Embryological Development of Nervous System

FETUS Essential elements of embryology 

16th Edition

ABEDUR RAHMAN MBBS (DMC), M Phil (DU) Editorial Assistant

Dr. Farzana Iqbal

Published by Afrazul Haque Bhelejan  Thakurgaon On behalf of Fetus Publications

First published………. September, 1991. Second Edition………. September, 1993.  Third Edition………. February, 1995. Fourth Edition………. September, 995. Fifth Edition……….January, 1997 Sixth Edition………. May, 1998 Seventh Edition……….March, 2000 Eighth Edition……….August, 2000 Ninth Edition………. May, 2002  Tenth Edition………. October, 2003 Eleventh Edition………. April, 2004  Twelfth Edition………. December, 2004  Thirteenth Edition………. February, 2006 Fourteenth Edition……….October, 2006 Fifteenth edition ……….January, 2008 Sixteenth edition ……….November, 2008

MD. ABEDUR RAHMAN

AII rights reserved. No part of this book may be reproduced or transmitted in any form or by any means without the written permission of the author. Cover Design: Abedur Rahman Price: Taka Three hundred and Twenty (320/-) only. For all kinds of correspondence:

DR MD ABEDUR RAHMAN Phone: +88 01819-050041 01819-050041 E-mail: [email protected]

DISTRIBUTORS

Ahad Book Center Allied Book Center Bangladesh Book Center Capital Book Center Keya Medical Book Center Mukti Book House New Bengal Library National Book Center Samima Book Center Setu Book Center  Taj  Taj Medical Medic al Books Bo oks Nilkhet, Dhaka

Dedicated to My father 

for the uncompromising principle that guided his life.

ACKNOWLEDGEMENTS I remember  Dr. A. Hye Fakir EX-Head EX-Head of the t he department of anatomy, BSMMU.  Dr. Habibur Rahman. EX Head of the department of anatomy, SBMC

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Dr. Shahid-UlIah EX-Head of the department of anatomy, RPMC Dr. Kazi Rafiqul Haque Head of the department of anatomy, USTC. USTC. Chittogong Late Dr. S.S. Banik. Ex-Associate Professor of anatomy, SSMC. Dr. Dr. Motahar Hossain. Ex-Head of the department of anatomy, DMC. Dr. Dr. Manjar-e-Shamim. Professor Professor & head of the department of anatomy, BSMMU. Dr. Shamim Ara Head of the department of anatomy, DMC Dr. Shafiq Haider Asst prof. of anatomy, CMC.

for their good wishes to this publication  

Dr. Nazrul Islam Principal, Dinajpur Medical College Dr. Rubaiual Morshed Ex Asst. Professor, Pediatric Surgery, DMCH for their kind efforts in revising this book.

I am also grateful to Alauddin (SOMC) and other students who made constructive criticism to make the book more helpful for the students. I want to acknowledge my students Juthy (K-63, (K-63, DMC) and Sristi (K-63, DMC) for their whole hearted th co-operation in editing this 16 edition of the book; Ilias (K-62, DMC), DMC), Juwel (K-63, (K-63, DMC), Pritom (K(K63, DMC), Fauzia (NUB) for their constructive criticism for making necessary correction of in this edition. I am also grateful to the doctors and students of different institutions and medical colleges who made constructive criticism to make the book more helpful for the embryology student.

Forewords Excellent one I have gone through the book and found that the author has been succeeded in presenting the essential elements of embryology in an excellent manner. The elements served here are authentic. I hope that this humble presentation will serve its purposes well. My best wishes go to the author.

Prof. Dr. Md. Nazrul Islam MBBS, M. Phil (DU), MS (Glasgow). MHPED (Australia) Principal, Dinajpur Medical College Ex Vice president, BMA

Really charmed to find the simplicity I have gone through the book Fetus by Dr. Dr. Abedur Rahman interest & have been really charmed to find the simplicity of presentation & diagrams which depict the wide subject of  embryo embryolog logy y into into the small small space space of this this handy handy volume volume.. can peep eep into the memory of the whole aspect of  embr embryo yolo logy gy thro throug ugh h this this book book inst instan anta tane neou ousl sly y and and comfor comfortab tably ly even even at rest rest or in leisur leisure e like like the cow which which taste of food by cutting its jaw while at rest. I wish wish the promis promising ing young young author author & his book book a glorio glorious us the days to come.

with its Studen Studentt enjoys enjoys the Dr. Kazi Rafiqul Huq Head, dept. of  Anatomy USTC, Chittogong.

succes successs in

AUTHOR’S SAYINGS SAYINGS “The “The hist histor ory y of man man for for nine nine mont months hs prec preced edin ing g his his birt birth h woul would, d, prob probab ably ly,, be far far more more inte intere rest stin ing, g, and and cont contai ain n even events ts of grea greate terr moment than all three score and ten years that follow it.” --- Samuel Taylor Coleridge It is now well proved that ‘Fetus’  is the most read embryology book in our country. The last 15 editions of the book have proven that it is unique in its field. In this edition, I have tried my best to make it more useful for the students making necessary changes elsewhere. New to this edition 

Development of different organs at a glance Answers of all first professional SAQ

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Some new information Some figures and information are modified.

All praises for the Almighty. Almighty. Thanks to all the anatomy teachers and students – past, present, and an d future.

November 2008

Dr Md Abedur Rahman

Contents Part-1: Introduction 1.

Introduction to embryology

1

2.

Reproduction and Development Reproduction Some basic concepts in embryology Some historical elements on embryology

3 8 12

3. 4.

Part-2: General Embryology 5. 6. 7. 8. 9.

Gametogenesis: Conversion of germ cells into male & female gamete Female reproductive cycles and ovulation Pre-embryonic period – I: Fertilization, cleavage and implantation Pre-embryonic period-II: Formation of germ layers (Gastrulation) Embryonic period: Derivatives of germ layers

21 34 68 90 115

Fetal period Some facts concerning the fetus 11. Fetal membranes and placenta 12. Congenital malformations 13. Developmental genetics 10.

123 127 155 159

Part-3: Systemic Embryology

Cardiovascular system 15. Digestive system 16. Respiratory system 17. Diaphragm and septum transversum18. Urogenital system 19. Head neck and ear 20. Nervous system 21. Skeletal system 22. muscular system 23. Integumentary system Glossary 14.

165 190 231 237 241 279 304 325 329 332 339

Fetus 2 contents

SAQ in Embryology Development of Different organ at a Glance

Look for the other books by the same author

D”P evW †cÖmvi: cÖwZKvi I cÖwZ‡iva 2.Medical Genetics 3.Research methodology 4.How to Write a thesis 5.Essentials of Biostatistics 1.

Sample Chapter

20 Nervous System, Eye and Endocrine Gland

SAQ of professional examination

1. How neural neural tube tube is form formed? ed? Give Give its its subdivisions. 2. Give Give the develop developmen ments ts of brain brain & spinal cord. 3. What What are are the deriv derivati atives ves of of neural neural crest?

4. Give Give the deve developm lopment ent of of follow following ing glands. Pituitary gland Adrenal gland. 5. Give Give the develo developmen pmentt of various various components of N.S. 6. Give Give the develo developmen pmentt of retina retina 7. Give the development of lens. • •

Introduction for grasping the system

  The The whole whole nervo nervous us Syst System em deve develo lops ps from from ecto ectode derm rm (exc (excep eptt blood blood vesse vessels ls & some some neurological elements). The part of ectoderm overlying the notochord becomes thickened to form the neural plate. It is folded and fused to form neural tube (Fig 20.2). 20.2). The cells in the junction between neural plate & rest ectoderm ectoderm forms neural crest. The neural crest & neural tube together give rise to N S. Eyes begin to develop as optic vesicle of each side of  the forebrain. Part of the adrenal gland and pituitary gland develop from this system also, Derivation of different components of nervous system from ectoderm is shown in the table below.

Diagram showing the derivation of different components of nervous system from ectoderm

Neural Tube Development / Formation (neurulation)

1. Ectode Ectoderm rm overlying overlying the notochor notochordal dal process process bec become omess thic thicke kened ned to for form m the neural plate. 2. The neural plate become becomess depress depressed ed to to form form neural groov grooves es 3. No Now w ed edge gess of the neura neurall gr groo oove ve come come ne near arer er to ea each ch other other & fu fuse se to co conv nver ertt th the e neural groove into neural tube.

 The neural tube is initially connected to the amniotic cavity via the anterior and posterior neuropores. The lamina terminalis marks the location of the anterior neuropore in the adult. Derivatives

1. CNS with Adenohypophys Adenohypophysis is of pituitary pituitary gland. gland. 2. Neurob Neuroblast lastss – They will form form nerve nerve cells. cells. 3. Spongio Spongiobla blasts sts - They will will form form neurogl neuroglia. ia.

Subdivision of CNS

 The caudal end of the neural tube becomes elongated to form spinal cord. The cran crania iall end end beco become mess expa expand nded ed to form form brain. brain. The The expa expand nded ed brain brain form formss vesicles from which different parts of brain develop.

Neural Crest  The specialized group of cells in the dorsolateral aspect of primitive neural tube which give rise to some components of nervous system is called neural crest. When When neural neural plate plate forms, forms, the primord primordial ial of neural neural .crest .crest appear appearss in the  junction between the plate and surface ectoderm.

Figure: Neural crest 

Derivatives

Please see in derivatives of germ layers in capter-8.

Development of CNS Development Developme nt of Spinal Cord

It deve develo lops ps from from cauda caudall elon elonga gate ted d part part of neura neurall tube tube.. Diffe Differe rent nt part partss & components of it develop as follows The wall of the tube is subdivided into 3 layers-ependymal layer, mantle layer & marginal layer These are again subdivided into dorsal alar lamina and ventral basal lamina. Basal lamina gives rise to structures that are motor in function and alar lamina into those that are sensory in function.

• • • • •

Grey Column: from mantle layer of lateral wall of neural tube. While matter: Comes from marginal layer of lateral wall of neural tube. Nerve cells: Come from neuroblasts of mantle layer of neural tube. Neuroglia: Comes from spongioblasts of neural tube. Lining of central canal: c anal: Comes from ependymal layer. layer.

Fig.: Formation of filum terminale

Development of Brain

Fig.: Primary brain vesicles.

It develops from cranial expanded part of neural tube. This part of tube forms 3 vesicles from where the parts of the brain develop as follows— (a) Prosencephalon (Forebrain vesicle)

1. Telencephalon (cerebrum) 2. Diencephalon (thalamus & hypothalamus)

(b) Mesencephalon (Midbrain vesicle)

Midbrain

(c) Rhombencephalon (Hindbrain vesicle)

1 Myelencephalon (Medulla) 2. Metencephalon (pons & cerebellum)

Development of Meninges

 The dura mater arises from mesoderm that surrounds the neural tube. B.  The pia mater and arachnoid membrane arises form neural crest cells. A.

Development of autonomic nervous system 1. The The sy sympa mpath thet etic ic ne nervo rvous us sy syst stem em ori origin ginat ates es fr from om th the e ba basa sall pl plat ate e of the neural tube and neural crest cells . 2. The parasympath parasympathetic etic nervous nervous system system also originate originatess from the the basal plate plate of  the neural tube and neural crest cells. Table: Origination of the Sympathetic Nervous System

Embryonic Structure

Adult Derivative

Basal plate of  neural tube

Preganglionic sympathetic neurons within the intermediolateral cell column

Neural crest cells

Postganglionic sympathetic neurons within the sympathetic chain ganglia and prevertebral ganglia

Table: Origination of the Parasympathetic Nervous System

Embryonic Structure Basal plate of  neural tube

Neural crest cells

Adult Derivative 1. Prega Pregangli nglionic onic paras parasympa ympathe thetic tic neurons within the nuclei of the midbrain (III), pons (VIII), and medulla (IX, X) 2. Pr Prega egangli nglionic onic para parasym sympat pathet hetic ic neurons within the spinal cord nucleus at S2-S4 1. Po Postg stgang anglion lionic ic parasymp parasympath atheti eticc neurons within the ciliary (111), pterygopalatine (VII), submandibular (VII), otic (IX), and enteric (X) ganglia 2. Po Postg stgang anglion lionic ic parasymp parasympath atheti eticc neurons within the ganglia of the abdominal and pelvic cavities

Some Important Anomalies in Development of CNS

 Anencephaly—Here neural folds in the brain region fail to fuse. A secondary

failure of development of vault of the skull occurs. fusion of verteb vertebral ral column column (usual (usually ly in sacro sacroilia iliacc Spina bifida —Failure —Failure of  fusion regions) is called spina bifida.

Development of Neuron

A. Ther There e is a fant fantas asti ticc vari variet ety y in the the neur neuron onal al fami family ly.. Neve Nevert rthe hele less ss,, the the differentaiation of a motor neuron in the spinal cord will serve to illustrate the major principles of neuronal differentiation. 1. The motor motor neurons neurons in the spinal spinal cord develo develop p from neurobl neuroblast astss that have very few processes The neuroblasts, once formed, migrate away from the lumen of the spinal cord, and as they do so they begin to form a small number of processes 2. Some of these processes develop lop into a dendrit ritic., gro group of  moderately tong processes that receive inputs form other cells via synapses 3. One One axon axonal al proc process ess beco become mess extr extrem emel ely y elon elongat gated ed and and may may grow grow extensively in the marginal layer if it is destined to carry impulses parallel to the long axis of the spinal cord, or it may grow a process that begins to project through the marginal layer out of the central nervous system into the peripheral nervous system. 4. Motor Motor neurons neurons eventuall eventually y will contrac contractt develo developing ping muscle muscle fibers fibers and form motor end plates with them B. Some neuroblast neuroblastss form motor motor neurons, neurons, while others form form small interneurons, interneurons, or large pyramidal neurons of the cerebral cortex, or purkinje cells of the cerebellum, or another of the may types of neurons, These diverse cell types diff differ er in the the size size and and shap shape e of thei theirr cell cell bodi bodies es,, exten xtentt of dend dendri riti ticc arborization. and length of axons and in may functional criteria as well [Ref: Kurt E Johnson, NMS, page- 170]

Development of Endocrine glands Parts of pituitary and adrenal gland have been derived from CNS. These two endocrin endo crine e gla glands nds only will be con consid sidere ered d in thi thiss cha chapte pterr. Oth Other er has bee been n described in the previous chapters. Development Developme nt of Pituitary Gland

Fig.: Development of hypophysis cerebri (Pituitary gland).,

1. Aden Adenohyp ohypophy ophysis sis (ant. (ant. & inter intermedi mediate ate lobe) lobe)

An ect ectode oderma rmall out outpoc pocke keting ting dev develo elops ps fr from om sto stomod modeum eum in fr front ont of the buccopharyngeal membrane. This is Rathke’s pouch. Its anterior wall forms the ant. lobe & post. wall forms intermediate lobe. An extension from it forms the tuberal lobe.  Adenohypophysis is ectodermal. 

2. Neur Neurohyp ohypophy ophysis sis (post (post lobe lobe and and the the stalk) stalk) • •

A funnel shaped diverticulum from the floor of 3rd ventricle forms it. It is neuroectodermal.

Development Developme nt of Adrenal Gland

Cortex 

Mesodermal.  Develops from coelomic epithelium that lies in the angle between the upper end of mesonephros & dorsal mesentery of the gut. 

Medulla

Neuroectodermal Cells lls fr from om th the e ne neur ural al cr cres estt in inva vade de me media diall as aspec pectt of co cort rtex ex an and d fo form rm th the e  Ce medulla. 

Figure: A, Drawing showing the chromaffin (sympathetic) cells penetrating the total tot al cor cortex tex of the suprare suprarenal nal gland gland B At a lat late e sta stage ge of dev develo elopm pment ent,, th the e definitive cortex surrounds the medulla almost completely 

Development of Eye  The eye develops from the following sources— 1. Optic vesicle— It is an outpocketing of Prosencephalon (neuroectodermal (Fig A). 2. Lens placode—From surface ectoderm by the induction of optic vesicle (Fig B) 3. Surr Surrou oundi nding ng mesenc mesenchy hyme me

Fig. A: The development of the eye showing the optic vesicle

Fig. B- The development of the eye e ye showing the formation of optic cup and the lens

Fig 20.. 7. C-The development of the eye from the forebrain Different components of the eyeball develop from these sources as follows—  A. Refractive Media—

1. Lens—

Ectodermal From the two walled lens vesicle The vesicle is first lined by a single layer cells in the anterior wall of  the vesicle vesicle of cubica cubicall cells cells (fig.A) (fig.A) The cells remain cubical.Those in the posterior wall gradually become elongated (Fig.B C 0). As they do so, the cavity of the vesicle is encroached upon and eventually obliterated. The elongated cells of he posterior wall lose their nuclei and are converted into fibres and anterior layer forms cubical lining epithelium covering this aspect of lens. (I Singh) 2 Vitreous body—Protoplasmic filaments are derived from ectoderm; rest from the mesoderm. •

•

B. lnnerlayer— 2. Retina—

•

•

Neuroectodermal. From opitc vesicle. Optic vesicle forms the two layered optic cup, a larger posterior part, that becomes thick and forms the retina proper and an anterior part that remains thin and forms an epithelial covering for the ciliary body and iris. a. The outer outer wall wall of the post. post. part of the the optic cup cup remain remainss thin. Its Its cells form the pigment layer of the retina.  b.  The inner wall of the cup differentiates into matrix cell, mantle and marginal marginal layers as in the neural tube. After After giving origin to cells of  the mantle layer, the cells of the matrix layer forms rods and cones. The cells of the mantle layer form the bipolar cells, the gang gangli lion on cell cellss and and othe otherr neur neuron onss of the the reti retina na and and also also the the supporting elements. The axons of the ganglion cells grow into the original layer to form the layer of nerve fibers.

Fig : Development of retina

C. Middle layer  1. Choroid – Mesodermal.. From mesenchyme surrounding optic cup • •

2 Cilliary body •

•

Mesodermal.. from forward prolongation of the mesoderm forming the choroid.

3. Iris Iris muscl muscles es----- Deve Develop lop from from optic optic cup cup (neuro (neuroec ectod toderm erm)) and rest rest mesenchyme. from D. Outer layer  1. Sclera- From mesenchyme. 2. Cornea --Corneal epithelium is derived from surface ectoderm and

substance proper from mesenchyme. Q. Ans:

Neur Neural al tub tube e def defec ectt lead leads s to to anen anence ceph phal aly y why why? ? (Jan (Januu-07 07))

•

•

•

•

Anencephaly is a condition in which the vault of the skul does not formed (cranioschisis). As a result brain exposed to amniotic fluid and degenerates, leaving a mass of necrotic tissue During During neurula neurulatio tion n (Proc (Process ess of format formation ion of nerual nerual tube) tube) anteri anterior or or cranial neuropore closes at day 25 & post or caudal neuropore at day 27. Forming a closed tube. But in some cases there is failure to close cranial neuropore. That’s why vault does not formed.