Maybe it's
the smell of a Christmas tree in your house in December. Whatever your favorite
memory is, you have it because of your five senses: sight, hearing, touch,
taste, and smell. The senses are how we experience the world.
Almost
everyone knows what it's like to lose one of the five senses, if only for a
short time. You may have tried to pin the tail on the donkey while blindfolded.
Or maybe you covered your ears when a loud train raced by. It's almost
impossible to taste and smell if you have a cold. A shot from the dentist can
take away the sense of touch in your mouth. But to imagine life without any of
your senses is impossible. You experience life through the senses.
This kid is
experiencing life through all five senses: sight, hearing, touch,
taste, and
smell.
Different parts
of
the brain get information from each of the senses. Let's say your brain gets
news from your nose that something smells good. The brain may tell your hand to
grab a fork and dig in. Or the brain may get news that a car is coming down the
street. It will tell your feet to stay on the sidewalk.
Animals have
all
the senses people do, but they may work differently. A cat, for instance, sees
some colors but not as brightly as people do.
Sight
Every day, your five senses bring you information about the world. But they are
not equal partners in the job. Eighty percent of the information your brain
gets comes through your eyes unless you are blind.
Yet, in a
sense, your eyes do not see. They basically collect light. Your brain turns the
collected light into images that make sense. In other words, what you
"see" with your eyes has no meaning to you until your brain makes
sense of it.
Your brain
also lets you “see” events from the past. You may recall last year's birthday
party. You can imagine scenes that have never been. Can you “see” yourself
being elected president? Even someone who goes blind in later life can recall
visual images, thanks to the brain.
So, we know
the brain plays a major role in the sense of sight. Still, the eyes are super
important. Without them collecting light, the brain would have no raw material
to work with.
Use your
mouse or finger to scrub through the animation below.
Retina
Optic nerve
Conjunctiva
Vitreous
body
Cornea
Fovea
Pupil
Lens
Blind spot
Iris
Choroid
Sclera
Ciliary body
Light enters
the
eye through the pupil.
That's a
hole in the iris. Behind the iris, the lens focuses images onto the retina. The
retina turns light rays into electrical impulses. The optic nerve carries these
impulses to the brain.
Birds of
prey need great eyesight. Some can spot a mouse on the ground from several
hundred feet in the air. If an eagle could read, it could read this screen from
230 feet away. That's as tall as a 20-story building.
Stevie
Wonder was
born blind. He became a recording artist when he was just ten. He sings,
composes, and plays the piano, clarinet, drums, organ, and harmonica.
Of course,
plants do
not have eyes. But at least one plant has a sense of sight. The fungus Pilobolus
has an area that is sensitive to light. The fungus aims its spores at the
lightest spot it can find. This gives it a better chance of survival.
You see in color
because of rods and cones. These cells are in the retina. About 125 million rod
cells in each eye work well in dim light. They see in shades of gray. Six
million cone cells in each eye respond to color.
Check It
Out!
Some
pictures, often called optical illusions, play tricks on our eyes. Look at the
two horizontal lines above and figure out which is longer.
VIEW ANSWER
Both lines
are the same length.
BACK TO
QUESTION
Check It
Out!
Look at the
two shapes above. Which is
smaller?
VIEW ANSWER
Both shapes
are the same size.
BACK TO
QUESTION
What do
microscopes, binoculars, and telescopes all have in common? They all
have lenses, of course. And they are all meant to make our eyes stronger. There
are two main kinds of microscopes. An optical microscope bends light rays
passing through an object. The bent rays then join to form an enlarged image.
Such a microscope can make an image up to 2,000 times bigger. The electron
microscope is a newer invention. Instead of light rays, it uses a beam of
electrons to magnify. Electrons are negatively charged particles of an atom. An
electron microscope can enlarge an object up to 2 million times!
Check It
Out!
Tears keep
eyes clean and moist. They come from glands over the eyes and drain into the
nose. Eventually they are swallowed. Can you figure out why you get a runny
nose when you cry?
VIEW ANSWER
