ANATOMY, PHYSIOLOGY, AND DISORDERS OF THE AUDITORY SYSTEM - PART 1 pps

ANATOMY, PHYSIOLOGY, AND DISORDERS OF THE AUDITORY SYSTEM Second Edition... ANATOMY, PHYSIOLOGY, AND DISORDERS OF THE AUDITORY SYSTEM Second Edition A... Hearing : anatomy, physiology, a

ANATOMY, PHYSIOLOGY, AND DISORDERS OF THE AUDITORY SYSTEM

Second Edition

T his page intentionally left blank

ANATOMY, PHYSIOLOGY, AND DISORDERS OF THE AUDITORY SYSTEM

Second Edition

A R Møller

School of Behavioral and Brain Sciences

University of Texas at Dallas

Texas

AMSTERDAM • BOSTON • HEIDELBERG • LONDON NEW YORK • OXFORD • PARIS • SAN DIEGO SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO

Academic Press is an imprint of Elsevier

Academic Press is an imprint of Elsevier

30 Corporate Drive, Suite 400, Burlington, MA 01803, USA

525 B Street, Suite 1900, San Diego, California 92101-4495, USA

84 Theobald’s Road, London WC1X 8RR, UK

This book is printed on acid-free paper

Copyright © 2006, 2000 Elsevier Inc All rights reserved.

No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publisher.

Permissions may be sought directly from Elsevier’s Science & Technology Rights Department in Oxford, UK: phone: (+44) 1865 843830, fax: (+44) 1865 853333, E-mail: permissions@elsevier.com You may also complete your request on-line via the Elsevier homepage (http://elsevier.com), by selecting “Support & Contact” then “Copyright and Permission” and then “Obtaining Permissions.”

Front cover design concept by Milda Dorsett.

Library of Congress Cataloging-in-Publication Data

Møller, Aage R.

Hearing : anatomy, physiology, and disorders of the auditory system/A.R Moller, 2nd ed.

p cm.

Includes bibliographical references and index.

ISBN-13: 978-0-12-372519-6 (casebound : alk paper)

ISBN-10: 0-12-372519-4 (casebound : alk paper)

1 Hearing Physiological aspects 2 Hearing disorders Pathophysiology

3 Ear Anatomy I Title.

RF290.M58 2006

British Library Cataloguing-in-Publication Data

A catalogue record for this book is available from the British Library.

ISBN 13: 978-0-12-372519-6

ISBN 10: 0-12-372519-4

For information on all Academic Press publications

visit our Web site at www.books.elsevier.com

Printed in the United States of America

06 07 08 09 10 11 9 8 7 6 5 4 3 2 1

5.3 Innervation of Hair Cells 13

5.4 Fluid Systems of the Cochlea 15

5.5 Blood Supply to the Cochlea 16

4.2 Transfer Function of the Human Middle Ear 27

4.3 Impulse Response of the Human Middle Ear 29

4.4 Linearity of the Middle Ear 294.5 Acoustic Impedance of the Ear 294.6 Contributions of Individual Parts of theMiddle Ear to Its Impedance 32

3.4 Role of the Outer Hair Cells in BasilarMembrane Motion 46

3.5 Epochs of Research in Cochlear Mechanics 47

4 Sensory Transduction in the Cochlea 484.1 Excitation of Hair Cells 48

4.2 Which Phase of a Sound Excites Hair Cells(Rarefaction or Condensation)? 484.3 Molecular Basis for Sensory Transduction 50

4.4 Endocochlear Potential 524.5 Cochlea as a Generator of Sound 534.6 Efferent Control of Hair Cells 554.7 Autonomic Control of the Cochlea 55

5 Autoregulation of Blood Flow to the Cochlea 56

Contents

v

3.3 Superior Olivary Complex 81

3.4 Lateral Lemniscus and Its Nuclei 81

3.5 Inferior Colliculus 81

3.6 Medial Geniculate Body 81

3.7 Auditory Cerebral Cortex 82

3.8 Differences between the Classical Auditory

Pathways in Humans and in Animals 84

4 Non-classical Ascending Auditory Pathways 85

5 Parallel Processing and Stream Segregation 87

3.4 Frequency Tuning in Nuclei of theAscending Auditory Pathways 1023.5 Tonotopic Organization in the Nuclei of theAscending Auditory Pathways 1043.6 Extraction of Information from PlaceCoding of Frequency 106

4 Coding of Temporal Features 1064.1 Coding of Periodic Sounds 1074.2 Extraction of Information from theTemporal Pattern of Neural Discharges 111

5 Is Temporal or Place Code the Basis forDiscrimination of Frequency? 1125.1 Temporal Hypothesis for FrequencyDiscrimination of Complex Sounds 1125.2 Place Hypothesis for Frequency

Discrimination of Complex Sounds 1135.3 Preservation of the Temporal Code ofFrequency 115

5.4 Preservation of the Place Code 1175.5 Robustness of the Temporal Code 1175.6 Robustness of the Place Code of Frequency 117

5.7 Coding of Speech Sounds 1175.8 A Duplex Hypothesis of FrequencyDiscrimination 118

5.9 Cochlear Spectral Filtering May Be Important in other Ways than FrequencyDiscrimination 118

5.10 Speech Discrimination on SpectralInformation Only 118

5.11 Conclusion 119

6 Coding of Complex Sounds 1196.1 Response to Tone Bursts 1206.2 Coding of Small Changes in Amplitude 121

6.3 Response to Tones with Changing Frequency 128

6.4 Selectivity to Other Temporal Patterns

of Sounds 1386.5 Coding of Sound Intensity 1406.6 Conclusion 140

7 Directional Hearing 1427.1 Physical Basis for Directional Hearing 1427.2 Neurophysiologic Basis for Sound

Localization 1437.3 Localization in the Vertical Plane 1467.4 Representation of Auditory Space (Maps) 146

8 Efferent System 149

9 Non-classical Pathways 149

10 Effect of Anesthesia 150

3.1 Recordings from the Auditory Nerve 152

3.2 Recordings from the Cochlear

Nucleus 160

3.3 Recordings from More Central Parts of the

Ascending Auditory Pathways 163

4 Far-field Auditory Evoked Potentials 163

4.1 Auditory Brainstem Responses 165

4.2 Middle Latency Responses 175

4.3 Far-field Frequency Following Responses

4.1 Responses to Stimulation with Tones 184

4.2 Functional Importance of the Acoustic

DISORDERS OF THE AUDITORY

SYSTEM AND THEIR

3.4 Accuracy of Measurements of ConductiveHearing Loss 213

3.5 Implications of Impairment of Conduction

of Sound to the Cochlea 214

4 Pathologies of the Cochlea 2154.1 General Audiometric Signs of CochlearPathologies 215

4.2 Age-related Hearing Loss (Presbycusis) 2164.3 Noise Induced Hearing Loss 219

4.4 Implications of Hearing Loss on CentralAuditory Processing 226

4.5 Modification of Noise Induced Hearing Loss 226

4.6 Hearing Loss Caused by Ototoxic Agents(Drugs) 227

4.7 Diseases that Affect the Function of theCochlea 229

4.8 Congenital Hearing Impairment 2334.9 Infectious Diseases 234

4.10 Perilymphatic Fistulae 2344.11 Changes in Blood Flow in the Cochlea 2344.12 Injuries to the Cochlea from Trauma 2344.13 Sudden Hearing Loss 234

5 Implications of Hearing Loss on Central AuditoryProcessing 235

5.1 Neural Components of Hearing Loss 2365.2 Role of Expression of Neural Plasticity 237

6 Pathologies from Damage to the Auditory System 239

6.1 Auditory Nerve 2396.2 Other Space-occupying Lesions 243

7 Pathologies of the Central Auditory NervousSystem 243

7.1 Disorders of the Brainstem AuditoryPathways 244

7.2 Auditory Cortices 2447.3 Efferent System 2467.4 Pathologies that Can Affect Binaural Hearing 246

7.5 Viral Infections 2467.6 Ototoxic Drugs 2477.7 Sudden Hearing Loss 247

8 Role of Neural Plasticity in Disorders of theCentral Auditory Nervous System 2478.1 What Is Neural Plasticity? 2478.2 What Can Initiate Expression of NeuralPlasticity? 250

2.1 Development of Cochlear Implants 268

2.2 Function and Design of Cochlear

Implants 268

2.3 Physiological Basis for Cochlear Implants 273

2.4 Coding of Sound Intensity 275

2.5 Functions that Are Not Covered by Modern

Cochlear Implants 275

2.6 Success of Cochlear Implants 276

2.7 Selection Criteria for Cochlear Implant

Candidates 277

3 Cochlear Nucleus Implants 277

3.1 Function and Design of Auditory Brainstem Implants 277

3.2 Physiological Basis for Auditory BrainstemImplants 277

3.3 Success of Auditory Brainstem Implants 2783.4 Patient Selection for Auditory BrainstemImplants 279

4 Role of Neural Plasticity 279Section III References 280

2.1 Basis for Hearing Conservation Programs 292

3 Establishment of Noise Standards 2953.1 Noise Level and Exposure Time 2963.2 Effect of Age-related Hearing Loss 2963.3 What Degree of Hearing Loss is

Acceptable? 296

4 Measurement of Noise 2974.1 Sound Level Meters 2974.2 Noise Dosimeters 298

5 Personal Protection 2995.1 Earplugs and Earmuffs 2995.2 Active Noise Cancellation 3005.3 Other Means of Reducing the Risk of NoiseInduced Hearing Loss 300

6 Non-occupational Noise Exposure 300

7 Effect of Noise on Bodily Functions 3007.1 Effect of Ultrasound and Infrasound 300Appendices References 301

List of Abbreviations 303

Index 305

ix

This book is intended for otologists, audiologists,

neurologists and researchers in the field of hearing The

book will also be of interest to psychologists and

psy-chiatrists who treat patients with tinnitus and other

hyperactive auditory disorders The book provides the

basis for a broad understanding of the anatomy and

function of the ear and the auditory nervous system,

and it discusses the cause and treatment of hearing

disorders Most books on hearing focus either on the

anatomy and function of the ear, the auditory nervous

system or on peripheral or central hearing disorders

This book covers both anatomy and physiology of the

ear and the nervous system The book also provides a

comprehensive coverage of disorders of the auditory

system emphasizing the interaction between

patholo-gies of the middle ear and the cochlea and the function

of the nervous system and vice versa Hyperactive

dis-orders of the auditory nervous system and the role of

expression of neural plasticity in causing auditory

symptoms are also topics of the book An extensive list

of references makes it possible for the reader to find

original work on the different subjects

Understanding of the anatomy and the function of

the auditory system together with knowledge about

the pathophysiology of the auditory system are

essen-tial for all clinicians who are involved in diagnosis and

treatment of disorders of the auditory system The

book prepares the clinician and the clinical researcher

for the challenges of the modern clinical auditory

disci-pline The book also provides basic information about

the auditory system in a form that is suitable for the

sci-entist who does basic research on the auditory system

The book thus aims at cross-fertilization between

clini-cians, clinical researchers and basic scientists It is my

hope that such knowledge can guide basic auditory

research into clinically relevant questions

The book is the third edition of books on the auditory

system, the first, Auditory Physiology, published in 1983

by Academic Press, and the second, Hearing: Its

Physiology and Pathophysiology, published in 2000, also

by Academic Press

The book has 11 chapters that are organized in threesections Chapters from earlier editions have been re-organized and most parts have been re-written andnew information has been added A separate chapter

is devoted to an extended coverage of hyperactive disorders, most importantly tinnitus, the cause andtreatment of which is discussed in detail A new chap-ter describes cochlear and brainstem implants andhearing conservation programs are discussed in anappendix

The four chapters of Section I cover anatomy andphysiology of the middle ear and the cochlea, includ-ing a chapter on the electrical potentials that are gen-erated by the cochlea Section II has two chapters thatcover anatomy and physiology of the nervous system.Both the classical and the less known non-classical(extralemniscal) auditory pathways are covered exten-sively The latter is involved in some forms of tinnitusand may be activated in other disorders also A thirdchapter is devoted to evoked potentials from the nerv-ous system The neural generators of the ABR are dis-cussed in detail The anatomy and physiology of theacoustic middle-ear reflex is covered in a fourth chapter

in this section

The final section (Section III) discusses disorders ofthe auditory system Two chapters regard hearingimpairment and hyperactive disorders, focusing on tin-nitus, its etiology, and treatment These two chaptersstress the role of expression of neural plasticity A thirdchapter in this section concerns cochlear implants andauditory brainstem implants The basic design andfunction of the processors in these modern auditoryprostheses are described and the physiologic basis forthe function of these prostheses is discussed Anappendix discusses hearing conservation programs

T his page intentionally left blank

xi

I want to thank Hilda Dorsett for help with the new

artwork and for revising some of the illustrations from

the first edition of the book and Karen Riddle for

tran-scribing many of the revisions of the manuscript I also

want to thank Johannes Menzel, Senior Publishing

Editor, Elsevier Science, and Heather Furrow and John

Donahue, Project Managers, Elsevier, Burlington, MA

for their excellent work on the book

I would not have been able to write this book

with-out the support from the School of Behavioral and

Brain Sciences at the University of Texas at Dallas

Last but not least I want to thank my dear wife,Margareta B Møller, MD, DMedSci., for her supportduring writing of this book and for her valuable comments on earlier versions of the manuscripts forthis book

Dallas, November, 2005Aage R Møller

T his page intentionally left blank

It is now recognized that disorders of one part of the

auditory system often affect the function of other parts

of the auditory system This is especially apparent

with regard to hyperactive disorders such as tinnitus

and hyperacusis, but even noise induced hearing loss

and presbycusis are not isolated cochlear phenomena,

for the auditory nervous system is involved in these

disorders Expression of neural plasticity and a

com-plex series of events seem to be necessary in order that

such pathologies become manifest This means that it

is no longer valid to divide disorders of the auditory

system in to peripheral and central disorders This

book therefore takes an integrated approach to

disor-ders of the auditory system

While most disorders of the auditory system have

detectable morphologic abnormalities, hyperactive

disorders lack such detectable morphologic changes,

and even other objective signs are often absent

Symptoms such as tinnitus, hyperacusis, and

phono-phobia even involve physiological abnormalities in

other parts of the central nervous system than the

clas-sical auditory pathways A part of the auditory nervous

system, known as the non-classical, or extralemniscal,

auditory pathways, seems to be involved in some of

these hyperactive disorders, and that may also cause

abnormal activation of structures of the limbic system,

which can explain why patients with tinnitus often

present with symptoms of affective disorders such as

fear and depression The role of the non-classical

audi-tory nervous system may have much wider importance

than previously known This book provides a thorough

description of the anatomy and physiology of this part

of the auditory nervous system and it discusses how

their function can change and cause different

symp-toms The book also covers less common disorders such

as bilirubinemia and cortical lesions and it discusses

vestibular Schwannoma and their diagnosis

Because of the complexity of many disorders of the

auditory system the clinician must have a thorough

understanding of the basic functions of the entire tory system and the interactions between the periph-eral and the central portions of the auditory systemthat may occur in various hearing disorders

audi-Cochlear implants now provide an effective way totreat severe hearing loss The implementation ofcochlear and brainstem implants requires a thoroughknowledge not only about the function of such devicesbut also an understanding of the way sounds are nor-mally coded and processed in the nervous system is aprerequisite for understanding how such prosthesescan provide useful hearing The more recent addition

to auditory prostheses, namely auditory brainstem(cochlear nucleus) implants, present an even greaterchallenge for the clinician and there are ample possi-bilities to do important research in this area A separatechapter in the book deals with cochlear and brainstem(cochlear nucleus) implants and the physiologicalbasis for their success is discussed

Cochlear implants and auditory brainstem implants

do not provide the same coding of sounds in the ous system as provided by the normal ear and expres-sion of neural plasticity is essential for the success ofsuch prostheses Thus, optimal implementation ofsuch prostheses requires understanding of basic audi-tory physiology

nerv-The advent of these new aspects in treatment of orders of the auditory system should not detract atten-tions from classical problems such as hearing loss frommiddle ear and cochlear pathologies Also in these areas

dis-of hearing new knowledge has contributed to betterunderstanding of pathologies of the auditory system.The surprising research results that show that exposure

to sound can reduce presbycusis and that noise inducedhearing loss is affected by pre-exposure to sound areexamples of signs of a greater complexity of disorders

of the auditory system than previously assumed Theresults indicate that the auditory nervous system isinvolved in disorders that earlier were assumed to be

Introduction

xiii

caused solely by morphological changes in the cochlea.

This means that altered function of the nervous system

caused by altered input contributes to the symptoms

and signs of such disorders This book provides insight

into the physiologic basis for the involvement of the

auditory nervous system in disorders that earlier were

assumed to only involve the ear The role of expression

of neural plasticity in creating the symptoms and signs

of these disorders is discussed

Understanding how electrical potentials are

gener-ated in the auditory nervous system is a prerequisite

for correct interpretation of clinical tests that make use

of such recordings The book describes the variouselectrical potentials that are generated in the auditorynervous system, what anatomical structures generatethe different components of such far-field potentials asthe ABR and the MLR, and how these potentials areaffected by different types of pathologies

Prevention of hearing loss is important and logists and otolaryngologists play important roles inreducing the risk of noise induced hearing loss Thebasis for that is discussed in several chapters in thebook The practical and legal aspects of hearing con-servation are covered in an appendix

The ear as a sensory organ is far more complex than other sensory organs The sensorycells are located in the cochlea but the cochlea not only serves to convert sound into

a code of neural impulses in the auditory nerve but it also performs the first analysis

of sounds that prepare sounds for further analysis in the auditory nervous system This analysis consists primarily of separating sounds into bands of frequencies beforethey are coded in the discharge pattern of individual auditory nerve fibers The separa-tion of sounds is accomplished by the properties of the basilar membrane and the sensory cells that are located along its length The cochlea is more frequency selectivefor weak sounds than louder sounds, which facilitates detection of weak sounds Thecochlea also compresses the amplitudes of sounds, which makes it possible to codesounds within the very large range of sound intensities that is covered by normal hearing.Without such amplitude compression the ear could not detect and analyze sounds inthe intensity range of normal hearing

The cochlea is fluid filled and that means that sounds must be converted into tions of fluid in order to activate the sensory cells Direct transfer of sound to a fluid isineffective The middle ear facilitates the transfer of sound to the cochlea by acting as

vibra-a trvibra-ansformer thvibra-at mvibra-atches the impedvibra-ance of the vibra-air to thvibra-at of the cochlevibra-a The middleear is the only part of the entire auditory system where medical or surgical interven-tions can remedy hearing loss from disease processes or trauma

During the past decade or so, our understanding of the function of the cochlea haschanged in a fundamental way and its function now appears far more complex thanperceived earlier Earlier it was believed that the basilar membrane was a linear systemwhere properties determined at one sound intensity were directly applicable to allsound intensities More recently, it has become evident that the frequency selectivity of

S E C T I O N

I

THE EAR

Chapter 1 Anatomy of the Ear

Chapter 2 Sound Conduction to the Cochlea

Chapter 3 Physiology of the Cochlea

Chapter 4 Sound Evoked Electrical Potentials in the Cochlea