The New Childrens Encyclopedia

SIGHT

Sensing the world

Humans have five senses: sight, hearing, touch,

smell, and taste. Your senses tell you about the

world around you. They work because billions

of nerve cells flash messages to your brain,

which interprets the messages and tells you

what you are sensing, whether good or bad.

O Messages about the

image travel from your

eye to your brain as

nerve impulses. Your

brain turns the

messages into the

detailed image that

you see.

Bright light

Dim light

 IRIS AND PUPIL

The colored part of your

eye, called the iris, has a

hole in the middle called

the pupil. In bright light,

the pupil shrinks to prevent

too much light from getting

into your eye. In dim light,

the pupil expands to allow

more light into your eye.

 INSIDE THE EAR

Your ear is made up

of three main parts—

the ear (auditory)

canal, the middle

ear, and the

inner ear.

HEARING

Sounds are made up of vibrations, which are funneled

inside the ear by the outer ear. Soundwaves first travel down

the ear canal and vibrate the eardrum. These vibrations

reach the cochlea. From here, messages pass to the brain,

which interprets the vibrations as the sounds we recognize.

TOUCH

You have about three million

pain sensors, and most of

these are in your skin. Your

fingertips are particularly

sensitive. You also have touch

receptors that detect light

touch, pressure, vibration,

heat, and cold.

Inner ear

Ear canal

Middle ear

Eardrum

Cochlea

BALANCE, TOO!

Your ear helps you to

balance. Hair cells in the

inner ear tell your brain

about your body’s position

and movements.

When the brain

gets messages from the

retina, it turns the

Retina Lens Iris image right way up.

Cornea

TAKE A LOOK: IRIS

Merkel’s disk Your eye will react differently depending on

how bright the light is that is shining into

it. How it reacts is controlled

by the iris, a ring of muscle.

The image is focused

on the retina upside

down.

THE HUMAN BODY

SIGHT

The eye works like a camera. Light

from an image passes through the

cornea, is adjusted by the lens behind

it, and forms an upside-down image

on the retina at the back of the eye.

This is translated by the brain.

 TOUCH SENSATIONS Skin layers

are full of touch receptors. Some receptors

are contained in a capsule, while others

are free nerve endings.

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THE HUMAN BODY

Skull bone

Outer ear

Free nerve

ending

Meissner’s corpuscle

Pacinian corpuscle

Dermis

THE HUMAN BODY

Iris

Pupil