CLI ICALNEUROANATOMY

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CLINICALNEURHANATMY

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IN MEMORIAMRichard S. Snell, MRCS, LRCP, MB, MD, PhD

1925—201 5Clinical Anatomy by RegionsClinical Anatomy by Systems

Clinical Neuroanatomy

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CLINICALNEUROANATOMY

RYAN SPLITI'GERBER, PhDAssociate Professor, Department of SurgeryVanderbilt University Medical CenterOffice of Health Sciences EducationVanderbilt University School of MedicineNashville, Tennessee

Formerly CQuence Distinguished ProfessorAssistant DeanCollege of Allied Health ProfessionsUniversity of Nebraska Medical CenterOmaha, Nebraska

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Senior Acquisitions Editor: Crystal TaylorDevelopment Editor: Andrea Vosburgh, Kelly HorvathEditorial Coordinator: John LarkinMarketing Manager: Michael McMahonProduction Project Manager: Marian BellusDesign Coordinator: Teresa MallonManufacturing Coordinator: Margie OrzechPrepress Vendor: Aptara, Inc.

Eighth editionCopyright © 2019 Wolters Kluwer.

Copyright © 2010, 2006, 2001, 1997, 1992, 1987, 1980 Wolters Kluwer Health/Lippincott Williams& Wilkins. All rights reserved. This book is protected by copyright. N0 part of this book may bereproduced or transmitted in any form or by any means, including as photocopies or scanned-inor other electronic copies, or utilized by any information storage and retrieval system withoutwritten permission from the copyright owner, except for brief quotations embodied in criticalarticles and reviews. Materials appearing in this book prepared by individuals as part oftheir official duties as U.S. government employees are not covered by the above-mentionedcopyright. To request permission, please contact Wolters Kluwer at Two Commerce Square,2001 Market Street, Philadelphia, PA 19103, via email at permissions@lww.com, or via ourwebsite at shop.lww.com (products and services).

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Library of Congress Cataloging-in-Publication Data

Names: Splittgerber, Ryan, author. | Preceded by (work): Snell, Richard S.Clinical neuroanatomy.

Title: Snell’s clinical neuroanatomy / Ryan Splittgerber.Other titles: Clinical neuroanatomyDescription: Eighth edition. | Philadelphia : Wolters Kluwer, [2019] |

Preceded by: Clinical neuroanatomy / Richard S. Snell. 7th ed.Philadelphia : Wolters Kluwer Lippincott Williams & Wilkins, c2010. |Includes index.

Identifiers: LCCN 2018033967 | ISBN 9781496346759 (paperback)Subjects: | MESH: Nervous System—anatomy & histologyClassification: LCC QM451 | NLM WL 101 | DDC 616.8—dc23LC record available at https://lccn.loc.gov/2018033967

This work is provided “as is,” and the publisher disclaims any and all warranties, expressor implied, including any warranties as to accuracy, comprehensiveness, or currency of thecontent of this work.

This work is no substitute for individual patient assessment based upon healthcareprofessionals’ examination of each patient and consideration of, among other things, age,weight, gender, current or prior medical conditions, medication history, laboratory dataand other factors unique to the patient. The publisher does not provide medical advice orguidance and this work is merely a reference tool. Healthcare professionals, and not thepublisher, are solely responsible for the use of this work including all medical judgments andfor any resulting diagnosis and treatments.

Given continuous, rapid advances in medical science and health information, independentprofessional verification of medical diagnoses, indications, appropriate pharmaceuticalselections and dosages, and treatment options should be made and healthcare professionalsshould consult a variety of sources. When prescribing medication, healthcare professionalsare 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 sideeffects and identify any changes in dosage schedule or contraindications, particularly if themedication to be administered is new, infrequently used or has a narrow therapeutic range.To the maximum extent permitted under applicable law, no responsibility is assumed bythe publisher for any injury and/or damage to persons or property, as a matter of productsliability, negligence law or otherwise, or from any reference to or use by any person of thiswork.

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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 I deserve.

To my boys, Carter and Caden

For providing inspiration and humor...a lot of humor.

To my students

May you find your Tower.

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0 Preface

This book contains the basic neuroanatomical factsnecessary for the practice of medicine. It is suitable formedical students, dental students, nurses, and alliedhealth students. Residents find this book useful duringtheir rotations.

The functional organization of the nervous systemhas been emphasized and indicates how injury anddisease can result in neurologic deficits. The amountof factual information has been strictly limited to thatwhich is clinically important.

In this edition, authorship has transitioned fromthe late Dr. Richard Snell, who, with brilliance anddedication, fathered the previous seven editions andprovided the framework for the eighth. The content ofeach chapter has been reviewed and edited to be morestraightforward and concise. The traditional artworkhas been recolored and updated to enhance the clarityand to provide additional information to each image.High-quality magnetic resonance images and histo-logic photomicrographs have been updated to providegreater visual details.

Each chapter introduces the relevance of neuroanat-omy through a short case report.

0 Clinical Example. A short case report that serves todramatize the relevance of neuroanatomy introduceseach chapter.

0 Chapter Objectives. This section details the materialthat is most important to learn and understand in eachchapter.

0 Basic Neuroanatomy. This section provides basicinformation on neuroanatomical structures that areof clinical importance. Numerous examples of normalradiographs, CT scans, MRls, and PET scans are alsoprovided. Many cross-sectional diagrams have beenincluded to stimulate students to think in terms ofthree-dimensional anatomy, which is so important in

the interpretation of CT scans and MR images.0 Clinical Notes. This section provides the practical

application of neuroanatomical facts that are essentialin clinical practice. It emphasizes the structures thatthe clinician will encounter when making a diagnosisand treating a patient. It also provides the informationnecessary to understand many procedures and tech-niques and notes the anatomical “pitfalls” commonlyencountered.

0 NEW! Key Concepts. These quick, bulleted reviews ofkey topics and information are provided at the end ofeach chapter.

0 Clinical Problem Solving. This section provides the stu-dent with many examples of clinical situations in whicha knowledge of neuroanatomy is necessary to solve clin-ical problems and to institute treatment; solutions to theproblems are provided at the end of the chapter.

0 Review Questions. The purpose of the questions isthreefold: to focus attention on areas of importance, toenable students to assess their areas of weakness, andto provide a form of self-evaluation when questions areanswered under examination conditions. Some of thequestions are centered around a clinical problem thatrequires a neuroanatomical answer. Solutions to theproblem are provided at the end of each chapter.

An interactive Review Test, including over 450 ques-tions, is provided online.

The book is extensively illustrated. The majority of thefigures have been kept simple and are in color. As in theprevious edition, a concise Color Atlas of the dissectedbrain is included prior to the text. This small but import-ant group of colored plates enables the reader to quicklyrelate a particular part of the brain to the whole organ.

R.S.R.S.S.

vii

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0 Acknowledgments

Starting with the first edition of Clinical Neuroanatomypublished in 1980, many people have provided theirexpertise and should be recognized for their contri-butions. First and foremost, thanks to Richard S. Snellwhose shoulders we stand upon to advance our ownintellectual progress.

Throughout this text and in previous editions, thefollowing individuals provided valuable contributionsand are gratefully acknowledged: N. Cauna, L. Clerk, D. 0.Davis, H. Dey, M. Feldman, T. M. J. Fitzgerald, l. Grunther,J. M. Kerns, T. McCarthy, A. Peters, G. Sze, and L. Wener.

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

Vosburgh, development editor, and John Larkin, editorialcoordinator. Thanks also to freelance development edi-tor Kelly Horvath, who provided invaluable direction andpatience with me throughout the entire process.

SPi Global is gratefully acknowledged for their bril-liant art recoloring and enhancing the personality ofthis textbook.

My special thanks to Stephanie Vas, Program Direc-tor of the Magnetic Resonance Imaging Program at theUniversity of Nebraska Medical Center, who producedexceptional MR images for this edition.

I would like to extend my gratitude to my students,colleagues, and mentors for their encouragement andwisdom---especially, Sabra Peetz, Art Dalley, CathyPettepher, Lillian Nanney, and Kyle Meyer.

R.S.

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0 Contents

CHAPTER 1

CHAPTER 2

CHAPTER 3

Preface .........................................

Acknowledgments ................................Color Atlas of Brain ...............................

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

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

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

............. vii

............. ix

............ xix

1

xi

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xii Contents

CHAPTER 4

CHAPTER 5

CHAPTER 6

CHAPTER 7

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

Brainstem 185

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

Cerebellum and Its Connections 229

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

Cerebrum 249

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

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CHAPTER 8

CHAPTER 9

CHAPTER 10

CHAPTER 11

Contents xiii

The Structure and Functional Localization of the Cerebral Cortex 279

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

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

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

Cranial Nerve Nuclei 323

Cranial Nerves 323Cranial Nerve Organization 323Olfactory Nerves (Cranial Nerve I) 326Optic Nerve (Cranial Nerve 11) 327Oculomotor Nerve (Cranial Nerve III) 331Trochlear Nerve (Cranial Nerve IV) 331Trigeminal Nerve (Cranial Nerve V) 332Abducens Nerve (Cranial Nerve VI) 335Facial Nerve (Cranial Nerve VII) 337Vestibulocochlear Nerve (Cranial Nerve VIII) 339Glossopharyngeal Nerve (Cranial Nerve IX) 341Vagus Nerve (Cranial Nerve X) 343Accessory Nerve (Cranial Nerve X1) 345Hypoglossal Nerve (Cranial Nerve XII) 347Clinical Notes 348Clinical Problem Solving 356Answers and Explanations to Clinical Problem Solving 357Review Questions 358Answers and Explanations to Review Questions 361

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xiv Contents

CHAPTER 12

CHAPTER 13

CHAPTER 14

CHAPTER 15

Thalamus 363

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

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

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

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

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Contents xv

CHAPTER 16 Ventricular System and Cerebrospinal Fluid 436

CHAPTER 17

CHAPTER 18

APPENDIX

Ventricular System 436Subarachnoid Space 447Cerebrospinal Fluid 448Blood—Brain and Blood—Cerebrospinal Fluid Barriers 452Clinical Notes 455Clinical Problem Solving 458Answers and Explanations to Clinical Problem Solving 459Review Questions 460Answers and Explanations to Review Questions 462

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

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

Neuroanatomical Data of Clinical Significance and ClinicalNeuroanatomy Techniques 507

Index 513

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CLINICALNEURHANATMY

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0 Color Atlas of Brain

Frontal pole .Longitudinal fissure' Precentral sulcus

Frontal lobe _

__ ~ Precentral gyrus

Central sulcus

Left cerebralhemisphere ‘- - Postcentral gyrus

- Postcentral sulcus

Occipital lobe

Occipital pole

Frontal lobe - Longitudinal fissure

Olfactory tract

Right cerebral-hemisphere Optic chiasma

Temporal lobe

aOculomotor nerve

Midbrain

Pons_ _ _ -- Pyramid

Medulla oblongata - " " -

Figure CA-1 Top: Superior view of the brain. Bottom: Inferior view of the brain.

xix

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xx Color Atlas of Brain

Longitudinal fissure

Right cerebralhemisphere

. ‘ Superior frontalgyrus

Temporal pole -

_ _ - - Parieto-occipitalLeft cerebral '- sulcushemisphere

Occipital pole - _ _ _ _ _ Occupltal lobe

__ - Horizontal fissureof cerebellum

Cavity of fourthVermIs of- _ - _ ventricle

cerebellum

Inferior cerebellarLeft cerebellar peduncle

hemisphereGracile tubercle

Medulla- - ' 'oblongata - —_ ' " Cuneate tubercle

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

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Color Atlas of Brain xxi

Postcentral Postcentral Central Precentral Precentralsulcus_ gyrue sulcus gyrus _sulcus

__ .- Superior' frontal gyrus

Parieto-occipitalsulcus - Middle

frontal gyrus

. - Inferiorfrontal gyrus

. . Lateral sulcusOccupital lobe

Supenortemporal gyrus

Right cerebellarhemisphere

- Middletemporal gyrus

Medulla - - Inferioroblongata temporal gyrus

- Central sulcusCorpuscallosum _

- Cingulate gyrus

Cerebralaqueductof midbrain

Septum -pellucidum

. - Parieto-occipitalFornix - sulcus

Anterior --commissure

Optic chiasma —

Vermis ofcerebellum

- Cavity of fourthventricle

oblongata

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

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xxii Color Atlas of Brain

Anterior horn of'. __ -- Corpus callosumlateral ventricle -

Claustrum - - Septum pellucidum

lnsula- _ ' Caudate nucleus

Lateral sulcus ' ' Lentiform nucleus

Lateral ventricle -- __ - Corpus callosum

Caudate nucleus -

Third ventricle 'Fornix

Lentiform nucleus Medial thalamic nuclei

Mammillary body ' ' ' Lateral thalamic nuclei

' Optic nerve

._ - Corpus callosum

Choroid plexus inlateral ventricle

Figure CA-4 Coronal sections of the brain passing through the anterior horn of the lateralventricle (top), the mammillary bodies (middle), and the pons (bottom).

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Color Atlas of Brain xxiii

. --Genu of cor us callosumAnterior horn of- _ plateral ventricle

_. - Head of caudate nucleusInternal capsule-- _

(anterior limb) . Anterior column of fornix

Genu of internal capsule - ClaustrumPutamen— Lentiform

nucleusInternal capsule(posterior limb) -Globus pallidus

Third ventricle-

Posterior horn of- ' ' I I -' .. _ ' " Splenium oflateral ventricle

Caudate nucleus Corpus callosum

Thalamus- - Lateral ventricle

Lentiform nucleuS* Fornix

Third ventricle

Crus cerebri of midbrain -' "- .- — “ Third ventricle' . ' (inferior part)

' ' Cerebellum

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

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xxiv Color Atlas of Brain

Olfactory bulb

Olfactory tract

Optic nerve

Trigeminal nerve

Vestibulocochlearnerve- . ' -.' .. -. _ ' Trochlear nerve

Roots of glossopharyngeal,vagus, and cranial part

of accessory nerves .Spinal root ofaccessory nerve

Roots of-hypoglossal nerve

- Gyrus rectusLongitudinal fissure -

Optic chiasma

" __ . - lnfundibulum

C . . _ - :éf-b. . j ' . ”L"rus cerebrI —_-____ '. "“1"- . _ . _ _ _.____.LL 3‘ . .- "--'- ‘r "h , . _ _:_.i'—- Postenorperforating

' " substance in floor ofinterpeduncular fossa

Mammillary body

Trochlear nerve '——__

I _‘._ Oculomotor nerve. '—,'- Groove for basilar artery

Inferior cerebellar 'peduncle

Olive

Anterior median fissure

Pyramid

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

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Color Atlas of Brain xxv

Median MedialVestibular areainflooroffourth ventricle Mid_brain sulcus eminence

- Facial colliculus

Sulcus limitans

- Right cerebellarhemisphere (cut)

Hypoglossaltriangle

Vagal triangle -- -" - Gracile tubercle

Anterior lobe Superior aspect. . of vermis

Primary fissure- Culmen

Middle lobe-

Declive

Left cerebellarhemisphere

- Right cerebellarhemisphere

Middle cerebellar . _ __ Central lobulepeduncle _

Flocculus

__ -- Inferior aspectof vermis

Tonsil

Tuber

Right cerebellar-hemisphere

- "' " - Left cerebellarhemisphere

Figure CA-7 Top: Posterior view of the brainstem. The greater part of the cerebellum had beenremoved to expose the floor of the fourth ventricle. Middle: Superior view of the cerebellumshowing the vermis and right and left cerebellar hemispheres. Bottom: Inferior view of thecerebellum showing the vermis and right and left cerebellar hemispheres.

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xxvi Color Atlas of Brain

Anterior column lnterventricular foramenof fornix (entrance to lateral ventricle)

H II“... Central Cingulate Corpus Site of thirdSeptum pellucidum L '-.,I Fornix Thalamus sulcus gyrus callosum Jventricle

_. Splenium

__ - Pineal body

Genu of - a,corpus

callosum

Rostrum -- -Th'tl-_____I_

___l:..—_,- Posterior. j commissure

”Xi- Superior". I. 3-": "~55 medullary

' " - velum‘1! _—— Choroid

' ' plexus ofthe fourthventricle

-"'- - Vermis ofcerebellum

Anterior '. ~_,.--' "" Foramen ofcommissure .| . I " .. Magendie

l ventricle canal." I

Lamina Optic Region of Cerebral aqueductterminalis chiasma hypothalamus ofmidbrain

.-" .r/"l Tuber Mammillary Pons .' Fourth Central lVledulla oblongata

_ If cinereum body

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

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Introduction and Organization of the Nervous System

CHAPTER OBJECTIVES

• 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 frac­

ture 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 cutane­

ous 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 anal­

gesia. On the right side, he has total analgesia, thermoan­

esthesia, 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

of the cord on the left side at the level of the 10th thoracic

CENTRAL AND PERIPHERAL NERVOUS SYSTEMS As shown in Figure 1-1, the nervous system is divided into two main parts, for purposes of description: the central nervous system (CNS) , which consists of the brain and spinal cord, and the peripheral nervous system (PNS) , 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 inter­

ruption 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 surround­

ing 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 sys­

tem of higher species has the ability to store sensory infor­

mation 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 (meninges) and are suspended in cerebrospinal 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,

1

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(I. Cerebrum

In".Forebrain— _

Midbrain—l

Pons —

l-i.

Cerebellum

Hindbrain—Medulla —

oblongata

Cervical Ulnar nerve.___ _

Spinal— Thoraciccord

Lumbar

Sacral'— _ _ _ _ - Coccygeal

A

Brachial plexus.-___

Radial nerve..___

CHAPTER 1 Introduction and Organization of the Nervous System

Phrenic nerve

_ - Lumbar plexus

Median nerve.“__ _.- Sacral plexus

_ _ - - Obturator nerve

Sciatic nerve- _ _ __ _ — - Femoral nerve

B

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

known as axons or nerve fibers. Neurons are supportedby specialized tissue called neuroglia (Fig. 1-3).

The CNS interior is organized into gray and whitematter. Gray matter, which is gray in color, consistsof nerve cells embedded in neuroglia. White matterconsists of nerve fibers embedded in neuroglia and iswhite in color because of the presence of lipid materialin nerve fiber myelin sheaths.

In the PNS, the cranial and spinal nerves, whichconsist of bundles of nerve fibers (or axons), conductinformation to and from the CNS. Although the nervesare surrounded by fibrous sheaths as they run to differ-ent parts of the body, they are relatively unprotectedand are commonly damaged by trauma.

Autonomic Nervous SystemThe autonomic nervous system (ANS) is the partof the nervous system that innervates the body’s

involuntary structures, such as the heart, smoothmuscle, and glands. It is distributed throughoutthe CNS and PNS and is divided into two parts, thesympathetic and the parasympathetic, both contain-ing afferent and efferent nerve fibers. The activitiesof the sympathetic part of the ANS prepare the bodyfor an emergency, whereas those of the parasympa-thetic part are aimed at conserving and restoringenergy.

MAJOR DIVISIONS OF THE CENTRALNERVOUS SYSTEMBefore proceeding to a detailed description of the spi-nal cord and brain, understanding the main features ofthese structures and their general relationship to oneanother is essential (Table 1-1).

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Major Divisions of the Central Nervous System

Superior sagittal sinus ArachnoidMeningeal__Dura mater‘l: layer

Periosteal -. ".313. _”layer '

Arachnoidmater

Subarachnoidj' ' _ .- -. 1‘. spaceII I - l-hlu — '5':— '- I." “I I ”-I II- . I. 'n. '. I !Fused layers 'nit—dflh -_-. _

of dura mater—”3:3; . " ' Pia mater

.. r s . r —. _ _ 7' -' ' Quadrigeminal cistern-" .. . __-:'-.

Chiasmatic cistern" .-I r, ..-" :3a

Optic chiasmli -; ll_ Fused layers., .. . r“

_, 114.25. Ofdura mater. ' .ul'' -i' J A?

I. .. ll- 1"???“

. . .._..-' r -:_I’ -'. fHd—flfllfil‘

Pontine Cisw...--' 4 I _ .5.--

lnterpeduncular cistern" |_ ‘ s-

.-

1'_I'.

Cisterna magna

Location ofin lSp a l l foramen magnumarachnoid mater lSpinal l !

pia mater l l -—Spinal dura mater(meningeal layer only)

Venous sinus

_ _ - - - -'-___ _Arachnoid villus' ' I I' I

I -| ‘-..I_ L. -_ II___ ‘

I. II I

I _ ._ I

*- l'. ' aria-"qr; Periosteal layer---"l 'J l .r-f. Meningeal layer

Arachnoid mater

Skull bone—ET"--.._355' 1-3-

Cranial epidural space—E33." :-(potential space)

_-."

i _ 'n'Cranial dura mater

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Subarachnoidspace

Arachnoidtrabeculae

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

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4 CHAPTER 1 Introduction and Organization of the Nervous System

Figure 1-3 Photomicrograph of several large nerve cellswith 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 CordThe spinal cord is situated within the vertebral canalof the vertebral column and is surrounded by threemeninges (Figs. 1-4 and 1-5): the dura mater, the arach-noid mater, and the pia mater. Further protection isprovided by the CSF, which surrounds the spinal cordin the subarachnoid space.

The spinal cord is roughly cylindrical and beginssuperiorly at the foramen magnum in the skull, where itis continuous with the medulla oblongata of the brain.It terminates inferiorly in the lumbar region. Below, thespinal cord tapers off into the conus medullaris, fromthe apex of which the filum terminale (a prolongationof the pia mater) descends to attach to the back of thecocc (see Fig. 1-4B).

Along the entire length of the spinal cord, 31 pairsof spinal nerves are attached by the anterior or motorroots and the posterior or sensory roots (Fig. 1-6; alsosee Fig. 1-5). Each root is attached to the cord by aseries of rootlets, which extend the whole length ofthe corresponding segment of the cord. Each posterior

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Central Nervous SystemBrain

ForebrainCerebrumDiencephalon (between brain)

MidbrainHindbrain

Medulla oblongataPonsCerebellum

Spinal cordCervical segmentsThoracic segmentsLumbar segmentsSacral segmentsCoccygeal segments

Peripheral Nervous SystemCranial nerves and their ganglia—1 2 pairs that exit the

skull through the foraminaSpinal nerves and their ganglia—31 pairs that exit the

vertebral column through the intervertebral foramina8 Cervical12 Thoracic5 Lumbar5 Sacral1 Coccygeal

nerve root possesses a posterior root ganglion, thecells of which give rise to peripheral and central nervefibers.

The spinal cord is composed of an inner core of graymatter, which is surrounded by an outer covering ofwhite matter. The gray matter is seen on cross sectionas an H-shaped pillar with anterior and posterior graycolumns, or horns, united by a thin gray commissurecontaining the small central canal. The white matter,for purposes of description, is divided into anterior,lateral, and posterior white columns (see Fig. 1-6).

BrainThe brain (Fig. 1-7) lies in the cranial cavity and iscontinuous with the spinal cord through the foramenmagnum (see Fig. 1-5A). As shown in Figure 1-2, it issurrounded by the dura mater, the arachnoid mater,and the pia mater. These three meninges are contin-uous with the corresponding meninges of the spinalcord. The CSF surrounds the brain in the subarachnoidspace.

The brain is conventionally divided into threemajor divisions: the hindbrain, the midbrain, andthe forebrain in ascending order from the spinal cord(see Fig. 1-1A). The brainstem (a collective term for the

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Spinal cord

,.--"" magnum

First lumbar -v r r - 'e teb a __ _ -‘ Conus medullaris

of spinal cord

Subarachnoid space- — ‘filled with cerebrospinal

fluid

_ _ _ - - Filum terminale

__._- _. Lower limit of-"' subarachnoid

space

Second sacral'vertebra

B C

Major Divisions of the Central Nervous System 5

Medulla oblongata

Foramen'

_ ' Spinal cord- — - _ _, and meninges

' ‘ ' Level of lowerend of spinal cord

— Lower limit ofsubarachnoidspace

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

medulla oblongata, pons, and midbrain) is what remainsafter the cerebral hemispheres and cerebellum (seebelow) are removed.

The hindbrain comprises the medulla oblongata, thepens, and the cerebellum.

Medulla OblongataThe medulla oblongata is conical in shape and connectsthe pons superiorly to the spinal cord inferiorly (Fig. 1-8).It contains many collections of neurons, called nuclei,

and serves as a conduit for ascending and descendingnerve fibers.

Pens

The pons is situated on the anterior surface of thecerebellum, inferior to the midbrain and superiorto the medulla oblongata (Fig. 1-9; also see Fig. 1-8).The pons, or bridge, derives its name from the largenumber of transverse fibers on its anterior aspectconnecting the two cerebellar hemispheres. It alsocontains many nuclei and ascending and descendingnerve fibers.

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6 CHAPTER 1 Introduction and Organization of the Nervous System

i_ - ' -- .' Pia materH' -Brain

Ligamentummndenticulatum ~

— Cl Eta.

Cervicalsegments

— ' C8 HUI-Ill.“— T1 ‘

Gray matter

Thoracicsegments

—T12—L1 _

Lumbar, lsacral,

and coccygealsegments

._ — — '- "Lower limit ofsubarachnoid space

_—-- 85

Filum terminale -— Cl

Arachnoid materfi1

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Posterior rootgangHon

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_.- Dura and arachnoid mater

' ___---' Conus medullaris

--- -. _ _ — —First lumbarspinal nerve

_ __ :__-..- Cauda equina

s": _ ____.._.r-- Roots of----'..---" spinal nerves

" ' ____-- Posterior root__,--- ganglion

. __ __———Lower limit of' '_—-=-_.-',—' subarachnoid space

—— Sacrum

__— Filum terminale

-- —‘ Coccygeal spinal nerve

- _ "' Coccyx

C

Figure 1-5 A: Brain, spinal cord, spinal nerve roots, and spinal nerves as seen on their posterioraspect. B: Transverse section through the thoracic region of the spinal cord showing the anteriorand posterior roots of a spinal nerve and the meninges. C: Posterior view of the lower end of thespinal cord and cauda equina showing their relationship with the lumbar vertebrae, sacrum, andcoccyx.

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Major Divisions of the Central Nervous System 7

One segment of spinal cordWhite matter . .Posterior rootlets of spinal nerve

'-._ _f' I, Posterior root of spinal nerveI __f Posterior root ganglion

Centre] canaL- '- 3.5-. f. Spinal nerve

""- --_ HE f' _ _ - Posterior ramus ofspinal nerve

III

III

__ ‘1 ._ Anterior ramus of. '. 's inal nerveA Gray matter 'i . p .' Anterior root of spinal nerveIla!

Posterior median S.UlCUS "'Anterior rootlets of spinal nervePosterior median septum Posterior white column

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Posterior gray column "i ll __Lateral white columnI '

.I .'__- Posterior root ganglionGray commissure.___

Central canal" — — _"

- Figure 1-6 A: Transverse section----“ through the lumbar part of the spinal

cord, oblique view. B: Transverse5-. _ section through the lumbar part of

"'~i_ Spinal nerve the spinal cord, face view, showing-. _ _ the anterior and posterior roots of a

Anterior white column spinal nerve.

Anterior gray column”.

B Anterior median fissure

_Central sulcusParietal boneFrontal bone

Frontal lobe

Occipital..,__ i“:bone ” Ti

Occipitallobe

Cerebellum: "-i_ . .- Temporal lobe Figure 1-7 Lateral View of the brainLateral fissure Temporal bone within the skull.

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