UNSW Embryology

Week 4 - Neural

© Dr Mark Hill (2008)

Acknowledgements

Introduction

During week 4 early neural development commences. Ectodermal cells thicken to a columnar epithelium in the midline of the embryonic disc forming the neural plate. This occurs directly over the notochord (in the mesoderm). This neural plate will forld to form a simple tube, from which the entire central nervous system (brain and spinal cord) will form. At the edge of this plate a special population (neural crest) will contribute the peripheral nervous system (sensory, sympathetic and peripheral ganglia). The process of nervous system formation is known as neurogenesis or neuralation (More? Neural Development).

Embryo Development Week 4 (Carnegie stage 10) (Carnegie stage 13)

Page Links: Introduction | Some Recent Findings | Human Neuralation | Neural Derivatives | Neural Genes | Neural Patterning | Development Overview | Molecular Factors | References | Glossary

Related Pages: Neural Development

Some Recent Findings

Human Neuralation

• 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.

  From: Neurulation in the normal human embryo. O'Rahilly R, Muller F Ciba Found Symp 1994;181:70-82

Early Development and Neural Derivatives

• trilaminar embryo
  • ectoderm layer
  • neural plate
  • neural groove
  • neural tube and neural crest
    • neural tube will form the central nervous system
    
• cranial expansion of neural tube - brain and brain stem
• 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

Neural Tube and Genes

neural plate 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

Development Overview

Week 4 (Clinical Week 6)

Day	Stage	Event
22	Stage 10	Neural Crest – differentiation at spinal cord level from day 22 until day 26 Neural – neural folds begin to fuse near the junction between brain and spinal cord, when Neural Crest cells are arising mainly from the neural ectoderm Neural Crest – trigeminal, facial, and postotic ganglia components visible (PMID: 17848161) Brain – rostral neural tube forms 3 primary brain vesicles (week 4) Respire – Week 4 - laryngotracheal groove forms on floor foregut.
23		Heart – begins to beat in Humans by day 22-23, first functioning embryonic organ formed.
24	Stage 11	Thyroid – thyroid median endodermal thickening in the floor of pharynx Neural – 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 two areas simultaneously. The two lips, however, behave differently. Optic ventricle appears
25	Stage 12	Pituitary Week 4 – hypophysial pouch, Rathke’s pouch, diverticulum from roof GIT - Liver – septum transversum forming liver stroma and hepatic diverticulum forming hepatic trabeculae (PMID: 9407542) Neural – caudal neuropore takes a day to close (closure is approximately at future somitic pair 31/sacral vertebra 2) Neural – secondary neurulation begins Neural Crest – cardiac crest, neural crest from rhombomeres 6 and 7 that migrates to pharyngeal arch 3 and from there the truncus arteriosus (PMID: 17848161)
26
27
28	Stage 13	Neural – the neural tube is normally completely closed, ventricular system now separated from amniotic fluid. Neural crest at spinal level is segregating, and spinal ganglia are in series with the somites. Spinal cord ventral roots beginning to develop. (PMID: 3354839) GIT - Liver – epithelial cord proliferation enmeshing stromal capillaries (PMID: 9407542) Sense - Smell – Crest comes from the nasal plates (PMID: 15604533) Skin – 4 weeks - simple ectoderm epithelium over mesenchyme Skin – 1-3 months ectoderm- germinative (basal) cell repeated division of generates stratified epithelium; mesoderm- differentiates into connective tissue and blood vessels

References

Links: Textbooks | Online Textbooks | Search Textbooks | Reviews | Articles | Search PubMed | Glossary

Specific references can also be found on each notes page and Selected References 1999

Textbooks

• Human Embryology (2nd ed.) Larson Ch
• The Developing Human: Clinically Oriented Embryology (6th ed.) Moore and Persaud
• Before we Are Born (5th ed.) Moore and Persaud Ch
• Essentials of Human Embryology Larson Ch
• Human Embryology Fitzgerald and Fitzgerald Ch2 p8-14
• UNSW Embryology Selected Week 3 References

Online Textbooks

Developmental Biology (6th ed) Gilbert, Scott F. Sunderland (MA): Sinauer Associates, Inc.; c2000. Early Mammalian Development

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

Reviews

Streit A. The preplacodal region: an ectodermal domain with multipotential progenitors that contribute to sense organs and cranial sensory ganglia. Int J Dev Biol. 2007;51(6-7):447-61.

Articles

Kageyama R, Ohtsuka T, Kobayashi T. Roles of Hes genes in neural development. Dev Growth Differ. 2008 Jun;50 Suppl 1:S97-103.

Search Jun 2008 "neurogenesis" 6302 reference articles of which 1182 were reviews.

Search PubMed: term = neurogenesis | week 4 neurogenesis | neuralation |

Glossary of Terms

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

Quick Links

Week 4 Pages:

Introduction | Abnormalities | Placodes | Somite Development | Early Nervous System | References | Text only | WWW Links | Week 1 | Week 2 | Week 3 | Week 4 |

Development Notes ----------------- Menstrual Cycle Week 1 Week 2 Week 3 Week 4 Placenta Serial Images Genes/DNA Molecular Dev Abnormal Dev Postnatal Dev Notes Index

System Notes ----------------- Heart/Cardiovascular Respiratory Coelomic cavity Gastrointestinal Tract Head and Neck Neural Neural Crest Eye Ear Nose Endocrine Urogenital Musculoskeletal Integumentary

Movies ----------------- Embryo Growth Ultrasound Week 1 Week 2 Week 3 Week 4 Stage 13/14 Stage 22 Neural Head and Neck Heart Vasculature Gastrointestinal Urogenital Other Embryos Larsen Internet

Other Embryos ----------------- Chicken Fly Frog Mouse Rabbit Rat Worm Zebrafish Guinea Pig

UNSW Embryology ISBN: 978 0 7334 2609 4

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