The Facts on File Encyclopedia of Health and Medicine

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THE FACTS ON FILE ENCYCLOPEDIA OF
HEALTH AND MEDICINE
IN FOUR VOLUMES:
VOLUME 1
The Eyes i
Medical Advisory Review Panel
Kyra J. Becker, M.D.
James C. Blair, III, PA-C
Alexa Fleckenstein, M.D.
Nancy A. Lewis, Pharm.D.
Gary R. McClain, Ph.D.
Maureen Ann Mooney, M.D.
Margaret J. Neff, M.D., M.Sc.
Maureen Pelletier, M.D., C.C.N., F.A.C.O.G.
Otelio S. Randall, M.D., F.A.C.C.
Susan D. Reed, M.D., M.P.H.
Jerry Richard Shields, M.D.
Christina M. Surawicz, M.D.

Denise L. Wych, R.N., C.M.
Editorial Staff
James Chambers, General Editor
Lee Ann Chearney, Book Producer
Deborah S. Romaine, Senior Writer
Candace B. Levy, Ph.D., ELS, Copyeditor
Cathy Jewell, Proofreader
Wendy Frost, Medical Illustrator
ii The Eyes
THE FACTS ON FILE ENCYCLOPEDIA OF
HEALTH AND MEDICINE
IN FOUR VOLUMES:
VOLUME 1
An Amaranth Book
The Eyes iii
To your health!
The information presented in The Facts On File Encyclopedia of Health and Medicine is provided for research
purposes only and is not intended to replace consultation with or diagnosis and treatment by medical doctors
or other qualified experts. Readers who may be experiencing a condition or disease described herein
should seek medical attention and not rely on the information found here as medical advice.
The Facts On File Encyclopedia of Health and Medicine in Four Volumes: Volume 1
Copyright © 2007 by Amaranth Illuminare
All rights reserved. No part of this book may be reproduced or utilized in any form or by any means,
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The Facts on File encyclopedia of health and medicine / Amaranth Illuminare and Deborah S. Romaine.
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Includes index.
ISBN 0-8160-6063-0 (hc : alk. paper)
1. Medicine—Encyclopedias. 2. Health—Encyclopedias.
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Processes—Encyclopedias—English. WB 13 R842f 2006] I. Title:
Encyclopedia of health and medicine. II. Romaine, Deborah S., 1956- III.
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iv The Eyes
CONTENTS
VOLUME 1
Foreword by Maureen Pelletier, M.D., C.C.N., F.A.C.O.G. vii

How to Use The Facts On File Encyclopedia
of Health and Medicine ix
Preface to Volume 1 xiii
The Ear, Nose, Mouth, and Throat 1
The Eyes 65
The Integumentary System 125
The Nervous System 212
The Musculoskeletal System 290
Pain and Pain Management 361
Medical Advisory Review Panel 391
Index 395
The Eyes v
v
vi The Eyes
FOREWORD
A big part of my role as a physician is educating
my patients about their health. I take as much
time as each person needs to explain prevention
measures, test results, and treatment options. I
encourage questions. But in the moment, sitting
there in my office, most people do not yet know
what to ask me. By the time questions flood
their thoughts, they may be back at work or at
home.
Numerous events and circumstances can chal-
lenge health, and we all need to know what
actions we can take to keep ourselves healthy as
well as to obtain appropriate treatment for health
conditions that do affect us. Knowledge empow-
ers all of us to make informed and appropriate

decisions about health care. Certainly there is no
shortage of reference material. Yet there is so
much information available today! Even for
physicians, it is challenging to keep up. How can
you get to the core of what you want to know,
reliably and to the level of detail you need?
The Facts On File Encyclopedia of Health and Medi-
cine is a great resource for up-to-date health infor-
mation presented in a manner that is both
comprehensive and easy to understand no matter
what your level of medical knowledge. The ency-
clopedia organizes entries by body system. The
progression of body systems—and entries—
throughout the encyclopedia presents topics the
way you think about them.
Going beyond this basic structure, however, is
another layer of organization that particularly
appeals to me, which is a comprehensive structure
of cross references that integrates entries across
body systems. After all, your body functions in an
integrated way; so, too, should a reference series
that discusses your body’s health. Not very much
that happens with your health affects one part of
your body in isolation from other body structures
and functions. Your body attempts to compensate
and adjust, often without your awareness, until it
can no longer accommodate the injury or illness.
The symptoms you bring to your doctor may
reflect this compensation, for example frequent
headaches that point not to brain tumor (as many

people fear but is very rare) but to eye strain or
muscle tension or sometimes to hypertension
(high blood pressure).
In my medical practice I emphasize integrative
health care, embracing the philosophy that health
exists as the intricate intertwining of the body’s
many systems, structures, and functions. So, too,
does the care of health. I received my medical
degree from Tufts University School of Medicine
in Boston, an institution noted for remaining at
the forefront of the medical profession. I also
completed clinical programs in Mind-Body Medi-
cine at Harvard University, Integrative Medicine at
the University of Arizona School of Medicine, and
Medical Acupuncture at the University of Califor-
nia-Los Angeles (UCLA). I am a board-certified
obstetrician-gynecologist, a board-certified clinical
nutritionist, and a licensed acupuncturist. I see
patients in my practice in Cincinnati, Ohio; I
teach, I lecture, and I frequently go on television
and radio to talk about health topics. In each of
these areas, I encourage people to think about
their health and health concerns from an integra-
tive perspective. When you understand your
health from multiple dimensions, you can better
understand what to do to keep yourself as healthy
as possible.
I wish you the best of health for all of a long,
satisfying life. But when the time comes that you
must make decisions about medical care, I want

you to have the knowledge to make informed
vii
choices that are right for you. Whether you start
here and move on to more specialized resources
or locate all the information you need within
these four volumes, you will find The Facts On File
Encyclopedia of Health and Medicine to be a most
valuable reference resource.
—Maureen M. Pelletier, M.D., C.C.N.,
F.A.C.O.G.
viii Foreword
HOW TO USE
THE FACTS ON FILE ENCYCLOPEDIA OF HEALTH AND MEDICINE
Welcome to The Facts On File Encyclopedia of Health
and Medicine, a four-volume reference set. This
comprehensive resource is an indispensable refer-
ence for students, allied health professionals,
physicians, caregivers, lay researchers, and people
seeking information about health circumstances
and conditions for themselves or others. Entries
present the latest health concepts and medical
knowledge in a clear, concise format. Readers may
easily accumulate information and build a com-
plete medical profile on just about any health or
medical topic of interest or concern.
A New Paradigm for the
Health and Medical Encyclopedia
As the art and science of health and medicine con-
tinues to evolve, with complex and elegant discov-
eries and new techniques, medications, and

treatments emerging all the time, the need has
arisen for a new paradigm for the encyclopedia of
health and medicine—a rethinking of the old, and
increasingly outmoded, presentations. Carefully
researched and compiled, The Facts On File Encyclope-
dia of Health and Medicine offers many distinguishing
features that present readers and researchers with
an organization as up-to-date and compelling as the
breakthrough information its entries contain.
Recognizing the current emphasis on present-
ing a truly integrative approach to both health
and disease, The Facts On File Encyclopedia of Health
and Medicine organizes content across volumes
within a distinctive format that groups related
entries by body system (for example, “The Cardio-
vascular System”) or by general health topic (for
example, “Genetics and Molecular Medicine”):
• Volume 1 presents the sensory and structural
body systems that allow the body to engage
with its surroundings and the external envi-
ronment.
• Volume 2 presents the cell- and fluid-based
body systems that transport nutrients, remove
molecular wastes, and provide protection from
infection.
• Volume 3 presents the biochemical body sys-
tems that support cellular functions.
• Volume 4 presents topics that apply across
body systems (such as “Fitness: Exercise and
Health”) or that address broad areas within

health care (such as “Preventive Medicine”).
• The appendixes provide supportive or additional
reference information (such as “Appendix X:
Immunization and Routine Examination
Schedules”).
Following Research Pathways
The Facts On File Encyclopedia of Health and Medi-
cine’s organization and structure support the
reader’s and researcher’s ease of use. Many ency-
clopedia users will find all the information they
desire within one volume. Others may use several
or all four of the encyclopedia’s volumes to arrive
at a comprehensive, multifaceted, in-depth under-
standing of related health and medical concepts
and information. Researchers efficiently look up
information in The Facts On File Encyclopedia of
Health and Medicine in several ways.
Each section’s entries appear in alphabetical
order (except the entries in Volume 4’s “Emer-
gency and First Aid” section, which are grouped
by type of emergency). The researcher finds a
desired entry by looking in the relevant volume
and section. For example, the entry for acne is in
Volume 1 in the section “The Integumentary Sys-
tem” and the entry for stomach is in Volume 3 in
ix
the section “The Gastrointestinal System.” The
researcher can also consult the index at the back
of the volume to locate the entry, then turn to the
appropriate page in the volume.

Terms that appear in
SMALL CAPS within the text
of an entry are themselves entries elsewhere in
The Facts On File Encyclopedia of Health and Medicine.
Encyclopedia users can look up the entries for
those terms as well, for further information of
potential interest. Such
SMALL CAPS cross references
typically provide related content that expands
upon the primary topic, sometimes leading the
user in new research directions he or she might
otherwise not have explored.
For example, the entry hypertension is in the
section “The Cardiovascular System.” The entry
presents a comprehensive discussion of the health
condition hypertension (high blood pressure),
covering symptoms, diagnosis, treatment options,
risk factors, and prevention efforts. Among the
numerous
SMALL CAPS cross references within the
hypertension entry are the entries for
• retinopathy, an entry in the section “The
Eyes” in Volume 1, which discusses damage to
the eye that may result from untreated or
poorly managed hypertension
• blood pressure, an entry in the Volume 2 sec-
tion “The Cardiovascular System,” which dis-
cusses the body’s mechanisms for maintaining
appropriate pressure within the circulatory sys-
tem

• stroke and heart attack, entries in Volume 2’s
“The Cardiovascular System” about significant
health conditions that may result from hyper-
tension
• kidney, an entry in the section “The Urinary
System” in Volume 3, which discusses the kid-
ney’s role in regulating the body’s electrolyte
balances and fluid volume to control blood
pressure
• atherosclerosis, diabetes, hyperlipidemia,
and obesity, entries in the sections “The Car-
diovascular System” in Volume 2, “The
Endocrine System” in Volume 3, and “Lifestyle
Variables: Smoking and Obesity” in Volume 4,
and all of which are health conditions that con-
tribute to hypertension
Following the path of an encyclopedic entry’s
internal cross references, as shown above, can
illuminate connections between body systems;
define and apply medical terminology; reveal a
broad matrix of related health conditions, issues,
and concerns; and more. The
SMALL CAPS cross ref-
erences indicated within the text of encyclopedic
entries lead encyclopedia users on wide-ranging
research pathways that branch and blossom.
At the end of the entry for hypertension a list
of cross references gathered in alphabetical order
links together groups of related entries in other
sections and volumes, such as smoking cessa-

tion in Volume 4’s “Lifestyle Variables: Smoking
and Obesity,” to provide specific, highly relevant
research strings. These see also cross references also
appear in
SMALL CAPS, identifying them at a glance.
Encyclopedia users are encouraged to look here
for leads on honing research with precision to a
direct pathway of connected entries.
So, extensive cross-references in The Facts On
File Encyclopedia of Health and Medicine link related
topics within and across sections and volumes, in
both broad and narrow research pathways. This
approach encourages researchers to investigate
beyond the conventional level and focus of infor-
mation, providing logical direction to relevant
subjects. Each cross-referenced entry correspond-
ingly has its own set of cross references, ever
widening the web of knowledge.
Using the Facts On File Encyclopedia
of Health and Medicine
Each section of the encyclopedia begins with an
overview that introduces the section and its key
concepts, connecting information to present a
comprehensive view of the relevant system of the
human body or health and medical subject area.
For most body systems, this overview begins with
a list and drawings of the system’s structures and
incorporates discussion of historic, current, and
future contexts.
Entries present a spectrum of information from

lifestyle factors and complementary methods to
the most current technologic advances and
approaches, as appropriate. Text that is set apart or
bold within an entry gives an important health
warning, or targets salient points of interest to add
layers of meaning and context. Lists and tables
x How to Use
collect concise presentations of related informa-
tion for easy reference.
Each type of entry (mid-length and longer)
incorporates consistent elements, identified by
standardized subheadings:
• Entries for health conditions and diseases begin
with a general discussion of the condition and
its known or possible causes and then incorpo-
rate content under the subheadings “Symptoms
and Diagnostic Path,” “Treatment Options and
Outlook,” and “Risk Factors and Preventive
Measures.”
• Entries for surgery operations begin with a gen-
eral discussion of the procedure and then incor-
porate content under the subheadings “Surgical
Procedure,” “Risks and Complications,” and
“Outlook and Lifestyle Modifications.”
• Entries for medication classifications begin with
a general discussion of the type of medication
and its common uses and then incorporate con-
tent under the subheadings “How These Med-
ications Work,” “Therapeutic Applications,” and
“Risks and Side Effects.”

• Entries for diagnostic procedures begin with a
general discussion of the test or procedure and
then incorporate content under the subhead-
ings “Reasons for Doing This Test,” “Prepara-
tion, Procedure, and Recovery,” and “Risks and
Complications.”
Entries in Volume 4’s section “Emergency and
First Aid” are unique within the orientation of The
Facts On File Encyclopedia of Health and Medicine in
that they feature instructional rather than infor-
mational content. These entries do not replace
appropriate training in emergency response
and first aid methods. Rather, these entries pro-
vide brief directives that are appropriate for guid-
ing the actions of a person with little or no first aid
training who is first on the scene of an emergency.
Each volume concludes with a complete, full
index for the sections and entries within the vol-
ume. Volume 4 of The Facts On File Encyclopedia of
Medicine contains a comprehensive index for all
four encyclopedia volumes that researchers can
use to quickly and easily determine which vol-
umes contain desired sections or entries.
How to Use xi
xii How to Use
Volume 1
The Ear, Nose, Mouth, and Throat
The Eyes
The Integumentary System
The Nervous System

The Musculoskeletal System
Pain and Pain Management
Volume Index
Volume 2
The Cardiovascular System
The Blood and Lymph
The Pulmonary System
The Immune System and Allergies
Infectious Diseases
Cancer
Volume Index
Volume 3
The Gastrointestinal System
The Endocrine System
The Urinary System
The Reproductive System
Psychiatric Disorders and Psychologic Conditions
Volume Index
Volume 4
Preventive Medicine
Alternative and Complementary Approaches
Genetics and Molecular Medicine
Drugs
Nutrition and Diet
Fitness: Exercise and Health
Human Relations
Surgery
Lifestyle Variables: Smoking and Obesity
Substance Abuse
Emergency and First Aid

Appendixes:
I. Vital Signs
II. Advance Directives
III. Glossary of Medical Terms
IV. Abbreviations and Symbols
V. Medical Specialties and Allied Health Fields
VI. Resources
VII. Biographies of Notable Personalities
VIII. Diagnostic Imaging Procedures
IX. Family Medical Tree
X. Immunization and Routine Examination
Schedules
XI. Modern Medicine Timeline
XII. Nobel Laureates in Physiology or Medicine
Selected Bibliography and Further Reading
Series Index: Volumes 1–4
The Facts On File Encyclopedia of Health and Medicine in Four Volumes
PREFACE TO VOLUME 1
Leading the reader into the four-volume The Facts
On File Encyclopedia of Health and Medicine through
Volume 1 are the structures and functions that
lead the body’s way in the world. These are the
body systems that equip the body to interact with
its external environment. Some people refer to
these as the “interface” systems, drawing from the
concepts and terminology of computers. These
systems allow the body to receive and respond to
sensory input.
The Ear, Nose, Mouth, and Throat
Volume 1’s first section is the “The Ear, Nose,

Mouth, and Throat.” Through these structures the
body receives auditory, olfactory, and gustatory
sensory information—sounds, smells, and tastes.
The throat does double duty as the conduit to
carry both air and nutrition, essential sustenance
for the body, and also makes possible the uniquely
human form of communication—speech.
The functions of these sensory organs and
structures overlap and integrate with each other
in ways such that the loss of one sensory system
affects others. Speech is difficult without the abil-
ity to hear, for example, and the sensory path-
ways for smell and taste are so intertwined that
both networks become impaired when one or the
other does not function properly. Olfactory nerve
fibers are capable of detecting thousands of odors,
enhancing the brain’s ability to interpret hundreds
of flavors with input from only four basic taste
qualities (sweet, sour, salt, and bitter).
The sense of touch resides in specialized nerves
that populate the surface of the skin in varying
concentrations to provide different levels of tactile
response. The lips and fingertips, for example, are
exquisitely sensitive, while the surfaces of the
arms and legs are less responsive to touch. The
structures of the inner ear also regulate the body’s
balance, integrating with the nervous system as
well as the musculoskeletal system (as anyone
who has found it challenging to walk after spin-
ning in circles well knows).

The Eyes
Sight is so highly refined in humans that many
people consider it the most important of the five
senses. The structures of vision function inde-
pendently from other sensory structures, though
the brain combines sensory information to
develop complex perspectives about the body’s
placement and function within its external envi-
ronment.
The two eyes work independently as well,
though synchronously. The brain blends and
interprets the information it receives from each
eye to form images that have spatial dimension.
This provides depth perception, which interplays
with proprioception (the body’s sense of its place-
ment within its physical environment) and move-
ment. The loss of vision in one eye requires the
brain to rely more on other sensory input and on
learned responses to help the body navigate in a
dimensional world.
The Integumentary System
The structures of the integumentary system—
skin, nails, and hair—cover and protect the body
from the external environment as well as provide
the basis for appearance and identity. Integument
is Latin for “cloak,” an apt term for the system
that envelops the body and literally holds it
together.
The integumentary system provides front-line
defense against infection as a barrier as well as

through immune cells and substances that reside
xiii
among the skin cells, helps maintains fluid and
body temperature, and contains millions of sen-
sory nerve cells. Most of the body’s pain receptors
are among these nerve cells. Remarkably resilient
and flexible, the skin continually renews itself.
The Nervous System
The nervous system is both command central (the
brain) and intercellular highway (the nerves),
orchestrating every function within the body—
more often than not without conscious awareness
of its myriad activities. The nervous system inter-
prets and responds to sensory information, contin-
uously adjusting and accommodating its functions.
These functions require chemical messengers—
neurotransmitters—as well as electrical activity
among cells. Nerves range in size from microscopic
to several feet in length.
The Musculoskeletal System
Giving the body the ability to resist the force of
gravity to provide shape and mobility is the mus-
culoskeletal system—the bones, connective tis-
sues, and muscles. These structures have density
and strength. They use leverage and oppositional
function to move the body—walk, run, jump,
skip, and even turn cartwheels. These functions
require coordination with the nervous system,
sensory systems, and balance structures within the
inner ear. Health conditions that affect the muscu-

loskeletal system—ranging from injuries such as
sprains and fractures to degenerative processes
such as osteoarthritis—are among the most com-
mon reasons people seek medical care.
Pain and Pain Management
The final section in Volume 1 is “Pain and Pain
Management”—not, of course, a body system but
rather a discipline (specialty) within the practice
of medicine that examines the interactions of the
foundational body systems that, when disrupted,
result in pain. A complex physiologic experience,
pain typically arising from multiple causes that
cross these body systems. Consequently, so must
its treatment approaches. The entries in “Pain and
Pain Management” cover the mechanisms of pain
as well as health conditions in which pain is the
primary symptom.
xiv Preface
THE FACTS ON FILE ENCYCLOPEDIA OF
HEALTH AND MEDICINE
IN FOUR VOLUMES:
VOLUME 1
The Eyes xv
xvi The Eyes
Structures of the Ear, Nose, Mouth, and Throat
EAR SINUSES
outer ear frontal
auricle (pinna) ethmoid
auditory canal sphenoid
middle ear maxillary

TYMPANIC MEMBRANE (eardrum) olfactory bulb
EUSTACHIAN TUBE olfactory nerve ending
inner ear
MOUTH
malleus (hammer) lips
incus (anvil) cheeks
stapes (stirrup) tongue
oval window taste buds
COCHLEA palate
organ of Corti
SALIVARY GLANDS
round window parotid
cochlear
NERVE submandibular
bony labyrinth glossopharyngeal
membranous labyrinth lingual
semicircular canals sublingual
vestibule buccal
saccule labial
utricle
THROAT
vestibular nerve uvula
NOSE pharynx
nasal cavity epiglottis
nasal septum hyoid bone
nostrils larynx
mucous lining VOCAL CORDS
nasal conchae
Functions of the Ear, Nose, Mouth, and Throat
The ears, nose, and mouth (along with the eyes)

are the primary features of the head and face.
They form the hallmarks of recognition and indi-
vidual identity throughout life. Yet the functions
of these features are far more than cosmetic. They
are important for survival as well as for refined
sensory perception, making it possible to compre-
hend and interact with the external environment.
Taste and smell, the chemosenses, provide the
combined sensation of flavor—a blend of the
mouth’s ability to perceive four distinct tastes and
the nose’s ability to detect thousands of odors.
Hearing allows the
BRAIN to register sounds across
a broad spectrum of frequency and volume.
The structures responsible for sensory percep-
tion begin to take shape as early as the third week
of embryonic development and function at a fairly
high level by birth. These senses—taste, smell,
and hearing—serve as basic survival mechanisms
for newborns, helping them identify their moth-
ers, food sources, and hazards until other senses
and cognitive abilities adequately develop. Sur-
vival also depends on the ability to suck or chew
and swallow, requiring coordinated movements of
the structures of the mouth and throat. The
brain’s temporal lobe, which processes hearing,
language, and speech as well as smell, takes a
developmental leap about three months after a
baby’s birth, vastly expanding sensory perceptions
and communication capabilities. Further cerebral

THE EAR, NOSE, MOUTH,
AND THROAT
The structures of the ear, nose, mouth, and throat carry out the functions of hearing, balance, smell, taste, speech, and
swallowing. Practitioners in the medical field of otolaryngology specialize in providing care for these structures. This
section, “The Ear, Nose, Mouth, and Throat,” presents a discussion of the structures and their functions, an overview
of otolaryngologic health and disorders, and entries about the health conditions that can affect them.
1
development continues well into ADOLESCENCE,
refining the brain’s ability to interpret and catego-
rize the signals the senses send to it.
Functions of the ear: hearing and balance
Hearing (audition) occurs through air conduction
and
BONE conduction of sound waves. The struc-
tures of the outer and middle ear facilitate air con-
duction. The outer ear, called the auricle or pinna,
is a structure of
CARTILAGE and SKIN that extends
from the side of the head. Its somewhat dishlike
structure serves to “catch” sound waves traveling
through the air; its ridges and curves channel
those sound waves into the auditory canal. The
auditory canal funnels and focuses the sound
waves, directing them to the
TYMPANIC MEMBRANE
or eardrum, which vibrates in response. The tym-
panic membrane marks the end of the outer ear
and the start of the middle ear, creating a sealed
chamber. Its vibration activates, in sequence, the

three tiny auditory ossicles, or bones, of the mid-
dle ear: first the malleus (hammer), then the incus
(anvil), and finally the stapes (stirrup). The flat of
the stapes rests against the oval window, a small
translucent membrane in the wall of the
COCHLEA.
This point of contact represents the transition
from the middle ear to the inner ear and from an
environment of air to one of fluid.
The middle ear is pressurized, allowing the
tympanic membrane and the auditory ossicles to
vibrate freely and without resistance. The
EUSTACHIAN TUBE, a short canal of tissue, connects
the middle ear with the upper throat at the back
of the nose. Somewhat like an elongated valve, it
serves to equalize pressure between the middle
ear and the external environment. Swallowing
and yawning force air into the eustachian tube,
causing it to open (sometimes with a perceptible
pop). Unequal pressure between the middle ear
and the atmosphere causes the tympanic mem-
brane to bulge in the direction of the lower pres-
sure, altering its ability to convey the vibrations of
sound waves. Circumstances that prevent the
eustachian tube from opening to balance air pres-
sure, such as a cold that fills the nasal passages
and eustachian tubes with congestion, causes the
sensation of muffled hearing and pressure in the
ear. When pressure in the middle ear remains
lower than the atmospheric pressure for a pro-

longed time, the body attempts to compensate by
drawing fluid into the middle ear. Though the
fluid may relieve the sensation of pressure, it fur-
ther constrains middle ear function. Blocked
eustachian tubes establish ideal conditions for
middle ear
INFECTION (OTITIS media), allowing BAC-
TERIA to move into the middle ear. Until about age
10, the eustachian tubes are nearly horizontal. As
the child’s facial structure lengthens with maturity
the eustachian tubes shift and angle downward
from the ears to the throat, improving their ability
to drain congestion and remain open.
The vibration of the stapes against the oval
window amplifies the energy of the sound waves
and sets in motion the fluid (endolymph) within
the cochlea on the other side of the oval window.
Fluid further focuses and aligns the sound waves
into patterns. A second membrane, the round
window, dissipates excessive vibration into the
fluid of the inner ear (perilymph) on its other side.
The moving endolymph within the cochlea in
turn stimulates microscopic fibers along a mem-
brane that forms a structure within the cochlea
called the organ of Corti. The fibers resonate to
specific sound waves, activating
NERVE impulses in
specialized cells called
HAIR cells. The cochlear
nerve carries the nerve impulses to the eighth cra-

nial nerve (vestibulocochlear nerve), which in
turn transmits them to the brain’s temporal lobe.
The temporal lobe filters, interprets, and analyzes
the nerve impulses, translating them into sound
messages including language.
The bony structures of the head and face also
conduct sound waves. Bone conduction bypasses
the outer and middle ears. Sound waves instead
travel as vibrations along the bones to the inner
ear, where they pass to the bony part of the
cochlea. The vibrations of the bony cochlea pass to
the endolymph, and the rest of the hearing
process unfolds. Sounds conveyed through bone
conduction are significantly restricted in tonal
range and volume because they bypass the ampli-
fying structures of the tympanic membrane and
auditory ossicles. The sound waves of one’s own
voice travel primarily through bone conduction
along the bones of the face, which explains why it
seems so different when heard as a recording in
which the sound waves travel by air conduction.
The inner ear also manages the body’s balance
and motion in relation to gravity. The structures
The Ear, Nose, Mouth, and Throat 3
and functions that do so make up the vestibular
system. The bony labyrinth, which also houses the
cochlea, supports the membranous labyrinth. Five
fluid-filled structures within the membranous
labyrinth sense motion and movement: the three
semicircular canals, which sense rotational move-

ment, and the saccule and utricle, which sense
linear movement. The saccule senses movement
that is up-and-down; the utricle senses back-and-
forth and left-to-right movement. These structures
are all open to one another; however, they form a
closed network among themselves that contains
endolymph. Movement causes shifts in pressure of
the endolymph, which nerve cells register and
send as electrical impulses to the vestibular nerve.
The vestibular nerve conveys these impulses to
the eighth cranial nerve, which in turn carries
them to the brain. The brain interprets the
vestibular messages along with other input from
sensory nerve cells (proprioceptors) located
throughout the body, nearly instantaneously
responding with neuromuscular signals that initi-
ate movement.
Extremes of movement, such as rapid swinging
or spinning, can temporarily disrupt the vestibular
system, causing dizziness and
NAUSEA. Some people
experience such symptoms with less extreme
movement, such as riding in a car, boat, or airplane,
known commonly as motion sickness. More seri-
ous dysfunctions and disorders of the vestibular
system, such as M
ÉNIÈRE’S DISEASE and LABYRINTHITIS,
can result in debilitating loss of balance.
Functions of the nose: breathing and smell The
nose protrudes from the front of the face. Its

placement allows it to draw air into the body in
one of life’s most basic activities,
BREATHING. Most
of the nose’s external structure is
CARTILAGE and
SKIN; the nasal bone is less than one half inch long.
The ethmoid, vomer, and maxilla bones frame the
back of the nose. Ridges in these bones, the nasal
conchae, direct the flow of air into the
SINUSES.
These chambers, along with the nose’s mucus lin-
ing, moisturize and warm each breath so it does
not irritate the airways and lungs. A tissue wall,
the nasal septum, divides the nasal cavity into two
channels, the nostrils. Tiny hairs line the inner
nostrils and are responsible for keeping the nasal
passages clear of debris.
The nose is also the body’s organ of smell,
responsible for the functions of olfaction. The first
cranial nerve (olfactory nerve) terminates in the
olfactory bulb and a bristlelike patch of olfactory
nerve endings along the roof of the nose. These
olfactory nerve endings detect the presence of
odor molecules in the air that enters the nose.
Fibers of the palatine nerves, which detect taste,
are also present along the floor of the nose,
though not nearly in the abundance with which
they infiltrate the mouth. The brain interprets the
blend of nerve impulses from the palatine nerve
endings and the olfactory nerve endings and inte-

grates them into perceptions of flavor.
Functions of the mouth and throat: taste, swal-
lowing, and speech The mouth and throat make it
possible to eat and speak. The powerful masseter
muscles open and close the mandible (lower jaw),
generating over 500 pounds per square inch of
pressure as the
TEETH come together to bite and in
excess of 3,500 pounds per square inch of force at
the back teeth (molars) with chewing. The hyoid
bone helps anchor the back of the tongue, another
powerful
MUSCLE. The SALIVARY GLANDS, present in
pairs on each side of the mouth, produce two to
three pints of saliva every day. This watery liquid
contains enzymes and mixes with food to begin
breaking it down, an early stage of digestion, as
well as to soften it for swallowing. The cheeks,
tongue, and lips help contain food within the
mouth and push it to the back of the throat for
swallowing; they also shape the flow of air and
create the formation of words during speech.
These functions require muscular control and
coordination.
The sense of taste is called gustation. Though
common perception is that the bumps on the
tongue are the taste buds, taste buds are micro-
scopic. The bumps are called papillae; they contain
clusters of taste buds. Each taste bud contains
dozens of taste cells. Though taste buds for the

four categories of taste—sweet, sour, salt, and bit-
ter—are present throughout the mouth, the
roughly 10,000 of them on the tongue align in
patterns of concentration:
• Taste buds on the tip of the tongue are concen-
trated to detect sweet.
4 The Ear, Nose, Mouth and Throat
• Taste buds on the sides of the tongue are con-
centrated to detect sour and salt.
• Taste buds at the back of the tongue are con-
centrated to detect bitter.
Three
CRANIAL NERVES—the 7th (facial), 9th
(glossopharyngeal), and 10th (vagus)—carry
nerve impulses related to taste to the brain. At its
most primitive level, taste helps the brain deter-
mine what is safe and what is hazardous to eat.
Sweet substances generally contain sugars and
carbohydrates, essential nutrients for energy,
whereas bitter substances may contain acids or
chemicals that are potentially harmful. Recent
research indicates that gustation is far more com-
plex than simple delineation among taste buds,
however, with some scientists speculating that
taste represents learned interpretations as much as
response to specific qualities. Further, taste and
smell are inextricably intertwined. Though distinct
nerve impulses from each reach the brain, the
brain analyzes them and creates collective inter-
pretations.

The functions of breathing and swallowing share
the structures of the throat. The chamber at the
back of the mouth and the top of the throat is the
pharynx; it receives both air and food. A flap of car-
tilage at the base of the pharynx, the epiglottis,
closes across the
TRACHEA when swallowing and
opens to allow the passage of air during inhalation
and exhalation. The small flap of tissue that hangs
visibly at the back of the throat, the uvula, is an
extension of the soft palate. Doctors are uncertain
of the uvula’s function; it may help keep swallowed
food from entering the nasal passages.
The larynx is a sequence of connected cartilage
structures that makes speech possible. Air passing
through the larynx causes these cartilages and the
folds of tissue known as the
VOCAL CORDS to
vibrate, generating sounds. The muscles of the
throat help move the sound vibrations into the
mouth, which then forms them into noises and
words. Hearing further helps shape speech, pro-
viding instant auditory feedback. It is difficult,
although not impossible, for someone who has
profound
HEARING LOSS to speak clearly enough for
others to understand. S
TROKE and neuromuscular
disorders such as P
ARKINSON’S DISEASE are among

the common causes of dysfunctions affecting swal-
lowing and speech.
Health and Disorders of the Ears, Nose,
Mouth, and Throat
Disorders and dysfunctions of the ears, nose,
mouth, and throat range from structural defects
present at birth to infections to trauma resulting
from
ACCIDENTAL INJURIES or diseases such as
CANCER. Disturbances of taste, smell, hearing, and
balance may accompany numerous health condi-
tions from
COLDS to DIABETES, stroke, and Parkin-
son’s disease. Health experts estimate that about 2
million Americans have diminished, altered, or
lost functions of taste and smell. More than 28
million have a perceptible loss of hearing ability; 2
million of them are profoundly deaf (unable to
hear at a functional level). Disturbances of balance
resulting from dysfunctions of the inner ear affect
as many as 45 million Americans.
Nearly everyone experiences the most frequent
health condition that affects the chemosenses
simultaneously: the common cold. Its familiar
symptoms include nasal congestion and runny
nose (
RHINORRHEA), sore throat (PHARYNGITIS), and
the sensation of “stuffy” ears and muffled hearing
(and sometimes dizziness, when the congestion
alters the inner ear’s balance mechanisms). This

choreography of discomfort results from the inti-
mate integration of both structure and function of
these senses.
Limiting or avoiding exposure to loud noise
could protect millions of people from hearing loss.
Surgical and technological advances hold great
promise for restoring some kinds of hearing loss.
Though some diminishment occurs naturally with
aging, hearing, taste, and smell require minimal
effort to maintain healthy function across the
spectrum of age.
Traditions in Medical History
Before the advent of
ANTIBIOTIC MEDICATIONS and
vaccines in the middle of the 20th century, many of
today’s commonplace ailments involving the ears,
nose, mouth, and throat were serious and even life-
threatening illnesses. Otitis media (middle ear
infection), though less common or perhaps simply
less frequently diagnosed 50 years ago than it is
The Ear, Nose, Mouth, and Throat 5
today, accounted for much childhood deafness and
frequently led to the complication of
MASTOIDITIS, a
bacterial infection in the porous mastoid bone
behind the ear that in turn often spread to the
brain, causing
MENINGITIS or ENCEPHALITIS. Even TON-
SILLITIS frequently resulted in abscesses in children
and adults alike; tonsillectomy, in the absence of

adequate
ANESTHESIA, was not an option.
These infections had grim outlooks, leading to
desperate treatments such as lancing (cutting open
the
ABSCESS or infection) and application of chemi-
cal disinfectants (for example, iodine and carbolic
acid), which were the standard of treatment for
external wounds. The highly toxic nature of these
approaches became a calculated risk in the fight
for life. Lancing an abscess opened a direct chan-
nel into the bloodstream for the
BACTERIA, virtually
guaranteeing rapid death due to
SEPTICEMIA (“blood
poisoning” or septic shock). The alternative, how-
ever, was suffocation from the swelling that closed
off the throat. D
IPHTHERIA and PERTUSSIS (whooping
COUGH), bacterial infections of the throat,
remained the leading causes of childhood death
until the 1950s. Today antibiotics, surgery, and
routine childhood vaccinations have relegated
these diseases, for the most part, to entries in text-
books and encyclopedias.
Breakthrough Research and Treatment Advances
Some the most profound breakthroughs in oto-
laryngology have been in the area of hearing loss.
Digital technology brings the computer to the ear,
allowing tiny and fully programmable hearing aids

that fit far enough within the auditory canal to be
undetectable. Computerized adjustments accom-
modate individual variations in tonal loss, helping
people screen out the kinds of noise interference
that have made the traditional
HEARING AID a less
than ideal solution. The
COCHLEAR IMPLANT, which
debuted in the 1980s, makes hearing possible for
thousands of people with sensorineural hearing
loss for whom hearing aids do not work. Hair-thin
wires reside within the inner ear, receiving input
from outside the ear and conveying it directly to
the hair cells within the cochlea in much the same
way nerves do. External components collect and,
using digital technology, interpret sound signals.
Other advances mark improvements in treat-
ments for ear infections, sinus infections, seasonal
allergies, and operations on structures of the oro-
facial structures. Infants born with cleft deformi-
ties today will grow up with little evidence of this
once disfiguring
CONGENITAL ANOMALY, as advances
in anesthesia and surgical techniques now permit
surgeons to perform corrective procedures early in
childhood and often in a single operation. Endo-
scopic surgery reduces risk for numerous opera-
tions on the nose, middle and inner ear, and
throat. New understandings of immune function
and allergy response have led to new treatment

approaches for chronic
SINUSITIS and ALLERGIC RHINI-
TIS. Current research continues to explore age-
related changes in hearing, seeking approaches to
head off hearing loss.
6 The Ear, Nose, Mouth and Throat
A
acoustic neuroma A noncancerous tumor of the
eighth cranial (vestibulocochlear)
NERVE. Acoustic
neuromas typically grow over years to decades
and in some people cause no symptoms; doctors
detect them incidentally. An acoustic neuroma
does not invade the surrounding tissues, though it
can become life-threatening if it becomes large
enough to put pressure on the structures of the
brainstem. Most often doctors do not know why
acoustic neuromas develop and classify them as
idiopathic (of unknown cause). Acoustic neuro-
mas sometimes occur with neurofibromatosis type
2, a rare hereditary disorder in which fibrous
growths develop in the
CRANIAL NERVES and SPINAL
NERVES
.
Early symptoms of acoustic neuroma are vague
and often perceived as normal consequences of
aging because the tumor is so slow growing it typ-
ically appears in the later decades of life. Early
symptoms include

• gradual loss of hearing, especially difficulty
understanding speech, in one
EAR
• TINNITUS (rushing or roaring sound) in one ear
• balance disturbances such as dizziness or loss of
balance with motion
Advanced symptoms occur when the tumor’s
size begins to encroach on nearby structures such
as the seventh cranial (facial) nerve. Such symp-
toms might include facial
PAIN and disturbances of
facial expression. An
AUDIOLOGIC ASSESSMENT helps
determine the level of
HEARING LOSS and whether it
affects one or both ears. Hearing loss in both ears
suggests causes other than acoustic neuroma; it is
very rare that a person would have two tumors,
one affecting each vestibulocochlear nerve. M
AG-
NETIC RESONANCE IMAGING (MRI) can usually deter-
mine the presence of an acoustic neuroma.
Treatment depends on the extent of symptoms
and the person’s overall health status. For many
people, especially those who have no symptoms,
the preferred treatment is watchful waiting
(observation and regular tests to monitor the
tumor’s growth). Surgery to remove the tumor or
RADIATION THERAPY to shrink the tumor is an option
when symptoms interfere with

QUALITY OF LIFE or
affect vital brainstem functions such as regulation
of
BREATHING and HEART RATE or motor control.
Each method has risks and benefits; individual
health circumstances also influence the decision.
When it exists with no symptoms, acoustic
neuroma does not interfere with the regular activ-
ities of living or present any threat to health. For
most people who experience symptoms and
undergo treatment, recovery is complete. Idio-
pathic acoustic neuromas do not return, though
acoustic neuromas associated with neurofibro-
matosis type 2 often recur. Other than neurofibro-
matosis type 2, there are no known risk factors or
preventive measures for acoustic neuroma.
See also
AGING, OTOLARYNGOLOGIC CHANGES THAT
OCCUR WITH
; CENTRAL NERVOUS SYSTEM; MÉNIÈRE’S DIS-
EASE; SURGERY BENEFIT AND RISK ASSESSMENT; VESTIBU-
LAR NEURONITIS.
adenoid hypertrophy Enlargement of the ADE-
NOIDS, structures of LYMPHOID TISSUE at the back of
the
NOSE. The purpose of the adenoids is to trap and
destroy pathogens (disease-causing agents) in chil-
dren; by
ADOLESCENCE the adenoids atrophy (shrink)
and in adults are not distinguishable. When the

adenoids swell, they can block the nasal passage.
This disrupts
BREATHING and can affect the speech.
The eustachian tubes open near the adenoids;
7