Duus topical diagnosis in neurology anatomy, physiology, signs, symptoms, 5th edition PDF (jan 19, 2012) (3136128052) (springer)

· III

Duus’

Topical Diagnosis
in Neurology
An atom y, Physiology, Sign s,
Sym ptom s
5th edition

Math ias Baeh r, MD
Professor of Neu rology an d Ch airm an

Dep artm en t of Neu rology
Un iversit y of Gött in gen
Göt tin gen , Germ any

Mich ael Frotsch er, MD
Hertie Sen ior Research Professor
for Neu roscien ce an d Ch airm an
Dep artm en t of Stru ct u ral Neu robiology
Cen ter for Molecu lar Neu robiology
Ham bu rg (ZMNH)
Un iversit y of Ham bu rg
Ham bu rg, Germ any

W ith con tribu t ion s by
W ilh elm Ku eker
Fou n din g au th or Peter Du u s

40 0 illu stration s, m ost in color,
by Professor Gerh ard Sp itzer an d Barbara Gay
Th iem e
Stu t tgart · New York


IV ·

Library of Congress Cataloging-in-Publication Data
Baeh r, Math ias.
[Du us’ n eu rologisch -topisch e Diagn ostik. En glish ]
Duu s’ topical diagn osis in n eu rology : an atom y,
Physiology, sign s, sym ptom s/Math ias Baeh r,
Mich ael Frotsch er ; w ith con tribution s by
Wilh elm Ku eker ; tran slated by Eth an Tau b ;
Illu strated by Gerh ard Spitzer. 5th , rev. ed.
p. ; cm .
Rev. tran slation of th e 8th Germ an ed. c20 03.
In cludes in dex.
ISBN 978-3-13-612805-3 (GTV : alk. pap er)

1. Nervou s system Diseases Diagn osis. 2. Neu roan atom y.
3. An atom y, Path ological. 4. Nervou s system Path ophysiology. I. Frotsch er,
M. (Mich ael), 1947- . II. Du us, Peter, 1908-. Top ical
diagn osis in n eu rology. III. Title. IV. Title: Topical
diagn osis in n eu rology. [DNLM: 1. Nervou s System
Diseases–diagn osis. 2. Nervou s System –an atom y &
h istology. 3. Nervous System –physiopath ology.
WL 141 B139d 2011]
RC347.D8813 2011
616.8’04754 dc22
2011016421

1st Brazilian
(Portuguese) edition 1985
2nd Brazilian
(Portuguese) edition 1990
1st Chinese edition 1996
1st English edition 1983
2nd English edition 1989
3rd English edition 1998
1st French edition 1998
1st Germ an edition 1976
2nd Germ an edition 1980
3rd Germ an edition 1983

4th Germ an edition 1987
5th Germ an edition 1990
6th Germ an edition 1995
7th Germ an edition 2001
8th Germ an edition 20 03
9th Germ an edition 2009

1st Greek edition 1992
2nd Greek edition 2009
1st Indonesian
edition 1996
1st Italian edition 1987

1st Japanese edition 1982
2nd Japanese edition 1984
3rd Japanese edition 1988
4th Japanese edition 1999
1st Korean edition 1990

Th is book is an auth orized an d revised tran slation of th e 9th
Germ an edition pu blish ed an d copyrigh ted 20 09 by Georg
Th iem e Verlag, Stu ttgart, Germ any. Title of th e Germ an
edition : Neu rologisch -topisch e Diagn ostik. An atom ie—
Fu n ktion —Klin ik.
Con tribu tor: Wilh em Ku eker, MD, Radiological Clin ic, Dep artm en t of Neu roradiology, Un iversity Hospital Tü bin gen ,

Germ any

1st Portuguese edition 2008

4th edition tran slated by Eth an Tau b, MD, Klin ik im Park,
Zu rich , Sw itzerlan d. Updates tran slated by Geraldin e
O’Su llivan , Dublin , Rep. of Irelan d

1st Russian edition 1996
2nd Russian edition 2009

Illustrators: Gerh ard Spitzer, Fran kfurt/M, Germ any;

Barbara Gay, Stu ttgart, Germ any

1st Polish edition 1990

1st Spanish edition 1985
1st Turkish edition 2001

© 2012 Georg Th iem e Verlag,
Rü digerstrasse 14, 70469 Stu ttgart,
Germ any
h ttp://w w w.th iem e.de
Th iem e New York, 333 Seven th Aven u e,

New York, NY 10 0 01 USA
h ttp://w w w.th iem e.com
Cover design : Th iem e Pu blish in g Grou p
Typesettin g by prim u stype Hu rler, Notzin gen , Germ any
Prin ted in Ch in a by Everbest Prin tin g Co., Ltd
ISBN 978 3 13-612805 3

Im po rtant note : Medicin e is an ever-ch an gin g scien ce un dergoin g con tin u al developm en t. Research an d clin ical experien ce are con tin u ally exp an din g our kn ow ledge, in p articu lar ou r kn ow ledge of proper treatm en t an d dru g th erapy. In sofar as th is book m en tion s any dosage or application ,
readers m ay rest assu red th at th e auth ors, editors, an d p ublish ers h ave m ade every effort to en su re th at su ch referen ces are in accordan ce w ith the state of know ledge at the
time of production of the book.
Neverth eless, th is does n ot involve, im ply, or express any
gu aran tee or respon sibility on th e p art of th e p ublish ers in

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V

Preface
In 20 05 w e pu blish ed a com plete revision of Du us’
textbook of topical diagn osis in n eu rology, th e first

n ew edition sin ce th e death of its origin al auth or,
Professor Peter Du u s, in 1994. Feedback from readers w as extrem ely positive an d th e book w as tran slated in to n u m erou s lan gu ages, provin g th at th e
con cept of th is book w as a su ccessful on e: com bin in g an in tegrated p resen tation of basic n eu roan atom y w ith t h e su bject of n eurological syn drom es, in cludin g m odern im agin g tech n iqu es. In
th is regard w e th an k ou r n eu roradiology colleagu es, an d especially Dr. Kueker, for providin g us
w ith im ages of very h igh qu ality.
In th is fifth edition of “Du u s,” w e h ave preserved
th e rem arkably effect ive didactic con cept of th e
book, w h ich particularly m eets th e n eeds of m edical stu den ts. Modern m edical cu rricula require in tegrative kn ow ledge, an d m edical stu den ts sh ould
be tau gh t h ow to apply th eoret ical kn ow ledge in a
clin ical settin g an d, on th e oth er h an d, to recogn ize
clin ical sym ptom s by delvin g in to th eir basic
kn ow ledge of n euroan atom y an d n eu rophysiology.

Our book fulfils th ese requ irem en ts an d illust rates
th e im portan ce of basic n eu roan atom ical kn ow ledge for subsequ en t practical w ork, as it in clu des
actu al case st udies. We h ave color-coded th e section h eadin gs to en able readers to dist in gu ish at a
glan ce betw een n euroan atom ical (blu e) an d clin ical (green ) m aterial, w ith ou t disruptin g th e th em atic con tin uity of th e text.

Alth ou gh th e book w ill be u sefu l to advan ced
stu den ts, also physician s or n eurobiologists in terested in en rich in g th eir kn ow ledge of n eu roan atom y w ith basic in form ation in n eu rology, or
for revision of th e basics of n eu roan atom y w ill
ben efit even m ore from it.
Th is book does n ot preten d to be a textbook of
clin ical n eu rology. Th at w ou ld go beyon d th e scope
of th e book an d also con t radict th e basic con cept

described above. First an d forem ost w e w an t to dem on strate h ow, on th e basis of th eoretical an atom ical kn ow ledge an d a good n eurological exam in ation , it is p ossible to localize a lesion in th e
n ervou s system an d com e to a decision on fu rth er
diagn ostic step s. Th e cau se of a lesion is in itially
irrelevan t for th e p rim ary topical diagn osis, an d
elucidation of th e etiology takes place in a secon d
stage. Our book con tain s a cursory overview of th e
m ajor n eurological disorders, an d it is n ot in ten ded
to replace th e system atic an d com preh en sive
coverage offered by stan dard n eu rological textbooks.
We h ope th at th is n ew “Duu s,” like th e earlier
edition s, w ill m erit th e appreciation of its
au dien ce, an d w e look forw ard to receivin g readers’ com m en ts in any form .

Professor M. Baehr
Professor M. Frotscher


VI · Preface

Contents
1

Elements of the Nervous System

.............................................

2

Info rm atio n Flo w in the Nervo us System .

2

Functio nal Gro ups o f Ne uro ns . . . . . . . . . . . .

7

Ne uro ns and Synapses . . . . . . . . . . . . . . . . . . . .
Neu ron s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Syn apses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2
2
4

Glial Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7

De velo pm ent o f the Ne rvo us Syste m . . . . . .

8

Ne uro transm itters and Recepto rs . . . . . . . . .

7

2

Somatosensory System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Periphe ral Co m po ne nts o f the So m ato senso ry Syste m and Peripheral Regulato ry
Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Recep tor Organ s . . . . . . . . . . . . . . . . . . . . . . . . . .
Periph eral Nerve, Dorsal Root Gan glion ,
Posterior Root . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Periph eral Regulatory Circuits . . . . . . . . . . . . . .
Central Co m po ne nts o f the So m ato senso ry System . . . . . . . . . . . . . . . . . . . . . . . . . . .
Posterior an d An terior Spin ocerebellar
Tracts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3

Motor System

12
12
14
18
24

Posterior Colu m n s . . . . . . . . . . . . . . . . . . . . . . . . .
An terior Spin oth alam ic Tract . . . . . . . . . . . . . .
Lateral Spin oth alam ic Tract . . . . . . . . . . . . . . . .
Oth er Afferen t Tracts of th e Spin al Cord . . . .

28
30
30
31

Central Pro ce ssing o f So m ato senso ry
Info rm atio n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

32

So m ato se nso ry Deficits due to Le sio ns at

Specific Sites alo ng the So m ato senso ry
Pathw ays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

32

25

....................................................................

Ce ntral Co m po nents o f the Mo to r System
and Clinical Syndro m es o f Le sio ns Affecting Them . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Motor Cortical Areas . . . . . . . . . . . . . . . . . . . . . .

Corticospin al Tract (Pyram idal Tract) . . . . . . .
Corticon u clear (Corticobulbar) Tract . . . . . . . .
Oth er Cen tral Com p on en ts of th e Motor
System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Lesion s of Cen tral Motor Path w ays . . . . . . . . .
Peripheral Co m po nents o f the Mo to r
System and Clinical Syndro m e s o f Lesio ns
Affecting Them . . . . . . . . . . . . . . . . . . . . . . . . . . .
Clin ical Syn drom es of Motor Un it Lesion s . . .

12

36
36
38
39
39
41

43
44

Co m plex Clinical Syndro m e s due to
Le sio ns o f Specific Co m po nents o f the

Ne rvo us Syste m . . . . . . . . . . . . . . . . . . . . . . . . . .
Spin al Cord Syn drom es . . . . . . . . . . . . . . . . . . . .
Vascular Spin al Cord Syn drom es . . . . . . . . . . .
Nerve Root Syn drom es (Radicu lar
Syn drom es) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Plexus Syn drom es . . . . . . . . . . . . . . . . . . . . . . . . .
Periph eral Nerve Syn drom es . . . . . . . . . . . . . . .
Syn drom es of th e Neu rom u scu lar Ju n ction
an d Mu scle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

36

45
45
56
57
62
67
72


Contents · VII

4

Brainstem

.........................................................................

Surface Anato m y o f the Brainstem . . . . . . . .
Medu lla . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pon s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Mid brain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

74
74

75
75

Cranial Ne rves . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Origin , Com p on en ts, an d Fu n ction s . . . . . . . . . 77
Olfactory System (CN I) . . . . . . . . . . . . . . . . . . . . 81
Visual System (CN II) . . . . . . . . . . . . . . . . . . . . . . 84
Eye Movem en ts (CN III, IV, an d VI) . . . . . . . . . 89
Trigem in al Nerve (CN V) . . . . . . . . . . . . . . . . . . . 103
Facial Nerve (CN VII) an d Nervu s
In term ediu s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109

5

Cerebellum

Internal Structure . . . . . . . . . . . . . . . . . . . . . . . .
Cerebellar Cortex . . . . . . . . . . . . . . . . . . . . . . . . . .
Cerebellar Nu clei . . . . . . . . . . . . . . . . . . . . . . . . . .
Afferen t an d Efferen t Projection s of th e
Cerebellar Cortex an d Nu clei . . . . . . . . . . . . . . .

159
159

160
162

Co nne ctio ns o f the Ce re be llum w ith
Other Parts o f the Nervo us Syste m . . . . . . . . 162

Thalam us . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Nu clei . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Position of th e Th alam ic Nuclei in
Ascen din g an d Descen din g Path w ays . . . . . . .
Fu n ction s of th e Th alam u s . . . . . . . . . . . . . . . . .
Syn drom es of Th alam ic Lesion s . . . . . . . . . . . .

Th alam ic Vascular Syn drom es . . . . . . . . . . . . . .

172
172
172
176
176
177

Epithalam us . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
Subthalam us . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178

120
126
132

Brainstem Diso rders . . . . . . . . . . . . . . . . . . . . . . 145
Isch em ic Brain stem Syn drom es . . . . . . . . . . . . 145

Cerebellar Functio n and Ce rebe llar
Syndro m es . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Vestibulocerebellum . . . . . . . . . . . . . . . . . . . . . . .
Sp in ocerebellu m . . . . . . . . . . . . . . . . . . . . . . . . . .
Cerebrocerebellu m . . . . . . . . . . . . . . . . . . . . . . . .

158
164
164
165
166

Cerebellar Diso rders . . . . . . . . . . . . . . . . . . . . . . 167
Cerebellar Isch em ia an d Hem orrh age . . . . . . . 167
Cerebellar Tum ors . . . . . . . . . . . . . . . . . . . . . . . . . 167

Diencephalon and Autonomic Nervous System

Lo catio n and Co m po nents o f the
Die ncephalo n . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170

113

Topo graphical Anato m y o f the Brainstem . 134
In tern al Stru ctu re of th e Brain stem . . . . . . . . . 134

.......................................................................

Surface Anato m y . . . . . . . . . . . . . . . . . . . . . . . . . 158

6

Vestibulococh lear Nerve (CN VIII)—Coch lear
Com p on en t an d th e Organ of Hearin g . . . . . .
Vestibulococh lear Nerve (CN VIII)—
Vestibular Com pon en t an d Vestibular
System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Vagal System (CN IX, X, an d th e Cran ial
Portion of XI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Hyp oglossal Nerve (CN XII) . . . . . . . . . . . . . . . .

74

...........................

170

Hypo thalam us . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Location an d Com pon en ts . . . . . . . . . . . . . . . . .
Hyp oth alam ic Nu clei . . . . . . . . . . . . . . . . . . . . . .
Afferen t an d Efferen t Projection s of th e
Hyp oth alam u s . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fu n ction s of th e Hyp oth alam u s . . . . . . . . . . . .

178
178
179

Peripheral Auto no m ic Ne rvo us Syste m . . .
Fu n d am en tals . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sym path etic Nervou s System . . . . . . . . . . . . . .
Parasym path etic Nervous System . . . . . . . . . .
Auton om ic In nervation an d Fun ction al
Distu rban ces of In dividu al Organ s . . . . . . . . . .
Visceral an d Referred Pain . . . . . . . . . . . . . . . . .

188
188
190
192

180
184

193
199

VIII · Contents

7

Limbic System

....................................................................

Anato m ical Overview . . . . . . . . . . . . . . . . . . . . . 202
In tern al an d Extern al Con n ection s . . . . . . . . . . 203
Majo r Co m po nents o f the Lim bic System .

Hip p ocam p u s . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Microan atom y of th e Hip pocam p al
Form ation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Am ygdala . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8

Basal Ganglia

203
203

202

Functio ns o f the Lim bic Syste m . . . . . . . . . . . 206
Types of Mem ory . . . . . . . . . . . . . . . . . . . . . . . . . 206
Mem ory Dysfu n ction —th e Am n estic
Syn drom e an d Its Cau ses . . . . . . . . . . . . . . . . . . 208

203
205

.....................................................................

Prelim inary Rem arks o n Term ino lo gy . . . . 214
The Ro le o f the Basal Ganglia in the Mo to r
System : Phylo genetic Aspe cts . . . . . . . . . . . . . 214

214

Functio n and Dysfunctio n o f the Basal
Ganglia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
Clin ical Syn drom es of Basal Gan glia
Lesion s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219

Co m po nents o f the Basal Ganglia and

The ir Connectio ns . . . . . . . . . . . . . . . . . . . . . . . . 215
Nu clei . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
Con n ection s of th e Basal Gan glia . . . . . . . . . . . 217

9

Cerebrum

.........................................................................

De velo pm ent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226
Gro ss Anatom y and Subdivisio n o f the

Cerebrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228
Gyri an d Su lci . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228
Histo lo gical Organizatio n of the Cerebral
Co rte x . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
Lam in ar Arch itecture . . . . . . . . . . . . . . . . . . . . . . 231
Cerebral White Matter . . . . . . . . . . . . . . . . . . . . 235
Projection Fibers . . . . . . . . . . . . . . . . . . . . . . . . . . 235

10

Association Fibers . . . . . . . . . . . . . . . . . . . . . . . . . 236
Com m issu ral Fibers . . . . . . . . . . . . . . . . . . . . . . . 238

Functio nal Lo calizatio n in the Cerebral
Co rte x . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Prim ary Cortical Fields . . . . . . . . . . . . . . . . . . . .
Association Areas . . . . . . . . . . . . . . . . . . . . . . . . .
Fron tal Lobe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
High er Cortical Fu n ction s an d Th eir
Im pairm en t by Cortical Lesion s . . . . . . . . . . . .

Coverings of the Brain and Spinal Cord;
Cerebrospinal Fluid and Ventricular System

Co ve rings o f the Brain and Spinal Co rd . . .

Du ra Mater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Arach n oid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pia Mater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

260
260
262
262

226

...............................

Cerebro spinal Fluid and Ventricular
System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stru ctu re of th e Ven tricu lar System . . . . . . . .
Cerebrospin al Flu id Circu lation an d
Resorp tion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Distu rban ces of Cerebrosp in al Flu id
Circu lation —Hydroceph alu s . . . . . . . . . . . . . . . .

238
239
247

248
248

260

263
263
263
266


Contents · IX

11

Blood Supply and Vascular Disorders
of the Central Nervous System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Arteries o f the Brain . . . . . . . . . . . . . . . . . . . . . .
Extradu ral Course of th e Arteries of th e
Brain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Arteries of th e An terior an d Middle Cran ial
Fossae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Arteries of th e Posterior Fossa . . . . . . . . . . . . .

Collateral Circu lation in th e Brain . . . . . . . . . .

270
270
273
275
278

Veins o f the Brain . . . . . . . . . . . . . . . . . . . . . . . . 279
Su perficial an d Deep Vein s of th e Brain . . . . . 279
Du ral Sin u ses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280
Blo o d Supply o f the Spinal Co rd . . . . . . . . . . 281

Arterial An astom otic Netw ork . . . . . . . . . . . . . 281
Ven ous Drain age . . . . . . . . . . . . . . . . . . . . . . . . . . 283

Further Reading
Index

270

Cerebral Ische m ia . . . . . . . . . . . . . . . . . . . . . . . .
Arterial Hypoperfusion . . . . . . . . . . . . . . . . . . . .
Particular Cerebrovascular Syn drom es . . . . . .
Im paired Ven ou s Drain age from th e Brain . .

283
283
295
302

Intracranial Hem o rrhage . . . . . . . . . . . . . . . . .
In tracerebral Hem orrh age (Non trau m atic) . .
Su barach n oid Hem orrh age . . . . . . . . . . . . . . . . .
Su bdu ral an d Ep id u ral Hem atom a . . . . . . . . . .

305

305
307
311

Vascular Syndro m es o f the Spinal Co rd . . .
Arterial Hypoperfusion . . . . . . . . . . . . . . . . . . . .
Im paired Ven ou s Drain age . . . . . . . . . . . . . . . . .
Sp in al Cord Hem orrh age an d Hem atom a . . .

312
312
312

314

.......................................................................

315

.....................................................................................

319


X · Contents

Abbreviations
5-HT3
ACA
ACTH
ADH
AIDS
AMPA
ARAS
Asp
BAEP
BPPV

CA
CCA
CNS
CRF
CSF
CT
DREZ
ECA
ECG
EEG
EMG
EPSP

FLAIR
fMRI
FSH
GABA
GH (STH)
GHRH
Glu
Gn RH
Gpe
GPi
HIV
HMSN

Hz
ICA
INO
IP
IPSP
LH

seroton in
an terior cerebral artery
adren ocorticotrop ic h orm on e (corticotropin )
an tidiu retic h orm on e
acqu ired im m u n odeficien cy syn drom e

α-am in o-3-hydroxy-5-m ethyl-4-isoxazolepropion ate acid
ascen din g ret icu lar act ivatin g system
aspartate
brain stem au ditory evoked poten tials
ben ign paroxysm al p osition in g
vertigo
corn u am m on is
com m on carotid artery
cen tral n ervou s system
corticotropin -releasin g factor
cerebrospin al flu id
com p uted tom ography

dorsal root en try zon e (also called t h e
Redlich –Oberstein er zon e)
extern al carotid artery
electrocardiography/electrocardiogram
electroen ceph alography/elect roen ceph alogram
electrom yography/electrom yogram
excitatory postsyn aptic poten tial
flu id-at ten uated inversion recovery
fu n ction al m agn etic reson an ce
im agin g
follicle-stim u latin g h orm on e
γ-am in obu tyric acid

grow t h h orm on e (som atot ropic
h orm on e)
grow th -h orm on e-releasin g h orm on e
glutam ate
gon adotrop in -releasin g h orm on e
globu s pallidu s
globu s pallidu s, in tern al segm en t
h u m an im m u n odeficien cy viru s
h ereditary m otor an d sen sory polyn eu ropathy
Hertz
in tern al carotid artery
in tern uclear oph th alm oplegia

in terph alan geal
in h ibitory postsyn aptic poten tial
luten in izin g h orm on e

LPH
LTM
MCA
MD
MEG
MIF
m .l.
MLF

MP
MRF
MRI
MSH
NMDA
PCA
PET
PICA
PIF
PPRF
PRF
PRL

Py
rCBF
r.n .
rtPA
SCD
SNg
sp .-th .
SRIF
STM
STN
T3
T4

Th
TRH
TSH
VA
VEP
VI
VL
VOR
VPL
VPM

lipotropin

lon g-term m em ory
m iddle cerebral artery
m edial dorsal n u cleu s of th e th alam u s
m agn etoen ceph alography
m elan ocyte-stim u latin g h orm on ein h ibitin g factor
m edial lem n iscu s
m edial lon gitu din al fasciculu s
m etacarp oph alan geal
m elan ocyte-stim u latin g h orm on ereleasin g factor
m agn etic reson an ce im gin g
m elan ocyte-stim u latin g h orm on e
N-m ethyl- D-aspartate

posterior cerebral artery
posit ron em ission tom ography
posterior in ferior cerebellar artery
prolactin -in h ibitin g factor
(= dop am in e)
param edian pon tin e reticular form ation
prolactin -releasin g factor
prolactin
pyram idal tract
region al cerebral blood flow
red n ucleus
recom bin an t tissue plasm in ogen activator

subacu te com bin ed degen eration
su bstan tia nigra
spin oth alm ic tract
som atotropin in h ibit in g factor
sh ort-term m em ory
subt h alm ic n u cleu s
triiodothyron in e
tetraiodothyron in e (thyroxin e)
th alam u s
thyrotropin -releasin g h orm on e
thyroid-stim u latin g h orm on e
ven tral an terior n u cleus

visual evoked poten tials
ven tral in term ediate n ucleu s
ven tral lateral n u cleus
vestibulo-ocular reflex
ven tral posterolateral n ucleu s of th e
th alam u s
ven tral p osterom edial n u cleus of th e
th alam u s


1

1 Elements of the
Nervous System
Information Flow in the
Nervous System . . . . . . . . . . . . . . . . . .

2

Neurons and Synapses . . . . . . . . . . . . .

2

Neurotransmitters and Receptors . . . .

7

Functional Groups of Neurons . . . . . . .

7

Glial Cells . . . . . . . . . . . . . . . . . . . . . . . .

7

Development of the Nervous

System . . . . . . . . . . . . . . . . . . . . . . . . . .

8


1

2

1

Elements of the Nervous System

Th e n ervous system is com posed of cells, called
neurons, th at are sp ecialized for in form ation p rocessin g an d tran sm ission . Neuron s m ake con tact
w ith each oth er at ju n ction s called synapses, at
w h ich in form ation is tran sferred from on e n eu ron
to th e n ext by m ean s of ch em ical m essen ger

Information Flow in the Nervous
System
In form ation flow in th e n ervous system can be
broken dow n sch em atically in to th ree steps
(Fig. 1.1): an extern al or in tern al stim u lus im pin gin g on th e sen se organ s in duces th e gen eration of

n erve im pu lses th at travel tow ard th e cen tral
n ervou s system (CNS) (afferent impulses); com plex processin g occu rs w ith in th e CNS (information processing); an d, as th e product of th is processin g, th e CNS gen erates im pu lses th at travel
tow ard th e periph ery (efferent impulses) an d effect th e (m otor) resp on se of t h e organ ism to th e
stim u lus. Th u s, w h en a pedestrian sees a green
traffic ligh t, afferen t im pu lses are gen erated in th e
opt ic n erves an d visual system th at convey in form ation about th e sp ecific color p resen t. Th en , at
h igh er levels in th e CNS, th e stim ulu s is in terpreted
an d assign ed a m ean in g (green ligh t = go). Efferen t
im pu lses to th e legs th en effect th e m otor respon se
(crossin g th e street).
In th e sim plest case, in form ation can be tran sferred directly from th e afferen t to th e efferen t

CNS
processing

Afferent impulses
from receptors
at the body surface
or in the internal organs

Efferent impulses,
e.g., to the skeletal
m uscles

Fig. 1.1 Basic organization of information processing in
the nervous system

su bstan ces called neurotransmitters. In gen eral,
n eu ron s can be divided in to tw o classes: excitatory an d inhibitory. Th e organ ization of t h e
n ervou s system is easier to un derstan d after a
brief con sideration of its (on togen etic) developm en t.

arm , w ith ou t any in terven in g com p lex processin g
in th e CNS; th is is w h at h appen s, for exam ple, in an
in trin sic m u scle reflex su ch as th e kn ee-jerk
(patellar) reflex.

Neurons and Synapses
Neurons
Th e neurons an d th eir processes (see below ) an d
th e synapses (see p. 4) are respon sible for th e flow
of in form ation in th e n ervous system . At th e syn apses, in form ation is t ran sferred from on e n eu ron
to th e n ext by m ean s of ch em ical su bstan ces called
n eu rotran sm itters.
Dendrites and axons. Neuron s tran sfer in form ation
in on e direction on ly becau se th ey are bipolar: th ey
receive in form at ion from ot h er n eu ron s at on e en d,
an d tran sm it in form ation to ot h er n euron s at th e

oth er en d.
Th e receptive structures of a n erve cell, called
dendrites, are bran ch ed processes attach ed to th e
cell body. Neuron s vary con siderably w ith regard
to th e n um ber an d bran ch in g pattern of th eir den drites. Th e forw ard conducting structure is th e
axon, w h ich in h u m an s can be up to a m eter in
len gth . In con trast to th e variable n um ber of den drites, each n eu ron p ossesses on ly a single axon . At
its distal en d, th e axon splits in to a n um ber of term in al bran ch es, each of w h ich en ds in a so-called
term in al bouton th at m akes con tact w ith th e n ext
n eu ron (Fig. 1.2).
Th e lon g periph eral p rocesses of th e pseudoun ipolar n euron s of t h e spin al gan glia are an im portan t special case. Th ese are th e fibers th at relay
in form ation regardin g touch , pain , an d tem peratu re from th e body surface to th e CNS. Alth ou gh

Neurons and Synapses · 3

th ey are receptive structu res, th ey n on eth eless
possess t h e structu ral ch aracteristics of axon s an d
are design ated as such .
Th e troph ic (n ut ritive) cen ter of th e n eu ron is its
cell body (soma or perikaryon), w h ich con tain s th e
cell n ucleu s an d various differen t types of su bcellular organ elles.

Dendrites

Barr
body

Nucleolus

Perikaryon

Nucleus

Axonal transport. Th e n eu rotran sm itters, or th e
en zym es catalyzin g th eir biosyn th esis, are syn th esized in th e perikaryon an d th en carried dow n

axon al m icrot ubu les to th e en d of th e axon in a
process kn ow n as axoplasm ic tran sport . Th e n eurotran sm it ter m olecu les are stored in syn aptic
vesicles in side th e term in al bou ton s (each bou ton
con tain s m any syn aptic vesicles). Axoplasm ic
tran sport, gen erally speakin g, can be in eith er
direct ion —from th e cell body tow ard th e en d of
th e axon (anterograde transport), or in th e
reverse direction (retrograde transport). Rapid
axoplasm ic tran sport proceeds at a speed of 20 0–
40 0 m m /day. Th is is distin ct from axoplasm ic
flow, w h ose sp eed is 1–5 m m /day. Axoplasm ic
tran sport is exploited in th e research laboratory

by an terograde an d retrograde tracer tech n iques
for th e an atom ical dem on st ration of n eu ral projection s (Fig. 1.3).
Axon myelination. Axon s are surroun ded by a
sh eath of m yelin (Fig. 1.4). Th e m yelin sh eath ,
w h ich is form ed by oligodendrocytes (a special
class of glial cells) in th e cen tral n ervou s system
an d by Schw ann cells in th e periph eral n ervou s
system , is a sh eet like con tin u ation of th e oligoden drocyte or Sch w an n cell m em bran e th at w rap s itself arou n d th e axon m u ltip le t im es, providin g
electrical in sulation . Many oligoden drocytes or
Sch w an n cells form th e m yelin surroun din g a
sin gle axon . Th e segm en ts of m yelin sh eath form ed
by tw o adjacen t cells are sep arated by an area of

un covered axon al m em bran e called a node of Ranvier. Becau se of th e in su latin g p roperty of m yelin ,
an action poten tial cau ses depolarization on ly at
th e n odes of Ranvier; th u s, n eu ral excitation ju m ps
from on e n ode of Ranvier to th e n ext, a process
kn ow n as saltatory conduction. It follow s th at
n eu ral con du ction is fastest in n euron s th at h ave
th ick in su latin g m yelin w ith n odes of Ranvier
sp aced w idely apart. On t h e ot h er h an d, in axon s
th at lack a m yelin coverin g, excitation m u st travel
relatively slow ly dow n t h e en tire axon al m em -

Axon hillock

Axon (neurite)
Myelin sheath

Collateral axon

Collateral axon

Axon ending (term inal)
with term inal bouton

Fig. 1.2 Structure of a neuron (schem atic drawing).
From : Kahle W and Frotscher M: Color Atlas of Hum an Anatomy, Vol. 3, 6th ed., Thiem e, Stuttgart, 2010.

bran e. Betw een th ese tw o extrem es t h ere are
axon s w ith m yelin of in term ediate t h ickn ess. Th u s,
axon s are divided in to thickly myelinated, thinly
myelinated, an d unmyelinated axons (n erve
fibers); th ese classes are also design ated by th e letters A, B, an d C. Th e th ickly m yelin ated A fibers are
of 3–20 µm diam eter an d con du ct at speeds u p to
120 m /s. Th e th in ly m yelin ated B fibers are up to
3 µm t h ick an d con duct at speeds up to 15 m /s. Th e

1

1

4 · 1 Elem ents of the Nervous System

1

6
5

3
2

7

4

Fig. 1.4 Nerve fiber in the central nervous system, w ith
oligodendrocyte and myelin sheath (schem atic drawing).
1, Oligodendrocyte. 2, Axon. 3, Myelin sheath. 4, Node of
Ranvier. 5, Inner m esaxon. 6, Outer m esaxon. 7, Pockets of
cytoplasm . From : Kahle W and Frotscher M: Color Atlas of
Hum an Anatomy, Vol. 3, 6th ed., Thiem e, Stuttgart, 2010.

Fig. 1.3 Tracing of neuronal projections w ith retrograde and anterograde tracer substances. Tracer substances, such as fluorescent dyes, are injected either at the
site of origin or at the destination of the neuronal pathway
in question. The tracer substances are then transported
along the neurons, either from the cell bodies to the axon
term inals (anterograde transport) or in the reverse direction (retrograde transport). It is thus possible to trace the
entire projection from one end to the other.
a Retrograde transport.
b Retrograde transport from m ultiple projection areas of a
single neuron.
c Anterograde transport from a single cell body into m ultiple projection areas.
From : Kahle W and Frotscher M: Color Atlas of Hum an Anatomy, vol. 3, 6th ed., Thiem e, Stuttgart, 2010.

un m yelin ated C fibers con du ct n o faster th an
2 m /s.

Synapses
General structure. As late as th e 1950s, it w as st ill
un clear w h eth er n eu ron s w ere con n ected to each
oth er in a con tin uou s n etw ork (syn cytium ), w h ich
w ould th eoretically allow rapid electrical com m u n ication betw een n euron s, or w h eth er each
n eu ron w as en tirely en closed in its ow n m em bran e. Su bsequ en t visualization of syn ap ses u n der
th e electron m icroscope settled th e qu estion : th ere
is n o direct spatial con tin u ity betw een n euron s.
Th e axon en ds on on e side of th e syn apse, an d

n eu ral im pu lses are conveyed across it by special
tran sm itter substan ces (Fig. 1.5). Th e axon term in al
(bou ton ) is th e presynaptic part of th e syn apse, an d
th e m em bran e of th e cell receivin g th e tran sm itted
in form ation is th e postsynaptic part . Th e p resyn aptic an d postsyn aptic m em bran es are separated


Neurons and Synapses · 5

by th e syn aptic cleft. Th e bouton con tain s vesicles
filled w ith th e n eu rotran sm itter subst an ce.
Exam in ation of syn apses u n der th e electron m icroscope reveals specialized, osm ioph ilic th icken in gs of th e presyn aptic an d p ostsyn aptic m em bran es, w h ich are m ore pron ou n ced on t h e postsyn aptic side in so-called asymmetrical synapses,

an d are app roxim ately equally th ick on bot h sides
in so-called symmetrical synapses. Th ese tw o
types of syn apse are also kn ow n , after th eir origin al describer, as Gray type I an d Gray type II synapses, respect ively. Asym m etrical syn apses w ere
fou n d to be excitatory an d sym m etrical syn ap ses
to be in h ibitory (see below for th e con cepts of excitation an d in h ibition ). Th is hypoth esis w as later
con firm ed by im m u n ocytoch em ical stu dies usin g
an tibodies directed again st n eurotran sm itter su bstan ces an d th e en zym es involved in th eir biosyn th esis.
Synaptic transmission (Fig. 1.6) is essen tially a
sequen ce of th ree differen t processes:
¼ Th e excitatory im pu lse (action potential) arrivin g at th e axon term in al depolarizes th e presyn aptic m em bran e, cau sin g voltage-depen den t
calciu m ch an n els to open . As a result, calciu m
ion s flow in to th e term in al bouton an d th en in teract w ith variou s protein s to cau se fusion of

syn aptic vesicles w ith th e p resyn aptic m em bran e. Th e n eu rotran sm it ter m olecu les w it h in
th e vesicles are th ereby released in to th e syn aptic cleft.
¼ Th e n eu rot ran sm itter m olecu les diffu se across
th e syn aptic cleft an d bin d to specific receptors
on t h e postsyn aptic m em bran e.
¼ Th e bin din g of n eurotran sm itter m olecules to
receptors causes ion ch an n els to open , in du cin g
ion ic curren ts th at cau se eith er a depolarization
or a hyperp olarization of th e postsyn aptic
m em bran e—i.e., eith er an excitatory postsynaptic potential (EPSP) or an inhibitory postsynaptic
potential (IPSP). Th u s, syn aptic tran sm ission result s in eit h er an excit ation or an in h ibition of
th e postsyn aptic n eu ron .

In addition to th ese fast-actin g tran sm itter-gated
or ligand-gated ion channels, th ere are also G-protein-coupled receptors th at gen erate a m u ch slow er
respon se by m ean s of an in tracellu lar sign al cascade.

7

6

4

5

1

2
3

Fig. 1.5 Synaptic structure (schem atic drawing). 1, Presynaptic m em brane with gridlike thickening, leaving hexagonal spaces in between. 2, Synaptic cleft. 3, Postsynaptic
m em brane. 4, Synaptic vesicle. 5, Fusion of a synaptic vesicle with the presynaptic m em brane (so-called Ω [om ega]
figure), with release of the neurotransm itter (green) into
the synaptic cleft. 6, Vesicle with neurotransm itter
m olecules taken back up into the term inal bouton. 7, Axon
filam ents. From : Kahle W and Frotscher M: Color Atlas of
Hum an Anatomy, Vol. 3, 6th ed., Thiem e, Stuttgart, 2010.

1
4

5
K+
Na +

4
K+
Mg 2+
Ca 2+

Glutamate

Na +

2
3

Fig. 1.6 Synaptic transmission at a glutamatergic (excitatory) synapse (schem atic drawing). The arriving action
potential induces an influx of Ca 2+ (1), which, in turn, causes
the synaptic vesicles (2) to fuse with the presynaptic m em brane, resulting in the release of neurotransm itter (in this
case, glutam ate) into the synaptic cleft (3). The neurotransm itter m olecules then diffuse across the cleft to the
specific receptors in the postsynaptic m em brane (4) and

bind to them , causing ion channels (5) to open, in this case
Na + channels. The resulting Na + influx, accom panied by a
Ca 2+ influx, causes an excitatory depolarization of the postsynaptic neuron (excitatory postsynaptic potential, EPSP).
This depolarization also rem oves a blockade of the so-called
NMDA receptor by Mg 2+ ions. From : Kahle W and Frotscher
M: Taschenatlas der Anatom ie, vol. 3, 8th ed., Thiem e,
Stuttgart, 2002.

1


1

6 · 1 Elem ents of the Nervous System
Fig. 1.7 Three types of
neuronal inhibition.
a, Recurrent inhibition.
b, Forward inhibition.
c, Disinhibition. From :
Kahle W and Frotscher M:
Taschenatlas der Anatom ie,
vol. 3, 8th ed., Thiem e,
Stuttgart, 2002.

Chemical and electrical synapses. Th e t ype of syn aptic tran sm ission described above, involvin g th e
release an d receptor bin din g of a n eu rot ran sm itter,
is th e typ e m ost com m on ly foun d. Th ere are also
so-called elect rical syn apses in w h ich th e excitation is tran sm itted directly to th e n ext n eu ron
across a gap junction.
Types of synapses. Syn ap ses m ediate th e tran sfer of
in form ation from on e n eu ron to th e n ext; th e syn apses th at brin g in form ation to a particu lar cell are
kn ow n as its input synapses. Most inp ut syn apses
are to be fou n d on a cell’s den drites (axodendritic
synapses). Th e den drites of m any n eu ron s (e.g., cortical pyram idal cells) p ossess th orn like p rocesses,
th e dendritic spines, th at en able th e com partm en talization of syn aptic inpu t. Many spin es con tain a
spine apparatus for th e in tern al storage of calciu m

ion s. Th e syn apses on den dritic spin es are m ain ly
asym m et rical, excit atory syn apses.
Inpu t syn apses are fou n d n ot on ly on th e den drites bu t also on th e cell body itself (perikaryon ;
axosomatic synapses) an d even on th e axon an d its
in itial segm en t, th e axon h illock (axo -axonal synapses).
Convergence and divergence of synaptic connections. In gen eral, each in dividual n eu ron receives
in form ation th rou gh syn ap ses from m any differen t
n eu ron s an d n eu ron types (convergence of in form ation tran sfer). Th e n eu ron can , in tu rn , m ake
syn aptic con tact w it h a large n um ber of oth er n eu -

ron s th rough n u m erou s collateral axon al bran ch es
(divergence of in form at ion tran sfer).

Excitation and inhibition. Th e n ervous system is
con stru cted in su ch a w ay th at each n eu ron can be
in on e of tw o basic states at any m om en t: eith er
th e n eu ron is electrically disch argin g an d tran sm ittin g in form ation via syn apses to oth er n eu ron s,
or else it is silen t. Excitatory inpu t to th e n euron
cau ses it to disch arge, w h ile in h ibitory inpu t
cau ses it to be silen t.
It follow s th at n euron s can be classified as excitatory an d in h ibitory in term s of th eir effect on
th e n eu ron s to w h ich th ey provide inpu t. Excitatory neurons are u su ally prin cip al n euron s (e.g.,
th e pyram idal cells of th e cerebral cortex), w h ich
often project over lon g dist an ces an d t h u s h ave
lon g axon s. Inhibitory neurons, on th e ot h er h an d,

are often in tern eu ron s an d h ave sh ort axon s.
Principles of neuronal inhibition (Fig. 1.7). Collaterals of excitatory cells can act ivate in h ibitory in tern eu ron s, w h ich th en in h ibit th e prin cipal n eu ron
itself (recurrent inhibition, a form of n egative feedback). In forw ard inhibition, collaterals of p rin cipal
n eu ron s activate in h ibitory in tern eu ron s th at th en
in h ibit oth er prin cipal n eu ron s. Wh en an in h ibitory n eu ron in h ibits an oth er in h ibitory n euron , th e
result in g decrease in in h ibition of th e postsyn aptic
p rin cip al cell causes a n et in crease in its activity
(disinhibition).


Glial Cells · 7

Neurotransmitters and
Receptors
Excitatory and inhibitory neurotransmitters. In
classic n eu roan atom ical stu dies, n euron s w ere
divided in to tw o m ajor types on th e basis of th eir
sh ape an d th e len gt h of th eir project ion s: prin cipal
n eu ron s w it h distan t projection s w ere called Golgi
type I n eu ron s, w h ile in tern eu ron s w ith sh ort
axon s w ere called Golgi type II n euron s. Curren tly,
n eu ron s are u su ally classified accordin g to th eir
neurotransm itter phenotype, w h ich gen erally determ in es w h eth er th ey are excitatory or in h ibitory.
Th e com m on est excitatory n eu rotran sm itter in t h e

CNS is glutamate, w h ile th e com m on est in h ibitory
n eu rotran sm itter is γ-aminobutyric acid (GABA).
Th e in h ibitory n eu rotran sm itter in th e sp in al cord
is glycine. Acetylcholine an d norepinephrine are
th e m ost im portan t n eu rotran sm itters in th e au ton om ic n ervous system bu t are also fou n d in th e
CNS. Oth er im portan t n eu rotran sm itters in clu de
dopamine, serotonin, an d variou s neuropeptides,
m any of w h ich h ave been (an d con tin u e to be)
iden tified; th ese are fou n d m ain ly in in tern eu ron s.
Ligand-gated receptors. Ligan d-gated ion ch an n els
are con stru cted of m u ltiple su bun its th at span th e
cell m em bran e. Th e bin din g of n eu rotran sm itter to

th e receptor op en s th e ion ch an n el (i.e., m akes it
perm eable) for on e or m ore particular sp ecies of
ion .

Excitatory am ino acid receptors. Glu tam ate receptors are subdivided in to th ree types called AMPA,
NMDA, an d kainate receptors. Glutam ate bin din g to
an AMPA receptor resu lts in an in flu x of Na + ion s,
w h ich dep olarizes th e cell. Th e activation of an
NMDA receptor also cau ses an Na + in flux, accom pan ied by a Ca 2+ in flux. Th e NMDA receptor,
h ow ever, can be activated on ly after th e blockade
of it s ion ch an n el by a m agn esiu m ion is rem oved;
th is, in turn , is accom plish ed th rou gh an AMPAreceptor-in du ced

m em bran e
depolarization
(Fig. 1.6). Th e excitatory n eurotran sm itter glu tam ate th us h as a graded effect: it activates AMPA receptors first an d NMDA receptors later, after th e
m em bran e h as been depolarized.

Inhibitory GABA and glycine receptors. Th e activation of eit h er of th ese tw o types of receptor causes

an in flu x of n egat ively ch arged ch loride ion s, an d
th us a hyperpolarization of th e postsyn aptic cell.
Oth er types of ligan d-gated ion ch an n el in clu de
th e nicotinic acetylcholine receptor an d th e seroton in (5-HT3 ) receptor.
G-protein-coupled receptors. Th e respon se to a

st im u lus actin g th rough a G-protein -cou pled receptor lasts con siderably lon ger, as it results from
th e activation of an in tracellu lar sign al cascade. Th e
respon se m ay con sist of ch an ges in ion ch an n els or
in gen e exp ression . Exam ples of G-protein -cou pled
receptors in clude m uscarin ic acetylch olin e receptors an d m etabotropic glu tam ate receptors.

Functional Groups of Neurons
As discussed earlier, n euron s are cu rren t ly
classified accordin g to th e n eu rotran sm itters th at
th ey release. Th u s, on e speaks of th e glutam atergic,
GABAergic, cholinergic, an d dopam inergic system s,
am on g oth ers. Th ese system s h ave distin ct properties. Glu tam atergic n eu ron s m ake poin t-to-p oin t

con n ection s w ith th eir target cells, w h ile th e
dopam in ergic system , for exam ple, h as rath er m ore
diffu se con n ection s: a sin gle dopam in ergic n eu ron
gen erally projects to a large n u m ber of target n eu ron s. Th e con n ection s of th e GABAergic system are
particu larly h igh ly specialized. Som e GABAergic
n eu ron s (basket cells) m ake n um erous syn aptic
con n ection s on to th e cell body of th e postsyn aptic
n eu ron , form in g a basketlike stru ctu re arou n d it;
oth ers form m ain ly axoden dritic or axo-axon al
syn apses. Th e latter are fou n d at th e axon h illock.

Neurotransm itter analogues or receptor blockers can

be applied pharm acologically for th e specific en h an cem en t or w eaken in g of th e effects of a particular n eu rotran sm itter on n euron s.

Glial Cells
Th e n u m erically m ost com m on cells in th e n ervou s
system are, in fact, n ot th e n eu ron s, bu t th e glial
cells (also called glia or n eu roglia). Th ese cells play
an in dispen sable su pportive role for th e fun ction of
n eu ron s. Th e th ree typ es of glial cells in th e CNS

1

1

8 · 1 Elem ents of the Nervous System

are t h e astroglial cells (astrocytes), oligoden droglia
(oligoden drocytes), an d m icroglial cells.
Astrocytes are divided in to tw o types: p rotoplasm ic an d fibrillary. In th e in tact n ervou s system ,
astrocytes are respon sible for th e m ain ten an ce of
th e in tern al environ m en t (h om eostasis), particularly w ith respect to ion con cen tration s. Fin e astrocyte processes su rrou n d each syn apse, sealin g it off
from its su rroun din gs so th at th e n eu rotran sm it ter
can n ot escap e from th e syn aptic cleft. Wh en th e
cen tral n ervous system is in ju red, astrocytes are

respon sible for th e form ation of scar tissu e (gliosis).
Th e oligodendrocytes form th e m yelin sh eat h s
of th e CNS (see p. 7). Th e microglial cells are ph agocytes th at are activated in in flam m atory an d
degen erative p rocesses affectin g th e n ervou s system .

Development of the Nervous
System
A detailed discu ssion of th e develop m en t of th e
n ervou s system w ou ld be beyon d th e scope of th is
book an d n ot direct ly relevan t to its pu rpose. Th e
physician sh ou ld u n derstan d som e of th e basic
prin ciples of n eu ral developm en t, h ow ever, as

develop m en tal dist urban ces accou n t for a large
n u m ber of diseases affectin g th e n ervou s system .
Th e n ervou s system develops from th e (in itially)
lon git udin ally orien ted neural tube, w h ich con sists
of a solid w all an d a cen tral flu id-filled cavity. Th e
cran ial portion of th e n eural tube grow s m ore exten sively th an th e rest to form three distinct brain
vesicles, th e rhom bencephalon (h in dbrain ), th e
m esencephalon (m idbrain ), an d th e prosencephalon
(forebrain ). Th e prosen ceph alon , in tu rn , becom es
fu rth er differen tiated in to a cau dal part, th e diencephalon, an d th e m ost cran ial portion of th e en tire
n eu ral tube, th e paired telencephalon (en dbrain ).
Th e cen tral cavit y of th e tw o telen ceph alic ven tricles com m u n icates w ith th at of th e dien ceph alon th rou gh th e in terven tricular foram en

(destin ed to becom e th e foram en of Mon ro). Th e
cen tral cavity u n dergoes its greatest en largem en t
in th e areas w h ere th e n eu ral tu be h as its m ost
pron oun ced grow th ; th u s, th e lateral ven t ricles
form in th e t w o h alves of th e telen ceph alon , th e
th ird ven tricle w ith in th e dien ceph alon , an d th e

fou rth ven tricle in th e brain stem . In th ose segm en ts of th e n eu ral tu be th at grow to a relatively
lesser exten t, su ch as th e m esen ceph alon , n o ven tricle is form ed (in th e fu lly develop ed organ ism ,
th e cerebral aqu edu ct ru n s th rou gh th e m esen ceph alon ).
Over th e course of vertebrate phylogeny, progressive en largem en t of th e telen ceph alon h as
cau sed it to overlie th e brain stem an d to rotate

back on itself in sem icircular fash ion . Th is rotation
is reflected in th e stru ctu re of variou s com pon en ts
of th e telen ceph alic gray m atter, in cludin g th e cau date n u cleus an d h ippocam pu s; in th e cou rse of
certain w h ite m atter tracts, such as th e forn ix; an d
in th e sh ape of th e lateral ven tricles, each of w h ich
is com p osed of a fron tal h orn , a cen tral portion
(atriu m ), an d a tem poral h orn , as sh ow n in
Fig. 10.3, p . 262.
Cellular proliferation. Im m ature n euron s (n eu roblasts) proliferate in th e ven tricu lar zon e of th e
n eu ral tu be, i.e., th e zon e n eigh borin g its cen tral
cavity. It is a m ajor aim of cu rren t research in n eu roem bryology to u nveil th e m olecular m ech an ism s
con trollin g n eu ron al proliferation .

Neuronal migration. New ly form ed n erve cells
leave th e ven tricu lar zon e in w h ich th ey arise, m igratin g alon g radially orien ted glial fibers tow ard
th eir defin itive location in th e cortical plate. Migratory processes are described in greater detail on
pp. 227 ff.
Grow th of cellular processes. On ce th ey h ave arrived at th eir destin ation s, th e postm igratory n euroblasts begin to form den drites an d axon s. On e of
th e m ajor qu estion s in n eu robiology today is h ow
th e n ew ly sprou ted axon s fin d th eir w ay to th eir
correct targets over w h at are, in som e cases, very
lon g distan ces. Im portan t roles are p layed in th is
process by m em bran e-bou n d an d soluble factors
th at are presen t in a con cen tration gradien t, as
w ell as by extracellular m atrix protein s. Th ere are

ligan d–receptor system s th at exert both attractive
an d repulsive in flu en ces to steer th e axon in to th e
appropriate target area. Th ese system s can n ot be
described in greater detail h ere.
Synaptogenesis. Th e axon term in als, h avin g fou n d
th eir w ay to th eir targets, proceed to form syn aptic
con tacts. Recen t stu dies h ave sh ow n th at th e for-


Developm ent of the Nervous System · 9

m ation of syn apses, an d of den dritic spin es, is activity-depen den t. Mu ch eviden ce su ggests th at

n ew syn apses can be laid dow n th rou gh ou t th e
lifespan of th e in dividu al, providin g th e basis of
adaptive processes su ch as learn in g an d m em ory.

Physiological neuronal death (program m ed cell
death , apoptosis). Many n eu ron s die as th e CNS
develop s, presu m ably as p art of th e m ech an ism
en ablin g th e precise an d specific form ation of in tern euron al con n ection s. Th e regu lation of n euron al su rvival an d n eu ron al death is a m ajor topic
of cu rren t research .

1

1

10 · 1 Elem ents of the Nervous System


2

2 Somatosensory
System
Peripheral Components of the
Somatosensory System and

Peripheral Regulatory Circuits . . . . . . .

12

Central Components of the
Somatosensory System . . . . . . . . . . . .

24

Central Processing of Somatosensory
Information . . . . . . . . . . . . . . . . . . . . . .

32

Somatosensory Deficits due
to Lesions at Specific Sites along
the Somatosensory Pathw ays . . . . . . .

32


2

12

2

Somatosensory System

After a prelim in ary ch apter on t h e stru ctu ral elem en ts of th e n ervou s system , th e discu ssion of its
m ajor fu n ction al com pon en ts an d m ech an ism s
n ow begin s w ith th e perceptual processes m ediated by receptor organs: as depicted earlier in
Figure 1.1, th ese organ s are th e site of origin of in form at ion flow in th e n ervou s system , in accordan ce w ith t h e basic organ izin g prin cip le, perception processin g respon se. Som atosen sory im pulses from th e p eriph ery are con ducted alon g an
afferent nerve fiber to its n eu ron al cell body, w h ich
lies in a dorsal root ganglion (spinal ganglion). Th e
im pu lses are th en con du cted onw ard in to th e

Peripheral Components of the
Somatosensory System and
Peripheral Regulatory Circuits
Receptor Organs
Receptors are specialized sen sory organ s th at register physical an d ch em ical ch an ges in th e extern al
an d in tern al environ m en t of t h e organ ism an d
convert (tran sduce) th em in to th e electrical im pu lses th at are processed by th e n ervou s system .
Th ey are fou n d at th e periph eral en d of afferen t
n erve fibers. Som e receptors in form th e body
abou t ch an ges in th e n earby extern al environ m en t
(exteroceptors) or in th e distan t extern al environ m en t (teleceptors, su ch as th e eye an d ear). Proprioceptors, su ch as th e labyrin th of th e in n er ear,

convey in form ation abou t th e p osition an d m ovem en t of th e h ead in space, ten sion in m u scles an d
ten don s, th e position of th e join ts, th e force
n eeded to carry out a particu lar m ovem en t, an d so
on . Fin ally, processes w it h in th e body are reported
on by enteroceptors, also called visceroceptors (in clu din g osmoceptors, chemoceptors, an d baroceptors, am on g oth ers). Each type of receptor respon ds to a stim u lus of th e appropriate, sp ecific
kin d, p rovided th at th e in ten sity of th e stim ulu s is
above th resh old.
Sen sory receptor organ s are abu n dan t ly p resen t
in th e skin bu t are also fou n d in deeper region s of
th e body an d in th e viscera.

central nervous system, w ith ou t any in terven in g

syn apses, alon g t h e cen tral process (axon ) of th e
sam e n eu ron . Th is axon m akes syn aptic con tact
w ith a second neuron in th e spin al cord or brain stem , w h ose axon , in tu rn , proceeds fu rth er cen trally, an d crosses the midline to th e opposite side
at som e level alon g its path . Th e third neuron lies
in th e thalamus, th e so-called “gatew ay to con sciousn ess”; it projects to variou s cortical areas,
m ost im portan tly th e prim ary som atosen sory
cortex, w h ich is located in th e postcentral gyrus of
th e parietal lobe.

Receptors in the Skin
Most receptors in th e skin are exteroceptors. Th ese
are divided in to t w o classes: (1) free n erve en din gs

an d (2) en capsu lated en d organ s.
Th e en cap su lated, differen tiated en d organ s are
probably m ain ly respon sible for th e m ediation of
epicrit ic sen sory m odalities su ch as fin e touch , discrim in ation , vibration , p ressu re, an d so forth ,
w h ile th e free n erve en din gs m ediate protopath ic
m odalities such as pain an d tem p eratu re. Th e eviden ce for th is fu n ction al distin ction is in com plete,
h ow ever (see below ).
Various receptor organ s of th e skin an d its appen dages are depicted in Figu re 2.1, in clu din g
mechanoreceptors (for tou ch an d p ressu re), thermoreceptors (for w arm an d cold), an d nociceptors
(for pain ). Th ese receptors are located m ain ly in
th e zon e betw een th e ep iderm is an d th e con n ective tissue. Th e skin can th us be regarded as a
sen sory organ th at covers th e en tire body.

Special receptor organs. Th e peritrichial nerve
endings aroun d t h e h air follicles are fou n d in all
areas of h air-bearin g skin an d are activated by th e
m ovem en t of h airs. In con trast, th e tactile corpuscles of Meissner are foun d on ly on glabrou s
skin , particu larly on th e palm s an d soles bu t also
on th e lips, th e tip of th e ton gue, an d th e gen it als,
an d respon d best to tou ch an d ligh t pressu re. Th e
laminated Vater–Pacini corpuscles (pacin ian corpu scles) are foun d in deep er layers of th e skin ,
especially in th e area betw een th e cut is an d th e
subcu tis, an d m ediate pressu re sen sation s. Th e end

Peripheral Com ponents of the Som atosensory System and Peripheral Regulatory Circuits · 13

bulbs of Krause w ere on ce th ou gh t to be cold receptors, w h ile th e corpuscles of Ruffini w ere
th ough t to be w arm receptors, but th ere is som e
dou bt abou t th is at presen t. Free n erve en din gs
h ave been foun d to be able to tran sm it in form ation
abou t w arm th an d cold as w ell as about posit ion .
In th e corn ea, for exam ple, on ly free n erve en din gs
are presen t to tran sm it in form ation abou t all of
th ese sen sory m odalities. Aside from th e receptor
types specifically m en tion ed h ere, t h ere are also
m any oth ers in th e skin an d elsew h ere w h ose

fu n ction m ostly rem ain s u n clear.
Free nerve endings (Fig. 2.1) are fou n d in th e clefts
betw een epiderm al cells, an d som et im es also on
m ore specialized cells of n eu ral origin , su ch as th e
tactile disks of Merkel. Free n erve en din gs are p resen t, h ow ever, n ot just in th e skin but in pract ically
all organ s of th e body, from w h ich th ey convey
n ociceptive an d th erm al in form ation relatin g to
cellular in jury. Merkel’s disks are m ain ly located in
th e pads of th e fin gers an d respon d to tou ch an d
ligh t p ressu re.

Receptors in Deeper Regions of the Body

A secon d grou p of receptor organ s lies deep to th e
skin , in th e m u scles, ten don s, fasciae, an d join ts
(Fig. 2.2). In th e m u scles, for exam ple, on e fin ds
m uscle sp in dles, w h ich respon d to stretch in g of
th e m u sculature. Oth er types of receptors are
fou n d at th e t ran sit ion betw een m uscles an d ten don s, in th e fasciae, or in join t capsules.
Muscle spindles are very th in , spin dle-sh aped bodies th at are en closed in a con n ective-tissue capsule an d lie bet w een th e striated fibers of th e
skelet al m uscu latu re. Each m u scle sp in dle it self
usu ally con tain s 3–10 fin e striated m uscle fibers,
w h ich are called intrafusal muscle fibers in con trast to th e extrafusal fibers of th e m u scular tissu e
proper. Th e tw o en ds of each spin dle, com posed of
con n ective tissu e, are fixed w ith in th e con n ective

tissu e betw een m uscle fascicles, so th at th ey m ove
in con ju n ction w ith th e m u scle. An afferen t n erve
fiber called an an n ulospiral en din g or prim ary
en din g w in ds arou n d th e m iddle of th e m u scle
spin dle. Th is afferen t fiber h as a very th ick m yelin
sh eath an d belon gs to th e m ost rapidly con du ctin g
grou p of n erve fibers in th e body, th e so-called Ia
fibers. For fu rth er details, see p . 18 ff. (m on osyn aptic in trin sic m u scle reflex; polysyn aptic reflexes).

Fig. 2.1 Somatosensory receptors in the skin. a Free
nerve ending (pain, tem perature). b Tactile disk of Merkel.
c Peritrichial nerve endings around a hair follicle (touch).

d Tactile corpuscle of Meissner. e Vater−Pacini corpuscle
(pressure, vibration). f End bulb of Krause (cold?). g Ruffini
corpuscle (warm th?).

Golgi tendon organs con tain fin e n erve en din gs,
derived from bran ch es of th ickly m yelin ated n erve
fibers, th at su rrou n d a grou p of collagen ou s ten don
fibers. Th ey are en closed in a con n ective-tissue
capsu le, are located at th e ju n ction betw een ten don an d m u scle, an d are con n ected in series to th e
adjacen t m uscle fibers. Like m u scle sp in dles, th ey
respon d to st ret ch (i.e., ten sion ), bu t at a h igh er
th resh old (see Fig. 2.12, p. 22).

Other receptor types. In addition to th e m uscle
sp in dles an d Golgi ten don organ s, receptor types in
th e deep tissu es in clu de th e lam in ated Vater–

2


2

14 · 2 Som atosensory System

Pacin i corpu scles an d th e Golgi–Mazzon i corpuscles as w ell as oth er term in al n erve en din gs

th at m ediate pressure, pain , etc.

Peripheral Nerve, Dorsal Root
Ganglion, Posterior Root
Th e fu rth er “w ay station s” th rou gh w h ich an afferen t im pulse m u st travel as it m akes it s w ay to th e
CNS are th e p eriph eral n erve, th e dorsal root gan glion , an d th e posterior n erve root, th rou gh w h ich
it en ters th e spin al cord.

Fig. 2.2 Receptors in muscle, tendons, and fascia. a Annulospiral ending of a m uscle spindle (stretch). b Golgi tendon organ (tension). c Golgi−Mazzoni corpuscle (pressure).

Blood vessel

Unmyelinated
fibers, mostly
automatic

Fat

Myelinated,
segmented
fibres, m otor
or sensory

Endoneurium

Perineurium
Epineurium

Fig. 2.3

Cross section of a mixed peripheral nerve

Peripheral nerve. Action poten tials arisin g in a receptor organ of on e of th e types described above
are con du cted cen trally alon g an afferen t fiber,
w h ich is th e periph eral process of th e first som atosen sory n eu ron , w h ose cell body is located in a
dorsal root gan glion (see p. 16). Th e afferen t fibers
from a circu m scribed area of th e body run togeth er

in a periph eral n erve; su ch n erves con tain n ot on ly
fibers for su perficial an d deep sen sation (som atic
afferent fibers) bu t also efferen t fibers to striated
m u scle (som atic efferent fibers) an d fibers in n ervat in g th e in tern al organ s, t h e sw eat glan ds, an d
vascu lar sm ooth m u scle (visceral afferent an d
visceral efferent fibers). Fibers (axon s) of all of th ese
types are bu n dled togeth er in side a series of con n ective-tissu e coverin gs (en don eu rium , perin eu riu m , an d epin eu riu m ) to form a “n erve cable”
(Fig. 2.3). Th e perin eu riu m also con tain s th e blood
vessels th at su pply th e n erve (vasa nervorum ).
Nerve plexus and posterior root. On ce th e perip h eral n erve en ters th e spin al can al th rough t h e in tervertebral foram en , th e afferen t an d efferen t
fibers go th eir sep arate w ays: th e periph eral n erve
divides in to its tw o “sources,” th e an terior an d

posterior sp in al roots (Fig. 2.4). Th e an terior root
con tain s th e efferen t n erve fibers exitin g th e spin al
cord, w h ile th e posterior root con tain s th e afferen t
fibers en terin g it. A direct t ran sit ion from th e p eriph eral n erve to t h e spin al n erve roots is foun d,
h ow ever, on ly in th e th oracic region . At cervical
an d lu m bosacral levels, n erve plexu ses are in terposed betw een t h e periph eral n erves an d th e spin al n erve roots (th e cervical, brach ial, lu m bar, an d
sacral plexu ses). In t h ese plexu ses, w h ich are located outside th e spin al can al, th e afferen t fibers of
th e periph eral n erves are redistributed so th at
fibers from each in dividual n erve ultim ately join


Peripheral Com ponents of the Som atosensory System and Peripheral Regulatory Circuits · 15

1

–

C

8

Posterior root

C

Dorsal ram us

T1

T1
T2
T3

T4
T5

T6
2

T7

1

Ventral ramus

–

T

Anterior root

T

1

T8
T9

Fig. 2.4 Nerve root segments and their relationship to the vertebral
bodies. a Anatomy of the

anterior and posterior spinal roots.
b Enum eration of the nerve
root segm ents and the
levels of exit of the spinal
nerves from the spinal
canal. The spinal cord
grows to a shorter final
length than the vertebral
colum n, so that the nerve
roots (proceeding caudally)
m ust travel increasingly
long distances to reach

their exit foram ina. See
also p. 45, Chapter 3
(Motor System ).

T10
T11

S

1

–

S

5

L

1

–

L

5

T12

Coccygeal nn. and
filum term inale

spin al n erves at m u ltip le segm en tal levels
(Fig. 2.5). (In an alogou s fash ion , th e m otor fibers of
a sin gle segm en tal n erve root travel to m u ltiple periph eral n erves; cf. Fig. 2.5 an d p. 62 ff. in Ch apter 3.) Th e redistribu ted afferen t fibers th en en ter
th e spin al cord at m u ltiple levels an d ascen d a variable distan ce in t h e spin al cord before m akin g syn aptic con t act w ith th e secon d sen sory n euron ,

w h ich m ay be at or n ear th e level of th e en terin g af-

feren t fibers or, in som e cases, as h igh as t h e brain stem . Th u s, in gen eral, a perip h eral n erve is com posed of fibers from m ultiple radicular segm en ts;
th is is true of both afferen t an d efferen t fibers.

Digression: Anatom y of the spinal roots and nerves.
In total, th ere are 31 pairs of spin al n erves; each
spin al n erve is form ed by t h e jun ction of an an terior an d a p osterior n erve root w ith in th e spin al

2

2

16 · 2 Som atosensory System

Nerve root (posterior root)
Spinal
cord

Plexus

Peripheral n.

Derm atom e

n erves in each of th ese region s as th ere are vertebrae (12 th oracic, 5 lu m bar, an d 5 sacral) (Fig. 2.4).
Lastly, th ere is a sin gle p air of coccygeal n erves (or,
occasion ally, m ore th an on e p air).

Spatial organization of som atosensory fibers in the
posterior root. Nerve im pu lses relat in g to differen t

a

b

Nerve root
Plexus
Radicular (anterior root)
segments

Peripheral n.
Myotome

Fig. 2.5 Redistribution of afferent and efferent nerve
fibers in a nerve plexus. The sensory fibers contained in a
single peripheral nerve are distributed to m ultiple dorsal

spinal nerve roots, and, analogously, the m otor fibers of a
single nerve root are distributed to m ultiple peripheral
nerves. a In the periphery, the sensory fibers of a single
radicular segm ent are grouped together once again to
supply a characteristic segm ental region of the skin (derm atom e). b Radicular and peripheral nerve innervation of
m uscle: each m uscle is supplied by a single peripheral
nerve, which, however, generally contains fibers from m ultiple nerve roots (so-called polyradicular or plurisegm ental
innervation).

can al. Th e n u m berin g of t h e sp in al n erves is based
on th at of th e vertebral bodies (Fig. 2.4). Even
th ough th ere are on ly seven cervical vertebrae,

th ere are eight pairs of cervical n erves, because th e
h igh est spin al n erve exits (or en ters) th e spin al
can al ju st above th e first cervical vertebra. Th u s,
th is n erve, th e first cervical n erve (C1), exits th e
spin al can al betw een th e occipital bon e an d th e
first cervical vertebra (atlas); th e rem ain in g cervical n erves, dow n to C7, exit above th e corresp on din gly n u m bered vertebra; an d C8 exits betw een
th e seven th (low est) cervical vertebra an d t h e first
th oracic vertebra. At th oracic, lu m bar, an d sacral
levels, each spin al n erve exits (or en ters) th e sp in al
can al below th e correspon din gly n um bered vertebra. Th ere are, th erefore, ju st as m any pairs of

som atosen sory m odalities origin ate in differen t

types of periph eral receptor an d are con du cted
cen trally in sep arate group s of afferen t fibers,
w h ich are spatially arran ged in th e posterior root in
a ch aracteristic pattern . As sh ow n in Figu re 2.15
(p. 25), th e m ost th ickly m yelin ated n erve fibers,
w h ich origin ate in m u scle spin dles, ru n in th e m edial portion of th e root; th ese fibers are respon sible
for proprioception . Fibers origin atin g in receptor
organ s, w h ich m ediate th e sen ses of tou ch , vibration , pressu re, an d discrim in ation , ru n in th e cen tral portion of th e root, an d th e sm all an d th in ly
m yelin ated fibers m ediatin g pain an d tem p eratu re
sen sation run in it s lateral portion .
Dorsal root ganglion. Th e dorsal root gan glion is
m acroscopically visible as a sw ellin g of th e dorsal

root, im m ediately proxim al to it s ju n ction w it h t h e
ven tral root (Fig. 2.4). Th e n eu ron s of th e dorsal root
gan glion are pseu dou n ipolar, i.e., th ey possess a
sin gle process th at divides in to tw o p rocesses a
sh ort distan ce from th e cell, in a T-sh ap ed con figurat ion . On e of th ese tw o processes travels to th e receptor organ s of th e periph ery, givin g off n u m erou s
collateral bran ch es alon g th e w ay, so th at a sin gle
gan glion cell receives inpu t from m u ltip le receptor
organ s. Th e oth er process (th e cen t ral process)
travels by w ay of th e posterior root in to th e spin al
cord, w h ere it eith er m akes syn aptic con tact w ith
th e secon d sen sory n eu ron im m ediately, or else ascen ds tow ard th e brain stem (see Fig. 2.17, p. 27).
Th ere are n o syn apses w ith in th e dorsal root gan glion itself.

Somatosensory Innerva tion by Nerve Roots
and Periphera l Nerves
Th e fibers of in dividual n erve roots are redistributed in to m u ltiple periph eral n erves by w ay of
th e plexu ses (cf. p. 14 ff.), an d each n erve con tain s
fibers from m u ltiple adjacen t radicu lar segm en ts
(see also Figs. 3.31, 3.32, an d 3.33, pp. 63, 64). Th e
fibers of each radicu lar segm en t regrou p in th e periph ery, h ow ever (Fig. 2.5), to in n ervate a particu -