Childrens Illustrated Encyclopedia

168

Ears E

BALANCE

The ears help us keep our balance. The three

semicircular canals inside the ear contain fluid. As you

move your head, the fluid flows around.

Tiny hair cells sense this movement and

produce nerve signals to tell the brain

which way “up” you are.

ANIMAL HEARING

Creatures such as fish and squid

have sense organs to detect

vibrations in the water. Fish

have a lateral line—a

narrow groove along each

side of the body. Hair

cells in the lateral line

can sense the sound or

movement of nearby

animals. The catfish, shown

here, has whiskers called

barbels to smell and feel for

prey in murky river bottoms.

OUTER AND MIDDLE EAR

The ear flap on the side of the head funnels
sound waves into the ear canal. The sound

waves bounce off the eardrum at the end and
make it vibrate. These vibrations pass along the

ossicles, each of which is hardly bigger than a
rice grain. The ossicles have a leverlike action

that makes the vibrations louder.

THE EARS ARE THE ORGANS of hearing and balance.

They collect sound vibrations from the air and turn them

into messages called nerve signals that are passed to the

brain. Each ear has three main parts—the outer ear, the

middle ear, and the inner ear. The outer ear includes the

part you can see. It consists of the ear flap, or auricle, and

the ear canal. The middle ear consists of the eardrum and

three tiny bones called the ossicles. These three bones send

sounds from the eardrum to the inner ear. The main part

of the inner ear is the snail-shaped cochlea, which is full of

fluid. The cochlea changes vibrations into nerve signals. The

inner ear also makes sure that the body keeps its balance.

Although we can hear many different sounds, we cannot

hear as wide a range as most animals. Also, unlike rabbits

and horses, we cannot swivel our ears toward the direction of a

sound we have to turn our heads.we have to turn our heads.

RANGE OF HEARING

Humans can hear sounds that vary

from a low growl to a piercing

scream. Many animals, including

dogs, can hear sounds that are far

too high-pitched for us to detect. A

human’s range of hearing is

30-20,000 hertz (vibrations per

second); a bat’s range of hearing

is up to 100,000 hertz.

Human Dog Dolphin

INSIDE THE EAR
The ear canal is slightly
curved. It measures about
1 in (2.5 cm) in length.
The delicate parts of the
middle and inner ear lie well
protected deep inside the
skull bone, just behind and
below the level of the eye.

Cochlea

Eardrum

(tympanum)

Hair

cells

Ear canal

Bone

Outer ear

canal

Ear flap (auricle)

INNER EAR

The stirrup bone

presses like a piston on

a thin, flexible membrane

called the oval window that

covers the entrance to the inner

ear. Movements of the oval window

send vibrations passing through the fluid

inside the inner ear and into the cochlea.

The vibrations bend “hairs” attached to some

of the 20,000 hair cells that rest on a

membrane that runs the length of the

cochlea. This bending action causes those

hair cells to send signals to the brain,

which processes the signals and identifies

the sounds that were being made so that

they can be heard.

Inside

the cochlea

Inner ear

MIDDLE EAR BONES

The middle ear bones (ossicles)

are called the malleus (hammer),

incus (anvil), and the stapes

(stirrup).

Bones of

middle ear

Stapes (stirrup)

Malleus (hammer)

Inner ear

Middle ear

Fluid in cochlea

Semicircular canals

Find out more

Human body

Skeletons

Sound

Tight-rope

walker

Bat

Incus (anvil)

Ultrasonic sound is above the

human range of hearing.