Human Body: Pushing the Limits

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NARRATOR:
Too often,

we take our bodies for granted,

but under pressure,

our bodies can show us

how extraordinary

they truly are.

This complex machine grew

out of millions of years

of evolution.

So intricate,

we're still mystified

by many of the things

going on inside us.

A hidden world,

but one we can now explore

in 3-D as never before.

Our sight relies on the most

complex system in our bodies.

Using three-quarters

of our brain power'

when we're challenged,

our eyes focus on the smallest

detail at lightning speed.

They allow us to see

in the dark'

even to see to the magic

of the impossible.

Our brain allows us to see

even while we sleep.

And someday, we may be able

to see without our eyes.

That's how extraordinary

our sight truly is

when we're pushed to the limits.

[ Siren wailing ]

[ l ndistinct talking on radio ]

A murder suspect races

through downtown Los Angeles.

[ Tires screeching ]

Pursuing him is LAPD officer

Stan Berry.

What he's got to do

in this superfast world

is to figure out what matters

and what doesn't

at 1 00 miles an hour.

MAN:
1 4, there's two occupants

in the car.

[ Horn blares ]

NARRATOR:
And to keep up with

the suspect without crashing.

BERRY:
l need to know about

the traffic to the right of me,

traffic coming

to the left of me.

But you also need to focus

on what's ahead of you.

ls there pedestrians

walking down the street?

And then also try to keep up

with the fleeing suspect'

as well.

NARRATOR:
Nature designed the

eyes to let him do just that.

Sight guides the human body.

[ Tires screeching ]

[ Siren wailing ]

NARRATOR:
Many animals

have special kinds of vision.

But in humans, we can do it all.

Like no other creature on Earth,

our vision can distinguish

around 1 0 million colors...

[ Horn blaring ]

...switch focus from infinity

to mere inches

in a fifth of a second...

... pinpoint detail

in the brightest sunshine

or darkest shadow...

...take in a wide-angle view

of almost 1 80 degrees.

All of this takes the massive

power of the human brain.

in some way subserve

the visual system.

lt's been given

an extraordinarily high degree

of emphasis

by all the mechanisms that

have gone into its creation.

[ l ndistinct talking on radio ]

NARRATOR:
Human eyes function

as survival sensors,

giving us essential information

at the crucial time.

Berry constantly relies on them.

The eyes' mechanics are

the most complex in the body.

Their intricacy is unmatched.

As a ball, the eye pivots

in all directions,

locking onto moving targets.

lt does so with the help

of unlikely allies --

two cups of fat -- shock

absorbers for the eyeballs.

Light enters through an aperture

in the iris,

an elastic mesh

of interlocking fibers.

l n bright light' it snaps down

to the size of a pinhole

in a fifth of a second.

Light hits the lens --

not a hard disk'

but a bag of fluid.

The lens projects an image the

size of a large postage stamp

onto the retina

at the back of the eye.

Then the retina'

a mass of nerves,

sends impulses to the brain.

Surprisingly, the right eye

signals the left side

of the brain,

and the left eye transmits

to the right side.

Our eyes have evolved

a crucial feature

that still keeps us

from going extinct.

Officer Berry is about to test

that feature to its limits.

Speeding into a dangerous

intersection,

he faces questions literally

involving life or death.

[ Engine revving ]

ls anything moving?

Where is it?

What is it?

[ Siren wailing ]

A vehicle is stopped ahead,

blocking the way.

To the right' a car speeds

toward the intersection.

On the left'

a third driver about to move.

[ Horn blares ]

But suddenly,

something else comes into view.

And here's where

the human eye's design pays off.

At the back of the eye,

most of the retina consists

of millions of rods.

These cells see no color

or detail.

But let anything anywhere

in our field of view move,

and the rods spot it.

The eyes swivel

to look directly at the vehicle.

Now other cells at mid-retina

kick in.

A pinhead-sized dot holds

six million cells called cones.

They're all about color

and detail.

DR. D'AM l CO:
That's why,

when we look at something,

we look directly at it --

because we have

our highest visual acuity

right in the center.

NARRATOR:
Locking his eyes

on the moving object'

Officer Berry can judge speed,

direction, and danger.

The brain responds,

sending signals

at an amazing 1 80 miles per hour

to his hands and feet in time

to clear the intersection.

[ Horn blares ]

[ Siren wailing ]

This is one of hundreds

of life-or-death decisions

that Officer Berry makes

to bring the 40-minute chase

to a safe end.

[ l ndistinct talking on radio ]

He does this thanks to the eye's

incredible skill at adjusting

when information threatens

to overload what we're seeing.

This ability matters

as much today

as it did for our ancestors.

Evolution left us

with another skill,

one that's still priceless.

l n the dark'

we can make out the world

with only the smallest

of clues.

The will to live through a fire

depends on our skill

at navigating the murderous

darkness of smoke-filled rooms.

Firefighters reach a house

in Bradenton, Florida.

Agent 56, go ahead

and charge the line.

NARRATOR:
But they don't know

if anyone's trapped inside.

l'm set.

Ready?

NARRATOR:

Now firefighter Dan Fleming

enters a dangerous world

of shadows and shapes...

...so murky and cloudy,

you'd think it impossible

to see anything.

Dan struggles to build a picture

of the whole house

from frag ments he makes out

in the haze.

[ Heavy breathing ]

How is the house laid out?

Where is the fire?

Are there any survivors?

You're trying to determine

what the house looks like,

what the occupants are about'

who would be inside this home.

NARRATOR:

Despite the darkness,

Dan's eyes im mediately start

to adjust.

They have amazing sensitivity.

l n complete darkness,

from 1 4 miles away,

we can detect the light

from a single candle.

You try to find bits and pieces

of light

to help you

find your way through.

[ l ndistinct talking on radio ]

NARRATOR:
l n low light'

we rely on the rod cells

that cover most of the retina.

Highly sensitive, they only

register black and white.

But Dan needs to see in color.

He's searching for a fire.

FLEM l NG:

lt was very faint at first.

l thought to myself' "That must

be the seat of the fire."

very orange glow --

l mean, it was really orange.

NARRATOR:

To see color'

you use cone cells

at the retina's center.

We get all our color vision

from being able to distinguish

only three colors.

SADU N:
The cones are sensitive

to different colors.

There's those that are

particularly sensitive

to blue light' those to green

light' and those to red light.

And they need a lot more light

to fire.

So if they get enough of

the photons of the right color'

they fire and say to you,

"There's a spot of green

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