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First Edition

Britannica Educational PublishingMichael I. Levy: Executive EditorJ.E. Luebering: Senior Manager Marilyn L. Barton: Senior Coordinator, Production ControlSteven Bosco: Director, Editorial TechnologiesLisa S. Braucher: Senior Producer and Data EditorYvette Charboneau: Senior Copy EditorKathy Nakamura: Manager, Media AcquisitionKara Rogers: Senior Editor, Biomedical Sciences

Rosen Educational ServicesAlexandra Hanson-Harding: EditorNelson Sá: Art DirectorCindy Reiman: Photography ManagerMatthew Cauli: Designer, Cover DesignIntroduction by Monique Vescia

Library of Congress Cataloging-in-Publication Data

Ear, nose, and throat / edited by Kara Rogers.—1st ed. p. cm.—(The human body)“In association with Britannica Educational Publishing, Rosen Educational Services.”Includes bibliographical references and index.ISBN 978-1-61530-709-8 (eBook)1. Otolaryngology—Popular works. I. Rogers, Kara.RF59.E17 2012617.5'1—dc23

2011013432

On the cover: A side view of the ear, nose, and throat. © SuperStock, Inc.

On page x: Dr. Maura Shea examines a patient’s ear through an otoscope at the Codman Square Health Center April 11, 2006, in Dorchester, Massachusetts. Joe Raedle/Getty Images

On pages 1, 28, 60, 93, 118, 140, 165, 167, 170, 172: The human inner ear. Shutterstock.com

CONTENTS2

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52

Introduction x

Chapter 1: Anatomy of the Human Ear 1

The Outer Ear 4The Tympanic Membrane and Middle Ear 5

Auditory Ossicles 6Muscles of the Middle Ear 8Nerves of the Middle Ear 9Eustachian Tube 10

The Inner Ear 11Vestibular System 12Cochlea 17

Endolymph and Perilymph 26

Chapter 2: Hearing and Balance 28

The Physiology of Hearing 28Transmission of Sound Waves Through the Outer and Middle Ear 30Transmission of Sound within the Inner Ear 36Cochlear Nerve and Central Auditory Pathways 44Analysis of Sound by the Auditory Nervous System 48

The Physiology of Balance 51Detection of Angular Acceleration: Dynamic Equilibrium 54

Detection of Linear Acceleration: Static Equilibrium 56Disturbances of the Vestibular System 57

Chapter 3: Anatomy and Physiology of the Nose and Throat 60

Structures of the Nose and Nasal Cavity 60

The Nose 61Nasal Concha 62Paranasal Air Sinuses 63Palate 65

The Throat and Associated Structures 67

Pharynx 67Larynx 69Vocal Cords 71Tonsils 72Adenoids 72

The Physiology of Taste and Smell 75

Taste Sense 76Nerve Supply 78Physiological Basis of Taste 79The Qualities of Taste 80Flavour 83Factors Affecting Taste Sensitivity 84Food Choice 86

Smell Sense 87Olfactory Qualities 88Odourous Substances 89Odour Sensitivity 90Effects on Behaviour 91

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61

81

112

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Chapter 4: Diseases of the Ear 93Diseases of the Outer Ear 94

Infections and Injuries of the Outer Ear 95Deformities and Other Conditions of the Outer Ear 98

Diseases of the Middle Ear 100Acute Middle-Ear Infection 101Chronic Middle-Ear Infection 103Ossicular Interruption 104Otosclerosis 105

Diseases of the Inner Ear 107Congenital Nerve Deafness 108Viral Nerve Deafness 110

Effects of Injury and Trauma 110Ototoxic Drugs 111Skull Fracture and Concussion 111Exposure to Noise 111

Infl ammation and Tumours 113Acoustic Neuroma 113Labyrinthitis 113Ménière Disease 114Presbycusis 114Tinnitus 115

Chapter 5: Communication Disorders Involving Structures of the Ear, Nose, and Throat 118

Prevalence of Communication Disorders 118Speech Disorders 119

Voice Disorders 121Articulation Disorders 123

Cluttering 123Lisping 124Stuttering, or Stammering 124

Speech of the Hard of Hearing 127Speech Impediments from Defective Articulators 129

Tongue-Tie 129Loss of Tongue 130Nasal Speech 130Cleft Palate Speech 132

Treatment and Rehabilitation 135Development of Speech Correction 136

Speech Synthesis 138Pseudolaryngeal Speech 139

Chapter 6: Disorders of the Nose and Throat and Approaches to Ear, Nose, and Throat Evaluation 140

Notable Diseases and Disorders of the nose and Throat 140

Laryngeal Cancer 141Nasal Polyp 142Nosebleed 142Oral and Oropharyngeal Cancer 144Sinus Disorders 147

Approaches to Ear, Nose, and Throat Evaluation 148

Otolaryngology 148Nasopharyn-golaryngoscopy 149

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Hearing Tests and Rehabilitation 149

Conclusion 165

Glossary 167Bibliography 170Index 172

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CHAPTER 1 1CHAPTER 1CHAPTER

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ANATOMY OF THE HUMAN EAR

The senses of hearing, smell, and taste, and the human ability to speak and produce sound, facilitate human

survival and undeniably enrich the human experience. The intricate structure of the ear, with its outer parts designed to funnel sound waves into the inner ear, where they are converted into electrical impulses that travel to the auditory nucleus (or sound-processing region) of the brain, enhances our survival by allowing us to detect sounds associated with potential danger. The ability to perceive pitch and distinguish between musical tones is arguably among the most affective features of hearing, enabling us to derive enjoyment from music and song. The human production of sound, in the form of speech and song, is made possible by the larynx (or voice box) and vocal cords and is infl uenced by surrounding structures of the throat and oral and nasal cavities.

The senses of smell and taste likewise enrich our lives. The sense of smell, or olfaction, is housed in a special membrane layer in the nose, which is lined with unique receptor cells that trap odour molecules and communi-cate information about these molecules to the brain, where the information is interpreted and perceived as smell. Taste, or gustation, which is imparted by special taste receptor cells clustered into taste buds on the tongue, combines with smell to produce the attribute of fl avour. The human perception of fl avour is a major factor in our enjoyment of food and greatly infl uences the culinary arts.

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7 Ear, Nose, and Throat 7

The structures of the outer, middle, and inner ear. Encyclopædia Britannica, Inc.

Although the ear, nose, and throat are structurally diverse, they are united by the fact that they serve impor-tant roles in both human survival and cultural experience. In addition, despite their individual uniqueness of form, they are associated anatomically. For example, the throat and ear communicate with one another via the eustachian tubes, and the nose and throat are connected by passages that facilitate the drainage of mucus from the sinuses (cavities) of the head. Hence, each component is influ-enced by the other. This is most evident in diseases and disorders that affect the tissues of these structures.

The exploration of the ear, nose, and throat in this volume begins with the human ear. In addition to hear-ing, the ear serves a fundamental role in maintaining a sense of balance. Thus, it detects and analyzes noises by transduction (or the conversion of sound waves into

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electrochemical impulses), and it influences postural equilibrium, or balance, and coordinates movements of the head and eyes.

Anatomically the ear has three distinguishable parts: the outer, middle, and inner ear. The outer ear consists of the visible portion called the auricle, or pinna, which proj-ects from the side of the head, and the short external auditory canal, the inner end of which is closed by the tympanic membrane, commonly called the eardrum. The function of the outer ear is to collect sound waves and guide them to the tympanic membrane. The middle ear is a narrow, air-filled cavity in the temporal bone. It is spanned by a chain of three tiny bones—the malleus (ham-mer), incus (anvil), and stapes (stirrup), collectively called the auditory ossicles. This ossicular chain conducts sound from the tympanic membrane to the inner ear, which has been known since the time of Galen, a prominent physi-cian in the 2nd century ce, as the labyrinth. It is a complicated system of fluid-filled passages and cavities located deep within the petrous portion of the temporal bone. The temporal bone is the bone that contains the internal auditory organs, and the petrous part of the tem-poral bone is an especially dense and hard part of that bone. The inner ear consists of two functional units: the vestibular apparatus and the snail-shell-like cochlea. The vestibular apparatus consists of the vestibule and semicir-cular canals, which contains the sensory organs of postural equilibrium, and the cochlea contains the sensory organ of hearing. Both sensory organs are highly specialized endings of the eighth cranial nerve, also called the vestibu-locochlear nerve. The cranial nerves are a group of 12 pairs of nerves that connect the brainstem and other parts of the brain to the sense organs of the head as well as to mus-cles, internal organs, and glands in the head, neck, chest, and upper abdomen.

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7 Ear, Nose, and Throat 7

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The OuTer ear

The most striking differences between the human ear and the ears of other mammals are in the structure of the outermost part, the auricle. In humans the auricle is an almost rudimentary, usually immobile shell that lies close to the side of the head. It consists of a thin plate of yel-low fibrocartilage covered by closely adherent skin. The cartilage is molded into clearly defined hollows, ridges, and furrows that form an irregular, shallow funnel. The deepest depression, which leads directly to the external auditory canal, or acoustic meatus, is called the concha. It is partly covered by two small projections, the tongue-like tragus in front and the antitragus behind. Above the tragus a prominent ridge, the helix, arises from the floor of the concha and continues as the incurved rim of the upper portion of the auricle. An inner, concentric ridge, the antihelix, surrounds the concha and is separated from the helix by a furrow, the scapha, also called the fossa of the helix.

In some ears a little prominence known as Darwin’s tubercle is seen along the upper, posterior portion of the helix. It is the vestige of the folded-over point of the ear of a remote human ancestor. The lobule, the fleshy lower part of the auricle, is the only area of the outer ear that contains no cartilage. The auricle also has several small rudimentary muscles, which fasten it to the skull and scalp. In most individuals these muscles do not function, although some persons can voluntarily activate them to produce limited movements. The external auditory canal is a slightly curved tube that extends inward from the floor of the concha and ends blindly at the tympanic membrane. In its outer third the wall of the canal consists of cartilage, and in its inner two-thirds, of bone. The entire length of the passage (24 mm, or almost 1 inch) is lined with skin,

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which also covers the outer surface of the tympanic mem-brane. Fine hairs directed outward and modified sweat glands that produce earwax, or cerumen, line the canal and discourage insects from entering it.

The Tympanic membrane and middle ear

The thin, semitransparent tympanic membrane, or ear-drum, which forms the boundary between the outer and middle ear, is stretched obliquely across the end of the external canal. Its diameter is about 9 mm (0.35 inch), its shape that of a flattened cone with its apex directed inward. Thus, its outer surface is slightly concave. The edge of the membrane is thickened and attached to a groove in an incomplete ring of bone, the tympanic annu-lus, which almost encircles it and holds it in place. The uppermost small area of the membrane where the ring is open is slack and is called the pars flaccida, but the far greater portion is tightly stretched and is called the pars tensa. The appearance and mobility of the tympanic mem-brane are important for the diagnosis of middle-ear disease, which is especially common in young children. When viewed with a medical instrument called an oto-scope, the healthy membrane is translucent and pearl-gray in colour, sometimes with a pinkish or yellowish tinge.

The entire tympanic membrane consists of three lay-ers. The outer layer of skin is continuous with that of the external canal. The inner layer of mucous membrane is continuous with the lining of the tympanic cavity of the middle ear. Between these layers is a layer of fibrous tissue made up of circular and radial fibres that give the mem-brane its stiffness and tension. The membrane is well supplied with blood vessels and sensory nerve fibres that make it acutely sensitive to pain.

7 Anatomy of the Human Ear 7