The Incredible Human Hand Dissected

We're about to embark on something most of us

have never witnessed before.

It will take us inside two of the most amazing structures

in the natural world.

Our hands...

and feet.

Two parts of our body that define us as human.

I'm George McGavin.

And as a biologist, I think that to truly understand our hands and feet

we need to look inside them.

To do this we've created our own dissection lab.

We've brought together the tools, the technology,

and leading experts in human anatomy.

Over two programmes, we're going to dissect a human hand and foot

to discover what makes them unique.

And we're going to start with our hands.

We're about to reveal them as you've never seen them before.

We're going to take a real human hand apart,

systematically, layer by layer.

Wow, that is absolutely gorgeous.

We'll discover the incredible natural engineering

that drives our actions,

and the microscopic structures

that give us our remarkable sense of touch.

I'll meet people whose hands have astonishing abilities.

-Whoa! Sorry, whoa!

-Surprise!

Beyond the lab, I'll be putting my hands to the test.

-37.5.

-Yes!

And I'll look at other animals

whose hands give us clues to the origins of our own.

If you're going to have a contest with a chimp, thumb wrestling?!

We might win that one, yeah!

Taking a hand apart will be challenging.

It is something I've never seen before.

And it might provoke strong reaction.

But it will reveal

how the extraordinary anatomy of the hands

has brought about some of the greatest achievements

of human civilisation.

Our hands are unique in the animal kingdom.

They give us immense strength, yet also the finest of control.

And this combination of power and precision has given us,

alone among species, the ability to shape the world around us.

We take our hands for granted

but if you think about it, they really are truly remarkable.

Without them there would have been no Michelangelo. No Mozart.

And we rely on them for simple, everyday tasks.

No other animal has hands like us.

So I really want to understand how they work

and what gives them their special capabilities.

To reveal the hand's secrets we've set up our dissection lab

in the Anatomy Museum of Glasgow University.

They've been studying the human body here for over 100 years.

And to perform the delicate operation of dissecting the hand,

we've brought together an expert team.

Donald Sammut is one of the country's leading hand surgeons.

Our hands are what we use to mould the world.

Everything we achieve, in a practical sense,

is directed by our brain but achieved with our hands.

Many of us will express ourselves with our hands, and in fact,

in some fields, for example, musicians, live through their hands.

Their identity is entirely tied up in their hands.

-And it's the first thing you do when you meet someone.

-That's right.

And incidentally, as you do that,

you realise that is the only part of anatomy

-that you can touch, in polite society.

-Yeah.

Anatomy expert Dr Quentin Fogg will lead our dissection.

He has carefully prepared our specimen

following the strict medical and ethical protocols

that govern the dissection of human tissue.

-Hi, Quentin.

-Hi.

-So this is the arm that we'll be looking at today.

This is the upper limb of a person who has donated themselves

to medical education and research.

Now, for some people, this might seem a distasteful,

or even shocking thing.

But it is essential, isn't it?

It's the only way that we can truly appreciate

the detail of the human body,

and understand anatomy in its real working condition.

We're ready to start our dissection. For me, this is a first.

And I must admit, I'm feeling a bit apprehensive.

To really understand how the hand works,

we need to begin by looking just outside it.

In the forearm.

OK. I'll make the incision at the top

and then we'll raise the skin flap together.

Right.

And as I make an incision,

the first thing you will notice is fat pouty out.

Because fat is the first layer beneath the skin.

I'm finding this a bit difficult to watch.

But it is absolutely fascinating.

So the skin and fat are being lifted as one layer.

Once the fat is removed, the first thing we see are muscles.

These muscles, that Quentin is exposing here,

which come from above the elbow,

this entire bulk here is dedicated to giving power to the hand.

So, the hand is like a puppet, and all the strings are up here.

And they are the ones that give it power

while all the fine movements happen in the hand.

If you show me your forearm,

you can feel the muscles contract as you make and un-make a fist.

-From that point, all the way down to here.

-Yes.

So, essentially, all the power that I generate with my fingers

-comes from way up here.

-Precisely.

So that's where the power in my hand comes from.

But it still needs to get from the muscles in my arm into my hand.

And that's the job of tendons.

Each muscle belly connects to a tendon.

You can see this tendon here, very tough, like a bit of rope, really.

Very slippery, as you can see. Very shiny.

Because it has to glide through various tunnels.

And they are the actuators of the fingers,

-all the bits that have to be moved.

-Precisely.

They transmit power from this muscle belly,

generated by this muscle belly, to its destination.

Tendons connect muscle to bone.

They're vital for making the hand move.

If I tug on that, look at the little finger, flexing.

That's beautiful, yeah.

So you can see the connection between this fine muscle belly,

all the way down, transmitting its force to the little finger.

And you could do this for each muscle.

For example, here, is the ring finger.

You can see, you can find them all individually, and pull on them, see?

And make each finger contract individually.

It's a bit unsettling to see a lifeless hand move like this,

but it's an extraordinary insight into how the hand works.

And all these have to pass through the wrist,

which is quite a small space.

Yes. That is part of their function, really.

If you want to pass through a confined space,

or to go round corners, then you cannot do it with a muscle belly.

If you make a muscle belly go around a corner,

that bit is going to be deprived of blood.

And muscle needs blood, while tendon can survive on relatively much less.

These tendons are very long.

They stretch all the way from the forearm,

as far as the tips of our fingers.

And that brings a major advantage.

It's a principle that mechanics use all the time.

So one good way to think about that is,

if you tried to take the nut off a car tyre,

and used a very, very short lever, short spanner,

it'd be really difficult.

But if you extend the length of that

and make it a really, really long lever,

it becomes amazingly easy all of a sudden.

This is what a tendon is doing. If we had a tiny tendon here,

the amount of force generated there would be quite small.

Whereas if we elongate the tendon down to the tip of the fingers,

it, all of a sudden, becomes a really powerful output.

Power is the first key attribute of the hand.

And it's brought about some of our greatest achievements,

from sporting success...

..to building the man-made world.

The power of our hands is also vital to our everyday actions.

As Quentin gets on with the dissection,

Donald can show me the surprising ways

we use this strength all the time.

We can break down the tasks that the hand achieves

into different forms of grip.

At its most primitive, the hand is a scoop.

So if I gave you these to bring towards you

without picking them up, you'd do that.

So you're using your hand as a paddle, as a scoop.

If you had to pick up a large object like this...

-Well, I'd just do that.

-Right.

So you see, what you're doing there,

your hand is being used as a simple, straightforward paddle.

All the force is coming from further up in your arm,

those big muscles there,

so you're not using your hand as a very sophisticated instrument,

but it's effective.

'This primitive grip is something other animals can do.

'But we are capable of different power grips

'that are uniquely human.'

If you were to pick this up...you are using power grip.

And you can only do that because your thumb is now dialoguing,

if you like, with your other fingers,

to grasp that object.

-Yes, if I didn't have that, it'd just fall out of my hand.

-Yes.

So suddenly, you've added a whole new range of tasks.

Another example of that sort of clamping action is a key grip,

so if you hold that...

You see, you've clamped onto that key.

We are still using these muscles, look -

as you do that opening action, you are rotating at the elbow

and using these muscles to clamp onto that object.

These strong grips make our hands amazingly versatile.

They enable us to lift and lower, pull and push,

twist and turn,

carry, hit and chop.

But there are some people who push the power of their hands

to the absolute limit.

Rock climbers trust their lives to the strength of their hands.

They often support and lift their entire weight

using only their fingertips.

To me, it seems almost superhuman.

So what makes their hands capable of such extremes?

Dr Nigel Callender studies what's different

about the hands of high-performance climbers.

Some of these guys are able to hang their entire body weight

off a single finger.

Essentially, this demonstrates the extremes

that the anatomy of the hand is able to withstand.

Ned Feehally is one of the UK's top rock climbers.

To see how my hands compare with his,

we're going to put them to the test.

This is a device that we use for testing hand grip strength

which we've modified to look more specifically

at finger strength alone.

What we're going to do is set this up so that Ned is able to use it.

Nigel is going to see how much force we can generate with our fingers.

I'm going to get you to line up just your fingertips

on the force bar on our device, here.

Let's see what Ned can do.

He has to push down with his fingertips,

as hard as he can, for five seconds.

That's it, come on - push, push, push, push!

Excellent, good stuff.

And relax. OK, so we have our first reading there,

which is coming in at 49 kilos.

Quite impressive, isn't it?

And now it's my turn.

I want your middle finger to line up

just on the edge of the force bar on there.

-On there?

-On the first joint, that's right.

-Rrrrgggghhh!

-Push, push, push! Excellent.

Oh! That is...that's actually much harder

than I thought it was going to be.

-You have about 36.5 kilos there.

-36...

'We're allowed three attempts, so can I do any better?'

That's it - come on, George, push, push, push, push!

Excellent, good stuff.

-That time, we actually went up as far as 37.5.

-Yes!

Pretty pleased with my efforts,

but it's almost a quarter less force

than Ned managed to exert with his fingers.

As a percentage, that's really quite a large difference,

in terms of Ned's performance versus yours.

Given their training, we might expect some extra muscle power,

but Nigel's work suggests there's more to climbers' abilities

than just strength.

He's going to show me what's happening inside a climber's hand.

We have a piece of string, which is going to act as our tendon.

If I pop our "tendon" on here -

which roughly runs pretty much the length of the finger

and attaches to the muscles up here in the forearm,

we'll pop pieces of tape around the fingers

to act as just the main pulleys in the fingers.

'Pulleys are soft tissues that hold tendons against the finger bone.

'It's believed that, through heavy use,

'both the pulleys and the tendons become thicker in frequent climbers

'and that actually helps them keep a tight grip.'

As the finger comes under load,

there's going to be a certain amount of friction between these pulleys...

-And the tendon itself?

-And the tendon itself.

That makes sense. I can feel that, actually, in a way.

-It's interesting, I can actually feel that.

-Yeah.

And how does that make a difference to climbing?

Well, this assists the whole system in maintaining a closed grip.

It helps to stop the finger from being forced open.

So essentially, we're not relying purely on muscular strength

to hold our hand closed.

So if you're a regular climber, the soft tissues in your hand

actually change in ways that allow you to grip for longer.

And if we look deeper into climbers' hands,

there's an even more fundamental way

that they differ from the rest of us.

Take a look at these X-rays.

What we have here, on the right,

we have an X-ray of one of the finger bones of a climber

who's been at it for over ten years,

and on the left, we've that of a normal person.

And what I think is probably quite clear

is this white bone...is quite considerably thicker

than in our non-climber over here.

I mean, I know we adapt to the environment,

but that is quite remarkable.

The bright white part is a hard outer layer on the bone,

and we can see, on the climber's hand,

that there's far more of it.

And that's not the only difference in the bones, Nigel has discovered.

Over time, the bone density, the actual bone mineral content,

increases in climbers, compared to non-climbers.

So you wind up with bone that's not only bigger, but also stronger.

The climbers' bones have a higher concentration of minerals

such as calcium.

This helps make the bones more able to withstand weight.

The more you use your fingers,

the more stresses and strains you put on your bone,

-the stronger the bones of your hand become.

-Yeah.

It's not just a fixed structure within the body.

It's constantly in a state of turnover,

and it will respond to increased demands placed on it.

Nigel's work has shown

that our hands adapt to what we do with them,

and it's not just at a skin-deep level.

We can physically change their structure

through the way we use them.

Our hand is capable of more than just power.

It also gives us precision -

exceptional fine control

that allows us to manipulate our world

as no other species can.

We use this dexterity in an infinite number of ways.

And it can be put to mystifying effect.

Kevin McMahon has been a magician for nine years.

-Hi, Kevin.

-Hi, George.

Now, you've made a career out of the incredible things you can do

with your hands, specifically, your fingers and thumbs.

Magic is a really intriguing art form for me

and every performance that I do in close-up magic settings

is underpinned by sleight of hand.

How much do you appreciate

what you can actually achieve with your hands?

Anything - even the pressure there, for instance,

for me to do a normal fan...

This movement here took me a good couple of weeks to get that right.

The main reason, I think, is because the pressure between your thumb

and your finger is released as you're going round.

Then there's fancy cuts -

there's ways of mixing the cards up

in a way that's appeasing to the eye.

These things take a lot of time to get right.

There's a lot of co-ordinated finger action,

things that all happen at the same time,

that you just have to get right,

cos you can't afford to have a card explosion

and all the cards go over the floor.

So you have to spend hours

making sure the cards are moving in the right way

and the right rhythm is there.

But of all the digits,

there's one in particular that's essential to Kevin -

the thumb.

The thumb's involved in everything,

from the flourishes to the card fan -

to simply pick a card,

I have to spread the cards out with my thumb.

This action happens automatically,

but my thumb is - quite impressively -

distributing the cards very evenly into a fan.

I've never thought about that before, if I'm honest.

Even a colour change, for instance,

having the card change from the jack

-into the three...

-Wow!

-That is...

-Wow! Sorry...

Surprise!

That is something which requires

a lot of action on the thumb

to create that pivot, to hold the card in place.

Everything that you do as a magician will use your thumb

to make the magic happen.

-It's probably the most important digit I have.

-Oh...what's that?

-Oh, look, there we are...

-Oh, George(!)

KEVIN LAUGHS

Couldn't resist that.

-Kevin, thanks very much.

-Thanks, George. Bye, now.

Of all our five digits,

it's our thumb that's the most versatile

and the most important.

In order to discover

exactly what gives our thumb its unique abilities,

we're about to take our first look inside the hand.

So we're now under the palm skin there -

what's the first thing that's obvious?

Yes - Quentin has removed only the skin,

so everything you see here was just beneath the skin

and the first and most striking thing

is that the general arrangement of the hand

is that it's got two hills and a valley in the middle.

And these two hills consist of muscle

and they serve the little finger and the thumb.

To look at the thumb in more detail,

we need to strip away this tough tissue between the muscles.

It protects vital structures in the palm.

So the very tough sheet

that is now being peeled back,

which will reveal the real inner...

-..machinery, if you like...

-Yes.

It'll be surrounded by fat, but, yes,

it covers all the important structures that come through -

the major artery, the major nerves

and all of the flexor tendons.

Now, we can begin to see what gives our thumb its precision -

no fewer than nine muscles are dedicated to controlling it.

And these small muscles here, this entire group of muscles here

which belong specifically to the thumb,

they're dedicated to the thumb,

orientate it in space.

All of this is very precise.

You can see these muscles here - for example, this muscle,

its job is to lift the thumb away from the palm

and then, you have another short muscle here,

which flexes the thumb,

So already, it can curl round an object.

And there's a very powerful muscle in here,

which you can just about glimpse, there,

and that's going from the thumb to this bone, here.

You can imagine, therefore, that if you've got an object here,

that will slam the thumb right against it

and be a very powerful pinch, produce a very powerful pinch.

You can see those muscles there - those fibres will all contract

and bring the thumb against your other fingers, quite hard.

I'm beginning to appreciate the complex machinery it takes

to move our thumb with such precision.

And it doesn't end with the muscles.

We also need to look even deeper, at the skeleton of the hand.

Well, the thumb skeleton is very specialised, as you can imagine.

This is where the base of the thumb is

and that joint...

It may surprise you to learn

that most of the movement doesn't happen here.

It happens at the base -

90% of your movement happens at the base,

so the thumb moves as one big column.

And that joint - I've been trying to doodle it here,

it's very difficult to render the double plane in which it moves,

but it's a saddle joint.

Conventionally, it's known as a saddle joint

and this bone is the one you've got at the base of your thumb, here,

and there is the platform on which it lies.

We can show it on this bone here.

This is your thumb metacarpal

and this is the trapezium, which is at the base here.

And so if I put them together, there's a saddle shape -

it permits me to move in this plane

and it also permits me to move in that plane.

-I can do that.

-Yes - you're moving mainly at the base.

So the muscles we've seen are able to act

on this very versatile and mobile joint.

But there's a price to be paid for the mobility in our thumb.

As with any joint in our body, the bigger the range of movement,

the greater the danger of injury.

The more mobile a joint is,

the more likely it is to wear or to dislocate.

In fact, this joint is the most commonly worn joint in the body.

-It beats the hip, it beats the knee.

-Really?

-Yes.

-Wow.

And the reason is that the platform, the trapezium here,

has to be at a slant

in order to enable the thumb to live away from the palm.

If you were to apply force directly like that to the thumb,

that would be quite stable.

As soon as you put it on a slant and you take force,

it's going to slip out,

so there's a whole system of ligaments to hold it back in place

and you can imagine how much more likely

that will be to wear.

Though the saddle joint is susceptible to injury,

it gives us a crucial ability.

An opposable thumb.

In other words, our thumb can move directly opposite

each of our fingers, to touch them tip-to-tip.

It's something no other animal can do with this much precision.

So how did we come to have such a dextrous hand?

-Hi, Tracy, how are you doing?

-Hi, nice to meet you.

Dr Tracy Kivell is researching the origins of the human hand.

She's been investigating the differences between our hands

and those of our closest animal relatives - chimpanzees.

The most obvious thing about chimpanzees is

they have much longer fingers and a longer palm than we do

and it allows them to grasp onto the branch like this,

with a hooked grip.

So the chimpanzee's palm and fingers are longer than ours.

But what about our thumbs?

A lot of people think that the main difference between a human hand

and a chimpanzee hand is our opposable thumbs.

But chimpanzees also have opposable thumbs.

Actually, all apes and monkeys have opposable thumbs.

But there is a key difference that sets our thumb apart.

It's longer than the chimp's,

so it can more easily reach the tips of all our fingers.

Their thumb is actually quite short and much weaker than ours.

If you were going to have a contest with a chimp, arm wrestling,

you would lose,

but thumb wrestling, you might actually get off with.

We might win that one, yeah.

Having shorter fingers and longer thumbs

gives us far more precise movements than the chimp's.

The ability in humans to use precision grips,

not just to our index finger, but to all of our fingers,

allows us to manipulate objects, particularly small objects,

with great accuracy.

But what caused the hands of our early ancestors

to change in this fundamental way?

Researchers like Tracy are delving deep into our past

to look for answers.

Well, I think it's a combination of two things -

it's one, that we no longer use our hands for locomotion.

We no longer needed these really long fingers

that we see in chimpanzees.

It allowed our fingers to get a little bit shorter

and that may have sort of pre-adapted us

to being more manipulative.

And the other main reason, it's likely, is tool use,

and, specifically, stone tool use.

When you think about making a stone tool,

you need both precision and force

and that's exactly what we have in the human hand.

So it's likely that the very act of using stone tools

drove the evolution of a more versatile and dextrous hand,

and this allowed our early ancestors to manipulate objects

in ways that no other species could -

an ability that would allow us to shape and dominate our world.

We've seen that the thumb is the main player in our hand,

but our other four digits also have a vital role in our dexterity.

So do they all play an equal part?

That's what we're going to look at next in our dissection.

Wow - that is absolutely gorgeous.

You've laid bare the internal workings of the hand.

Yes, you can see Quentin's isolated

and identified all of the major structures in the palm, now.

Can I ask you, George -

you can see the four fingers here,

almost equal as a group against the thumb,

but if you were to lose a finger by choice,

which one do you think you could do without?

I've a feeling I'm going to get this wrong,

but I would've said the small finger,

but I just know it's wrong.

You were right, first time - you got it wrong, yes!

GEORGE LAUGHS

The one...again, it might surprise you even more

that one would lose would be the index.

The index finger?

The index finger would be the one you could most do without.

-That is surprising.

-The index is a bit of a paradox, really.

Although it's included in everything we do,

you can exclude it from everything you do.

You can hold a pen and write in the same handwriting

-with the index excluded.

-Hm.

The little finger, in fact, is much more important than one thinks.

It's vital for grip.

It can approach the thumb very much more than the other fingers.

We've shown the group of muscles that are dedicated to the thumb,

and there's an identical group of muscles

dedicated to the little finger.

They're slimmer and finer, but actually,

they do exactly the same thing.

They even have the same names, virtually.

And in fact, when the thumb comes across to give you precision grip,

the little finger's able to approach it, in a way,

to make its task easier

and the little finger is the most mobile finger after the thumb.

Before we can see inside the other fingers,

Quentin has to remove the skin.

While he does this, Donald's going to show me

how our fingers give us unparalleled fine control.

So far, we've looked at grip, which is immensely strong,

but not very versatile.

If we wanted versatility,

we're going to have to go down to these small joints.

And an example of this would be...unscrew a bottle.

You see that?

You're using your fingertips now

and that is three points - or "chuck" - grip.

-That's...

-I'll do it.

-My goodness.

-Oh, George...

If you do that...

You see, now, I'm using only those end joints.

That's a very much more precise, but of course weaker action.

If we wanted to be very precise - for instance, to write -

then what we must do

is eliminate all the big...let's call them "clumsy boys"...

GEORGE CHUCKLES

The clumsy muscles.

Precisely - they're powerful, but they're not very precise.

And by putting my arm down

like that,

I've eliminated all action

of the big, strong muscles.

That's interesting, because if you want to be precise,

you've got to isolate the hand

-so you can do that.

-You must stabilise...

-Stabilise your hand.

-Have it flat.

-Yes.

-Or artists often have a...a brace...

-That's right.

..a stick, which they can paint with.

I am using - and I need to use - these very precise, small muscles

and small joints in the hand.

When I operate, for example...

You will see any surgeon, operating with any precision,

he will often immobilise his entire forearm

right down to the tip of the little finger

in order to be precise with his instruments.

All these types of grip I've given you, to some extent,

that's an artificial division.

Every task requires the right amount of force or precision.

So one's always going from one type of grip to another.

It's these very precise grips that allow us to fine-tune the world.

And much of this precision

is down to the amazing flexibility of our fingers.

Back at the dissection table,

Quentin is ready to show us

what gives our fingers this ability.

We've removed the skin over the front of the finger here

and we can see the full length of this sheath

which is encasing these tendons.

I'm going to put my scissors in and cut along the length of this.

This will unveil more and more of the tendon,

in absolutely pristine condition -

it's been protected by this tendon its entire life.

As we pull back the sides of that sheath...

..there's the tendon, the superficial one's splitting.

I'm going to either side to stop halfway down the finger

and then the deep one running through

this little tunnel that's been created,

so it can go all the way down to the end of that finger.

Tendons we saw in the forearm now reach their final destination -

at the ends of our fingers.

One threads through the other

so that each of the last two finger joints

has a separate tendon to move it.

And that gives our fingers both strength and flexibility.

If Quentin tugs on that,

you can see the finger bend on the superficial one -

only the superficial one.

Yeah, you can see,

this joint is not moving at all.

But if he tugs on the deep one,

this one, look -

you see the other joint moving as well.

Yes, yes...

That shows you that this deep one

is inserting last, into the tip.

I'm in awe at the elegance

of this natural machinery -

and that's just to let us bend both joints at the ends of our fingers.

But this doesn't fully explain the subtlety of control

we have over our digits.

MUSIC: "Fantaisie Impromptu, Op 66" by Frederic Chopin

Watching a pianist play, I can't help but be impressed

by the remarkable range and dexterity of the hand.

But there's something else that strikes me -

it's the co-ordination of the fingers,

striking the keys at precisely the right time

to achieve musical perfection.

How does the hand do that?

Our dissection has shown me a beautiful aspect

of the engineering of the hand -

the components all work together,

each building on the action of the others.

And Quentin's ready to show me

the next small, but influential, piece of the machine,

one that gives our fingers that co-ordinated movement.

We have these little, small muscles,

sitting between the big, long tendons

that run to each finger,

and these little slips of muscle here look a bit like worms.

Their name actually comes from the Latin for worm,

which is "lumbrical".

Their job is a really varied and important job.

They can do lots of different things to change how our fingers work.

So if I pull on the long tendon which is flexing this finger here,

then we get a complete flexion of the finger.

If I modify this now, with the lumbrical contracting,

then it subtly changes the angle.

So this can change not only the angle of the finger

but the rate of contraction

and the rate of flexion that we're getting

and we can do this for each of the four fingers.

That is just amazing.

These little, thin muscles

co-ordinate the action of the tendons -

they pull on them to slow down or speed up their movement.

They can refine the movement of each finger independently

and make us capable of truly astonishing co-ordinated precision.

So the idea of the lumbrical being able to modify

what each finger is doing and add in a whole lot of extra benefits,

like timing, is a really fantastic feature of our hand.

And that adds in a whole extra layer of fine control.

-It means we can be infinitely precise, really.

-Wow.

The mechanics of our hand is more complex and sophisticated

than I ever imagined.

Clearly, it can't work on its own.

It needs something to control it.

And there's one part of us

that determines how we use our hands more than anything else -

our brain.

The interaction between the brain and the hand intrigues me.

Perhaps it's because I'm left-handed -

I've always wondered why we use our hands differently.

Dr Gillian Forrester is a cognitive neuroscientist.

She studies how we use our dominant and non-dominant hands.

We're watching the children's handedness behaviour.

We want to see if they're using their left or their right hand

to do certain activities.

90% of the population are right-handed.

Gillian has gathered together a group of right-handed children

to observe how they use both their hands in everyday life.

We'd expect our right-handed kids to use the right hand

when doing anything that's manipulating an object -

for instance, throwing balls or writing with pencils.

But what we're finding out, actually, is that it doesn't mean

they use their right hand for all types of behaviours.

So what would they use their left hand for, then?

Something that has a social or emotional component -

so they're dealing with a friend or themselves.

The left hand comes into play a lot more during social interactions

than we would have expected it to.

Her research has found that right-handed children

use their left hand a lot for social actions...

..gestures like hugs, pats on the back,

or reaching out to a friend during play.

To investigate this further,

she set the children a challenging task.

They have to move all the disks from peg to peg

without placing a larger disk on top of a smaller one.

As they attempt this,

Gillian observes how they use both their hands.

We're expecting to see that they will use the right hand,

as their dominant hand,

to move the disks or the rings from one peg to the other.

She has noticed that something interesting begins to happen

when the children become confused or frustrated by the test.

What we're finding is that as a task becomes more complicated

or the child experiences more stress,

they're tending to get that left hand involved ever more.

So they bring the hand to the face...

-Head-scratching, that sort of thing?

-Yeah.

Gillian sees the children using their left hand more

when they experience strong emotion.

And she thinks the reason might lie in the way

the two hemispheres of the brain work.

Each hemisphere controls the opposite side of the body.

In simple terms, the left side of the brain,

which deals with practical tasks,

controls the right side of the body and the right side of the brain,

which deals with emotions, controls the left side of the body.

It's believed that this division developed so that each

side of the brain could specialise in different types of behaviour.

It's very advantageous

because it means that you can perform two tasks at the same time

so, for example,

the left hemisphere can help you control those structured

sequences of actions like a feeding behaviour,

but at the same time,

they can use that right hemisphere to keep them alert of predators.

So they're essentially getting a parallel processing system.

-And that aids survival?

-Absolutely.

New studies suggest that the right side of our brain developed

to deal with danger and unpredictable situations.

So, Gillian thinks this is why right-handers use their left hand

when they're experiencing strong emotion or in social interactions.

That's all very well - but what if you're left-handed, like me?

Now, I'm a natural left-hander.

Does that mean that my brain is wired up in a different way?

There's about 10% of the population that is left-handed

and within that 10%, about a third have the exact

reversal of the brain that us right-handers have so...

So, is it like a flipped-over brain?

Yeah, exactly, so in the remaining 70% of left-handers,

actually the brain is organised in the same way as right-handers.

It's likely that there's transference of signals

between the hemispheres before information passes to the hand.

Though our brain may be wired to our hands in different ways,

Gillian's work suggests that all of us

may be using our non-dominant hand more than we realised.

It responds to our emotional side

and may play an important part in our social lives.

We've looked in forensic detail at the mechanics of the hand,

what gives it its strength and phenomenal range of movement,

but there's one final secret we've yet to uncover.

Hidden beneath our fingertips are the workings of one of the most

complex and vital systems in our body - our sense of touch.

Our sense of touch is, for me,

the pinnacle of what the hand can achieve.

And there's a fascinating way to show just how powerful it can be.

Sarah McLean was born blind.

She's been reading Braille since she was five years old.

So, Sarah, the ends of your fingertips must be very

-sensitive indeed.

-Yeah, I guess they are.

I mean, touch is essential to everyone, but for me,

it's kind of like two senses in one, I guess.

It's how I read and how I perceive things so, yeah, they will be.

This machine here can actually print and...read Braille out, if you like.

Yeah, you can read off it via the wee keypad at the bottom.

And how does it work?

Well, these are just the raised dots. And Braille is a six-dot system.

So all the alphabet, all the letters and words,

are made up of different combinations of these six dots.

-So, can you read off this pad now?

-Yes.

I'm going to read an extract from A Christmas Carol by Charles Dickens.

OK.

"Marley was dead, to begin with.

"There is no doubt whatever about that.

"The register of his burial was signed by the clergyman, the clerk,

"the undertaker, and the chief mourner. Scrooge signed it

"and Scrooge's name was good upon change,

"for anything he chose to put his hand to.

"Old Marley was as dead as a door-nail."

HE CHUCKLES

-I should have a try at this, do you think?

-Yeah, why not?

Have you got anything I can read?

Yes. There are some words on there.

OK, so I'll just run my fingers over it

and I can feel a little series of raised dots there.

-Mm-hm.

-And there's a shorter series there.

'I can feel dots but I'm also using my eyes to help.

'How Sarah gets a language out of this series of bumps is

'really impressive.'

-Are you going to reveal what the word was?

-Yes, hidden secret, yes.

OK, so the top one says G-E-O-R-G-E

and then that tiny dot there is to show it's a capital,

cos obviously it's your name, and then that one says Sarah,

so my name obviously, and then this is a sentence and it just says,

"Hello, this is Braille."

-I'm blown away, actually.

-It's a great invention.

Sarah's sense of touch is incredibly refined.

But all humans have this unique capacity of feeling.

Our sense of touch is the most sophisticated

connection our hand has with the brain.

And it's our front-line contact with the world around us.

To understand this ultimate ability of the hand,

we're about to embark on the final part of our dissection,

our most complicated yet - the nerves.

Quentin's exposed and cleaned every single nerve here so that we can see

that all of this front of the hand, which is the crucial one,

especially for touch, is supplied by these two major nerves.

You can see the median nerve and the ulnar nerve here

and this median nerve, if we look at it and follow it through,

it goes through the tunnel, comes out at this end

-and if I now pick it up, you get an idea...

-It's like a little tree.

Precisely, how it gives branches to every single part of the hand.

All we are seeing here are the main trunks.

If this were a road network, these would be the motorways

and then there are smaller roads and smaller roads and little lanes

so that everything is reached.

What strikes me is the incredible intricacy of all those nerves.

I mean it must be really hard to dissect.

Well, this is probably the most difficult part

in the hand to dissect. It also makes them the most exciting.

It's really quite good fun to try and challenge ourselves to get

the smallest branch possible held in place.

Nerves work by sending and receiving electrical impulses.

When we touch a surface with our fingertips,

sensory information is converted into electrical signals.

These are sent all the way up to the brain via the spinal cord.

The brain sends responses back, instructing the hand what to do.

To get to the culmination of nerves within the hand, we have to open up

the last untouched part of our specimen - the ends of the fingers.

But as you get towards the end of the finger,

we're getting a real concentration of all the smallest

branches in the fat pad of the fingertip

and it's in this area that we're going to have

the highest concentration of sensation

for pretty much anywhere in the body.

If I make a cut through the middle of the fat pad...

..then we'll see where all of these nerves are ending.

It's at the microscopic level that we can properly see these nerves.

The green strands are the nerve fibres.

Over 20,000 of these terminate in each fingertip.

It's at these nerve ends that we take in sensory information.

Dr Francis McGlone is a specialist on sensation.

He's going to show me just how sensitive my fingertips are

compared with other parts of my body.

We can demonstrate just how acute the fingertips are at detecting

objects that are placed on them with a little experiment here, George.

If you want to pop this blindfold on, I can give you a little test.

-So, that is two layers of blindfold.

-OK.

I'm going to put some objects here on the forearm

and here on the fingertip and I want you to have

a bit of a guess at what I'm putting on your body.

Any idea what that is?

Well, it's quite cool, it's quite smooth.

Mmm, a piece of...plastic pipe or something?

OK, let's try it across the fingertips now.

-Ah. Oh, it's a banana.

-Very good. Perfectly.

Let's try another one, a little more difficult, possibly.

And again, I'll put it on your forearm and tell me

-what you think that is.

-I really...have no idea.

Now, let's try and put it on your fingertips

and have a go at telling me what you think that is now.

Oh, it's a coin.

Very good. Could you go one step further and say what coin it is?

Can you maybe guess it?

-Oh, it's a pound coin.

-Excellent.

THEY CHUCKLE

That's astonishing. I can tell so much more with my fingertips.

But that's not just down to nerves.

Our sense of touch also relies on tiny receptors just under our skin.

Welcome back.

This is a section of skin from the fingertip seen under the microscope.

The receptors are joined to the end of the black nerve fibres.

Some respond to pain, some temperature.

Others react to pressure and vibration.

These are the most important for our sense of touch.

There are more of these receptors in our fingertips

than anywhere else in our body.

They take in information as we touch

and move our finger across a surface.

What we've got here is a section through the skin and here,

beautifully, we can see one of these receptors, a Meissner's corpuscle.

This Meissner's corpuscle picks up transients,

very fast events that are happening on the surface of the skin

like fine texture,

and we can just about see the beginnings of a ghost

of another one here and this is a Merkel's disc

and the Merkel's disc is looking at pressure.

So if you indent the fingertip,

these will send information to the brain

all the time that indentation is there and it's

because of these little receptors that you are able to detect

the very fine detail of those objects that I placed in your hand.

We're still at the early stages of understanding

how the relationship between touch receptors and the brain works.

But that hasn't stopped one group of scientists attempting

a hugely ambitious project.

To replicate our sense of touch - artificially.

What if I could touch these clothes remotely

without even being here at all?

Well, the idea that we could physically interact

with objects in a virtual world may seem far-fetched but actually,

it might be closer than we think.

At Exeter University, Dr Ian Summers is developing technology

that simulates touch.

This is our tactile stimulator.

As incredible as it sounds, Ian claims he's designed

a machine that lets you feel what you're seeing on a computer screen.

-So, would you like to have a go?

-Yes, please.

-So, I just put my finger on here?

-That's right.

You rest your finger on it, you move it around like a mouse...

..and what you see on the screen

is a green rectangle that represents your fingertip

and also on the screen, you see the surface of the textile and...

That is a piece of corduroy

and I'm actually feeling virtual corduroy on my finger.

That's the idea. And you've got a piece of corduroy on the table,

-real corduroy, so you can compare the two.

-Very similar, very similar.

That's really rough across the way as you'd expect and then up

and down, it's not nearly as rough cos that's with

the grain of the corduroy.

So, Ian, how is this possible? What's actually happening here?

Well, what we're trying to do

is replicate what happens in a real touch situation.

So if you imagine, for example,

my finger running over the surface of this piece of hessian

and then what happens is the interaction with the surface

deforms the skin and vibrations travel through the tissue underneath

to the underlying touch receptors.

So, we're trying to reproduce that.

So the job of our tactile stimulator

is to deliver those kind of vibrations

to the touch receptors in the finger.

The machine works by making pins on top of the computer mouse vibrate

to trick the touch receptors in my fingertip.

By changing the strength of the vibration,

Ian can replicate the feel of different materials.

'As a general rule, rougher materials generate strong vibrations

'whereas smoother materials generate weak vibrations.'

-So, would you like to try another surface?

-Yes, please.

Right, we've got something a bit smoother, some kind of silk,

-I think, so we'll try switching to that one.

-So there's silk.

So, that's a nice silk texture. Very smooth.

Let's see how that feels.

Yes, it's good, it's not as great as the corduroy but it's good.

Yeah, I think that with smooth surfaces,

you're very aware of just the feel of the stimulator

whereas for rougher surfaces,

maybe you're more aware of what's coming out of the stimulator.

Ian has so far simulated over 70 types of material.

In studies, volunteers guess

what around 60% of the virtual versions are supposed to be.

What were the challenges you faced in making virtual touch work?

I think the sticking point at the moment is not really

the technology, in terms of the stimulator

and moving over the surface and whatever,

it's that we don't know enough about the nature of the real interaction

between a real finger and a real surface

and so we don't really have enough information to know

what are the right signals to put through our virtual system.

Because we understand so little about touch,

Ian is still some way off having a reliable system

but if he's successful, it does have many potential uses.

From online shopping and gaming

to helping surgeons perform operations remotely.

I'm genuinely surprised by Ian's work.

I would never have thought that we were

so close to being able to touch things in a virtual world

but what strikes me most is that even with all our technology,

we struggle to replicate the complexities of human touch and

that just demonstrates how amazingly sophisticated our hands really are.

I've discovered so much I didn't know

about what makes our hands unique.

Over the course of our dissection,

I've seen the incredible natural engineering

that lies behind every action,

the muscles that give our hands their strength,

the tendons that channel their power,

how the thumb gives us unrivalled movement,

the co-ordination and intricate control of the fingers,

the sensitivity of our fingertips that connects us to the world.

And what I find most impressive is the way it all works together

to give us such a versatile and powerful instrument.

If you'd asked me before we started what defines us as human,

I think, like most people, I'd have said our brain

but now I'd have to include the hand.

Having taken it apart, bit by bit,

and seen the incredible natural engineering inside, I've got

a new-found respect and admiration for this part of our anatomy.

Without hands, we wouldn't be who we are.

Next time, we take apart a human foot.

That is the first time I have ever seen inside the foot.

We'll uncover the extraordinary inner workings that drive

every step we take.

And I'll meet people with unique talents...

I should get you making a paper aeroplane, really, shouldn't I?

Oh, come on, Tom, come on.

..to discover what gives us a rare and crucial ability...

Oh! Jesus.

..to stand and walk upright.