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Larsen's human embryology
Schoenwolf, G.C., Bleyl, S.B., Brauer, P.R., Francis-West, P.H. & Philippa H. (2015). Larsen's human embryology (5th ed.). New York; Edinburgh: Churchill Livingstone. (links only function with UNSW connection)
Neural Movies
- Links: Movies | Postnatal - Neural Examination Movies
Human Early Neural Development
The stages below refer to specific Carneigie stages of development (modified from O'Rahilly and Müller 1994[6]).
- 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 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 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 12 - (about 26 days) The caudal neuropore takes a day to close.
- 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.
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.
Week 4 to Week 8
Week 8 - Stage 23
<html5media height="500" width="540">File:Stage23 MRI S01.mp4</html5media>
The above MRI scan movie shows the structure of the central nervous system at the end of the embryonic period. Note the relative size and position of the CNS parts, the flexures, the size of the ventricular spaces and chord plexus within this space. There are additional Stage 23 movies available in the links below.
Development Overview
Neuralation begins at the trilaminar embryo with formation of the notochord and somites, both of which underly the ectoderm and do not contribute to the nervous system, but are involved with patterning its initial formation. The central portion of the ectoderm then forms the neural plate that folds to form the neural tube, that will eventually form the entire central nervous system.
- Early developmental sequence: Epiblast - Ectoderm - Neural Plate - Neural groove and Neural Crest - Neural Tube and Neural Crest
Neural Tube Development
Neural Tube
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Primary Vesicles
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Secondary Vesicles
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Adult Structures
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week 3
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week 4
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week 5
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adult
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neural plate
neural groove
neural tube
Brain
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prosencephalon (forebrain)
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telencephalon
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Rhinencephalon, Amygdala, hippocampus, cerebrum (cortex), hypothalamus, pituitary | Basal Ganglia, lateral ventricles
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diencephalon
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epithalamus, thalamus, Subthalamus, pineal, posterior commissure, pretectum, third ventricle
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mesencephalon (midbrain)
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mesencephalon
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tectum, Cerebral peduncle, cerebral aqueduct, pons
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rhombencephalon (hindbrain)
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metencephalon
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cerebellum
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myelencephalon
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medulla oblongata, isthmus
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spinal cord, pyramidal decussation, central canal
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Notochord
Does not contribute to the final nervous system, but is critical to patterning the development.
- 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.
- Links: Notochord
Ectoderm
Two main parts with different morphology
- columnar - midline neural plate forming neural tube and neural crest
- cuboidal - lateral surface ectoderm forming epidermis and sensory placodes
- epidermis of skin, hair, glands, anterior pituitary, teeth enamel
- sensory placodes
- Links: Ectoderm
Neural Plate
The neural plate forms above the notochord and paraxial mesoderm and extends from the buccopharyngeal membrane to primitive node. The cells are described as neuroectodermal and form initially two regions along the head to tail axis: a cranial broad plate region (brain plate) and caudally a narrower plate region (spinal cord).
Neural Determination
Neuronal populations are thought to be specified before the plate folds by signals from underlying notochord and mesoderm, as well as signals spread laterally through teh plate.
- 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- generates "neural strips"
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Neural Bending
There are two bending processes occurring in the formation of the neural groove and neural tube.
- occuring in the midline due to cells in this region having a basal nuclear localisation. This initial bending leads to formation of the neural groove.
- occuring at the dorsolateral hinge points by different mechanism involving "buckling". This later bending leads to formation of the neural tube.
Mouse neural tube bending model (see review[7])
Neural Groove
- forms in the midline of the neural plate (day 18-19)
- either side of which are the neural folds
- continues to deepen until about week 4
- neural folds begins to fuse
- at 4th somite level
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Carnegie stage 10 Week 4
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Neural Tube
- fusion of neural groove extends rostrally and caudally
- begins at level of 4th somite, "zips up" neural groove
- leaves 2 openings at either end- Neuropores
- forms the brain and spinal cord
- Secondary Neuralation - 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
Neuropores
- cranial (anterior) neuropore closes before caudal (posterior)
- failure to close - Neural Tube Defects (NTD), severity dependent upon level, spina bifida anancephaly (More? [neuron2.htm Neural Abnormalities])
- found that supplementation of maternal diet with folate reduces incidence of NTDs
- 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)
Neural Crest
- 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
- cells migrate throughout the embryo
- studied by quail-chick chimeras - transplanted quail cells have obvious nucleoli compared with chicken Neural Crest Derivitives
- pluripotential, forms many different types of cells: dorsal root ganglia (neurons, sheath cells, glia), autonomic ganglia, adrenal medulla, pia-arachnoid sheath, skin melanocytes, connective tissue of cardiac outflow, thyroid parafollicular cells, craniofacial skeleton and teeth odontoblasts.
- Links: Neural Crest Development
Early Brain Structure
Primary Vesicles
- rostral neural tube forms 3 primary brain vesicles (week 4)
- 3 primary vesicles: prosencephalon (forebrain), mesencephalon (midbrain), rhombencephalon (hindbrain)
Secondary Vesicles
From the 3 primary vesicles developing to form 5 secondary vesicles (week 5)
- prosencephalon- telencephalon (endbrain, forms cerebral hemispheres), diencephalon (betweenbrain, forms optic outgrowth)
- mesencephalon
- rhombencephalon- metencephalon (behindbrain), myelencephalon (medullabrain)
Week 8 - Stage 23
Ventricles
- 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
- Links: Neural - Ventricular System Development)
Brain Flexures
Rapid growth folds the neural tube forming 3 brain flexures (cranial to caudal)
- cephalic flexure - (mesencephalic) pushes mesencephalon upwards
- pontine flexure - generates 4th ventricle
- cervical flexure - between brain stem and spinal cord
Neural Layers
Human Embryo (Week 8, Stage 22) developing head 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
- 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- Sonic Hedgehog
- 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
Early Development and Neural Derivatives
- bilaminar embryo- hyoblast
- trilaminar embryo then ectoderm layer, neural plate, neural groove, neural tube and neural crest
- cranial expansion of neural tube- central nervous system
- caudal remainder of neural tube- spinal cord
- neural crest
- dorsal root ganglia
- parasympathetic / sympathetic ganglia.
- ectodermal placodes- components of the special senses: otic placode (otocyst), nasal placode, lens placode
Links: Placodes
Neural tube and Genes: neural specification- Notch/Delta, patched receptor. Border- fibroblast growth factor (fgf), BMP (BMP4, msx1) Rostral border- Dlx5
Neural Tube Patterning
- segmented along its length- Hox/Lim gene expression
- ventral identity- sonic hedgehog, BMP7/chordin interaction
- dorsal identity- dorsalin
Fetal Development
Human Fetus (CRL 240mm) Brain (left dorsolateral view)
For more details see Neural System - Fetal
Fetal - Second Trimester
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Brain and Ventricular Development[8]
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Brain Fissure Development[8]
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Third Trimester
Human Fetus (CRL 240mm) Brain
Three-dimensional magnetic resonance imaging and image-processing algorithms have been used to quantitate between 29-41 weeks volumes of: total brain, cerebral gray matter, unmyelinated white matter, myelinated, and cerebrospinal fluid (grey matter- mainly neuronal cell bodies; white matter- mainly neural processes and glia). A study of 78 premature and mature newborns showed that total brain tissue volume increased linearly over this period at a rate of 22 ml/week. Total grey matter also showed a linear increase in relative intracranial volume of approximately 1.4% or 15 ml/week. The rapid increase in total grey matter is mainly due to a fourfold increase in cortical grey matter. Quantification of extracerebral and intraventricular CSF was found to change only minimally.[9]
Thyroid System and Neural Development
Human thyroid system and neural development
Timeline of human thyroid system and brain development from conception to birth.[10] (Estimation of neurogenesis adapted from Bayer et al.[11])
- Links: Endocrine - Thyroid Development
Gliogenesis and Myelination
Glial cells have many different types and roles in central and peripheral neural development, though they are typically described as "supportive", and have the same early embryonic origins as neurons. (More? [neuron7.htm Gliogenesis and Myelination])
Early in neural development a special type of developmental glia, radial glia, provide pathway for developing neuron (neuroblasts) migration out from the proliferating ventricular layer and are involved in the subsequent lamination and columnar organization of the central nervous system.
Types of glia: radial glia, astroglia, oligodendroglia, microglia and Schwann cells.
Gene Diseases - Sonic Hedgehog
SHH Human mutation- holoprosencephaly 3
- characteristic facies 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)
References
- ↑ <pubmed>23760472</pubmed>
- ↑ <pubmed>24014419</pubmed>
- ↑ <pubmed>23431204</pubmed>
- ↑ <pubmed>20558153</pubmed>
- ↑ <pubmed>19420217</pubmed>
- ↑ <pubmed>8005032</pubmed>
- ↑ <pubmed>26079577</pubmed>| PMC4528075 | Dev Biol.
- ↑ 8.0 8.1 <pubmed>19339620</pubmed>| PMC2721010 | J Neurosci.
- ↑ <pubmed>9485064</pubmed>
- ↑ <pubmed>12060827</pubmed>
- ↑ <pubmed>8361683</pubmed>
Journals
Online Textbooks
Developmental Biology (6th ed) Gilbert, Scott F. Sunderland (MA): Sinauer Associates, Inc.; c2000. Formation of the Neural Tube | Differentiation of the Neural Tube | Tissue Architecture of the Central Nervous System | Neuronal Types | Snapshot Summary: Central Nervous System and Epidermis
Neuroscience Purves, Dale; Augustine, George J.; Fitzpatrick, David; Katz, Lawrence C.; LaMantia, Anthony-Samuel; McNamara, James O.; Williams, S. Mark. Sunderland (MA): Sinauer Associates, Inc. ; c2001 Early Brain Development | Construction of Neural Circuits | Modification of Brain Circuits as a Result of Experience
Molecular Biology of the Cell (4th Edn) Alberts, Bruce; Johnson, Alexander; Lewis, Julian; Raff, Martin; Roberts, Keith; Walter, Peter. New York: Garland Publishing; 2002. Neural Development | The three phases of neural development
Health Services/Technology Assessment Text (HSTAT) Bethesda (MD): National Library of Medicine (US), 2003 Oct. Developmental Disorders Associated with Failure to Thrive
Search NLM Online Textbooks- "neural development" : Developmental Biology | The Cell- A molecular Approach | Molecular Biology of the Cell | Endocrinology
Reviews
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Search Pubmed: Neural System Development | Neural Development | Neural Tube Development | Spinal Cord Development
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Terms
Neural Terms
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Neural Development
- 3DMRI - Three-dimensional magnetic resonance imaging. A new technique that allows 3D analysis of embryonic structures. (More? Magnetic Resonance Imaging)
- 3rd ventricle - a fluid-filled space formed from neural tube lumen, located within the diencephalon (from the primary vesicle prosencephalon, forebrain).
- 4th ventricle - a fluid-filled space formed from neural tube lumen, located within the rhombencephalon (from the primary vesicle, hindbrain).
- adenohypophysis - (anterior pituitary) = 3 parts pars distalis, pars intermedia, pars tuberalis.
- afferent - refers to the direction of conduction from the periphery toward the central nervous system. Efferent is in the opposite direction.
- alar plate - embryonic dorsolateral region of the neural tube forming at spinal cord level dorsal horns (afferent) and brain level different structures.
- anlage - (German = primordium) structure or cells that will form a future adult structure.
- arachnoid mater - (G.) spider web-like used in reference to the middle layer of the brain meninges.
- astrocytes - cells named by their "star-like" branching appearance, are the most abundant glial cells in the brain, important for the blood-brain barrier.
- basal ganglia - (basal nuclei) neural structure derived from the secondary vesicle telencephalon (endbrain) structure from the earlier primary vesicle prosencephalon (forebrain).
- basal plate - embryonic ventrolateral region of the neural tube forming at spinal cord level ventral horns (efferent) and brain level different structures.
- brachial plexus - mixed spinal nerves innervating the upper limb form a complex meshwork (crossing).
- brain - general term for the central nervous system formed from 3 primary vesicles.
- buccopharyngeal membrane - (oral membrane) at cranial (mouth) end of gastrointestinal tract (GIT) where surface ectoderm and GIT endoderm meet. (see also cloacal membrane).
- cauda equina - (horse's tail) caudal extension of the mature spinal cord.
- central canal - lumen, cavity of neural tube within the spinal cord. Space is continuous with ventricular system of the brain.
- central cerebral sulcus - (central fissure, fissure of Rolando, Rolandic fissure) fold in the cerebral cortex associated with the sensorimotor cortex.
- cerebral aqueduct - ventricular cavity within the mesencephalon.
- cervical flexure - most caudal brain flexure (of 3) between spinal cord and rhompencephalon.
- choroid plexus - specialized vascular plexus responsible for secreting ventricular fluid that with further additions becomes cerebrospinal fluid (CSF).
- cloacal membrane - at caudal (anal) end of gastrointestinal tract (GIT) where surface ectoderm and GIT endoderm meet forms the openings for GIT, urinary, reproductive tracts. (see also buccopharyngeal membrane).
- connectome - term describing the detailed map of neural connections in the central nervous system.
- cortex - - CNS structure derived from the secondary vesicle telencephalon (endbrain) from the earlier primary vesicle prosencephalon (forebrain).
- cortical plate - outer neural tube region which post-mitotic neuroblasts migrate too along radial glia to form adult cortical layers.
- cranial flexure - (=midbrain flexure) most cranial brain flexure (of 3) between mesencephalon and prosencephalon.
- diencephalon - the caudal portion of forebrain after it divides into 2 parts in the 5 secondary vesicle brain (week 5). (cavity- 3rd ventricle) Forms the thalmus and other nuclei in the adult brain. (sc-My-Met-Mes-Di-Tel)
- dorsal root ganglia - (spinal ganglia) sensory ganglia derived from the neural crest lying laterally paired and dorsally to the spinal cord (in the embryo found ventral to the spinal cord). Connects centrally with the dorsal horn of the spinal cord.
- dura mater- "tough" (Latin, mater = mother) used in reference to the tough outer layer of the brain meninges.
- efferent - refers to the direction of conduction from the central nervous system toward the periphery. Afferent is in the opposite direction.
- ependyma - epithelia of remnant cells after neurons and glia have been generated and left the ventricular zone.
- floorplate - early forming thin region of neural tube closest to the notochord.
- ganglia - (pl. of ganglion) specialized neural cluster within either the CNS or PNS.
- glia - supporting, non-neuronal cells of the nervous system. Generated from the same neuroepithelial stem cells that form neurons in ventricular zone of neural tube. Form astrocytes, oligodendrocytes.
- grey matter - neural regions containing cell bodies (somas) of neurons. In the brain it is the outer layer, in the spinal cord it is inner layer. (see white matter white matter).
- growth factor - usually a protein or peptide that will bind a cell membrane receptor and then activates an intracellular signaling pathway. The function of the pathway will be to alter the cell directly or indirectly by changing gene expression. (eg SHH).
- HOX - (homeobox) family of transcription factors that bind DNA and activate gene expression. Expression of different Hox genes along neural tube defines rostral-caudal axis and segmental levels.
- hydrocephalus - abnormality as the result of an imbalance between the rate at which the CSF is being formed and the rate at which the CSF is passing through the arachnoidal villi back into the blood (hydrocephalus rate is a function of the degree of imbalance in these two). Very small imbalance exhibit subtle, if any, symptoms. Large imbalances will have rapidly evolving symptoms of unmistakable import.
- isthmus- (G. narrow passage).
- lamina terminalis - anterior region of brain where cranial neuropore closes.
- lumbar plexus - mixed spinal nerves innervating the lower limb form a complex meshwork (crossing).
- mantle layer - layer of cells generated by first neuroblasts migrating from the ventricular zone of the neural tube. Layers are rearranged during development of the brain and spinal cord. (Ven-Man-Mar-CP)
- marginal zone - layer of processes from neuroblasts in mantle layer. (Ven-Man-Mar-CP)
- mater - (Latin, mater = mother) used in relation to the 3 layers of the meninges.
- meninges - mesenchyme surrounding neural tube forms 3 layer (Dura-, pia-, arachnoid- mater) connective tissue sheath of nervous system. (D-P-A-cns)
- mesencephalon - (midbrain), the middle portion of the 3 primary vesicle brain (week 4). (sc-R-M-P)
- metencephalon - the cranial portion of hindbrain after it divides into 2 parts in the 5 secondary vesicle brain (week 5). Forms the pons and cerebellum in the adult brain. (sc-My-Met-Mes-Di-Tel)
- microglia - CNS innate immune cells that have a macrophage function, derive from yolk sac progenitor cells migrating into the CNS. microglia
- myelencephalon - the caudal portion of hindbrain after it divides into 2 parts in the 5 secondary vesicle brain (week 5). Forms the medulla in the adult brain. (sc-My-Met-Mes-Di-Tel)
- neural tube - neural plate region of ectoderm pinched off to form hollow ectodermal tube above notochord in mesoderm.
- neural tube defect - (NTD) any developmental abnormality that affects neural tube development. Commonly failure of neural tube closure.
- neuroblast - undifferentiated neuron found in ventricular layer of neural tube.
- neurohypophysis - (posterior pituitary; pas nervosa)
- neuromere - (prosomere) the model units for segmental brain development regions based upon a series of neural tube transverse subunits.
- neuron - The cellur "unit" of the nervous system, transmitting signals between neurons and other cells. The post-mitotic cells generated from neuroepithelial stem cells (neuroblasts) in ventricular zone of neural tube.
- neuropore - opening at either end of neural tube cranial (rostral, anterior) neuropore closes (day 25) about 2 days before caudal (posterior) that closes at somite level 32 to 34. Neural Tube Defects (NTDs) can be due to failure of these two neuropores to close.
- notochord - rod of cells lying in mesoderm layer ventral to the neural tube, induces neural tube and secretes sonic hedgehog which "ventralizes" the neural tube.
- olfactory bulb - (cranial nerve I, CN I) bipolar neurons from nasal epithelium project axons through cribiform palate into olfactory bulb of the brain associated with smell.
- optic nerve - (cranial nerve II, CN II) retinal ganglion neurons project from the retina as a tract into the brain (at the level of the diencephalon) associated with vision.
- optic vesicle - diencephalon region of neural tube outgrowth that forms the primordia of the retina associated with vision.
- opercularization - during fetal development of the sensorimotor cortex, the insula (located deep within the lateral sulcus) begins to invaginate from the surface of the immature cerebrum, until at term, the opercula completely cover the insula.
- otocyst - (otic vesicle) sensory placode that sinks into mesoderm to form spherical vesicle (stage 13/14 embryo) that will form components of the inner ear associated with hearing.
- pharyngeal arch - (branchial arch, Gk. gill) form the main structures of the head and neck. Humans have 5 arches appearing in week 4 that form 4 external swellings, each arch has a pouch, membrane and cleft.
- pharynx - uppermost end of GIT, beginning at the buccopharyngeal membrane and at the level of the pharyngeal arches.
- pia mater - (G.) (L. pius = soft, faithful + mater = mother) delicate vascular membrane which adheres to surface of brain and spinal cord, faithfully following their contours, the inner layer of the brain meninges.
- placode - specialized regions of ectoderm which form components of the sensory apparatus.
- pontine flexure - middle brain flexure (of 3) between cervical and cranial flexure in opposite direction, also generates thin roof of rhombencephalon and divides it into myelencephalon and metencephalon. ( sc-^V^ )
- posterior insula - during sensorimotor cortex development this region is composed of the anterior and posterior long insular gyri and the postcentral insular sulcus, which separates them.
- prosencephalon - (forebrain), the most cranial portion of the 3 primary vesicle brain (week 4). (sc-R-M-P)
- prosomere - (neuromere) a model for segmental brain development based upon a series of neural tube transverse subunits. PMID 12948657
- Rathke's pouch - a portion of the roof of the pharynx pushes upward towards the floor of the brain forming the anterior pituitary (adenohypophysis, pars distalis, pars tuberalis pars intermedia). Where it meets a portion of the brain pushing downward forming the posterior pituitary (neurohypophysis, pars nervosa). Rathke's pouch eventually looses its connection with the pharynx.
- rhombencephalon - (hindbrain), the most caudal portion of the 3 primary vesicle brain (week 4). (sc-R-M-P)
- rhombic lip - metencephalon posterior part extending from the roof of the fourth ventricle to dorsal neuroepithelial cells that contributes to the cerebellum.
- roofplate - early forming thin region of neural tube closest to the overlying ectoderm.
- spinal cord - caudal end of neural tube that does not contribute to brain. Note: the process of secondary neuralation contributes the caudal end of the spinal cord.
- spinal ganglia - (dorsal root ganglia, drg) sensory ganglia derived from the neural crest lying laterally paired and dorsally to the spinal cord (in the embryo found ventral to the spinal cord). Connects centrally with the dorsal horn of the spinal cord.
- spinal nerve - mixed nerve (motor and sensory) arising as latera pairs at each vertebral segmental level.
- sonic hedgehog - (shh) secreted growth factor that binds patched (ptc) receptor on cell membrane. SHH function is different for different tissues in the embryo. In the nervous system, it is secreted by the notochord, ventralizes the neural tube, inducing the floor plate and motor neurons.
- sulcus - (L. furrow) groove.
- sulcus limitans - longitudinal lateral groove in neural tube approx. midway between roofplate and floorplate. Groove divides alar (dorsal) and basal (ventral) plate regions.
- telencephalon - the cranial portion of forebrain after it divides into 2 parts in the 5 secondary vesicle brain (week 5). (cavity- lateral ventricles and some of 3rd ventricle) Forms the cerebral hemispheres in the adult brain. (sc-My-Met-Mes-Di-Tel)
- thalamus - (G. thalamos= bedchamber) cns nucleus, lateral to 3rd ventricle, paired (pl thalami).
- thyroid hormone - hormone required for brain development. T3 (3,5,3′-triiodothyronine) binding to nuclear receptors then act as a transcription factor in both neurons and glial cells. iodine deficiency
- transcription factor - a factor (protein or protein with steroid) that binds to DNA to alter gene expression, usually to activate. (eg steroid hormone+receptor, Retinoic acid+Receptor, Hox, Pax, Lim, Nkx-2.2)
- trigeminal ganglion - (cranial nerve V, CN V) first arch ganglion, very large and has 3 portions.
- vagal ganglion - (cranial nerve X, CN X) fourth and sixth arch ganglion, innervates the viscera and heart.
- ventricles - the fluid-filled interconnected cavity system with the brain. Fluid (cerebrospinal fluid, CSF) is generated by the specialized vascular network, the choroid plexus. The ventricles are directly connected to the spinal canal (within the spinal cord).
- ventricular zone - Neuroepithelial cell layer of neural tube closest to lumen. Neuroepithelial cells generate neurons, glia and ependymal cells. (Ven-Man-Mar-CP)
- vestibulocochlear nerve - (cranial nerve VIII, CN VIII, also called statoacoustic)
- white matter - - neural regions containing processes (axons) of neurons. In the brain it is the inner layer, in the spinal cord it is outer layer. (see grey matter).
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Additional Images
Historic Images
Bartelmez GW. The subdivisions of the neural folds in man. (1923) J. Comp. Neural., 35: 231-247.
fig 6 Stages in the differentiation of the brain segments
Glossary Links
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Cite this page: Hill, M.A. (2024, March 28) Embryology Neural System Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Neural_System_Development
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