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Snell’s Clinical Neuroanatomy

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Snell’s Clinical Neuroanatomy, Eighth Edition, equips medical and health professions students with a complete, clinically oriented understanding of neuroanatomy. Organized classically by system, this revised edition reflects the latest clinical approaches to neuroanatomy structures and reinforces concepts with enhanced, illustrations, diagnostic images, and surface anatomy photographs.
Each chapter begins with clear objectives and a clinical case for a practical introduction to key concepts. Throughout the text, Clinical Notes highlight important clinical considerations.Chapters end with bulleted key concepts, along with clinical problem solving cases and review questions that test students’ comprehension and ensure preparation for clinical application. 
Enhanced color illustrations, diagrams, and photographs enrich understanding of complex concepts and structures.
New bulleted key concepts in each chapter ensure a focused, clinically relevant understanding of neuroanatomy.
Chapter objectives and clinical cases emphasize the practical applications of chapter content.
Clinical Notes highlight important clinical considerations for quick reference and review.
Clinical Problem Solving and Chapter Review Questions equip students for the clinical challenges they’ll encounter in practice.

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" •Wolters Ktuwer


Richard S. Snell, MRCS, LRCP, MB, MD, PhD

Clinical Anatomy by Regions
Clinical Anatomy by Systems
Clinical Neuroanatomy


Associate Professor, Department of Surgery
Vanderbilt University Medical Center
Office of Health Sciences Education
Vanderbilt University School of Medicine
Nashville, Tennessee
Formerly CQuence Distinguished Professor
Assistant Dean
College of Allied Health Professions
University of Nebraska Medical Center
Omaha, Nebraska

• Wolters Kluwer


• Balt imore • New 'Yor~ ·lo <fon

6l!lrnCJ1 Aire,~ - Hong Kong - S}l'lin4o/ • okyC!l

Senior Acquisitions Editor: Crystal Taylor
Development Editor: Andrea Vosburgh, Kelly Horvath
Editorial Coordinator: John Larkin
Marketing Manager: Michael McMahon
Production Project Manager: Marian Bellus
Design Coordinator: Teresa Mallon
Manufacturing Coordinator: Margie Orzech
Prepress Vendor: Aptara, Inc.
Eighth edition
Copyright© 2019 Wolters Kluwer.
Copyright© 2010, 2006, 2001, 1997, 1992, 1987, 1980 Wolters Kluwer Health/Llppincott Williams
& Wilkins. All rights reserved. This book is protected by copyright. No part of this book may be

reproduced or transmitted In any form or by any means, including as photocopies or scanned-in
or other electronic copies, or utilized by any information storage and retrieval system without
written permission from the copyright owner, except for brief quotations embodied in critical
articles and reviews. Materials appearing in this book prepared by individuals as part of
their official duties as U.S. government employees are not covered by the above-mentioned
copyright. To request permission, please contact Wolters Kluwer at Two Commerce Square,
2001 Market Street, Philadelphia, PA 19103, via email at, or via our
website at (products and services).

9 8 7 6 5 4 3 2 1; 
Printed in China
Library of Congress Cataloging-in-Publication Data
Names: Splittgerber, Ryan, author. I Preceded by (work): Snell, Richard S.
Clinical neuroanatomy.
Title: Snell's clinical neuroanatomy/ Ryan Splittgerber.
Other titles: Clinical neuroanatomy
Description: Eighth edition. I Philadelphia: Wolters Kluwer, [2019]
Preceded by: Clinical neuroanatomy / Richard S. Snell. 7th ed.
Philadelphia: Wolters Kluwer Llppincott Williams & Wilkins, c2010.
Includes Index.
Identifiers: LCCN 2018033967 I ISBN 9781496346759 (paperback)
Subjects: I MESH: Nervous System-anatomy & histology
Classification: LCC QM451 I NLM WL 101 I DDC 616.8-dc23
LC record available at
This work ls provided "as ls," and the publisher disclaims any and all warranties, express
or implied, including any warranties as to accuracy, comprehensiveness, or currency of the
content of this work.
This work is no substitute for individual patient assessment based upon healthcare
professionals' examination of each patient and consideration of, among other things, age,
weight, gender, current or prior medical conditions, medication history, laboratory data
and other factors unique to the patient. The publisher does not provide medical advice or
guidance and this work is merely a reference tool. Healthcare professionals, and not the
publisher, are solely responsible for the use of this work including all medical Judgments and
for any resulting diagnosis and treatments.
Given continuous, rapid advances in medical science and health information, independent
professional verification of medical diagnoses, indications, appropriate pharmaceutical
selections and dosages, and treatment options should be made and healthcare professionals
should consult a variety of sources. When prescribing medication, healthcare professionals
are advised to consult the product information sheet (the manufacturer's package insert)
accompanying each drug to verify, among other things, conditions of use, warnings and side
effects and identify any changes in dosage schedule or contraindications, particularly if the
medication to be administered ls new, Infrequently used or has a narrow therapeutic range.
To the maximum extent permitted under applicable law, no responslblllty ls assumed by
the publisher for any injury and/or damage to persons or property, as a matter of products
liability, negligence law or otherwise, or from any reference to or use by any person of this

The trip has been long and the cost has been high ... but no great thing was
attained easily. A long tale, like a tall Tower, must be built a stone at a time.
-Stephen King
To my wife, Brienne
For providing more love and support than 1deserve.
To my boys, Carter and Caden
For providing inspiration and humor ... a lot of humor.
To my students
May you find your Tower.

• Preface
This book contains the basic neuroanatomlcal facts
necessary for the practice of medicine. It is suitable for
medical students, dental students, nurses, and allied
health students. Residents find this book useful during
their rotations.
The functional organization of the nervous system
has been emphasized and indicates how injury and
disease can result in neurologic deficits. The amount
of faclual Information bu been strictly Dmlted to that
which Is cllnlcally lmportanL
In this editlon, authorship has transitioned from
the late Dr. Richard Snell, who, with brilliance and
dedication, fathered the previous seven editions and
provided the framework for the eighth. The content of
each chapter has been reviewed and edited to be more
straightforward and concise. The traditional artwork
has been recolored and updated to enhance the clarity
and to provide additional information to each image.
High-quality magnetic resonance images and histologic photomicrographs have been updated to provide
greater visual details.
Each chapter Introduces the relevance of neuroanatomy through a short case report.

• Olnlcal Example. A short case report that serves to
dramatize the relevance of neuroanatomy introduces
each chapter.
• Chapter Objectives. This section details the material
that ls most important to learn and understand in each
• Balle Neuroanatomy. This section provides basic
information on neuroanatomical structures that are
of clinical importance. Numerous examples of normal
radiographs, CT scans, MRis, and PET scans are also
provided. Many cross-sectional diagrams have been
included to stlmulate students to think in terms of
three-dimensional anatomy, which ts so Important in





the Interpretation of CT scans and MR images.
amtn.I Notes. This section provides the practical
application of neuroanatomical facts that are essential
in clinical practice. It emphasizes the structures that
the clinician will encounter when making a diagnosis
and treating a patient It also provides the information
necessary to understand many procedures and tee~
niques and notes the anatomical ..pitfalls" commonly
NEWI Key Conceplll. These quick, bulleted reviews of
key topics and Information are provided at the end of
each chapter.
Ololcal Problem SoMog. This section provides the srudent with many examples of clinical situations 1n which
a knowledge of neuroanatomy Is necessary to solve clinical problems and to institute treatment; solutions to the
problems are provided at the end of the chapter.
Reriew Queetiont. The purpose of the questions is
threefold: to focus attention on areas of importance, to
enable students to assess their areas of weakness, and
to provide a form of self-evaluation when questions are
answered under exarnlnatlon condlttons. Some of the
questions are centered around a cllntcal problem that
requires a neuroanatomlcal answer. Solutions to the
problem are provided at the end of each chapter.

An interactive Review Test, including over 450 questions, ts provided online.
The book ts extensively illustrated. The majority of the
figures have been kept simple and are in color. As in the
previous edition, a concise Color Atlas of the dissected
brain is included prior to the text. This small but important group of colored plates enables the reader to quickly
relate a particular part of the brain to the whole organ.



• Acknowledgments
Starting with the first edition of Clinical Neuroanatomy
published in 1980, many people have provided their
expertise and should be recognized for their contributions. First and foremost, thanks to Richard S. Snell
whose shoulders we stand upon to advance our own
intellectual progress.
Throughout this text and in previous editions, the
following individuals provided valuable contributions
and are gratefully acknowledged: N. Cauna, L. Clerk, D. 0.
Davis, H. Dey, M. Feldman, T. M. J. Fitzgerald, I. Grunther,
J. M. Kerns, T. McCarthy, A Peters, G. Sze, and L. Wener.

I am greatly indebted to the staff of Wolters Kluwer,
including Crystal Taylor, who brought me in and provided
me with this wonderful opportunity, as well as Andrea

Vosburgh, development editor, and John Larkin, editorial
coordinator. Thanks also to freelance development editor Kelly Horvath, who provided invaluable direction and
patience with me throughout the entire process.
SPi Global is gratefully acknowledged for their brilliant art recoloring and enhancing the personality of
this textbook..
My special thanks to Stephanie Vas, Program Director of the Magnetic Resonance Imaging Program at the
University of Nebraska Medical Center, who produced
exceptional MR Images for this edltlon.
I would llke to extend my gratitude to my students,
colleagues, and mentors for their encouragement and
wisdom-especially, Sabra Peetz, Art Dalley, Cathy
Pettepher, Lillian Nanney, and Kyle Meyer.




Preface .............................................. ........ vii
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix
Color Atlas of Brain. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix

Introduction and Organization of the Nervous System
Central and Peripheral Nervous Systems 1
Major Divisions of the Central Nervous System 2
Major Divisions of the Peripheral Nervous System 12
Early Development of the Nervous System 14
Clinical Notes 16
Clinical Problem Solving 27
Answers and Explanations to Cllnical Problem Solving 28
Review Questions 29
Answers and Explanations to Review Questlons 31


Neurons and Neuroglia 33
Neurons 33
Neuroglla 54
Extracellular Space 60
Clinical Notes 62
Clinical Problem Solving 65
Answers and Explanations to Clinical Problem Solving 66
Review Questions 67
Answers and Explanations to Review Questions 69


Nerve Fibers and Peripheral Innervation


Nerve Fibers 71
Peripheral Nerves 80
Receptor Endings 84
Effector Endings 93
Segmental Innervation of Skin 98
Segmental Innervation of Muscles 100
Muscle Tone and Muscle Action 101
Motor Unit Summation 102
Muscle Fatigue 102
Posture 102
Clinical Notes 105
Clinical Problem Solving 119
Answers and Explanations to Clinical Problem Solving 122
Review Questions 125
Answers and Explanations to Review Questions 128





Spinal Cord and Ascending, Descending, and
lntersegmental Tracts 131
Brief Review of the Vertebral Column 131
Spinal Cord 136
Ascending Tracts 142
Descending Tracts 152
lntersegmental Tracts 160
Renshaw Cells and Lower Motor Neuron Inhibition 162
Clinical Notes 163
Clinical Problem Solving 175
Answers and Explanations to Cllnlcal Problem Solving 177
Review Questions 180
Answers and Explanations to Review Questions 182




Skull Anatomy 185
Cranial Cavity 191
Introduction to the Brainstem 195
Medulla Oblongata 196
Pons 204
Midbrain 209
Clinical Notes 215
Clinical Problem Solving 219
Answers and Explanations to Clinical Problem Solving 220
Review Questions 222
Answers and Explanations to Review Questions 226


Cerebellum and Its Connections


Gross Appearance 229
Structures 231
Cerebellar Cortical Mechanisms 234
Cerebellar Afferent Fibers 236
Cerebellar Efferent Fibers 239
Functions of the Cerebellum 240
Clinical Notes 241
Clinical Problem Solving 244
Answers and Explanations to Clinical Problem Solving 244
Review Questions 245
Answers and Explanations to Review Questions 247




Subdivisions 249
Diencephalon 249
General Appearance of the Cerebral Hemispheres 255
Main Suki 256
Cerebral Hemisphere Lobes 258
Internal Structure of the Cerebral Hemispheres (Atlas Plates 4 and 5) 260
Clinical Notes 267
Clinical Problem Solving 273
Answers and Explanations to Clinical Problem Solving 274
Review Questions 275
Answers and Explanations to Review Questions 277



The Structure and Functional Localization of the Cerebral Cortex 279
Structure 279
Cortical Mechanisms 283
Cortical Areas 283
Cerebral Dominance 289
Clinical Notes 290
Clinical Problem Solving 293
Answers and Explanations to Clinical Problem Solving 294
Review Questions 295
Answers and Explanations to Review Questions 297


Reticular Formation and Limbic System


Reticular Formation 299
Limbic System 301
Cllnical Notes 306
Clinical Problem Solving 307
Answers and Explanations to Cllnical Problem Solving 307
Review Questions 307
Answers and Explanations to Review Questions 308

CHAPTER 10 Basal Nuclei (Basal Ganglia)



Terminology 310
Corpus Strlatum 310
Amygdaloid Nucleus 311
Substantia Nigra and Subthalamic Nuclei 312
Claustrum 312
Connections of the Corpus Striatum and Globus Pallidus 312
Basal Nuclei Functions 314
Clinical Notes 315
Cllnical Problem Solving 319
Answers and Explanations to Clinical Problem Solving 319
Review Questions 320
Answers and Explanations to Review Questions 321

CHAPTER 11 Cranial Nerve Nuclei


Cranial Nerves 323
Cranial Nerve Organization 323
Olfactory Nerves (Cranial Nerve I) 326
Optic Nerve (Cranial Nerve 11) 327
Oculomotor Nerve (Cranial Nerve III) 331
Trochlear Nerve (Cranial Nerve IV) 331
Trigeminal Nerve (Cranial Nerve V) 332
Abducens Nerve (Cranial Nerve VI) 335
Facial Nerve (Cranial Nerve VII) 337
Vestlbulocochlear Nerve (Cranial Nerve VIII) 339
Glossopharyngeal Nerve (Cranial Nerve IX) 341
Vagus Nerve (Cranial Nerve X) 343
Accessory Nerve (Cranial Nerve XI) 345
Hypoglossal Nerve (Cranial Nerve XII) 347
Clinical Notes 348
Clinical Problem Solving 356
Answers and Explanations to Clinical Problem Solving 357
Review Questions 358
Answers and Explanations to Review Questions 361




CHAPTER 12 Thalamus 363
General Appearance 363
Subdivisions 363
Connections 366
Function 367
Clinical Notes 369
Clinical Problem Solving 370
Answers and Explanations to Clinical Problem Solving 370
Review Questions 370
Answers and Explanations to Review Questions 372

CHAPTER 13 Hypothalamus 373
Hypothalamus 373
Hypothalamic Nuclei 375
Hypothalamic Lines of Communication 376
Functions 380
Clinical Notes 382
Clinical Problem Solving 383
Answers and Explanations to Clinical Problem Solving 384
Review Questions 384
Answers and Explanations to Review Questions 385

CHAPTER 14 Autonomic Nervous System


Organization 387
Large Autonomic Plexuses 390
Autonomic Ganglia 390
Preganglionic Transmitters 392
Fast, Slow, and Inhibitory Synaptic Potentials 392
Ganglion-Stimulating Agents 392
Ganglion-Blocking Agents 392
Postganglionic Nerve Endings 393
Postganglionic Transmitters 393
Other Postganglionic Transmitters 394
Cholinergic Receptor Blockade 394
Adrenergic Receptor Blockade 394
Higher Control 394
Enterlc Nervous System 394
Functions 395
Differences Between Sympathetic and Parasympathetic Systems 395
Autonomic Innervations 396
Ans Physiologic Reflexes 406
Clinical Notes 406
Clinical Problem Solving 411
Answers and Explanations to Clinical Problem Solving 412
Review Questions 413
Answers and Explanations to Review Questions 416

CHAPTER 15 Meninges 418
Brain Meninges 418
Spinal Cord Meninges 425
Clinical Notes 428
Clinical Problem Solving 432
Answers and Explanations to Clinical Problem Solving 433
Review Questions 434
Answers and Explanations to Review Questions 435


CHAPTER 16 Ventricular System and Cerebrospinal Fluid


Ventricular System 436
Subarachnoid Space 44 7
Cerebrospinal Fluid 448
Blood-Brain and Blood-Cerebrospinal Fluid Barriers 452
Clinical Notes 455
Clinical Problem Solving 458
Answers and Explanations to Clinical Problem Solving 459
Review Questions 460
Answers and Explanations to Review Questions 462

CHAPTER 17 Blood Supply of the Brain and Spinal Cord


Arteries of the Brain 464
Veins of the Brain 469
Brain Capillaries 470
Cerebral Circulation 470
Spinal Cord Arteries 471
Spinal Cord Veins 472
Clinical Notes 472
Clinical Problem Solving 480
Answers and Explanations to Clinical Problem Solving 482
Review Questions 484
Answers and Explanations to Review Questions 486

CHAPTER 18 Nervous System Development


Spinal Cord 488
Brain 490
Clinical Notes 498
Clinical Problem Solving 502
Answers and Explanations to Clinical Problem Solving 503
Review Questions 503
Answers and Explanations to Review Questions 504


Neuroanatomical Data of Clinical Significance and Clinical
Neuroanatomy Techniques 507

Index 513



• Color Atlas of Brain

umgltudlnal fissure
Precentral sulcus
Frontal lobe

Precentral gyrus

Central ~.llcus
Left cerebral

- Poetoentral gyrus
Postcentral sulcus

Parietal lobe

Occipital lobe
Occipital pole

Frontal lobe

Longitudinal fissure
Olfactory tract

Right cerebral

Optic chiasma

Temporal lobe
Oculomotor nerve

- Pyramid


Medulla oblongata

Rgu... CA.-1


Top: Superior view of the brain. Bottom: Inferior view of the brain.



Color Atlas of Brain

Longltudlnal fissure

Right cerebral
Superfor frontal

Frontal pole
- Pona

Temporal pole

Left cerebral
Occipital pole

Medulla oblongata

Occipital lobe
Horizontal fissure
of cerebellum

Vermls of
Left cerebellar

cavtty of fourth

Inferior cerebellar

Graci le tubercle


Cuneate tubercle

Figure CA-2 Top: Anterior view of the brain. Bottom: Posterior view of the brain.

Color Atlas of Brain






frontal gyrus

frontal gyrus

frontal gyrus

Occipital lobe

Lateral sulcus

temporal gyrus
Right cerebellar

temporal gyrus


temporal gyrus
- Central sulcus




Clngulate gyrus

of midbrain

Optic chiasma

Calcarine sulcus

Temporal lobe



Cavity of fourth

Flgu... CA.-3 Top: Right lateral view of the brain. Bottom: Medial view of the right side of the
brain following median sagittal section.



Color Atla$ of Brain

Anterior horn of
lateral ventrlcle

Lateral sulctls

Lateral ventrlcle

. Corpus callosum
Septum pellucidum
Caudate nucleus

Lentlform nucleus

Corpus callosum

Cauclete nucleus
Third ventricle
Lentiform nucleus

Medial thalamic nuctei

Mammillary body

Lateral thalamic nuclei
Corpus callosum
Choroid plexus In
lateral ventrlcle


Flgw. CA4 Coronal sections of the brain passing through the anterior horn of the lateral
ventricle (top), the mammillary bodies (middle), and the pons (bottom).

Color Atlas of Brain

Anterior horn of
lateral ventric:fe
Internal capsule•
(anterior limb)
Genu of internal capsule

Genu of corpus callosum
Head of caudate nucleus
Anterior column of fornix


Internal capsule
(posterior limb)
Third ventrk:le-

Globus pallidus

Posterior horn of
lateral ventricle

Splenium of
corpus callosum

Caudate nucleus

Corpus callosum

Lentiform nucleus


Lateral ventricle
Third ventricle

Internal capsule
Crus cerebrt of mldbraln

Third ventrlcle
(Inferior part)

Medulla oblongata


Figure CA.-5 Top: Horizontal section of the cerebrum showing the lentiform nucleus, the c:audate
nucleus, the thalamus, and the internal capsule. Bottom: Oblique coronal section of the brain.



Color Atlas of Brain

Roots of glossopharyngeal,
vagus, and cranial part
of accessory nerves

accessory nerve

Gyrus rectus

Longitudinal flsaure

Optic chiasma
Crus cerebri
Trochlear nerve


- - --


~ Mammillary body
Poeterlor perforating
substance In floor of
lnterpeduncular fossa
~...,,.___ Oculomolor nerw


Groove for basilar artery

Inferior cerebellar



FiguN CA-6 Top: Inferior view of the brain showing cranial nerves. The abducens and facial
nerves cannot be seen. Bottom: Enlarged inferior view of the central part of the brain.

Color Atlas of Brain

Vestibular area In Hoor of fourth ventrk:le
Striae medullares




Facial oolliculus

Sulcus llmHan&

Right cembellar
hemisphere (cut)

Vaoar triangle

Gradle tubercle

Anterior lobe

Superior aspect

Primary fi~ure

Middle lobe
Left cerebellar

- Right cerebellar
Mlddle cerebellar

Central lobule


Inferior aspect

Right cerebellar

- Left cerebellar


Flgwe CA-7 Top: Posterior view of 1he brainstem. The greater part of 1he cerebellum had been
removed to expose the floor of the fourth ventricle. Middle: Superior view of 1he cerebellum
showing the vermis and right and left cerebellar hemispheres. Bottom: Inferior view of the
cerebellum showing the vermis and right and left cerebellar hemispheres.



Color Atlu of Brain

Anterior column
of fornlx

lnterventrlcular foramen
(entrance to lateral ventrlde)


I Pineal body

plexus of
the fourth


I cerebellum
Foramen of
terminal is

Region of

Cerebral aqueduct
of micl>rain

Rgure CA-8 Enlarged medial view of the right side of the brain following median sagittal
section, showing the continuity of the central canal, fourth ventricle, cerebral aqueduct, and
the third ventricle and entrance into the lateral ventride through the interventricular foramen.

Introduction and

Organization of the
Nervous System
• To understand the basic organization of the main
structures that form the nervous system

A 23-year-old student is driving home from a party and
crashes his car head-on into a tree. On examination in the
emergency department of the local hospital, he has a fracture dislocation of the 7th thoracic vertebra, with signs and
symptoms of severe damage to the spinal cord. Later, he
is found to have paralysis of the left leg. Testing of cutaneous sensibility reveals a band of cutaneous hyperesthesia
{increased sensitivity) extending around the abdominal
wall on the left side at the level of the umbilicus. Just
below this, he has a narrow band of anesthesia and analgesia. On the right side, he has total analgesia, thermoanesthesia, and partial loss of touch sensation of the skin of
the abdominal wall below the level of the umbilicus and
involving the whole of the right leg.
With knowledge of anatomy, a clinician knows that a
fracture dislocation of the 7th thoracic vertebra can result
in severe damage to the 10th thoracic segment of the
spinal cord. Because of the small size of the vertebral
foramen in the thoracic region, such an injury inevitably
results in damage to the spinal cord. Knowledge of the
vertebral levels of the various segments of the spinal cord
enables the clinician to determine the likely neurologic
deficits. The unequal sensory and motor losses on the two
sides indicate a left hemisection of the cord. The band of
anesthesia and analgesia was caused by the destruction
ofthe cord on the left side atthe level ofthe 10th thoracic


As shown in Figure 1-1, the nervous system is divided

into two main parts, for purposes of description: the
cenll'al nervous system (CNS), which consists of the
brain and spinal cord, and the peripheral nervous
system (P~. which consists of the cranial and spinal
nerves and their associated ganglia.

• To gain a three-dimensional appreciation of the parts
of the brain and their relative positions to one another

segment; all afferent nerve fibers entering the cord at
that point were interrupted. The loss of pain and thermal
sensibilities and the loss of light touch below the level of
the umbilicus on the right side were caused by the interruption of the lateral and anterior spinothalamic tracts on
the left side of the cord.
To comprehend what has happened to this patient,
the relationship between the spinal cord and its surrounding vertebral column must be understood. The various
neurologic deficits will be easier to understand after the
reader has learned how the nervous pathways pass up and
down the spinal cord. This information will be discussed
in Chapter 4.
The nervous system and the endocrine system control
the functions of the body. The nervous system is composed
basically of specialized cells, whose function is to receive
sensory stimuli and to transmit them to effector organs,
whether muscular or glandular. The sensory stimuli that arise
either outside or inside the body are correlated within the
nervous system, and the efferent impulses are coordinated
so that the effector organs work harmoniously together for
the well-being of the individual. In addition, the nervous system of higher species has the ability to store sensory information received during past experiences. This information,
when appropriate, is integrated with other nervous impulses
and channeled into the common efferent pathway.

In the CNS, the brain and spinal cord are the main
centers where correlation and integration of nervous
information occur. Both the brain and spinal cord are
covered with a system of membranes (menlngea) and
are suspended in cerebro1plnal fluid {CSF). Meninges
are further protected by the bones of the skull and the
vertebral column (Fig. 1-2).
The CNS is composed of large numbers of neurons,
which are excitable nerve cells, and their processes,



CHAPTER 1 Introduction and Organization of the Nervous System

Brachlal plexus-~­







./ Phrenic nerve

,/ /

Radial neNe--.-...__
Median nerve_____







...___Sa_at._ -~-- Coccygeal



Figure 1·1 A:. The main divisions of the central nervous system. B: The parts of the peripheral
nervous system (the cranial nerves have been omitted).

known as u.ons or nerve flbela. Neurons are supported
by specialized tissue called neuroglla (Fig. 1-3).
The CNS interior is organized into gray and white
matter. Gray matter, which is gray in color, consists
of nerve cells embedded in neuroglia. White matter
consists of nerve fibers embedded in neuroglia and is
white in color because of the presence of lipid material
in nerve fiber myelin sheaths.
In the PNS, the cranial and spinal nerves, which
consist of bwidles of nerve fibers (or axons), conduct
information to and from the CNS. Although the nerves
are surrounded by fibrous sheaths as they run to different parts of the body, they are relatively unprotected
and are commonly damaged by trauma.

Autonomic Nervous System
The autonomic nervous system (ANS) Is the part
of the nervous system that innervates the body's

Involuntary structures, such as the heart, smooth
muscle, and glands. It is distributed throughout
the CNS and PNS and ls divided Into two parts, the
sympathetic and the parasympathetic, both containing afferent and efferent nerve fibers. The activities
of the sympathetic part of the ANS prepare the body
for an emergency, whereas those of the parasympathetic part are aimed at conserving and restoring

Before proceeding to a detailed description of the spinal cord and brain, understanding the main features of
these structures and their general relationship to one
another is essential (Table 1-1).

Major Divisions of the Central Nervous System

Dura mater{

Superior sagitlal sinus Arachnoid

••!lll!!lil~~ililiilla ~illus

Fused layers
of dura mater
Quadrigeminal cistern

Spinal--arachnoid mater

Location of
foramen magnum
Spinal dura maier
(meningeal layer only)


Periosteal layer
Meningeal layer
Arachnoid mater
- Pia mater



Figure 1-2 A: The protective covering of the spinal cord, the meninges, is formed by dura,
arachnoid, and pia mater. The space between the arachnoid and pial membranes is called the
subarachnoid space and contains cerebrospinal fluid (CSF). The subarachnoid space is enlarged
at the cisterna magna and chiasmatic cistern. B: In the cranium, the dura consists of fused periosteal and meningeal layers that separate to form dural sinuses. Arachnoid mater projects into the
dural venous sinuses to drain CSF fram the subarachnoid space. (From Siegel, A., & Sapru, H. N.
[2015]. Essential neuroscience (3rd ed.]. Baltimore, MD: Wolters Kluwer.)



CHAPTER 1 Introduction and Organization of the Nervous System

Table 1-1

Major Divisions of the Central and
Peripheral Nervous Systems

Central Nervous System
Diencephalon (between brain)
Medulla oblongata
Spinal cord
Cervical segments
Thoracic segments
Lumbar segments
Sacral segments

Coceygeal segments
Peripheral Nervogs System

Cranial nerves and their ganglia-12 pairs that exit the
skull through the foramina
Spinal nerves and their ganglia-31 pairs that exit the
vertebral column through the intervertebral foramina

8 Cervical
12 Thoracic
5 Lumbar
5 Sacral

1 Coccygeal

Figure 1-3 Photomicrograph of several large nerve cells
with surrounding neuroglia. N, Neuron; n, nucleus; Ng,
neuroglia; Np, neuropili; arrows, neurites. (From Gartner, L P.
[2017]. Color atlas and text of histology [7th ed.]. Baltimore,
MD: Wolters Kluwer.)

Spinal Cord
The spinal cord Is situated within the vertebral c:anal
of the vertebral column and is surrounded by three
meninges (Figs. 1-4 and 1-5): the duna matert the arach·
nold mater, and the pla mater. Further protection is
provided by the C:SF, which surrounds the spinal cord
in the subaradmold space.
The spinal cord ls roughly cyllndrlcal and begins
superiorly at the foramen magnum in the skull, where lt
ls continuous wlth the medulla oblongata of the brain.
It terminates inferiorly In the lumbar region. Below, the
spinal cord tapers off Into the conus medullarle, from
the apex of which the mum termlnale (a prolongation
of the pia mater) descends to attach to the back of the
coccyx (see Fig. 1-48).
Along the entire length of the spinal cord, 31 pairs
of spinal nerves are attached by the anterior or motor
roots and the posterior or 1eD10ry roots (Fig. 1-6; also
see Fig. 1-5). Each root is attached to the cord by a
series of rootlets, which extend the whole length of
the corresponding segment of the cord. Each posterior

nerve root possesses a poeterlor root ganglion, the
cells of which give rise to peripheral and central nerve
Spinal Cord Struct\.IN
The spinal cord ls composed of an Inner core of gray
matter, which ls surrounded by an outer covering of
white matter. The gray matter Is seen on cross section
as an H-shaped pfllar with anterior and posterior gray
colUIDD9, or horns. united by a thin gray commllllUl'e
containing the small central canal. The white matter,
for purposes of description, ls divided into anterior,
lateral, and posterior white columm (see Fig. 1-6).

The brain (Fig. 1-7) Iles in the cranial cavity and ls
continuous with the spinal cord through the foramen
magnum (see Fig. I.SA). As shown in Figure 1-2, it ls
surrounded by the dura mater. the arachnoid mater,
and the pla mater. These three meninges are continuous with the corresponding meninges of the spinal
cord. The CSF surrounds the brain in the subarachnoid
The brain is conventionally divided into three
major divisions: the hlndbraln, the mldbraln, and
the forebraln in ascending order from the spinal cord
(see Fig. 1-lA). The brain.stem (a collective term for the

Major Divisions of the Central Nervou$ Syltem


Medulla oblongata






Conus medullaris
of spinal cord

Subaracfmoid space
with cerebrospinal

:~-- filled

,....-,=--=----..:...;..~-· Lower limit of


Second sacral


Lower limit of
sub arachnoid





Figure 1-4 A: Fetus with the brain and spinal cord exposed on the posterior surface. Note
that the spinal cord extends the full length of the vertebral column. B: Sagittal section of the
vertebral column in an adult showing the spinal cord terminating inferiorly at the level of the
lower border of the 1st lumbar vertebra. C: Adult spinal cord and covering meninges showing
the relationship to surrounding structures.

medulla oblongata. pons, and midbrain) is what remains
after the cerebral hemispheres and cerebellum (see
below) are removed.

and serves as a conduit for ascending and descending
nerve fibers.

Hind brain
The hindbrain comprises the medulla oblongala. the
pons. and the cerebellum.
Medulla Oblongata
The medulla oblongata Is conical In shape and connects
the pons superiorly to the spinal cord Inferiorly (Fig. 1-8).
It contains many collections of neW'Ons, called nuclei,

The pons is situated on the anterior surface of the
cerebellum, inferior to the midbrain and superior
to the medulla oblongata (Fig. 1-9; also see Fig. 1-8).
The pons, or bridge, derives its name from the large
number of transverse fibers on its anterior aspect
connecting the two cerebellar hemispheres. It also
contains many nuclei and ascending and descending
nerve fibers.


CHAPTER 1 Introduction and Organization of the Nervous System


Dura mater

Arachnoid mater



Pos1erior root





Spina! root

Anterior root
Gray matter

_./"-~Dura and




arachnoid mater

__,_- Conus medullarls

-~:::=---First lumbar

spinal nerve





and occcygeal



_.,. L5

_.,._.... s1
~-~---- Lower limit of

subarachnoid space


Filum terminal&

F'.gure 1-S A: Brain, spinal cord, spinal nerve roots, and spinal nerves as seen on their posterior
aspect B: Transverse section through the thoracic region of the spinal cord showing the anterior
and posterior roots of a spinal nerve and the meninges. C: Posterior view of the lower end of the
spinal cord and cauda equine showing their relationship with the lumbar vertebrae, sacrum, and

Major Divisions of the Central Nervou$ Syltem


One segment of spinal cord




Posterior rootlets of splnal nerw




Posterior root of spinal nerve

/ /



Central canal___


Posterior root ganglion
Spinal nerve


/ ___ Pos1erior ramus of
-- spinal nerve








Central canal



ramus of
spinal nerve
Anterior root of spinal nerve
Posterior median s,ulc:tls
Anterior rootlets of spinal nerve
Posterior median septum : Pos1erior white column
Posterior gray oolum~
\ I /'
Lateral white column





\\): ;








Anterior gray column~



Anterior median fissure



Spinal nerve


Anterior white column

Figure 1-6 A: Transverse section
through the lumbar part of the spinal
cord, oblique view. B: Transverse
section through the lumbar part of
the spinal cord, face view, showing
the anterior and posterior roots of a
spinal nerve.





Lateral 11ssure



Temporal lobe
Temporal bone

Figure 1-7 Lateral view of the brain
within the skull.


CHAPTER 1 Introduction and Organization of the Nervous System

Roots Of ---=·..,
hyp:lglo88al nerve
Median tieaure---

-. GloB80ptlaryngeal

Pyramld -----





Roots of vaguanEll\'9

' Ac:ce48ary nerve

oblongata _..--



Spinal part of acc&$$CllY nEll\'9

Occipital lobe--------

Figure 141 Inferior view of the brain.

Central sulctis

Mlddle temporal gyrus
Superior temporal gyrus

Inferior temporal gyrus

Figure 1-9 Brain viewed from its right lateral
Medulla oblongata


Major Divisions of the Central Nervou$ Syltem

Paracentral lobule




Central sulcus




Figure 1·10 Median sagittal section of the brain to show the third ventricle, the cerebral aqueduct,.
and the fourth ventricle.


The cerebellum lies within the posterior cranial fossa
of the skull (see Figs. 1-7 to 1-9), posterior to the pons
and the medulla oblongata. It consists of two laterally
placed hemispheres connected by a median portion,
the verml8. The cerebellum is connected to the midbrain by the nperlor cerebellar peduncles, to the
pons by the middle cerebellar peduncles, and to
the medulla by the Inferior cerebellar peduncles (see
Fig. 6-9). The peduncles are composed of large bundles of
nerve fibers connecting the cerebellum to the remainder of the nervous system.
The surface layer of each cerebellar hemisphere
ls called the cortex and ls composed of gray matter
(Fig. 1-10). The cerebellar cortex is thrown Into folds,
or folia, separated by closely set transverse fissures.
Certain masses of gray matter are found in the Interior
of the cerebellum, embedded in the white matter; the
largest of these is known as the dentate nucleus (see
Fig. 6-7).
The medulla oblongata, the pons, and the cerebellum
surround a cavity filled with CSF, called the fourth ventricle. This is connected superiorly to the third ventricle by the cerebral aqueduct; Inferiorly, lt Is continuous
with the central canal of the spinal cord (Flg. 1-11). It
conununlcates with the subarachnold space through

three openings In the Inferior part of the roof. Through
these openings, the CSF within the CNS can enter the
subarachnold space.
The mldbraln Is the narrow part of the brain that connects the forebraJn to the hlndbraln (see Figs. 1-lA and
1-10). The narrow cavity of the mldbraln Is the cerebral
aqueduct, which connects the third and fourth ventricles. The midbraJn contains many nuclei and bundles of
ascending and descending nerve fibers.
The forebraln comprises the dlencephalon (between
brain), which ls the central part of the forebraln, and
the cerebrum.

The diencephalon is almost completely hidden from
the surface of the brain. It consists of a dorsal thal·
amus and a ventral hypothalamu. (see Fig. 1-10).
The thalamus is a large, egg-shaped mass of gray
matter that lies on either side of the third ventricle.
The anterior end of the thalamus forms the posterior boundary of the lnterventrlcular foramen, the


CHAPTER 1 Introduction and Organiration of the Nervous System





Pons ._~

ot- - ,L- =---=n---ri'L.l,.,._._"""'

rounh ventricle

-~--~ Tuber

---- Cerebellar



Cortex of cerebellum

Figure 1-11 Sagittal section through the brainstem and the cerebellum.

opening between the third and lateral ventricles. The
hypothalamus forms the lower part of the lateral wall
and floor of the third ventricle.

The cerebrum, the largest part of the brain, consists of
two cerebral hemispheres, whlch are connected by a
mass of white matter called the corpus callosum. (see
Flgs. 1-9 and 1-10). Each hemisphere extends from the
frontal to the occipital bones ln the skull, superior to
the anterior and middle cranial fossae; posteriorly, the
cerebrum Iles above the tentorium cerebelll (see Pig. 15-3).
The hemispheres are separated by a deep cleft, the
loogltucllnal fiasure, into which projects the fah: cerebri
(see Fig. 1~1).
The surface layer of each hemisphere, the cortex, is
composed of gray matter. The cerebral cortex is thrown
tntofolds(gyd)separated byftssures,orlUl.d.{seeFtg.1-9).
This arrangement greatly increases the surface area of
the cortex. A number of the large sulcl are conveniently
used to subdlvtde the surface of each hemisphere Into
lobes. which are named from the bones of the cranium
they lie under.
Within the hemisphere ls a central core of white
matter containing several large masses of gray matter,

the basal nuclei or ganglia. A fan-shaped collectlon of
nerve fibers, the corona radlata (Fig. 1-12), passes ln
the white matter to and from the cerebral cortex to the
brainstem. The corona radiata converges on the basal
nuclei and passes between them as the Internal capsule. The tailed nucleus situated on the medial side of
the internal capsule ls the caudate nucleu (Fig. 1-13),
and the lens-shaped nucleus on the lateral side of the
internal capsule is the lendform nucleus.
Within each cerebral hemisphere is a cavity called
the lateral ventrlde (see Figs. 16-2 and 16-3). The lateral ventricles communicate with the third ventricle
through the lnterventrlcular foramlna.
During the process of development, the cerebrum
becomes enormously enlarged and overhangs the dlencephalon, the midbraln, and the hlndbraln.
Brain Structure
Unllke the spinal cord, the brain Is composed of an
inner core of white matter. which Is surrounded by an
outer covering of gray matter. However. as mentioned
previously, certain Important masses of gray matter are
situated deeply within the white matter: the gray cerebellar nuclei in the cerebellum and the gray thalamic,
caudate, and lentiform nuclei in the cerebrum.

Major Divisions of the Central Nervous System


Internal capsule,


/ "····-,.

t -'~-.



cerebellar peduncle~=------=-=~.

~ rlenti~rmnudou&
" \ Optic tract
Crus cerebri
Pons {cut open to r911'981
descending ilbera)

Middle cerebellar peduncle
Inferior cerebellar peduncle

Figure 1·12 Right lateral view showing continuity of the corona radiata, the internal capsule,
and the CTUS cerebri of the cerebral peduncles. Note the position of the lentiform nucleus lateral
to the internal capsule.
Body of caudate nucleus

Corona radla"


Internal capsule.

Parietopontine iibers



Fn>ntopontlne fibers

Head of caudate



nucleus" \ ''-.


..,, fibers

--Tail of caudate nucleus

Lentlform nucleus





Globus pallidus



Crus cerebrl

Amygdaloid nucleus

Figure 1·13 Diagram showing the
relationship between the lentiform
nudeus, the caudate nucleus, the
thalamus, and the internal capsule, as
seen from the left lateral side.


CHAPTER 1 Introduction and Organiration of the Nervous System

The PNS comprises the cranial and spinal nerves and
their associated ganglia.

Cranial and Spinal Nerves
The cranial and spinal nerves are made up of bundles of
nerve fibers supported by connective tissue.
The 12 pairs of cranlal nerves (see Fig. 1-8) leave
the brain and pass through foramina in the skull. The
31 pairs of spinal nerves (see Fig. 1-5) leave the spinal
cord and pass through lntervertebral foramlna In the
vertebral column. The spinal nerves are associated
with regions of the spinal cord: 8 cervical, 12 thoracic,
5 lumbar, 5 sacral, and 1 coceygeal. Note that there are
8 cervical nerves yet only 7 cervical vertebrae and that
there Is 1 coccygeal nerve but 4 coccygeal vertebrae.

Each spinal nerve Is connected to the spinal cord
by two roots: the anterior root and the polterlor root
{see Fig. 1-SB). The anterior root consists of bundles
of nerve fibers carrying nerve Impulses away from the
CNS-efferent flben. Those that go to skeletal muscles
and cause them to contract are motor flben. Their cells
of origin lie in the anterior gray horn of the spinal cord.
The posterior root consists of bundles of afferent
ftben that carry nervous impulses to the CNS. Because
these fibers convey information about sensations of
touch, pain, temperature, and vibration, they are called
semory ftben. The cell bodies of these nerve fibers are
situated ln a swelling on the posterior root called the
posterior root ganglion.
The spinal nerve roots pass from the spinal cord to
the level of their respective lntervertebral foramlna,
where they unite to form a 1plnal nerve (Fig. 1-14).
Here, the motor and sensory fibers mlx together; thus, a
spinal nerve comprises both motor and sensory fibers.

~Cl "'"" "'"'

Cervical segments
of spinal cord

Thoracic segments
of spinal cord

Lumbar, sacral, and
coa:ygeal segments
of spinal cord

Twelfth thoracic vertebra ~-___._

Fl rat lumbar vertebra -~-

Coccyx- - --~~


Coccygeal 1

Figure 1-14 Posterior view of the spinal cord showing the origins of the roots of the spinal
nerves and their relationship to the different vertebrae. On the right, the laminae have been
removed to expose the right half of the spinal cord and the nerve roots.

Major Divisions of the Peripheral Nervous SY'$tem



Tenth 1horacic vertebra

Cut sheath of dura and arachnoid mater


Filum terminale

lntervertebral disc between thiro and
fourth lumbar vertebrae

Anterior and posterior roots of spinal
nerves forming cauda equlna . _ ,__~ ·

'w---'!!:---,--- Posterior root ganglion of fourth


lumbar nerve

Posterior ramus of --_.::::~
second sacral nerve

- - Inferior llmlt of subaractmold space

--~ Thiro sacral spinal nerve


\ Anterior ram us of third sacral
spinal nerve


Coccygeal nerve

1r'l!:::-~-- Attachment of fllum termlnale

Flgure 1·15 Oblique posterior view of the lower end of the spinal cord and the cauda equina. On
the right, the laminae have been removed to expose the right half of the spinal cord and the nerve

Because of the disproportionate growth in length
of the vertebral column during development, compared with that of the spinal cord, the length of the
roots Increases progressively from above downward
(see Fig. 1-15). In the upper cervical region, the spinal
nerve roots are short and run almost horizontally, but
the roots of the lumbar and sacral nerves below the
level of the termination of the cord (lower border of
the 1st lumbar vertebra ln the adult) form a vertical
leash of nerves around the ftlum termlnale (Fig. 1-15).
Together, these lower nerve roots are called the cauda
After emerging from the intervertebral foranten, each
spinal nerve Immediately divides Into a large anterior
ramus and a smaller posterior ramua, each containing
both motor and sensory fibers. The posterior ramus

passes posteriorly around the vertebral column to
supply the muscles and skJn of the back. The anterior
ramus continues anteriorly to supply the muscles and
skin over the anterolateral body wall and all the muscles and skin of the limbs.
The anterior rami join one another at the root of the
llmbs to fonn complicated nerve pleJCllleS (see Fig. 1-IB).
The cervical and brachlal plexmes are found at the
root of the upper limbs, and the lumbar and lacral
plexuset are found at the root of the lower limbs.

Ganglia can be dlvtded Into sensory ganglia of spinal
nerves (posterior root ganglia) and cranial nerves and
autonomic ganglia.


CHAPTER 1 Introduction and Organiration of the Nervous System


Sensory Ganglia
Sensory ganglla are fusiform swellings (see Fig. 1-5) on
the posterior root of each spinal nerve just proximal
to the root's junction with a corresponding anterior
root. They are referred to as potterlor root ganglia.
Similar ganglia found along the course of cranial
nerves V, VII, VIII, IX, and X are the semory ganglia
of these nerves.

Before the fonnatlon of the nervous system In the embryo,
three main cell layers differentiate. The Innermost layer,
the entoclenn, gives rise to the gastrointestinal tract. the
lungs, and the liver. The meeoderm. gives rise to the muscle, co1U1ectlve tissues, and the vascular system. The third
and outermost layer, the ectoderm, formed of columnar
epithelium, gives rise to the entire nervous system.
During the third week of development. the ectoderm
on the dorsal surface of the embryo between the primitive knot and the buccopharyngeal membrane thickens to form the neural plate. The plate, which is pear
shaped and wider cranially, develops a longitudinal
neural groove. The groove now deepens so that it is
bounded on either side by neural folds (Fig. 1-16).

Autonomic Ganglfa

Autonomic ganglia, which are often irregular in shape,
are situated along the course of efferent nerve fibers of
the ANS. They are found in the paravertebral sympathetic chains (see Figs. 141and142) around the roots
of the great visceral arteries in the abdomen and close
to, or embedded within, the walls of various viscera.


Neural fold.

Neural plate


//_.,,.,, Neural groDYe




..... '




Neural groove

_L Fusion of neural folds

Neural fold



,.Anterior neuropore


Neural er~


"-... .


·" " ' '


Neural tube

/ _',


J,..r !, .-


j • "'



Cranial ~nsolryl










/\. f~~.:.i.<d~

gang ion ce s

Posterior root ~.........._
Cells of suprarenal medulla
ganglion cells
Autonomic ganglion cells

RguN 1-16 Formation of the
neural plate, neural groove, and
neural tube. The cells of the neural
crest differentiate into the c:ells
of the posterior root ganglia, the
sensory ganglia of cranial nerves,
autonomic ganglia, neurilemmal
cells (Schwann cells), the cells of
the suprarenal medulla, and melanocytes.

Early Development of the Nervous Sy$tem




Matrix oells ..__


Spinal cord









E_,rnal lin:!iting membrane

c \

















Cavity of neural tube\








-~--Neuroglial ceut





\ ,,,.;
Marginal zone :





With further development, the neural folds fuse,
converting the neural groove into a neanl tube. Fusion
starts at about the midpoint along the groove and
extends cranially and caudally so that, in the earliest
stage. the cavity of the tube remains in communication with the amniotic cavity through the anterior and
poeterlor neuropores. The anterior neuropore closes
first and the posterior neuropore 2 days later. Thus,
normally, the neural tube closure is complete within
28 days. Meanwhile, the neural tube has sunk beneath
the surface ectoderm.
During the invagination of the neural plate to form
the neural groove, the cells forming the lateral margin
of the plate do not become incorporated in the neural
tube but instead form a strip of ectodermal cells that

Figure 1-17 A: Expansion of the cephalic
end of the neural tube to form the forebrain,
midbrain, and hindbrain vesicles. B. C: Cross
section of the developing neural tube in the
region of the spinal cord. The cells of the neu-

roepithelial layer have been widely separated
for clarity.



Table 1-2











·~ ~



___. -,~-Neurolllast













~/ Neuron









./ 1




Ile between the neural tube and the covering ectoderm,
the neural creat (Fig. 1-16). Subsequently, this group of
cells will migrate ventrolaterally on each side around
the neural tube. Ultimately, the neural crest cells wm
differentiate Into the cells of the posterior root ganglia,
the SC1110ry ganglia of the cranial nerves, autonomic
ganglia, the cells of the wprarenal medulla. and the
melanocytea. These cells also probably give rise to
mesenchymal cells in the head and neck.
Meanwhile, the proliferation of cells at the cephalic
end of the neural tube causes it to dilate and form three
primary bndn vesicles: the forebraln, mldbraln, and
hlndbraln vesicles (Fig. 1-11) (Table 1-2). The rest of
the tube elongates and remains smaller In diameter; it
will form the 1plnal cord..

The Primary Divisions of the Developing Brain

Forebrain vesicle

Prosencephalon (forebrain}


Cerebral hemisphere, basal ganglia,


Thalamus, hypothalamus, pineal
body, infundibulum


Midbrain vesicle
Hindbrain vesicle

Mesencephalon (midbrain}

j Mesencephalon (midbra
_ i_n_,
) 11-l-e
i -ctum, tegmentum, crus cerebri

IRhombencephalon {hindbrain) IMetencephalon


Pons, cerebellum
Medulla oblongata


CHAPTER 1 Introduction and Organiration of the Nervous System

The subsequent differentiation of cells In the neural
tube ls brought about by the Inductive interactions of
one group of cells with another. The inducing factors
influence the control of the gene expression ln the target cells. Ultimately, the simplest progenitor cell will
dlfferentiate into neurons and neurogllal cells. Interestingly, excessive numbers of neurons and neurogllal cells
develop, and many (nearly half of the developing neurons) will be programmed to die by a process known as
programmed cell dealh. Research into the identification


of neurotrophlc factors that promote the development
and survival of neurons ls of great Importance, as
the results could possibly be applied to the problem
of regeneration of the spinal cord neurons following
trauma or the Inhibition of degenerative diseases such
as Alzheimer disease.
The further development of the nervous system will
be fully described in Chapter 18 following the description of the different parts of the nervous system and
their neuronal connections.

Clinical Notes

Relationship of Spinal Cord Segments to

Vertebral Numbers
Because the spinal cord Is shorter than the vertebral column, the spinal cord segments do not correspond nwnerically with the vertebrae that lie at the same level (see
Fig. 1-14). The following table will help a clinician determine
which spinal segment Is related to a given vertebral body
(Table 1-3).
F.x.amlnatlon of a patient's back shows that the spinous processes lie approximately at the same level as the
vertebral bodies. In the lower thoracic region, however,
because of the length and extreme obliquity of the splnous
processes, the tips of the spines lie at the level of the vertebral body below.

Spinal Cord and Brain Injuries
The spinal cord and brain are well protected. Both are suspended in cerebl'Glploal fluid (CSf) and are surrounded by
the bones of the vertebral column and skull (see Chapters 4
and 5). However, with enough force, these protective structures can be damaged, with consequent Injury to the delicate underlying nervous tissue. Moreover, the cranial and
spinal nerves and blood vessels are also likely to be injured.

Spinal Cord Injuries
The degree of spinal cord Injury at different vertebral levels
Is determined largely by anatomlcal factors. In the cervical
region, dislocation or fracture dislocation Is common, but

Table 1-3

Relationship of Spinal Cord
Segments to Vertebral Numbers

I Add 1

Cervical vertebrae
Upper thoracic vertebrae


Lower thoracic vertebrae (7-9)

Add 3

10th thoracic vertebra

L1-12 cord segments

11th thoracic vertebra

L3-L4 cord segments

12th thoracic vertebra

LS cord segment

1st lumbar vertebra


Sacral and coccygeal
cord segments

the large size of the vertebral canal usually prevents severe
injury to the spinal cord. However, with considerable displacement of the bones or bone i'Tagments, the cord Is sectioned. Respiration ceases if the cord is completely severed
above the segmental origin of the phrenic nerves (C3-CS)
because the lntercostal muscles and the diaphragm are paralyzed, resulting In death.
In fracture dislocations of the thoracic region, displacement can be conslderable. The small size of the vertebral
canal results in severe injury to this region of the spinal
In fracture dislocations of the lumbar region, two anatomic facts help prevent substantial nerve injury. First, the
spinal cord In the adult ex.tends down only as far as the
level of the lower border of the 1st lumbar vertebra (see
Fig. 1-lS). Second, the large size of the vertebral foram.en in
this region gives the roots of the cauda eqwna ample room.
Injury to the splnal cord may produce partial or complete loss of function at the level of the lesion and partial
or complete loss of function of afferent and efferent nerve
tracts below the level of the lesion. The symptoms and
signs of such lnJurles are discussed after the detailed structure of the spinal cord, and the ascending and descending
tracts are discussed In Chapter 4.

Spinal Nerve Injuries
The intervertebral foramina (Fig. 1-18) transmit the spinal
nerves and the small segmental arteries and veins, all of
which are embedded In areolar Ussue. Each foramen Is
bounded superiorly and Inferiorly by the pedlcles of adjar
cent vertebrae, anteriorly by the lower part of the vertebral body and the intervertebral disc, and posteriorly by
the articular processes and the joint between them. Jn this
situation, the spinal nerve is very vulnerable and may be
pressed on or irritated by disease of the surrounding structures. Herniation of the lntervertebral disc, fractures of the
vertebral bodies, and osteoarthritis involving the Joints of
the articular processes or the joints between the vertebral
bodies may all result in pressure, stretching, or edema of
the emerging spinal nerve. Such pressure would give rise
to dermatomal pain, muscle weakness, and diminished or
absent reflexes.

Herniation of the lntervertebral discs occurs most commonly In areas of the vertebral column where a mobile part
joins a relatively Immobile part-for e.sample, the cervlcothoracic and lumbosacral Junctions. In these areas, the

Clinical Notes

Superior articular process Inferior articular process




Joint between articular

-~/·[""·''processes (synovlaQ
...-- -..::f-Joint between bodies





(cartlaginous and synovial)


Superior articular process Joint between articular
proceases (synovlal)



~ "- ~~l~~~J l~erwrtebral

Joint between

bodes (cartiaginous)


""' Anulus "



Inferior artlcular process

~ Posterior longitudinal ligament



Spinal nerw






Anulus flbrosus
------- Nucleus pulposus

/ ~

!...-- Anterior

SUpertor artlcular process
Inferior articular process



Joint between /
articular processes/









lnterspinous \




Figure 1-18 A: Joints in the cervical, thoracic, and lumbar regions of the vertebral column.

B: Third lumbar vertebra seen from above showing the relationship between the intervertebral disc: and the cauda equina. C: Sagittal section through three lumbar vertebrae showing
the ligaments and the intervertebral discs. Note the relationship between the emerging spinal
nerve in an intervertebral foramen and the intervertebral disc.
posterior part of the anulus flbrosus of the disc ruptures,
and the central nucleus pulposus is forced posteriorly like
toothpaste out of a tube. This herniation of the nucleus
pulposus may result either in a central protrusion in the
mldllne under the posterior longitudinal ligament of the

Cervical dl8C herniations are less common than herniations in the lumbar region. The discs most susceptible
are those between the 5th and 6th and the 6th and 7th
cervical vertebrae. Lateral protrusions cause pressure
on a spinal nerve or its roots. Each spinal nerve emerges

vertebrae or In a latera1 protrusion at the side of the posterior ligament close to the lntervertebral forameo (Fig. 1-19).

above the corresponding vertebra; thus, the protrusion
of the disc between the 5th and 6th cervical vertebrae



CHAPTER 1 Introduction and Organiration of the Nervous System



Occipital bone
















Anulus fibrosus





may compress the C6 spinal nerve or its roots. Pain is felt
near the lower part of the back of the neck and shoulder
and along the area In the distribution of the spinal nerve
Involved. Central protrusions may press on the spinal
cord and the anterior spinal artery and Involve the variowi spinal tracts.
Lumbar d.blc hernlalfona are more common than cervical disc herniations. The discs usually alfected are those
between the 4th and 5th lumbar vertebrae and between the
5th lumbar vertebra and the sacrum. ln the lumbar region,
the roots of the cauda equlna run posteriorly over a number of intervertebral discs. A lateral herniation may press
on one or two roots and commonly involves the nerve root

Figure 1-19 A, I: Posterior
views of the vertebral bodies in
the cervical and lumbar regions
showing the relationship that
might exist between a herniated
nucleus pulposus and spinal
nerve roots. Note there are eight
cervical spinal nerves and only
seven cervical vertebrae. In the
lumbar region, for example, the
emerging L4 nerve roots pass
out laterally close to the pedicle
of the 4th lumbar vertebra and
are not related to the intervertebral disc between the 4th
and 5th lumbar vertebrae.
C: Posterolateral hemiation of
the nucleus pulposus of the
intervertebral disc between the
5th lumbar vertebra and the
1st sacral vertebra showing
pressure on the S1 nerve root.
D: An intervertebral disc that has
herniated its nucleus pulposus
posteriorly. E: Pressure on the
L5 motor nerve root produces
weakness of dorsiflexion of the
ankle; pressure on the 51 motor
nerve root produces weakness of
plantar flexion of the ankle joint.

going to the intervertebral foramen just below. The nucleus
pulposus occasionally herniates directly backward, and
if It Is a large herniation, the whole cauda equina may be
compressed, causing paraplegia.
In lumbar disc herniations, pain Is referred down the leg
and foot in the distribution of the affected nerve. Because
the sensory posterior roots most commonly pressed on
are the 5th lumbar and 1st sacral, pain ls usually felt down
the back and lateral side of the leg, radiating to the sole
of the foot, a condition known as 8datica. In severe cases,
paresthesla or actual sensory loss may occur.
Pressure on the anterior motor roots causes muscle weakness. Involvement of the Sth lumbar motor root weakens

Clinical Notes

dorsiflexion of the ankle, whereas pressure on the 1st sacral
motor root causes plantar flexion weakness. The ankle jerk
reflex may be diminished or absent (see Fig. 1-19E).
A large, centrally placed protrusion may give rise to
bilateral pain and muscle weakness In both legs. Acute
retention of urine may also occur.

Spinal Tap
Splnal tap (lumbar puncture) may be performed to withdraw
a sample of CSF for microscopic or bacterlologtc examination
or to Inject drugs to combat lnfectlon or Induce anesthesia.
Fortunately. the spinal cord terminates fnf-erlorly at the level
of the lower border of the 1st lumbar vertebra in adults (in
Infants, It may reach Inferiorly to the 3rd lumbar vertebra).
The subarachnold space extends Inferiorly as far as the lower
border of the 2nd sacral vertebra. The lower lumbar part of
the vertebral canal is thus occupied by the subarachnold
space, which contains the lumbar and sacral nerve roots and
the filum terminale {the cauda equina). A needle inserted
Into the subarachnold space In this region usually pushes the
nerve roots to one side without causing damage.
With the patient lying on his or her side or In the
upright sitting posltlon, with the vertebral column well

flexed, the space between adjoining laminae in the lumbar
region Is opened to a maximum (Fig. 1-20). An Imaginary
line joining the highest points on the mac crests passes
over the 4th lumbar spine. Using a careful aseptic technique and local anesthesia, the clinician passes the lumbar puncture needle fitted with a stylet Into the vertebral
canal above or below the 4th lumbar spine. The needle will
pass through the following anatomical structures before
It enters the subarachnold space: (a) skin, (b) superftdal
fascia, (c) suprasplnous ligament, (d) lntersplnous ligament, (e) llgamentum flavum, (f) areolar tissue containing
the internal vertebral venous plexus, (g) dura mater, and
(h) arachnoid mater. The depth to which the needle will
have to pass wlll vary from 1 In (2.5 cm) or Jess ln a child
to as much as 4 ln (10 cm) In an obese adult.
As the stylet Is withdrawn, a few drops of blood may
escape. This usually indicates that the point of the needle
is in one of the veins of the internal vertebral plexus and
has not yet reached the subarachnoid space. If the needle
stimulates one of the nerve roots of the cauda equlna,
the patient wtll experience a fleeting discomfort In one of
the dermatomes or a muscle will twitch, depending on
whether a sensory or a motor root was affected.

Spina! tap









-~ I



Dura mater


Arachnoid mater


Figure 1-20 Sagittal section through the lumbar part of the vertebral column in a position
of flexion. Note that the spines and laminae are
well separated in this position allowing insertion
of the spinal tap needle into the subarachnoid


CHAPTER 1 Introduction and Organization of the Nervous System

CSF pressure can be measured by attaching a manometer to the needle. When the patient ls In the recumbent
posltlon, the normal pftlllll'e 18 about 60 to 150 mm of
water. The pressure shows oscillations corresponding to
the movements of respiration and the arterial pulse.
A block of the subarachnoid space in the vertebral
canal, which may be caused by a tumor of the spinal
cord or the meninges, can be detected by compressing
the Internal jugular veins In the neck. This raises the
cerebral venous pressure and inhibits the absorption of
CSF in the arachnoid granulations, thereby increasing the
manometer reading of the CSF pressure. If thls rise does
not occur, the subarachnotd space Is blocked, and the
patient exhibits a positive Qoeckemtedt 91gn.

protected by a helmet, the brain can be severely damaged
without cltnlcaJ evidence of scalp Injury.

Skull Fractures
Severe blows to the head can change the shape of the skull
at the point of impact. Small objects may penetrate the skuU
and lacerate the brain. Larger objects applted with great
force may shatter the skull and drtve fragments of bone Into
the brain at the site of Impact.
In the adult, fractures of the skull are common, but they
are less common in the young child. ln the infant, the skull
bones are more resilient, and they are separated by fibrous
sutural ltgaments. In the adult, the Inner table of the skull ls
particularly brittle. Moreover, the sutural ligaments begin
to ossify during middle age.
The type of fracture that occurs in the skull will depend
on the age of the patient, the severity of the blow, and
the area of the skull receiving the trauma. The adult 8kull
resembles an eggsheU, with llmlted resWence. A severe,
localized blow will cause a local lndentaUon, commonly
with bone splintering. Blows to the vault can result In a
series of linear fractures, which radiate out through the
thin areas of the bone. The petrous parts of the temp~
raJ bones and the occipital crests (see Fig. 5-6) strongly
reinforce the base of the skulJ and tend to deftect linear
The yoq chlld•s skull resembles a plnf1>0ng ball.
because a localized blow produces a depression without
splintering. This common type of circumscribed lesion is
known as a "pond" fracture.

Caudal Anesthesia
Anesthetic solutions may be Injected into the sacral canal
through the sacral hiatus. The solutions pass upward In
the loose connective tissue and bathe the spinal nerves
as they emerge from the dural sheath (Fig. 1-21). Obstetricians use this method of nerve block to relieve the pains
of the first and second stages of labor because anesthetic
administered by this method does not affect the Infant.
Caudal anesthesia can also be used In operations In the
sacral region, including anorectal surgery.

Head Injuries
A blow to the head may merely bruise the scalp; severe
blows may tear or split the scalp. Even If the head Is

Alum termlnale ..


Csuda equlna

,,// ...~········· Dura mater

:.----- .....


..-···· • _


POattmor superior --lilac spine

~-:-',...Nerve roots of

·\!:,-- ....···

sacral nerves

_ =-,,.. Posterior root



g anglia

Posterior view of the sacrum.
Laminae have been removed to show the
sacral nerve roots lying within the sacral

Figure 1-21

Clinical Notes


Trauma due to negative pressure _

l.)irect cerebral trauma


Direct cerebral trauma


Trauma due to

negaave pressure

Distortion of bralnstem
Direct cerebral tmuma,,.......--


Epidural h~rrhage



Secondary trauma due 10 cerebral momentum



Figure 1-22 A:. Mechanisms of acute cerebral injury when a blow is applied to the lateral side
of the head. B: Varieties of intracranial hemorrhage. C: Mechanism of cerebral trauma following a
blow on the chin. The movement of the brain within the skull can also tear the cerebral veins.
Brain Injuries

Brain Injuries are caused by displacement and distortion of
the neuronal tissues at the moment of impact (Fig. 1-22). The
brain, which is incompressible, is like a water-soaked log
suspended in water. The brain Is fioallng In the CSF In the
subarachnold space and Is capable of a certain amount of
anteroposterior and lateral gilding movement. The anteropostertor movement is limited by the attachment of the
superior cerebral veins to the superior sagittal sinus. Lateral displacement of the brain Is limited by the falx cerebrl.
The tentorlum cerebelll and the falx cerebelll also re.strict
displacement of the brain.
Thus, blows on the front or back of the head lead to
displacement of the brain, which may cause severe cerebral damage, stretching and distortion of the brainstem,

and stretching and even tearing of brain commissures.
Blows to the side of the head cause less cerebral displacement, and the Injuries to the brain consequently
tend to be less severe. However, the falx cerebrl is a
tough structure and may cause considerable damage to
the softer brain tissue in cases of a severe blow to the
side of the head. Furthermore, remember that glancing
blows to the head may cause considerable brain rotation,
with shearing strains and brain distortion, particularly
in areas where further rotation ls prevented by bony
prominences in the anterior and middle cranial fossae.
Brain lacerations are very likely to occur when the brain
ts forclbly thrown against the sharp edges of bone within
the skull (see pp. 191-192,rthe lesser wings of the sphenold, for example.



CHAPTER 1 Introduction and Organiration of the Nervous System

When the brain moves suddenly within the skull, the
part of the brain that moves away from the skull wall is

subjected to diminished pressure because the CSF has not
had time to accommodate to the brain movement. This
results in a suction effect on the brain surface, with rupture
of swface blood vessels.
A sudden severe blow to the head, as In an automobile
accident, may result In damage to the brain at two sites: at
the point of impact and at the pole of the brain opposite
the point of impact, where the brain is thrown against the
skull wall. This ls refened to as contrecoop Injury.
The movement of the brain within the skull at the time
of head Injuries not only ls likely to cause avulslon of cranial nerves but commonly leads to rupture of tethering
blood vessels. Fortunately, the large arteries found at the
base of the brain are tortuous, and this, coupled with their
strength, explains why they are rarely tom. The thin-walled
cortical veins, which drain Into the large dural venous
sinuses, are very vulnerable and can cause severe subdural
or subarachnofd hemorrhage.

Traumatic Brain Injury Following an Explosion or Blast
Deployed soldiers are frequently exposed to explosive
devices, which may result in extensive injuries to the limbs,
eye.s, and ears. Open Injuries to the skull, where shrapnel
has entered the brain, are clearly visible and are dealt with
However, In closed Injuries, in which the skull remains
intact, the underlying brain may be damaged but left
untreated. In these cases, the explosion produces a blast
of air that strikes the skull and shakes up the brain,
resultJng In multiple Injuries to the soft brain tissue as It is
driven against the hard bony projections within the skull.
The symptoms and signs will depend on the extent of the
neurologic damage and will be mild, moderate, or severe.
Although the moderate and severe cases are quickly recognized by medical personnel, the mild cases may be missed,
and patients may later develop headaches, nausea. mood
changes, and memory loss. Early diagnosis ts Imperative
a.s studies of these patients have shown that mild neurologic damage can be successfully treated. Individuals who
have been exposed to explosive devices should undergo
computed tomography (Cl) scan or magnetic resonance
Imaging (MRI) before returning to civilian life.
lntracranial Hemonhage
Although the brain is cushioned by the surrounding CSF
in the subarachnoid space, any severe hemorrhage within
the relatlvely rigid skull will ultimately exert pressure on
the brain.
Four types of lntracranlal hemorrhage may result from
trauma or cerebral vascular lesions (see Fig. 1-22).
Epidural (extradural) hemonhage results from injuries
to the meningeal arteries (commonly the anterior dlvtsion
of the middle meningeal artery) or veins (see Fig. 1~. A
comparatively minor blow to the side of the head, resulting
In fracture of the skull In the region of the anterior-Inferior
portion of the parietal bone, may sever the artery (see
Fig. 1-22). Arterial or venous injury is especially likely to
occur if the vessels enter a bony canal In this region. Bleeding occurs and strips the meningeal layer of dura from the
Internal swface of the skull. The intracranlal pressure (ICP)
rises, and the enlarging blood clot exerts local pressure on
the underlying precentral gyros (motor area). Blood may
also pass laterally through the fracture line to form a soft

swelling on the side of the head. To stop the hemonhage,
the tom artery must be ligated or plugged. The burr hole
through the skull wall should be placed about 1.5 in (4 cm)
above the midpoint of the zygomatic arch.
Sobdural hemorrhage results from tearing of the superior cerebral veins where they enter the superior sagittal
sinus (see Figs. 1>1 and 17-5). The cause ls usually a blow
to the front or back of the head resulting In excessive
anteroposterior displacement of the brain within the skull.
This condition, which is much more common than middle
meningeal hemorrhage, can be caused by a sudden minor
blow. Once the vein Is tom, blood under low pressure
begins to accumulate ln the potential space between the
dura and the arachnoid. The condition ls rarely bilateral.
Acute and chronic forms occur depending on the speed
of accumulation of fluid in the subdural space. For example, if the patient starts to vomit. the venous pressure will
rise as the result of a rise In the lntrathoraclc pressure.
Under these circumstances, the subdural blood clot will
rapidly Increase tn size, causing acute symptoms. In the
chronic form, over a course of several months, the small
blood clot will attract Ouid by osmosis, in which case a
hemorrhagic cyst forms and gradually espands, causing
pressure symptoms. In both forms, the blood clot must be
removed through burr holes in the skull.
Subandmold hemorrba&e results from nontraumatic
leakage or rupture of a congenital aneurysm on the ce~
bral arterial circle (circle of WiJlis) or, less commonly, from
an arteriovenous malformation. Sudden onset of severe
headache, neck stiffness, and loss of consciousness occurs.
The diagnosis Is established by CT or MRI or by withdrawing heavily blood-stained CSF through a lumbar puncture.
With cerebral hemorrhage. spontaneoaa hdracerebral
hemorrhate (see Fig. 1-22) is most common in patients
with hypertension. It ls generally due to rupture of the thbl·
walled lendculomlale artery (see Ftg. 17-11), a branch of
the middle cerebral artery (see Fig. 174). The hemorrhage
involves important descending nerve Hbers in the Internal
capsule and causes hemiplegia on the contralateral side.
The patient Immediately loses consciousness, and paraly·
sis Is evident when consciousness ls regained. The diagnosis Is established by brain CT or MRI.

Shaken Baby Syndrome
Inflicted head lnJuryls the most common cause of traumatic
death ln Infancy. Sudden deceleration, which occurs when
an infant is held by the arms or trunk and shaken or the
head is forcefully struck against a hard surface, is believed
to be responsible for the brain injuries. Btomechanical studies have shown that the rotatJon of the floating brain around
its center of gravity causes diffuse brain Injuries, Including
diffuse axonal Injury and subdural hematoma. In shaken
baby syndrome, major rotational forces have to occur that
clearly exceed those encountered in normal child play

Most cases of shaken baby syndrome take place during
the first year of life, and they are usually restricted to
infants under 3 years of age. Common symptoms include
lethargy, irritability, seizures, altered muscle tone, and
symptoms Indicating raised ICP, such as Impaired consciousness, vomiting, breathing abnormalities, and apnea.
In severe cases, the baby may be unresponsive. the fontanelles are bulging, and the child may have retinal hemor·
rhages. Spinal tap may reveal blood in the CSF. Subdural or
subarachnoid hemonhages can be readily detected on CT

Clinical Notes

or MRI scans. Autopsy findings commonly Include localized
subdural hemorrhage In the parietal-occipital region and
subatachnoid blood, associated with massive cerebral
swelling and widespread neuronal loss.

Space-Occupying Lesions Within the Skull
Space-occupying or expanding lesions within the skull
Include tumor, hematoma, and abscess. Because the skull
is a rigid container of fixed volume, these lesions will add to
the normaJ bulk of the intracranial contents.
An expanding lesion ls first accommodated by the
expulsion of CSF from the cranial cavity. Later, the veins
become compressed, interference with the circulation
of blood and CSF begins, and the ICP starts to rise. The
venous congestion results in increased production and
diminished absorption of CSF, the CSF volume begins to
rise, and thus, a vicious circle Is established.
The position of the tumor within the brain may have a
dramatic effect on the signs and symptoms. For example, a
tumor that obstructs the outflow of CSP or directly presses
on the great veins will cause a rapid increase in ICP. The
signs and symptoms that enable the clinician to localize
the lesion wtll depend on the degree of Interference with
brain function and nervous tissue destruction. Severe
headache, possibly due to the stretching of the dura mater,
and vomiting, due to pressure on the bralnstem, are common complaints.
A spinal tap should not be performed In patients with
suspected lntracranlal tumor. The withdrawal of CSF may
lead to a sudden displacement of the cerebral hemisphere
through the notch In the tentorium cerebelli into the posterior cranial fossa (Fig. 1-23) or herniation of the medulla
oblongata and cerebellum through the foramen magnum.
CT scans or MRls are used In diagnosis.

Computed Tomography
CT ls used for the detection of lntracranlal lesions. The p~
cedure is quick, safe, and accurate. The total dose of Irradiation is no greater than for a conventional skull radiograph.
CT relies on the same physics as conventional radiographs, tn that structures are dlsUngulshed from one
another by their ability to absorb energy from x~ays. The
x~ay tube emits a narrow beam of radiation as It passes
In a series of scanning movements through an arc of 180
degrees around the patient's head. The x~ays having
passed through the head are collected by a special Hay
detector. The Information Is fed to a computer that processes the lnfonnation, which ls then displayed as a reco~
structed picture on a screen. Essentially, the observer sees
an Image of a thin slice through the head, which may then
be photographed for later examination (Fig. 1-24).
The sensitivity is such that small differences in x-ray
absorption can be easily displayed. The gray matter of
the cerebral cortex, white matter, Internal capsule, corpus
callosum, ventricles, and subarachnoid spaces can all be
recognized. An lodlne<ontainlng medium can be Injected
intravascularly, which enhances greatly the contrast
between tissues having a different blood flow.
Because a CT scan can be performed in 5 to 10 minutes,
It ls the method of choice In an emergency situation with
patients with head trauma or suspected intracranlal hemorrhage.

Magnetic Resonance Imaging
MRI uses the magnetic properUes of the hydrogen nucleus
excited by radlofrequency radiation transmitted by a coll
surrounding the head. The excited hydrogen nuclei emit
a signal that is detected as Induced electric currents tn
a receiver coil. MRI is absolutely safe to the patient. and

Rllx cerebrl

~Herniation of part of cerebrum
through tentorlal notch

Figure 1-23 Sudden displacement of the cerebral hemispheres through the tentorial notch
into the posterior cranial fossa following a lumbar puncture; the cerebral tumor is situated in
the right cerebral hemisphere. CT or MRI should be used rather than lumbar puncture when
investigating a cerebral tumor.



CHAPTER 1 Introduction and Organiration of the Nervous System

Frontal bone --

- - Frontal lobe

Gray matter --White matter- -

Longitudinal fissure
- Anterior horn of
lateral ventricle

Third ventricle --

Septum pellucidum
Parietal lobe

Pineal body

Faix cerebri

Posterior horn of
lateral ventricle

Occlpltal lobe

Gray matter ~....__

- crest of frontal bone

White matter-

-- Genu of
corpus callosum

Head of -._
caudate nucleus

Anterior horn of
lateral ventricle

Septum pellucidum -

- LentHorm nucleus

Anterior column
of fornlx

plneal body

Third ventricle

- Cistern superior to
superior colllcull

Fbs1erior horn of --lateral wnlricle

choroid plexus
Internal occipital

-...... Faix cerebri

Figure 1-24 CT scan showing the structure of the brain. A,, B: Horizontal cuts (axial sections).

Clinical Notes

because it provides better differentiation between gray and
white matter, MRI can be more revealing than CT. The reason
for this is that gray matter contains more hydrogen in the
form of water than white matter, and the hydrogen atoms
are less bound In fat (Fig. 1-25). MRI Is the best imaging

method for detecting low-contrast lesions such as brain
tumors or small multiple sclerosis plaques. It is also capable of showing clear images of the bra!nstem, cerebellum,

and the pituitary fossa, which, In the case of a CT scan, are
overshadowed by the dense bones of the base of the skull.

_ / Corpus callosum
Genu of -.__
corpus callosum

Fourth ventricle

Nasal sepllJm

---- Cerebellum
-.... Medulla oblongata


Lateral venb1cle


Langltudlnal fissure


Corpus c:allosum


caudate nucleus
Lsntifonn nucleus

Lateral sulcus

Internal capsule

Temporal lobe

Figure 1-25 MRI showing the structure of the brain. A: Sagittal. B: Coronal. Compare with
Figure 1-24. Note the better differentiation between gray and white matter.



CHAPTER 1 Introduction and Organiration of the Nervous System

The spinal cord structure Is much more clearly visualized
with MRI.
Unfortunately, an MRI taJces longer and costs two-thirds
more than a CT scan.

Positron Emission Tomography

Figure 146 Axial (horizontal) PET scan of a normal
brain following the injection of 18-fluorodeoxyglucose.
Regions of active metabolism (yellow areas) are seen
in the cerebral cortex. The lateral ventricles are also
demonstrated. (Courtesy Dr. Holley Dey.)

Figure 1-27 Axial (horizontal) PET scan of a 62-yearold male patient with a malignant glioma in the left
parietal lobe following the injection of 18-fluorodeoxygluc:ose. A high concentration of the compound
(circular yellow area) is seen in the region of the tumor.
(Courtesy Dr. Holley Dey.)

Positron emission tomography (PET) uses radioactive isotopes that decay with the emission of positively
charged electrons (positrons) to map the biochemical,
physiologic, and pharmacologlc processes taking place
In the brain.
The appropriate Isotope Is Incorporated Into molecules
of known biochemical behavior In the brain and then is
injected into the patient. The metabolic activity of the
compound can then be studied by making cross-sectional
tomographic Images of the brain using the same prlnclpJes
as in CT (Fig. 1-26). Making a series of time-lapse Images
at different anatomical sites allows variations In brain
metaboli$m to be studied at these sites. This technique
has been used to study the distribution and activity of
neurotransmltters, variations in oxygen utlllzatlon, and
cerebral blood now.
PET has been successfully used In the evaluation of
patients with brain tumors (Figs. 1-27 and 1-28), movement
disorders, seizures, and schizophrenia.

Figure 1-28 Coronal PET scan of a 62-year-old male
patient with a malignant glioma in the left parietal lobe
following the injection of 18-fluorodeoxyglucose (same
patient as in Fig. 1-25). A high concentration of the
compound {circular ye/low area) is seen in the region of
the tumor. (Courtesy Dr. Holley Dey.)

Clinical Problem Solving


Central and Peripheral Nervous Systems

Major Divisions of the Peripheral Nervous System

• The nervous system comprises the central nervous
system (CNS) and peripheral nervous system (PNS).
• The CNS consists of the brain and the spinal cord,
both of which are surrounded by the meninges and
the cerebrospinal fluid (CSI').
• The PNS consists of all other nerves In the body.
• The autonomic nervous system (ANS) Is concerned
with lnvolwttary structures and distributed
throughout both CNS and PNS.

• Motor and sensory roots connect the spinal nerve
to the spinal cord.
• The spinal nerves divide Into anterior and posterior
raml, both containing motor and sensory fibers.
• The posterior rarni are distributed to the muscles and
skin of the back.
• Anterior rami supply the muscles and skin of the limbs
and the anterolateral body wall.
• Ganglia are collections of neuronal cell bodies that
result In fusiform swellings within the dorsal roots,
or as Irregular swellings within the ANS.

Major Divisions of the Central Nervous System
• The brain has three major divisions: hindbraln,
midbrain, and forebrain.
• The hindbraln can be subdivided into the medulla
oblongata, the pons, and the cerebellum; the
forebrain Into the diencephalon and the cerebrum.
• The cerebrum ls the largest component of the
brain and consists of two hemispheres, covered by
cerebral cortex, which is made up of a series of folds
and fissures called gyri and sulci.
• The spinal cord is a cylindrical structure continuous
with the medulla oblongata of the brainstem.
• Along the length of the spinal cord, 31 pairs of spinal
nerves are attached.

Early Development of the Nervous System
• During development, the embryo differentiates into
three layers, entoderm, mesoderm, and ectoderm.
• The ectoderm gives rise to the entire nervous
system, initially forming the neural plate, then
neural folds, and subsequently fusing Into the neural
• The leading edge of the neural folds contains
neural crest cells which differentiate into ganglion
cells, Schwann cells, melanocytes, and cells of the
suprarenal medulla.

f) Clinical Problem Solving
1. A 45-year-old woman is examined by her physician
and found to have carcinoma of the thyroid gland.
Apart from swelling in the neck, the patient also
complains of back pain in the lower thoracic region,
with a burning soreness radiating around the right
side of her thorax over the 10th lntercostal space.
Although the back pain can be relieved by changing
posture, it ls worsened by coughing and sneezing.
A lateral radlograph of the thoracic part of the vertebral column reveals a secondary carcinomatous
deposit in the 10th thoracic vertebral body. Further
physical examination reveals muscular weakness
of both legs. Using your knowledge of neuroanatomy, explain the following: (a) the pain in the back,
(b) the soreness over the right 10th intercostal
space, (c) the muscular weakness of both legs, and

(d) which segments of the spinal cord lie at the level
of the 10th thoracic vertebral body.
2. A 35-year-old coal miner Is crouching down at the
mine face to Inspect a drilling machine. A large
rock suddenly dislodges from the roof of the mine
shaft and strikes the miner on the upper part of
his back. Examination shows an obvious forward
displacement of the 8th thoracic vertebra. What
anatomical factors in the thoracic region determine the degree of injury that may occur to the
spinal cord?
3. A 20-year-old man with a long history of tuberculosis of the lungs is examined by an orthopedic
surgeon because of the sudden development of
a humpback (kyphosls). He also has symptoms
of a stabbing pain radiating around both sides of


CHAPTER 1 Introduction and Organization of the Nervous System

his thorax intensified by coughing or sneezing. A
diagnosis of tuberculous osteltls of the 5th thoracic vertebra is made, with the collapse of the
vertebral body responsible for the kyphosis. Using
your knowledge of neuroanatomy, explain why the
collapse of the 5th thoracic vertebral body should
cause pain in the distribution of the 5th thoracic
segmental nerve on both sides.
4. A 50-year-old man wakes up one morning with a
severe pain near the lower part of the back of his
neck and left shoulder. The pain is also referred
along the outer side of the left upper arm. Movement of the neck causes an increase in the Intensity
of the pain, which ls also accentuated by coughing.
A lateral radlograph of the neck shows a slight narrowing of the space between the 5th and 6th cervical vertebral bodies. A magnetic resonance imaging
(MRI) shows disruption of the intervertebral disc
between the 5th and 6th cervical vertebrae. Using
your knowledge of anatomy, state which nerve root
was Involved. Also, state the nature of the disease.
5. A medical student offers to help a fellow student
straighten out the bumper of a car. He has Just
finished his course in neuroanatomy and Is in poor
physical shape. Undaunted, he attempts to lift the end
of the bumper while his friend stands on the other
end. Suddenly, he feels an acute pain in the back that
extends down the back and outer side of his right
leg. Later, he is examined by an orthopedic surgeon,
who finds that the pain is accentuated by coughing.
A lateral radiograph of the lumbar vertebral column
reveals nothing abnormal. A magnetic resonance
Imaging (MRI) taken in the sagittal plane shows a
small posterior prolapse of the nucleus pulposus in
the disc between the 5th lumbar and the 1st sacral
vertebrae. A diagnosis of herniation of the intervertebral disc between the 5th lumbar and 1st sacral
vertebrae ls made. Using your knowledge of neuroanatomy, explain the symptoms of this disease.
Which spinal nerve roots were pressed on?
6. A 5-year-old child is seen in the emergency department, and a diagnosis of acute meningitis is made.





The resident decides to perform a lumbar puncture
in order to confirm the diagnosis. Using your knowledge of neuroanatomy, where would you perform
a lumbar puncture? Name, in order, the structures
pierced when a lumbar puncture needle is inserted
into the subarachnoid space.
A pregnant young woman tells her friends that she
hates the Idea of going through the pain of childbirth
but that she equally detests the thought of having a
general anesthetic. Is there a specialized local analgesic technique that will alleviate labor pains?
While crossing the road, a pedestrian Is struck on the
right side of his head by a passing car. He falls to the
ground but does not lose consciousness. After resting
for an hour and then getting up, he appears to be
confused and irritable. Later, he staggers and falls to
the floor. On questioning, he is seen to be drowsy, and
twitching of the lower left half of his face and left arm
is noted. A diagnosis of epidural hemorrhage is made.
Which artery Is likely to have been damaged? What is
causing the drowsiness and muscle twitching?
A 45-year-old woman Is examined by a neurologist
and found to have an intracranial tumor. She complains of severe headaches, which occur during the
night and early morning. She describes the pain as
"bursting" in nature, and although at first, 6 months
ago, the headaches were intermittent, they are now
more or less continuous. Coughing, stooping, and
straining during defecation make the pain worse. The
pain is accompanied by vomiting on three recent
occasions. What is the sequence of events that
occurs within the skull as the intracranial pressure
(ICP) rises? Would you perform a routJne lumbar
puncture on every patient you suspected of having
an intracranial twnor?
While examining an unconscious 18-year-old
man admitted to the emergency room following a
motorcycle accident, the neurosurgeon asks the
attending medical student what happens to the brain
in an accident in which it is suddenly decelerated
within the skull. How would you answer the inquiry?
What is the value of wearing a helmet?

Answers and Explanations to Clinical Problem Solving
1. Carcinoma of the thyroid, breast, kidney, lung, and
prostate commonly gives rise to metastases in
bone. (a) The pain in the back was caused by the
carcinoma invading and destroying the 10th thoracic vertebral body. (b) Compression of the posterior
nerve root of the 10th thoracic spinal nerve by
the carcinoma of the vertebral column caused the
hyperesthesla and hyperalgesla over the right 10th
intercostal space. (c) Muscular weakness of the legs
was caused by pressure on the descending motor
nerve fibers In the spinal cord by the carcinoma's
invasion of the vertebral canal. (cl) Although dlsp~
portionate growth in length of the vertebral column
occurs during development compared with that of

the spinal cord, the upper cervical segments of the
spinal cord still lie posterior to the vertebral bodies
of the same number. However, the spinal cord in the
adult terminates inferiorly at the level of the lower
border of the 1st lumbar vertebra, and therefore,
the Isl and 2nd lumbar segments of the spinal cord
lie at the level of the 10th thoracic vertebral body.
2. This patient had a severe fracture dislocation
between the 7th and 8th thoracic vertebrae. The
vertical arrangement of the articular processes and
the low mobility of this region because of the thoracic cage mean that a dislocation can occur In this
region only if the articular processes are fractured
by a great force. The small circular vertebral canal

Review Questions






leaves little space around the spinal cord; thus,
severe cord Injuries are certain.
Each spinal nerve ls formed by the wlion of a posterior sensory root and an anterior motor root and
leaves the vertebral canal by traveling through an
intervertebral foramen. Each foramen ls bounded
superiorly and inferiorly by the pedicles of adjacent
vertebrae, anteriorly by the lower part of the vertebral body and by the intervertebral disc, and posteriorly by the articular processes and the joint between
them. In this patient, the 5th thoracic vertebral body
had collapsed and the lntervertebral forarnina on
both sides had been considerably reduced In size,
causing compression of the posterior sensory roots
and the spinal nerves. The consequent Irritation of
the sensory fibers was responsible for the pain.
This patient had symptoms suggestive of irritation of the left 6th cervical posterior nerve root.
The radlograph revealed narrowing of the space
between the 5th and 6th cervical vertebral bodies,
suggesting a herniation of the nucleus pulposus of
the intervertebral disc at this level. MRI showed the
nucleus pulposus extending posteriorly beyond the
anulus fibrosus, thus confirming the diagnosis.
The herniation occurred on the right side and was
relatively small. The pain occurred in the distribution of the 5th lumbar and 1st sacral segments of
the spinal cord, and the posterior sensory roots
of these segments of the cord were pressed on the
right side.
In a 5-year-old child, the spinal cord terminates inferiorly at about the level of the 2nd lumbar vertebra
(certainly no lower than the 3rd lumbar vertebra).
With the child lying on his side and with the operator
using an aseptic technique, the skin is anesthetized
in the midline just below the 4th lumbar spine. The
4th lumbar spine lies on an imaginary line joining the
highest points on the iliac crests. The lumbar puncture needle fitted with a stylet ts then passed carefully into the vertebral canal. The needle will pass
through the skin, superficial fascia, supraspinous
and lnterspinous ligaments, Ugamentum flavum, areolar tlssue containing the internal vertebral venous
plexus, and the dura and arachnoid mater before
entering the subarachnold space.


7. Caudal analgesia (anesthesia) Is very effective In
labor If It ts performed skillfully. The anesthetic solutions are Introduced into the sacral canal through
the sacral hiatus. Sufficient solution is given so that
the nerve roots up as far as Tll-T12 and L1 are
blocked. This will make the uterine contractions
painless during the first stage of labor. If the nerve
fibers of S2-S4 are also blocked, the perineum will
be anesthetized.
8. A blow on the side of the head can fracture the
thin anterior part of the parietal bone. The anterior
branch of the middle meningeal artery commonly
enters a bony canal In this region and ts sectioned
at the time of the fracture. The resulting hemorrhage
causes gradual accumulation of blood under high
pressure outside the meningeal layer of the dura
mater. The pressure ls exerted on the underlying
brain as the blood clot enlarges, and the symptoms
of confusion and Irritability become apparent. This is
followed later by drowsiness. Pressure on the lower
end of the motor area of the cerebral cortex (the
right precentral gyrus) causes facial muscle twitc~
ing and, later, left arm muscle twitching. As the blood
clot progressively enlarges, the intracranial pressure
(ICP) rises and the patient's condition deteriorates.
9. A detailed account of the various changes that
occur in the skull in patients with an intracranial
tumor Is given on page 23. A patient suspected of
having an lntracranlal twnor should not undergo
a spinal tap. The withdrawal of cerebrospinal fluid
(CSF) may lead to a sudden displacement of the
cerebral hemisphere through the opening In the
tentorlum cerebelli into the posterior cranial fossa
or herniation of the medulla oblongata and cerebellum through the foramen magnum. CT scans or
MRis are now used in making the diagnosis.
10. The brain is floating in the cerebrospinal fluid (CSF)
within the skull, so a blow to the head or sudden
deceleration leads to displacement of the brain. This
may produce severe cerebral damage; stretching
or distortion of the bralnstem; awlslon of cranial
nerves; and, commonly, rupture of tethering cerebral
veins. A hebnet helps to protect the brain by cus~
toning the blow and thus slowing the rate of brain

Review Questions

Directions: Each of the incomplete statements in this section is followed by completions of the statement. Select
the ONE lettered completion that ts BEST In each case.

1. The spinal cord has
(a) an outer covering of gray matter and an inner
core of white matter.
(b) an enlargement below that forms the conus

(c) anterior and posterior roots of a single spinal
nerve attached to a single segment.
(d) cells In the posterior gray horn that give
rise to efferent fibers that supply skeletal
(e) a central canal that ls situated In the white


CHAPTER 1 Introduction and Organization of the Nervous System

2. The medulla oblongata has
(a) a tubular shape.
(b) the fourth ventricle lying posterior to its lower
(c) the midbrain directly continuous with its upper
(d) no central canal in its lower part.
(e) the spinal cord directly continuous with its
lower end in the foramen magnum.
3. The mldbraln has
(a) a cavity called the cerebral aqueduct.
(b) a large size.
(c) no cerebrospinal fluid (CSF) around it.
(d) a cavity that opens above into the lateral ventricle.
(e) a location in the middle cranial fossa of the skull.
Directions: Each of the numbered items in this section
is followed by answers. Select the ONE lettered answer
that is CORRECT.
4. The following statements concern the cerebellum:
(a) It lies within the middle cranial fossa.
(b) The cerebellar cortex is composed of white
(c) The vermis is the name given to that part joining the cerebellar hemispheres together.
(d) The cerebellum lies anterior to the fourth ventricle.
(e) The dentate nucleus is a mass of white matter
found in each cerebellar hemisphere.
5. The following statements concern the cerebrum:
(a) The cerebral hemispheres are separated by a
fibrous septum called the te