to genetic order on chromosome. (Wilkinson, Nature, 341, p405, 1989) Hox Genes
    • Stands for Homeobox domain Genes
    • A family of transcription factors
    • Discovered in flies and conserved between all species. [../OtherEmb/fly.htm#antennapedia antennapedia]
    • Expressed in sequence along the embryo rostro-caudal axis.
    • Regulate many other aspects of development.
    • 180aa region binds DNA and regulate gene expression
    • large family of genes organized and expressed in sequence on the chromosome
    • Nkx-2.2 first detected at 1 somite stage
    • Lim hox gene expressed at spinal cord level

Ectodermal Placodes

  • Specialized ectodermal "patches" in the head region
  • Contribute sensory structures - otic placode (otocyst), nasal placode, lens placode
  • Contribute teeth

Human Neuralation - Early Stages

The stages below refer to specific Carneigie stages of development.

  • stage 8 (about 18 postovulatory days) neural groove and folds are first seen
  • stage 9 the three main divisions of the brain, which are not cerebral vesicles, can be distinguished while the neural groove is still completely open. Stage 9 SEM
  • stage 10 (two days later) neural folds begin to fuse near the junction between brain and spinal cord, when neural crest cells are arising mainly from the neural ectoderm Stage 10 SEM
  • stage 11 (about 24 days) the rostral (or cephalic) neuropore closes within a few hours; closure is bidirectional, it takes place from the dorsal and terminal lips and may occur in several areas simultaneously. The two lips, however, behave differently. Stage 11 SEM
  • stage 12 (about 26 days) The caudal neuropore takes a day to close Stage 12 SEM
  • the level of final closure is approximately at future somitic pair 31
  • corresponds to the level of sacral vertebra 2
  • stage 13 (4 weeks) the neural tube is normally completely closed Stage 13 SEM

Secondary neurulation begins at stage 12 - is the differentiation of the caudal part of the neural tube from the caudal eminence (or end-bud) without the intermediate phase of a neural plate.

(Stage text modified from: Neurulation in the normal human embryo. O'Rahilly R, Muller F Ciba Found Symp 1994;181:70-82)

Abnormalities

See also Neural Abnormalities

Australian Birth Statistics
Neural tube defect - Meningomyelocele

Neural Tube Defects (NTD)

Failure of neural tube closure either incorrectly or incomplete

  • Dysraphism is the term often used to describe the defective fusion of the neural folds. The position and degree of failure of fusion will result in either embryonic death or a range of different neural defects. The way (mode) in which the human neural tube fuses has been a source of contention. In humans, fusion appears to initiate at multiple sites but the mode is different from that found in many animal species used in developmental studies.
  • severity dependent upon level within the tube and degree of failure
  • caudal failure - spina bifida cranial failure - anancephaly

Maternal Diet

Found that supplementation of maternal diet with folate reduces incidence of NTDs (More? Folic Acid and Neural Tube Defects)

  • A randomised controlled trial conducted by the Medical Research Council of the United Kingdom demonstrated a 72% reduction in risk of recurrence by periconceptional (ie before and after conception) folic acid supplementation (4mg daily).
  • Women who have one infant with a neural tube defect have a significantly increased risk of recurrence (40-50 per thousand compared with 2 per thousand for all births)

USA spina bifida rates USA anencephaly rates

In the U.S.A. the Food and Drug Administration in 1996 authorized that all enriched cereal grain products be fortified with folic acid, with optional fortification beginning in March 1996 and mandatory fortification in January 1998. The data in the above graphs show the subsequent changes in anencephaly and spina bifida rate over that period.

Holoprosencephaly

Holoprosencephaly (HPE) is developmental abnormality where the forebrain does not divide into the two separate hemispheres and ventricles.

Critical Periods of Human Development

Exposure to teratogens during these "critical periods" results in specific abnormalities. Critical Periods

  • most systems are susceptible during embryonic development (first trimester)
  • the earlier the exposure the more severe the effects
  • each system has a different critical period
  • longest critical periods
    • longest developing systems (neural, genital)
    • complicated developmental origins (sensory systems)


UNSW Embryology Neural Links

Internet Links

References

Textbooks

  • The Developing Human: Clinically Oriented Embryology (8th Edition) by Keith L. Moore and T.V.N Persaud - Mesoderm Ch15,16: p405-423, 426-430 Body Cavities Ch9: p174-184
  • Larsen’s Human Embryology by GC. Schoenwolf, SB. Bleyl, PR. Brauer and PH. Francis-West - Mesoderm Ch11 p311-339 Body Cavities Ch6 p127-146

Additional Textbooks

  • Before We Are Born (5th ed.) Moore and Persaud Ch16,17: p379-397, 399-405
  • Essentials of Human Embryology Larson Ch11 p207-228
  • Human Embryology Fitzgerald and Fitzgerald Body Cavities Ch5 p29-32, Ch7 p47,48
  • Human Embryology and Developmental Biology ?Carlson Ch9,10: p173-193, 209-222 Body Cavities Ch5 p29-32, Ch7 p47,48

Online Textbooks

Search

Reviews

  • Temporal dynamics of patterning by morphogen gradients. Kutejova E, Briscoe J, Kicheva A. Curr Opin Genet Dev. 2009 Jul 9. PMID: 19596567
  • The Hedgehog, TGF-beta/BMP and Wnt families of morphogens in axon guidance. Charron F, Tessier-Lavigne M. Adv Exp Med Biol. 2007;621:116-33. Review.

PMID: 18269215

  • Novel brain wiring functions for classical morphogens: a role as graded positional cues in axon guidance. Charron F, Tessier-Lavigne M. Development. 2005 May;132(10):2251-62. Review.

PMID: 15857918 | Development Link

Movies

Neuralplate 001 icon.jpg Neuraltube 001 icon.jpg
Neural Plate Neural Tube

References


Reviews

Articles

Historic

Search PubMed

Search NLM Online Textbooks: "Ectoderm" : Developmental Biology | The Cell- A molecular Approach | Molecular Biology of the Cell


Search Pubmed: Ectoderm

Take the Quiz

1

Ectoderm refers only to the neural plate region of the trilaminar embryo

true
false

2

The central nervous system forms in the sequence:

norochord to neural plate to neural tube
neural tube to neural plate to neural groove
neural plate to neural groove to neural tube
neural plate to neural crest to neural zone

3

The neural plate is narrower at the caudal (tail) end and therefore closes earlier than the broad cranial (head) end.

true
false

4

The correct sequence from cranial to caudal of the secondary brain vesicles is:

prosencephalon, mesencephalon, metencephalon, myelencephalon, rhombencephalon
telencephalon, diencephalon, metencephalon, mesencephalon, myelencephalon
telencephalon, diencephalon, mesencephalon, metencephalon, myelencephalon
prosencephalon, diencephalon, mesencephalon, myelencephalon, metencephalon

Glossary Links

Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link

Cite this page: Hill, M.A. (2019, October 23) Embryology Ectoderm. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Ectoderm

What Links Here?
© Dr Mark Hill 2019, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G