How It Works: Science and Technology - Vol. 8

By Wendy Horobin | Go to book overview

Hearing

Hearing tests are
common tests for children
growing up. The machine
on the right is called an
audiometer and produces
sounds of varying pitch
and loudness that are sent
to one ear at a time
through headphones. The
sounds are decreased in
volume until they become
inaudible. The person
being tested signals (here
by raising a hand) each
time they hear a sound.
This type of hearing test,
called pure-tone
audiometry, is often used
to assess the extent of a
person's hearing loss
and to investigate
possible causes.

The ear is an extremely delicate and complex organ, giving us both our sense of hearing and our sense of balance. What is normally called the ear—the part we can see—is only part of the outer ear, itself the simplest of three sections. Behind it, stretching deep into the skull, lie the middle and inner ear, which in turn connect with the nose and throat.

The outer ear, called the pinna, has two important parts: the auricle, the fleshy part attached to the side of the head, and the opening called the external auditory canal. The auricle is shaped like a cup or radar bowl to collect sound waves and direct them into the external auditory canal. It is composed of fatty tissue and cartilage, a tissue softer than bone but harder than muscle, and although some individuals can move their ears, humans lack the ability to [prick] their ears as many animals do. The external auditory canal is the opening visible when looking' directly at the ear. It is a passage about 11/ in. (3.8 cm) long, which guides sounds from the auricle to the middle ear. Its outer third is lined with fine hairs and wax-producing glands. The hairs and wax trap dirt and other foreign matter to stop them from entering and possibly damaging the ear. Sometimes this wax hardens and causes discomfort, earache, temporary loss of hearing, and ringing in the ears (tinnitus). In such cases, doctors can syringe the wax out.


The middle ear

The middle ear, or tympanic cavity, resembles a six-sided box. It is separated from the external auditory canal by the eardrum, or tympanic membrane, a thin sheet of tissue about 14 in. (6 mm) across. Within the tympanic cavity, three small movable bones, called the auditory ossicles, link with each other to form a chain.

The outer bone, called the malleus or hammer, is attached to the eardrum. Next comes the middle bone, called the incus or anvil, which connects the malleus with the innermost bone, the stapes or stirrup. The outer and middle ears chan-

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How It Works: Science and Technology - Vol. 8
Table of contents

Table of contents

  • Title Page *
  • Contents *
  • Gold 1013
  • Governor 1017
  • Grass-Cutting Equipment 1018
  • Gravity 1020
  • Gun 1023
  • Gyrocompass 1028
  • Gyroscope 1030
  • Hair Treatment 1032
  • Halogen 1034
  • Hang Glider 1037
  • Head-Up Display 1039
  • Hearing 1041
  • Heart 1045
  • Heart Pacemaker 1048
  • Heart Surgery 1049
  • Heat Engine 1053
  • Heat Exchanger 1054
  • Heating and Ventilation Systems 1056
  • Heat Pump 1063
  • Helicopter 1065
  • Hi-Fi Systems 1071
  • High-Speed Photography 1077
  • Holography 1080
  • Hormone 1084
  • Horticulture 1088
  • Hosiery and Knitwear Manufacture 1090
  • Hurricane and Tornado 1094
  • Hydraulics 1100
  • Hydrocarbon 1105
  • Hydrodynamics 1109
  • Hydroelectric Power 1112
  • Hydrofoil 1116
  • Hydrogen 1118
  • Hydroponics 1120
  • Hygrometer 1123
  • Ignition System, Automobile 1124
  • Image Intensifier 1128
  • Immunology 1132
  • Induction 1138
  • Inertia 1142
  • Information Technology 1147
  • Ink 1151
  • Index i
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