embryological development of nervous system

FETUSEssential elements of embryology

16th Edition

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

Editorial Assistant

Dr. Farzana Iqbal

Published byAfrazul 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, 2000Eighth Edition……….August, 2000

Ninth Edition………. May, 2002 Tenth Edition………. October, 2003 Eleventh Edition………. April, 2004

Twelfth Edition………. December, 2004Thirteenth Edition………. February, 2006Fourteenth Edition……….October, 2006Fifteenth edition ……….January, 2008

Sixteenth edition ……….November, 2008

MD. ABEDUR RAHMANAII 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

E-mail: [email protected]

DISTRIBUTORS

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Nilkhet, Dhaka

Dedicated to

My father

for the uncompromising

principle that guided his life.

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ACKNOWLEDGEMENTS I remember Dr. A. Hye Fakir

EX-Head of the department of anatomy, BSMMU. Dr. Habibur Rahman.

EX Head of the department of anatomy, SBMC Dr. Shahid-UlIah EX-Head of the department of anatomy, RPMC Dr. Kazi Rafiqul Haque

Head of the department of anatomy, USTC. Chittogong Late Dr. S.S. Banik. Ex-Associate Professor of anatomy, SSMC. Dr. Motahar Hossain. Ex-Head of the department of anatomy, DMC. Dr. Manjar-e-Shamim. 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, DMC) and Sristi (K-63, DMC) for their whole hearted co-operation in editing this 16th edition of the book; Ilias (K-62, DMC), Juwel (K-63, DMC), Pritom (K-63, 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.

Nervous system, eye and endocrine gland 305

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

Dr. Kazi Rafiqul Huq Head, dept. of Anatomy USTC, Chittogong.

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Forewords

Excellent oneI 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.

Really charmed to find the simplicityI have gone through the book Fetus by Dr. Abedur Rahman with interest & have been really charmed to find the simplicity of its presentation & diagrams which depict the wide subject of embryology into the small space of this handy volume. Student can peep into the memory of the whole aspect of embryology through this book instantaneously and comfortably even at rest or in leisure like the cow which enjoys the taste of food by cutting its jaw while at rest.

I wish the promising young author & his book a glorious success in the days to come.


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AUTHOR’S SAYINGS

“The history of man for nine months preceding his birth would, probably, be far more interesting, and contain events of greater 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 Some new information Some figures and information are modified.

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

November 2008 Dr Md Abedur Rahman


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Contents

Part-1: Introduction

1. Introduction to embryology 1

2. Reproduction and Development 33. Some basic concepts in embryology 84. Some historical elements on embryology 12

Part-2: General Embryology

5. Gametogenesis: Conversion of germ cells into male & female gamete

21

6. Female reproductive cycles and ovulation 347. Pre-embryonic period – I: Fertilization, cleavage and

implantation68

8. Pre-embryonic period-II: Formation of germ layers (Gastrulation) 909. Embryonic period: Derivatives of germ layers 11510. Fetal period Some facts concerning the fetus 12311. Fetal membranes and placenta 12712. Congenital malformations 15513. Developmental genetics 159

Part-3: Systemic Embryology

14. Cardiovascular system 16515. Digestive system 19016. Respiratory system 23117. Diaphragm and septum transversum- 23718. Urogenital system 24119. Head neck and ear 279


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20. Nervous system 30421. Skeletal system 32522. muscular system 32923. Integumentary system 332Glossary 339

Fetus 2 contentsSAQ in EmbryologyDevelopment of Different organ at a Glance

Look for the other books by the same author

1. D”P evW †cÖmvi: cÖwZKvi I cÖwZ‡iva

2. Medical Genetics3. Research methodology4. How to Write a thesis5. Essentials of Biostatistics

Sample Chapter


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20Nervous System, Eye and Endocrine Gland

SAQ of professional examination1. How neural tube is

formed? Give its subdivisions.

2. Give the developments of brain & spinal cord.

3. What are the derivatives of neural crest?

4. Give the development of following glands.

Pituitary gland Adrenal gland.

5. Give the development of various components of N.S.

6. Give the development of retina

7. Give the development of lens.

Introduction for grasping the systemThe whole nervous System develops from ectoderm (except blood vessels & some neurological elements). The part of ectoderm


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overlying the notochord becomes thickened to form the neural plate. It is folded and fused to form neural tube (Fig 20.2). The cells in the junction between neural plate & rest 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. Ectoderm overlying the notochordal process becomes thickened to form the neural plate.

2. The neural plate becomes depressed to form neural grooves3. Now edges of the neural groove come nearer to each other &

fuse to convert the 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

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1. CNS with Adenohypophysis of pituitary gland.2. Neuroblasts – They will form nerve cells.3. Spongioblasts - They will form neuroglia.

Subdivision of CNSThe caudal end of the neural tube becomes elongated to form spinal cord. The cranial end becomes expanded to form brain. The expanded brain forms vesicles from which different parts of brain develop.

Some basic concepts in embryology ii

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Neural CrestThe 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 neural plate forms, the primordial of neural .crest appears in the junction between the plate and surface ectoderm.

Some basic concepts in embryology iii

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Figure: Neural crest

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

Some basic concepts in embryology iv

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Development of CNS

Development of Spinal CordIt develops from caudal elongated part of neural tube. Different parts &

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.

Some basic concepts in embryology v

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Grey Column: from mantle layer of lateral wall of neural tube. While matter: Comes from marginal layer of lateral wall of neural tube.

Some basic concepts in embryology vi

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Nerve cells: Come from neuroblasts of mantle layer of neural tube. Neuroglia: Comes from spongioblasts of neural tube. Lining of central canal: Comes from ependymal layer.

Fig.: Formation of filum terminale

Development of Brain

Fig.: Primary brain vesicles.

Some basic concepts in embryology vii

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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 1. Telencephalon (cerebrum)

Some basic concepts in embryology viii

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vesicle) 2. Diencephalon (thalamus & hypothalamus)

(b) Mesencephalon (Midbrain vesicle)

Midbrain

(c) Rhombencephalon (Hindbrain vesicle)

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

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

Development of autonomic nervous system

1. The sympathetic nervous system originates from the basal plate of the neural tube and neural crest cells .

2. The parasympathetic nervous system also originates from the basal 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 chainganglia and prevertebral ganglia

Table: Origination of the Parasympathetic Nervous SystemEmbryonic Structure

Adult Derivative

Basal plate of neural tube

1. Preganglionic parasympathetic neurons within the nuclei of the midbrain (III), pons (VIII), and medulla (IX, X)

2. Preganglionic parasympathetic neurons within the spinal cord nucleus at S2-S4

Neural crest cells

1. Postganglionic parasympathetic neurons within the ciliary (111), pterygopalatine (VII), submandibular (VII), otic (IX), and enteric (X)

Some basic concepts in embryology ix

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ganglia2. Postganglionic parasympathetic

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.

Spina bifida —Failure of fusion of vertebral column (usually in sacroiliac regions) is called spina bifida.

Some basic concepts in embryology x

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Development of NeuronA. There is a fantastic variety in the neuronal family. Nevertheless, the

differentaiation of a motor neuron in the spinal cord will serve to illustrate the major principles of neuronal differentiation.

1. The motor neurons in the spinal cord develop from neuroblasts 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 into a dendritic., group of moderately tong processes that receive inputs form other cells via synapses

3. One axonal process becomes extremely elongated and may 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 neurons eventually will contract developing muscle fibers and form motor end plates with them

B. Some neuroblasts form motor neurons, while others form small 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 differ in the size and shape of their cell bodies, extent of dendritic

Some basic concepts in embryology xi

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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 endocrine glands only will be considered in this chapter. Other has been described in the previous chapters.

Development of Pituitary Gland

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

1. Adenohypophysis (ant. & intermediate lobe) An ectodermal outpocketing develops from stomodeum in front 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. Neurohypophysis (post lobe and the stalk) A funnel shaped diverticulum from the floor of 3rd ventricle forms it. It is neuroectodermal.

Development of Adrenal Gland

Some basic concepts in embryology xii

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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 from the neural crest invade medial aspect of cortex and form the

medulla.

Some basic concepts in embryology xiii

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Figure: A, Drawing showing the chromaffin (sympathetic) cells penetrating the total cortex of the suprarenal gland B At a late stage of development, the 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. Surrounding mesenchyme

Some basic concepts in embryology xiv

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

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

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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

of cubical cells (fig.A) The cells in the anterior wall of the vesicle 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.

Some basic concepts in embryology xvii

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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 wall of the post. part of the optic cup remains thin. Its cells form the pigment layer of the retina.

b. The inner wall of the cup differentiates into matrix cell, mantle and marginal layers as in the neural tube. 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 ganglion cells and other neurons of the retina and also 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 muscles--- Develop from optic cup (neuroectoderm) and rest from mesenchyme. D. Outer layer

Some basic concepts in embryology xviii

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1. Sclera- From mesenchyme. 2. Cornea --Corneal epithelium is derived from surface ectoderm and substance proper from mesenchyme.

Q. Neural tube defect leads to anencephaly why? (Janu-07)

Ans:

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 neurulation (Process of formation of nerual tube) anterior 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.

Some basic concepts in embryology xix

embryological development of nervous system

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