0:00:06 > 0:00:09We're about to embark on something most of us
0:00:09 > 0:00:11have never witnessed before.
0:00:11 > 0:00:17It will take us inside two of the most amazing structures
0:00:17 > 0:00:19in the natural world.
0:00:19 > 0:00:21Our hands...
0:00:21 > 0:00:23and feet.
0:00:23 > 0:00:29Two parts of our body that define us as human.
0:00:29 > 0:00:30I'm George McGavin.
0:00:30 > 0:00:35And as a biologist, I think that to truly understand our hands and feet
0:00:35 > 0:00:37we need to look inside them.
0:00:39 > 0:00:43To do this we've created our own dissection lab.
0:00:43 > 0:00:46We've brought together the tools, the technology,
0:00:46 > 0:00:48and leading experts in human anatomy.
0:00:50 > 0:00:55Over two programmes, we're going to dissect a human hand and foot
0:00:55 > 0:00:57to discover what makes them unique.
0:00:59 > 0:01:02And we're going to start with our hands.
0:01:02 > 0:01:05We're about to reveal them as you've never seen them before.
0:01:07 > 0:01:10We're going to take a real human hand apart,
0:01:10 > 0:01:13systematically, layer by layer.
0:01:13 > 0:01:16Wow, that is absolutely gorgeous.
0:01:16 > 0:01:19We'll discover the incredible natural engineering
0:01:19 > 0:01:21that drives our actions,
0:01:21 > 0:01:23and the microscopic structures
0:01:23 > 0:01:26that give us our remarkable sense of touch.
0:01:29 > 0:01:31I'll meet people whose hands have astonishing abilities.
0:01:31 > 0:01:34- Whoa! Sorry, whoa! - Surprise!
0:01:37 > 0:01:41Beyond the lab, I'll be putting my hands to the test.
0:01:41 > 0:01:43- 37.5.- Yes!
0:01:43 > 0:01:45And I'll look at other animals
0:01:45 > 0:01:49whose hands give us clues to the origins of our own.
0:01:49 > 0:01:52If you're going to have a contest with a chimp, thumb wrestling?!
0:01:52 > 0:01:53We might win that one, yeah!
0:01:55 > 0:01:57Taking a hand apart will be challenging.
0:01:57 > 0:02:00It is something I've never seen before.
0:02:00 > 0:02:02And it might provoke strong reaction.
0:02:02 > 0:02:03But it will reveal
0:02:03 > 0:02:05how the extraordinary anatomy of the hands
0:02:05 > 0:02:09has brought about some of the greatest achievements
0:02:09 > 0:02:10of human civilisation.
0:02:21 > 0:02:24Our hands are unique in the animal kingdom.
0:02:24 > 0:02:28They give us immense strength, yet also the finest of control.
0:02:30 > 0:02:33And this combination of power and precision has given us,
0:02:33 > 0:02:37alone among species, the ability to shape the world around us.
0:02:40 > 0:02:42We take our hands for granted
0:02:42 > 0:02:46but if you think about it, they really are truly remarkable.
0:02:46 > 0:02:50Without them there would have been no Michelangelo. No Mozart.
0:02:50 > 0:02:54And we rely on them for simple, everyday tasks.
0:02:54 > 0:02:56No other animal has hands like us.
0:02:56 > 0:02:59So I really want to understand how they work
0:02:59 > 0:03:02and what gives them their special capabilities.
0:03:05 > 0:03:10To reveal the hand's secrets we've set up our dissection lab
0:03:10 > 0:03:13in the Anatomy Museum of Glasgow University.
0:03:13 > 0:03:17They've been studying the human body here for over 100 years.
0:03:18 > 0:03:22And to perform the delicate operation of dissecting the hand,
0:03:22 > 0:03:25we've brought together an expert team.
0:03:25 > 0:03:29Donald Sammut is one of the country's leading hand surgeons.
0:03:31 > 0:03:35Our hands are what we use to mould the world.
0:03:35 > 0:03:38Everything we achieve, in a practical sense,
0:03:38 > 0:03:41is directed by our brain but achieved with our hands.
0:03:41 > 0:03:45Many of us will express ourselves with our hands, and in fact,
0:03:45 > 0:03:48in some fields, for example, musicians, live through their hands.
0:03:48 > 0:03:51Their identity is entirely tied up in their hands.
0:03:51 > 0:03:54- And it's the first thing you do when you meet someone.- That's right.
0:03:54 > 0:03:56And incidentally, as you do that,
0:03:56 > 0:03:58you realise that is the only part of anatomy
0:03:58 > 0:04:01- that you can touch, in polite society.- Yeah.
0:04:08 > 0:04:12Anatomy expert Dr Quentin Fogg will lead our dissection.
0:04:17 > 0:04:20He has carefully prepared our specimen
0:04:20 > 0:04:23following the strict medical and ethical protocols
0:04:23 > 0:04:26that govern the dissection of human tissue.
0:04:28 > 0:04:32- Hi, Quentin.- Hi.- So this is the arm that we'll be looking at today.
0:04:32 > 0:04:36This is the upper limb of a person who has donated themselves
0:04:36 > 0:04:39to medical education and research.
0:04:39 > 0:04:43Now, for some people, this might seem a distasteful,
0:04:43 > 0:04:46or even shocking thing.
0:04:46 > 0:04:47But it is essential, isn't it?
0:04:47 > 0:04:50It's the only way that we can truly appreciate
0:04:50 > 0:04:52the detail of the human body,
0:04:52 > 0:04:55and understand anatomy in its real working condition.
0:04:58 > 0:05:03We're ready to start our dissection. For me, this is a first.
0:05:03 > 0:05:06And I must admit, I'm feeling a bit apprehensive.
0:05:11 > 0:05:14To really understand how the hand works,
0:05:14 > 0:05:17we need to begin by looking just outside it.
0:05:17 > 0:05:19In the forearm.
0:05:20 > 0:05:23OK. I'll make the incision at the top
0:05:23 > 0:05:25and then we'll raise the skin flap together.
0:05:25 > 0:05:27Right.
0:05:35 > 0:05:36And as I make an incision,
0:05:36 > 0:05:39the first thing you will notice is fat pouty out.
0:05:39 > 0:05:42Because fat is the first layer beneath the skin.
0:05:44 > 0:05:47I'm finding this a bit difficult to watch.
0:05:47 > 0:05:49But it is absolutely fascinating.
0:05:50 > 0:05:54So the skin and fat are being lifted as one layer.
0:05:54 > 0:05:58Once the fat is removed, the first thing we see are muscles.
0:05:59 > 0:06:02These muscles, that Quentin is exposing here,
0:06:02 > 0:06:03which come from above the elbow,
0:06:03 > 0:06:07this entire bulk here is dedicated to giving power to the hand.
0:06:07 > 0:06:11So, the hand is like a puppet, and all the strings are up here.
0:06:11 > 0:06:12And they are the ones that give it power
0:06:12 > 0:06:15while all the fine movements happen in the hand.
0:06:15 > 0:06:16If you show me your forearm,
0:06:16 > 0:06:19you can feel the muscles contract as you make and un-make a fist.
0:06:19 > 0:06:22- From that point, all the way down to here.- Yes.
0:06:24 > 0:06:28So, essentially, all the power that I generate with my fingers
0:06:28 > 0:06:30- comes from way up here. - Precisely.
0:06:32 > 0:06:35So that's where the power in my hand comes from.
0:06:35 > 0:06:40But it still needs to get from the muscles in my arm into my hand.
0:06:40 > 0:06:43And that's the job of tendons.
0:06:43 > 0:06:46Each muscle belly connects to a tendon.
0:06:46 > 0:06:50You can see this tendon here, very tough, like a bit of rope, really.
0:06:50 > 0:06:54Very slippery, as you can see. Very shiny.
0:06:54 > 0:06:57Because it has to glide through various tunnels.
0:06:57 > 0:06:59And they are the actuators of the fingers,
0:06:59 > 0:07:01- all the bits that have to be moved. - Precisely.
0:07:01 > 0:07:04They transmit power from this muscle belly,
0:07:04 > 0:07:07generated by this muscle belly, to its destination.
0:07:08 > 0:07:11Tendons connect muscle to bone.
0:07:11 > 0:07:13They're vital for making the hand move.
0:07:15 > 0:07:18If I tug on that, look at the little finger, flexing.
0:07:18 > 0:07:20That's beautiful, yeah.
0:07:20 > 0:07:23So you can see the connection between this fine muscle belly,
0:07:23 > 0:07:25all the way down, transmitting its force to the little finger.
0:07:25 > 0:07:27And you could do this for each muscle.
0:07:27 > 0:07:31For example, here, is the ring finger.
0:07:31 > 0:07:35You can see, you can find them all individually, and pull on them, see?
0:07:35 > 0:07:37And make each finger contract individually.
0:07:39 > 0:07:44It's a bit unsettling to see a lifeless hand move like this,
0:07:44 > 0:07:48but it's an extraordinary insight into how the hand works.
0:07:48 > 0:07:51And all these have to pass through the wrist,
0:07:51 > 0:07:52which is quite a small space.
0:07:52 > 0:07:55Yes. That is part of their function, really.
0:07:55 > 0:07:57If you want to pass through a confined space,
0:07:57 > 0:08:01or to go round corners, then you cannot do it with a muscle belly.
0:08:01 > 0:08:03If you make a muscle belly go around a corner,
0:08:03 > 0:08:05that bit is going to be deprived of blood.
0:08:05 > 0:08:09And muscle needs blood, while tendon can survive on relatively much less.
0:08:09 > 0:08:12These tendons are very long.
0:08:12 > 0:08:14They stretch all the way from the forearm,
0:08:14 > 0:08:16as far as the tips of our fingers.
0:08:16 > 0:08:19And that brings a major advantage.
0:08:19 > 0:08:23It's a principle that mechanics use all the time.
0:08:23 > 0:08:26So one good way to think about that is,
0:08:26 > 0:08:29if you tried to take the nut off a car tyre,
0:08:29 > 0:08:32and used a very, very short lever, short spanner,
0:08:32 > 0:08:33it'd be really difficult.
0:08:33 > 0:08:35But if you extend the length of that
0:08:35 > 0:08:37and make it a really, really long lever,
0:08:37 > 0:08:39it becomes amazingly easy all of a sudden.
0:08:39 > 0:08:42This is what a tendon is doing. If we had a tiny tendon here,
0:08:42 > 0:08:45the amount of force generated there would be quite small.
0:08:45 > 0:08:49Whereas if we elongate the tendon down to the tip of the fingers,
0:08:49 > 0:08:52it, all of a sudden, becomes a really powerful output.
0:09:00 > 0:09:04Power is the first key attribute of the hand.
0:09:04 > 0:09:07And it's brought about some of our greatest achievements,
0:09:07 > 0:09:10from sporting success...
0:09:12 > 0:09:14..to building the man-made world.
0:09:18 > 0:09:22The power of our hands is also vital to our everyday actions.
0:09:26 > 0:09:28As Quentin gets on with the dissection,
0:09:28 > 0:09:31Donald can show me the surprising ways
0:09:31 > 0:09:33we use this strength all the time.
0:09:34 > 0:09:38We can break down the tasks that the hand achieves
0:09:38 > 0:09:40into different forms of grip.
0:09:40 > 0:09:42At its most primitive, the hand is a scoop.
0:09:42 > 0:09:45So if I gave you these to bring towards you
0:09:45 > 0:09:48without picking them up, you'd do that.
0:09:48 > 0:09:51So you're using your hand as a paddle, as a scoop.
0:09:51 > 0:09:54If you had to pick up a large object like this...
0:09:54 > 0:09:56- Well, I'd just do that.- Right.
0:09:56 > 0:09:58So you see, what you're doing there,
0:09:58 > 0:10:01your hand is being used as a simple, straightforward paddle.
0:10:01 > 0:10:05All the force is coming from further up in your arm,
0:10:05 > 0:10:06those big muscles there,
0:10:06 > 0:10:09so you're not using your hand as a very sophisticated instrument,
0:10:09 > 0:10:11but it's effective.
0:10:11 > 0:10:14'This primitive grip is something other animals can do.
0:10:14 > 0:10:17'But we are capable of different power grips
0:10:17 > 0:10:19'that are uniquely human.'
0:10:19 > 0:10:24If you were to pick this up...you are using power grip.
0:10:24 > 0:10:28And you can only do that because your thumb is now dialoguing,
0:10:28 > 0:10:29if you like, with your other fingers,
0:10:29 > 0:10:30to grasp that object.
0:10:30 > 0:10:34- Yes, if I didn't have that, it'd just fall out of my hand.- Yes.
0:10:34 > 0:10:37So suddenly, you've added a whole new range of tasks.
0:10:37 > 0:10:41Another example of that sort of clamping action is a key grip,
0:10:41 > 0:10:43so if you hold that...
0:10:43 > 0:10:45You see, you've clamped onto that key.
0:10:45 > 0:10:48We are still using these muscles, look -
0:10:48 > 0:10:52as you do that opening action, you are rotating at the elbow
0:10:52 > 0:10:56and using these muscles to clamp onto that object.
0:10:58 > 0:11:02These strong grips make our hands amazingly versatile.
0:11:03 > 0:11:07They enable us to lift and lower, pull and push,
0:11:07 > 0:11:09twist and turn,
0:11:09 > 0:11:12carry, hit and chop.
0:11:16 > 0:11:20But there are some people who push the power of their hands
0:11:20 > 0:11:22to the absolute limit.
0:11:27 > 0:11:31Rock climbers trust their lives to the strength of their hands.
0:11:31 > 0:11:34They often support and lift their entire weight
0:11:34 > 0:11:36using only their fingertips.
0:11:37 > 0:11:40To me, it seems almost superhuman.
0:11:40 > 0:11:44So what makes their hands capable of such extremes?
0:11:45 > 0:11:48Dr Nigel Callender studies what's different
0:11:48 > 0:11:51about the hands of high-performance climbers.
0:11:51 > 0:11:54Some of these guys are able to hang their entire body weight
0:11:54 > 0:11:55off a single finger.
0:11:55 > 0:11:58Essentially, this demonstrates the extremes
0:11:58 > 0:12:02that the anatomy of the hand is able to withstand.
0:12:04 > 0:12:07Ned Feehally is one of the UK's top rock climbers.
0:12:10 > 0:12:13To see how my hands compare with his,
0:12:13 > 0:12:15we're going to put them to the test.
0:12:16 > 0:12:20This is a device that we use for testing hand grip strength
0:12:20 > 0:12:23which we've modified to look more specifically
0:12:23 > 0:12:24at finger strength alone.
0:12:24 > 0:12:27What we're going to do is set this up so that Ned is able to use it.
0:12:27 > 0:12:32Nigel is going to see how much force we can generate with our fingers.
0:12:32 > 0:12:36I'm going to get you to line up just your fingertips
0:12:36 > 0:12:38on the force bar on our device, here.
0:12:39 > 0:12:41Let's see what Ned can do.
0:12:41 > 0:12:44He has to push down with his fingertips,
0:12:44 > 0:12:46as hard as he can, for five seconds.
0:12:48 > 0:12:50That's it, come on - push, push, push, push!
0:12:50 > 0:12:52Excellent, good stuff.
0:12:53 > 0:12:55And relax. OK, so we have our first reading there,
0:12:55 > 0:12:58which is coming in at 49 kilos.
0:12:58 > 0:12:59Quite impressive, isn't it?
0:13:02 > 0:13:04And now it's my turn.
0:13:04 > 0:13:06I want your middle finger to line up
0:13:06 > 0:13:09just on the edge of the force bar on there.
0:13:09 > 0:13:11- On there?- On the first joint, that's right.
0:13:13 > 0:13:16- Rrrrgggghhh!- Push, push, push! Excellent.
0:13:16 > 0:13:18Oh! That is...that's actually much harder
0:13:18 > 0:13:20than I thought it was going to be.
0:13:20 > 0:13:23- You have about 36.5 kilos there. - 36...
0:13:23 > 0:13:27'We're allowed three attempts, so can I do any better?'
0:13:30 > 0:13:34That's it - come on, George, push, push, push, push!
0:13:34 > 0:13:36Excellent, good stuff.
0:13:36 > 0:13:40- That time, we actually went up as far as 37.5.- Yes!
0:13:41 > 0:13:42Pretty pleased with my efforts,
0:13:42 > 0:13:45but it's almost a quarter less force
0:13:45 > 0:13:47than Ned managed to exert with his fingers.
0:13:49 > 0:13:54As a percentage, that's really quite a large difference,
0:13:54 > 0:13:56in terms of Ned's performance versus yours.
0:13:57 > 0:14:01Given their training, we might expect some extra muscle power,
0:14:01 > 0:14:04but Nigel's work suggests there's more to climbers' abilities
0:14:04 > 0:14:07than just strength.
0:14:07 > 0:14:10He's going to show me what's happening inside a climber's hand.
0:14:12 > 0:14:16We have a piece of string, which is going to act as our tendon.
0:14:16 > 0:14:19If I pop our "tendon" on here -
0:14:19 > 0:14:22which roughly runs pretty much the length of the finger
0:14:22 > 0:14:25and attaches to the muscles up here in the forearm,
0:14:25 > 0:14:27we'll pop pieces of tape around the fingers
0:14:27 > 0:14:30to act as just the main pulleys in the fingers.
0:14:30 > 0:14:35'Pulleys are soft tissues that hold tendons against the finger bone.
0:14:35 > 0:14:36'It's believed that, through heavy use,
0:14:36 > 0:14:41'both the pulleys and the tendons become thicker in frequent climbers
0:14:41 > 0:14:44'and that actually helps them keep a tight grip.'
0:14:44 > 0:14:46As the finger comes under load,
0:14:46 > 0:14:50there's going to be a certain amount of friction between these pulleys...
0:14:50 > 0:14:52- And the tendon itself? - And the tendon itself.
0:14:52 > 0:14:55That makes sense. I can feel that, actually, in a way.
0:14:55 > 0:14:57- It's interesting, I can actually feel that.- Yeah.
0:14:57 > 0:15:00And how does that make a difference to climbing?
0:15:00 > 0:15:07Well, this assists the whole system in maintaining a closed grip.
0:15:07 > 0:15:11It helps to stop the finger from being forced open.
0:15:11 > 0:15:15So essentially, we're not relying purely on muscular strength
0:15:15 > 0:15:16to hold our hand closed.
0:15:18 > 0:15:22So if you're a regular climber, the soft tissues in your hand
0:15:22 > 0:15:26actually change in ways that allow you to grip for longer.
0:15:27 > 0:15:29And if we look deeper into climbers' hands,
0:15:29 > 0:15:32there's an even more fundamental way
0:15:32 > 0:15:34that they differ from the rest of us.
0:15:37 > 0:15:38Take a look at these X-rays.
0:15:41 > 0:15:45What we have here, on the right,
0:15:45 > 0:15:49we have an X-ray of one of the finger bones of a climber
0:15:49 > 0:15:51who's been at it for over ten years,
0:15:51 > 0:15:53and on the left, we've that of a normal person.
0:15:53 > 0:15:56And what I think is probably quite clear
0:15:56 > 0:16:01is this white bone...is quite considerably thicker
0:16:01 > 0:16:03than in our non-climber over here.
0:16:03 > 0:16:07I mean, I know we adapt to the environment,
0:16:07 > 0:16:09but that is quite remarkable.
0:16:09 > 0:16:13The bright white part is a hard outer layer on the bone,
0:16:13 > 0:16:15and we can see, on the climber's hand,
0:16:15 > 0:16:17that there's far more of it.
0:16:17 > 0:16:22And that's not the only difference in the bones, Nigel has discovered.
0:16:22 > 0:16:27Over time, the bone density, the actual bone mineral content,
0:16:27 > 0:16:30increases in climbers, compared to non-climbers.
0:16:30 > 0:16:35So you wind up with bone that's not only bigger, but also stronger.
0:16:37 > 0:16:40The climbers' bones have a higher concentration of minerals
0:16:40 > 0:16:42such as calcium.
0:16:42 > 0:16:45This helps make the bones more able to withstand weight.
0:16:45 > 0:16:47The more you use your fingers,
0:16:47 > 0:16:51the more stresses and strains you put on your bone,
0:16:51 > 0:16:54- the stronger the bones of your hand become.- Yeah.
0:16:54 > 0:16:58It's not just a fixed structure within the body.
0:16:58 > 0:17:00It's constantly in a state of turnover,
0:17:00 > 0:17:03and it will respond to increased demands placed on it.
0:17:03 > 0:17:04Nigel's work has shown
0:17:04 > 0:17:08that our hands adapt to what we do with them,
0:17:08 > 0:17:11and it's not just at a skin-deep level.
0:17:11 > 0:17:13We can physically change their structure
0:17:13 > 0:17:14through the way we use them.
0:17:22 > 0:17:25Our hand is capable of more than just power.
0:17:28 > 0:17:32It also gives us precision -
0:17:32 > 0:17:34exceptional fine control
0:17:34 > 0:17:36that allows us to manipulate our world
0:17:36 > 0:17:38as no other species can.
0:17:40 > 0:17:44We use this dexterity in an infinite number of ways.
0:17:46 > 0:17:48And it can be put to mystifying effect.
0:17:50 > 0:17:53Kevin McMahon has been a magician for nine years.
0:17:55 > 0:17:56- Hi, Kevin.- Hi, George.
0:17:56 > 0:18:00Now, you've made a career out of the incredible things you can do
0:18:00 > 0:18:03with your hands, specifically, your fingers and thumbs.
0:18:03 > 0:18:07Magic is a really intriguing art form for me
0:18:07 > 0:18:10and every performance that I do in close-up magic settings
0:18:10 > 0:18:12is underpinned by sleight of hand.
0:18:12 > 0:18:14How much do you appreciate
0:18:14 > 0:18:17what you can actually achieve with your hands?
0:18:17 > 0:18:19Anything - even the pressure there, for instance,
0:18:19 > 0:18:22for me to do a normal fan...
0:18:22 > 0:18:26This movement here took me a good couple of weeks to get that right.
0:18:26 > 0:18:30The main reason, I think, is because the pressure between your thumb
0:18:30 > 0:18:33and your finger is released as you're going round.
0:18:33 > 0:18:34Then there's fancy cuts -
0:18:34 > 0:18:37there's ways of mixing the cards up
0:18:37 > 0:18:41in a way that's appeasing to the eye.
0:18:41 > 0:18:44These things take a lot of time to get right.
0:18:44 > 0:18:47There's a lot of co-ordinated finger action,
0:18:47 > 0:18:49things that all happen at the same time,
0:18:49 > 0:18:50that you just have to get right,
0:18:50 > 0:18:52cos you can't afford to have a card explosion
0:18:52 > 0:18:54and all the cards go over the floor.
0:18:54 > 0:18:55So you have to spend hours
0:18:55 > 0:18:58making sure the cards are moving in the right way
0:18:58 > 0:18:59and the right rhythm is there.
0:18:59 > 0:19:02But of all the digits,
0:19:02 > 0:19:06there's one in particular that's essential to Kevin -
0:19:06 > 0:19:08the thumb.
0:19:08 > 0:19:09The thumb's involved in everything,
0:19:09 > 0:19:11from the flourishes to the card fan -
0:19:11 > 0:19:13to simply pick a card,
0:19:13 > 0:19:15I have to spread the cards out with my thumb.
0:19:15 > 0:19:17This action happens automatically,
0:19:17 > 0:19:21but my thumb is - quite impressively -
0:19:21 > 0:19:24distributing the cards very evenly into a fan.
0:19:24 > 0:19:28I've never thought about that before, if I'm honest.
0:19:28 > 0:19:29Even a colour change, for instance,
0:19:29 > 0:19:31having the card change from the jack
0:19:31 > 0:19:34- into the three...- Wow!
0:19:34 > 0:19:36- That is...- Wow! Sorry...
0:19:36 > 0:19:38Surprise!
0:19:38 > 0:19:40That is something which requires
0:19:40 > 0:19:42a lot of action on the thumb
0:19:42 > 0:19:44to create that pivot, to hold the card in place.
0:19:44 > 0:19:49Everything that you do as a magician will use your thumb
0:19:49 > 0:19:50to make the magic happen.
0:19:50 > 0:19:55- It's probably the most important digit I have.- Oh...what's that?
0:19:55 > 0:19:57- Oh, look, there we are... - Oh, George(!)
0:19:57 > 0:19:58KEVIN LAUGHS
0:19:58 > 0:20:00Couldn't resist that.
0:20:00 > 0:20:03- Kevin, thanks very much. - Thanks, George. Bye, now.
0:20:06 > 0:20:08Of all our five digits,
0:20:08 > 0:20:10it's our thumb that's the most versatile
0:20:10 > 0:20:12and the most important.
0:20:14 > 0:20:15In order to discover
0:20:15 > 0:20:18exactly what gives our thumb its unique abilities,
0:20:18 > 0:20:22we're about to take our first look inside the hand.
0:20:24 > 0:20:27So we're now under the palm skin there -
0:20:27 > 0:20:29what's the first thing that's obvious?
0:20:29 > 0:20:31Yes - Quentin has removed only the skin,
0:20:31 > 0:20:35so everything you see here was just beneath the skin
0:20:35 > 0:20:37and the first and most striking thing
0:20:37 > 0:20:39is that the general arrangement of the hand
0:20:39 > 0:20:43is that it's got two hills and a valley in the middle.
0:20:43 > 0:20:46And these two hills consist of muscle
0:20:46 > 0:20:49and they serve the little finger and the thumb.
0:20:51 > 0:20:53To look at the thumb in more detail,
0:20:53 > 0:20:57we need to strip away this tough tissue between the muscles.
0:20:57 > 0:21:00It protects vital structures in the palm.
0:21:01 > 0:21:04So the very tough sheet
0:21:04 > 0:21:07that is now being peeled back,
0:21:07 > 0:21:10which will reveal the real inner...
0:21:10 > 0:21:11- ..machinery, if you like...- Yes.
0:21:11 > 0:21:13It'll be surrounded by fat, but, yes,
0:21:13 > 0:21:16it covers all the important structures that come through -
0:21:16 > 0:21:18the major artery, the major nerves
0:21:18 > 0:21:20and all of the flexor tendons.
0:21:21 > 0:21:25Now, we can begin to see what gives our thumb its precision -
0:21:25 > 0:21:30no fewer than nine muscles are dedicated to controlling it.
0:21:30 > 0:21:34And these small muscles here, this entire group of muscles here
0:21:34 > 0:21:36which belong specifically to the thumb,
0:21:36 > 0:21:37they're dedicated to the thumb,
0:21:37 > 0:21:39orientate it in space.
0:21:39 > 0:21:42All of this is very precise.
0:21:42 > 0:21:45You can see these muscles here - for example, this muscle,
0:21:45 > 0:21:48its job is to lift the thumb away from the palm
0:21:48 > 0:21:50and then, you have another short muscle here,
0:21:50 > 0:21:52which flexes the thumb,
0:21:52 > 0:21:56So already, it can curl round an object.
0:21:56 > 0:21:57And there's a very powerful muscle in here,
0:21:57 > 0:22:00which you can just about glimpse, there,
0:22:00 > 0:22:03and that's going from the thumb to this bone, here.
0:22:03 > 0:22:06You can imagine, therefore, that if you've got an object here,
0:22:06 > 0:22:08that will slam the thumb right against it
0:22:08 > 0:22:11and be a very powerful pinch, produce a very powerful pinch.
0:22:11 > 0:22:15You can see those muscles there - those fibres will all contract
0:22:15 > 0:22:18and bring the thumb against your other fingers, quite hard.
0:22:20 > 0:22:24I'm beginning to appreciate the complex machinery it takes
0:22:24 > 0:22:26to move our thumb with such precision.
0:22:29 > 0:22:31And it doesn't end with the muscles.
0:22:31 > 0:22:36We also need to look even deeper, at the skeleton of the hand.
0:22:41 > 0:22:44Well, the thumb skeleton is very specialised, as you can imagine.
0:22:44 > 0:22:46This is where the base of the thumb is
0:22:46 > 0:22:48and that joint...
0:22:48 > 0:22:49It may surprise you to learn
0:22:49 > 0:22:52that most of the movement doesn't happen here.
0:22:52 > 0:22:53It happens at the base -
0:22:53 > 0:22:5590% of your movement happens at the base,
0:22:55 > 0:22:57so the thumb moves as one big column.
0:22:58 > 0:23:01And that joint - I've been trying to doodle it here,
0:23:01 > 0:23:04it's very difficult to render the double plane in which it moves,
0:23:04 > 0:23:06but it's a saddle joint.
0:23:06 > 0:23:08Conventionally, it's known as a saddle joint
0:23:08 > 0:23:12and this bone is the one you've got at the base of your thumb, here,
0:23:12 > 0:23:15and there is the platform on which it lies.
0:23:15 > 0:23:17We can show it on this bone here.
0:23:17 > 0:23:20This is your thumb metacarpal
0:23:20 > 0:23:23and this is the trapezium, which is at the base here.
0:23:23 > 0:23:26And so if I put them together, there's a saddle shape -
0:23:26 > 0:23:28it permits me to move in this plane
0:23:28 > 0:23:30and it also permits me to move in that plane.
0:23:30 > 0:23:36- I can do that.- Yes - you're moving mainly at the base.
0:23:36 > 0:23:39So the muscles we've seen are able to act
0:23:39 > 0:23:42on this very versatile and mobile joint.
0:23:44 > 0:23:47But there's a price to be paid for the mobility in our thumb.
0:23:48 > 0:23:52As with any joint in our body, the bigger the range of movement,
0:23:52 > 0:23:55the greater the danger of injury.
0:23:55 > 0:23:57The more mobile a joint is,
0:23:57 > 0:24:01the more likely it is to wear or to dislocate.
0:24:01 > 0:24:06In fact, this joint is the most commonly worn joint in the body.
0:24:06 > 0:24:10- It beats the hip, it beats the knee. - Really?- Yes.- Wow.
0:24:10 > 0:24:14And the reason is that the platform, the trapezium here,
0:24:14 > 0:24:16has to be at a slant
0:24:16 > 0:24:19in order to enable the thumb to live away from the palm.
0:24:19 > 0:24:23If you were to apply force directly like that to the thumb,
0:24:23 > 0:24:24that would be quite stable.
0:24:24 > 0:24:26As soon as you put it on a slant and you take force,
0:24:26 > 0:24:28it's going to slip out,
0:24:28 > 0:24:31so there's a whole system of ligaments to hold it back in place
0:24:31 > 0:24:34and you can imagine how much more likely
0:24:34 > 0:24:35that will be to wear.
0:24:36 > 0:24:39Though the saddle joint is susceptible to injury,
0:24:39 > 0:24:42it gives us a crucial ability.
0:24:44 > 0:24:46An opposable thumb.
0:24:47 > 0:24:51In other words, our thumb can move directly opposite
0:24:51 > 0:24:55each of our fingers, to touch them tip-to-tip.
0:24:55 > 0:24:59It's something no other animal can do with this much precision.
0:25:02 > 0:25:05So how did we come to have such a dextrous hand?
0:25:11 > 0:25:14- Hi, Tracy, how are you doing? - Hi, nice to meet you.
0:25:14 > 0:25:18Dr Tracy Kivell is researching the origins of the human hand.
0:25:18 > 0:25:21She's been investigating the differences between our hands
0:25:21 > 0:25:26and those of our closest animal relatives - chimpanzees.
0:25:28 > 0:25:30The most obvious thing about chimpanzees is
0:25:30 > 0:25:33they have much longer fingers and a longer palm than we do
0:25:33 > 0:25:37and it allows them to grasp onto the branch like this,
0:25:37 > 0:25:38with a hooked grip.
0:25:39 > 0:25:43So the chimpanzee's palm and fingers are longer than ours.
0:25:44 > 0:25:46But what about our thumbs?
0:25:46 > 0:25:50A lot of people think that the main difference between a human hand
0:25:50 > 0:25:53and a chimpanzee hand is our opposable thumbs.
0:25:53 > 0:25:57But chimpanzees also have opposable thumbs.
0:25:57 > 0:26:00Actually, all apes and monkeys have opposable thumbs.
0:26:00 > 0:26:04But there is a key difference that sets our thumb apart.
0:26:06 > 0:26:08It's longer than the chimp's,
0:26:08 > 0:26:12so it can more easily reach the tips of all our fingers.
0:26:12 > 0:26:15Their thumb is actually quite short and much weaker than ours.
0:26:15 > 0:26:18If you were going to have a contest with a chimp, arm wrestling,
0:26:18 > 0:26:19you would lose,
0:26:19 > 0:26:22but thumb wrestling, you might actually get off with.
0:26:22 > 0:26:24We might win that one, yeah.
0:26:24 > 0:26:27Having shorter fingers and longer thumbs
0:26:27 > 0:26:31gives us far more precise movements than the chimp's.
0:26:31 > 0:26:35The ability in humans to use precision grips,
0:26:35 > 0:26:39not just to our index finger, but to all of our fingers,
0:26:39 > 0:26:44allows us to manipulate objects, particularly small objects,
0:26:44 > 0:26:46with great accuracy.
0:26:47 > 0:26:50But what caused the hands of our early ancestors
0:26:50 > 0:26:54to change in this fundamental way?
0:26:54 > 0:26:57Researchers like Tracy are delving deep into our past
0:26:57 > 0:26:59to look for answers.
0:26:59 > 0:27:01Well, I think it's a combination of two things -
0:27:01 > 0:27:05it's one, that we no longer use our hands for locomotion.
0:27:05 > 0:27:08We no longer needed these really long fingers
0:27:08 > 0:27:10that we see in chimpanzees.
0:27:10 > 0:27:13It allowed our fingers to get a little bit shorter
0:27:13 > 0:27:15and that may have sort of pre-adapted us
0:27:15 > 0:27:17to being more manipulative.
0:27:17 > 0:27:21And the other main reason, it's likely, is tool use,
0:27:21 > 0:27:23and, specifically, stone tool use.
0:27:23 > 0:27:26When you think about making a stone tool,
0:27:26 > 0:27:29you need both precision and force
0:27:29 > 0:27:33and that's exactly what we have in the human hand.
0:27:35 > 0:27:39So it's likely that the very act of using stone tools
0:27:39 > 0:27:43drove the evolution of a more versatile and dextrous hand,
0:27:43 > 0:27:47and this allowed our early ancestors to manipulate objects
0:27:47 > 0:27:50in ways that no other species could -
0:27:50 > 0:27:55an ability that would allow us to shape and dominate our world.
0:27:59 > 0:28:04We've seen that the thumb is the main player in our hand,
0:28:04 > 0:28:08but our other four digits also have a vital role in our dexterity.
0:28:08 > 0:28:11So do they all play an equal part?
0:28:11 > 0:28:14That's what we're going to look at next in our dissection.
0:28:16 > 0:28:19Wow - that is absolutely gorgeous.
0:28:19 > 0:28:22You've laid bare the internal workings of the hand.
0:28:22 > 0:28:24Yes, you can see Quentin's isolated
0:28:24 > 0:28:29and identified all of the major structures in the palm, now.
0:28:29 > 0:28:30Can I ask you, George -
0:28:30 > 0:28:32you can see the four fingers here,
0:28:32 > 0:28:34almost equal as a group against the thumb,
0:28:34 > 0:28:38but if you were to lose a finger by choice,
0:28:38 > 0:28:41which one do you think you could do without?
0:28:41 > 0:28:43I've a feeling I'm going to get this wrong,
0:28:43 > 0:28:45but I would've said the small finger,
0:28:45 > 0:28:47but I just know it's wrong.
0:28:47 > 0:28:49You were right, first time - you got it wrong, yes!
0:28:49 > 0:28:50GEORGE LAUGHS
0:28:50 > 0:28:52The one...again, it might surprise you even more
0:28:52 > 0:28:54that one would lose would be the index.
0:28:54 > 0:28:56The index finger?
0:28:56 > 0:28:59The index finger would be the one you could most do without.
0:28:59 > 0:29:03- That is surprising.- The index is a bit of a paradox, really.
0:29:03 > 0:29:06Although it's included in everything we do,
0:29:06 > 0:29:08you can exclude it from everything you do.
0:29:08 > 0:29:11You can hold a pen and write in the same handwriting
0:29:11 > 0:29:13- with the index excluded.- Hm.
0:29:13 > 0:29:16The little finger, in fact, is much more important than one thinks.
0:29:16 > 0:29:18It's vital for grip.
0:29:18 > 0:29:22It can approach the thumb very much more than the other fingers.
0:29:22 > 0:29:25We've shown the group of muscles that are dedicated to the thumb,
0:29:25 > 0:29:27and there's an identical group of muscles
0:29:27 > 0:29:29dedicated to the little finger.
0:29:29 > 0:29:32They're slimmer and finer, but actually,
0:29:32 > 0:29:33they do exactly the same thing.
0:29:33 > 0:29:36They even have the same names, virtually.
0:29:36 > 0:29:40And in fact, when the thumb comes across to give you precision grip,
0:29:40 > 0:29:43the little finger's able to approach it, in a way,
0:29:43 > 0:29:44to make its task easier
0:29:44 > 0:29:49and the little finger is the most mobile finger after the thumb.
0:29:51 > 0:29:54Before we can see inside the other fingers,
0:29:54 > 0:29:56Quentin has to remove the skin.
0:29:57 > 0:30:00While he does this, Donald's going to show me
0:30:00 > 0:30:04how our fingers give us unparalleled fine control.
0:30:06 > 0:30:10So far, we've looked at grip, which is immensely strong,
0:30:10 > 0:30:12but not very versatile.
0:30:12 > 0:30:15If we wanted versatility,
0:30:15 > 0:30:17we're going to have to go down to these small joints.
0:30:17 > 0:30:21And an example of this would be...unscrew a bottle.
0:30:21 > 0:30:23You see that?
0:30:23 > 0:30:25You're using your fingertips now
0:30:25 > 0:30:28and that is three points - or "chuck" - grip.
0:30:28 > 0:30:30- That's...- I'll do it.
0:30:30 > 0:30:32- My goodness.- Oh, George...
0:30:32 > 0:30:33If you do that...
0:30:33 > 0:30:38You see, now, I'm using only those end joints.
0:30:38 > 0:30:42That's a very much more precise, but of course weaker action.
0:30:42 > 0:30:45If we wanted to be very precise - for instance, to write -
0:30:45 > 0:30:47then what we must do
0:30:47 > 0:30:50is eliminate all the big...let's call them "clumsy boys"...
0:30:50 > 0:30:51GEORGE CHUCKLES
0:30:51 > 0:30:53The clumsy muscles.
0:30:53 > 0:30:55Precisely - they're powerful, but they're not very precise.
0:30:55 > 0:30:57And by putting my arm down
0:30:57 > 0:30:58like that,
0:30:58 > 0:31:00I've eliminated all action
0:31:00 > 0:31:02of the big, strong muscles.
0:31:02 > 0:31:05That's interesting, because if you want to be precise,
0:31:05 > 0:31:07you've got to isolate the hand
0:31:07 > 0:31:09- so you can do that. - You must stabilise...
0:31:09 > 0:31:11- Stabilise your hand. - Have it flat.- Yes.
0:31:11 > 0:31:13- Or artists often have a...a brace... - That's right.
0:31:13 > 0:31:16..a stick, which they can paint with.
0:31:16 > 0:31:21I am using - and I need to use - these very precise, small muscles
0:31:21 > 0:31:23and small joints in the hand.
0:31:23 > 0:31:25When I operate, for example...
0:31:25 > 0:31:29You will see any surgeon, operating with any precision,
0:31:29 > 0:31:33he will often immobilise his entire forearm
0:31:33 > 0:31:36right down to the tip of the little finger
0:31:36 > 0:31:39in order to be precise with his instruments.
0:31:39 > 0:31:43All these types of grip I've given you, to some extent,
0:31:43 > 0:31:44that's an artificial division.
0:31:44 > 0:31:49Every task requires the right amount of force or precision.
0:31:49 > 0:31:52So one's always going from one type of grip to another.
0:31:55 > 0:31:59It's these very precise grips that allow us to fine-tune the world.
0:32:02 > 0:32:03And much of this precision
0:32:03 > 0:32:06is down to the amazing flexibility of our fingers.
0:32:10 > 0:32:12Back at the dissection table,
0:32:12 > 0:32:14Quentin is ready to show us
0:32:14 > 0:32:16what gives our fingers this ability.
0:32:18 > 0:32:21We've removed the skin over the front of the finger here
0:32:21 > 0:32:24and we can see the full length of this sheath
0:32:24 > 0:32:27which is encasing these tendons.
0:32:27 > 0:32:31I'm going to put my scissors in and cut along the length of this.
0:32:32 > 0:32:36This will unveil more and more of the tendon,
0:32:36 > 0:32:38in absolutely pristine condition -
0:32:38 > 0:32:41it's been protected by this tendon its entire life.
0:32:53 > 0:32:55As we pull back the sides of that sheath...
0:32:56 > 0:32:59..there's the tendon, the superficial one's splitting.
0:33:01 > 0:33:04I'm going to either side to stop halfway down the finger
0:33:04 > 0:33:06and then the deep one running through
0:33:06 > 0:33:08this little tunnel that's been created,
0:33:08 > 0:33:11so it can go all the way down to the end of that finger.
0:33:14 > 0:33:19Tendons we saw in the forearm now reach their final destination -
0:33:19 > 0:33:20at the ends of our fingers.
0:33:22 > 0:33:24One threads through the other
0:33:24 > 0:33:27so that each of the last two finger joints
0:33:27 > 0:33:29has a separate tendon to move it.
0:33:30 > 0:33:34And that gives our fingers both strength and flexibility.
0:33:36 > 0:33:38If Quentin tugs on that,
0:33:38 > 0:33:41you can see the finger bend on the superficial one -
0:33:41 > 0:33:43only the superficial one.
0:33:43 > 0:33:44Yeah, you can see,
0:33:44 > 0:33:46this joint is not moving at all.
0:33:46 > 0:33:48But if he tugs on the deep one,
0:33:48 > 0:33:49this one, look -
0:33:49 > 0:33:51you see the other joint moving as well.
0:33:51 > 0:33:52Yes, yes...
0:33:52 > 0:33:54That shows you that this deep one
0:33:54 > 0:33:56is inserting last, into the tip.
0:33:58 > 0:34:00I'm in awe at the elegance
0:34:00 > 0:34:02of this natural machinery -
0:34:02 > 0:34:06and that's just to let us bend both joints at the ends of our fingers.
0:34:07 > 0:34:10But this doesn't fully explain the subtlety of control
0:34:10 > 0:34:13we have over our digits.
0:34:14 > 0:34:18MUSIC: "Fantaisie Impromptu, Op 66" by Frederic Chopin
0:34:28 > 0:34:31Watching a pianist play, I can't help but be impressed
0:34:31 > 0:34:35by the remarkable range and dexterity of the hand.
0:34:35 > 0:34:38But there's something else that strikes me -
0:34:38 > 0:34:40it's the co-ordination of the fingers,
0:34:40 > 0:34:43striking the keys at precisely the right time
0:34:43 > 0:34:46to achieve musical perfection.
0:34:46 > 0:34:48How does the hand do that?
0:34:59 > 0:35:02Our dissection has shown me a beautiful aspect
0:35:02 > 0:35:05of the engineering of the hand -
0:35:05 > 0:35:06the components all work together,
0:35:06 > 0:35:09each building on the action of the others.
0:35:15 > 0:35:17And Quentin's ready to show me
0:35:17 > 0:35:21the next small, but influential, piece of the machine,
0:35:21 > 0:35:24one that gives our fingers that co-ordinated movement.
0:35:26 > 0:35:28We have these little, small muscles,
0:35:28 > 0:35:31sitting between the big, long tendons
0:35:31 > 0:35:32that run to each finger,
0:35:32 > 0:35:35and these little slips of muscle here look a bit like worms.
0:35:35 > 0:35:38Their name actually comes from the Latin for worm,
0:35:38 > 0:35:39which is "lumbrical".
0:35:39 > 0:35:42Their job is a really varied and important job.
0:35:42 > 0:35:45They can do lots of different things to change how our fingers work.
0:35:45 > 0:35:50So if I pull on the long tendon which is flexing this finger here,
0:35:50 > 0:35:54then we get a complete flexion of the finger.
0:35:54 > 0:35:57If I modify this now, with the lumbrical contracting,
0:35:57 > 0:36:00then it subtly changes the angle.
0:36:00 > 0:36:02So this can change not only the angle of the finger
0:36:02 > 0:36:04but the rate of contraction
0:36:04 > 0:36:06and the rate of flexion that we're getting
0:36:06 > 0:36:09and we can do this for each of the four fingers.
0:36:09 > 0:36:11That is just amazing.
0:36:15 > 0:36:17These little, thin muscles
0:36:17 > 0:36:20co-ordinate the action of the tendons -
0:36:20 > 0:36:23they pull on them to slow down or speed up their movement.
0:36:25 > 0:36:29They can refine the movement of each finger independently
0:36:29 > 0:36:33and make us capable of truly astonishing co-ordinated precision.
0:36:34 > 0:36:37So the idea of the lumbrical being able to modify
0:36:37 > 0:36:41what each finger is doing and add in a whole lot of extra benefits,
0:36:41 > 0:36:45like timing, is a really fantastic feature of our hand.
0:36:45 > 0:36:48And that adds in a whole extra layer of fine control.
0:36:48 > 0:36:51- It means we can be infinitely precise, really.- Wow.
0:36:56 > 0:36:59The mechanics of our hand is more complex and sophisticated
0:36:59 > 0:37:01than I ever imagined.
0:37:03 > 0:37:06Clearly, it can't work on its own.
0:37:06 > 0:37:08It needs something to control it.
0:37:09 > 0:37:11And there's one part of us
0:37:11 > 0:37:15that determines how we use our hands more than anything else -
0:37:15 > 0:37:16our brain.
0:37:25 > 0:37:29The interaction between the brain and the hand intrigues me.
0:37:31 > 0:37:33Perhaps it's because I'm left-handed -
0:37:33 > 0:37:37I've always wondered why we use our hands differently.
0:37:40 > 0:37:44Dr Gillian Forrester is a cognitive neuroscientist.
0:37:44 > 0:37:48She studies how we use our dominant and non-dominant hands.
0:37:50 > 0:37:53We're watching the children's handedness behaviour.
0:37:53 > 0:37:56We want to see if they're using their left or their right hand
0:37:56 > 0:37:57to do certain activities.
0:37:59 > 0:38:0390% of the population are right-handed.
0:38:03 > 0:38:06Gillian has gathered together a group of right-handed children
0:38:06 > 0:38:10to observe how they use both their hands in everyday life.
0:38:11 > 0:38:14We'd expect our right-handed kids to use the right hand
0:38:14 > 0:38:17when doing anything that's manipulating an object -
0:38:17 > 0:38:20for instance, throwing balls or writing with pencils.
0:38:20 > 0:38:23But what we're finding out, actually, is that it doesn't mean
0:38:23 > 0:38:27they use their right hand for all types of behaviours.
0:38:27 > 0:38:30So what would they use their left hand for, then?
0:38:30 > 0:38:33Something that has a social or emotional component -
0:38:33 > 0:38:36so they're dealing with a friend or themselves.
0:38:36 > 0:38:40The left hand comes into play a lot more during social interactions
0:38:40 > 0:38:41than we would have expected it to.
0:38:42 > 0:38:45Her research has found that right-handed children
0:38:45 > 0:38:49use their left hand a lot for social actions...
0:38:50 > 0:38:53..gestures like hugs, pats on the back,
0:38:53 > 0:38:56or reaching out to a friend during play.
0:38:57 > 0:38:59To investigate this further,
0:38:59 > 0:39:01she set the children a challenging task.
0:39:04 > 0:39:08They have to move all the disks from peg to peg
0:39:08 > 0:39:11without placing a larger disk on top of a smaller one.
0:39:13 > 0:39:14As they attempt this,
0:39:14 > 0:39:17Gillian observes how they use both their hands.
0:39:17 > 0:39:21We're expecting to see that they will use the right hand,
0:39:21 > 0:39:23as their dominant hand,
0:39:23 > 0:39:26to move the disks or the rings from one peg to the other.
0:39:29 > 0:39:32She has noticed that something interesting begins to happen
0:39:32 > 0:39:35when the children become confused or frustrated by the test.
0:39:41 > 0:39:45What we're finding is that as a task becomes more complicated
0:39:45 > 0:39:49or the child experiences more stress,
0:39:49 > 0:39:52they're tending to get that left hand involved ever more.
0:39:52 > 0:39:55So they bring the hand to the face...
0:39:55 > 0:39:57- Head-scratching, that sort of thing?- Yeah.
0:39:59 > 0:40:02Gillian sees the children using their left hand more
0:40:02 > 0:40:05when they experience strong emotion.
0:40:08 > 0:40:11And she thinks the reason might lie in the way
0:40:11 > 0:40:15the two hemispheres of the brain work.
0:40:15 > 0:40:18Each hemisphere controls the opposite side of the body.
0:40:19 > 0:40:22In simple terms, the left side of the brain,
0:40:22 > 0:40:24which deals with practical tasks,
0:40:24 > 0:40:28controls the right side of the body and the right side of the brain,
0:40:28 > 0:40:32which deals with emotions, controls the left side of the body.
0:40:34 > 0:40:37It's believed that this division developed so that each
0:40:37 > 0:40:42side of the brain could specialise in different types of behaviour.
0:40:42 > 0:40:43It's very advantageous
0:40:43 > 0:40:47because it means that you can perform two tasks at the same time
0:40:47 > 0:40:48so, for example,
0:40:48 > 0:40:52the left hemisphere can help you control those structured
0:40:52 > 0:40:54sequences of actions like a feeding behaviour,
0:40:54 > 0:40:55but at the same time,
0:40:55 > 0:41:01they can use that right hemisphere to keep them alert of predators.
0:41:01 > 0:41:04So they're essentially getting a parallel processing system.
0:41:04 > 0:41:07- And that aids survival?- Absolutely.
0:41:09 > 0:41:12New studies suggest that the right side of our brain developed
0:41:12 > 0:41:16to deal with danger and unpredictable situations.
0:41:16 > 0:41:20So, Gillian thinks this is why right-handers use their left hand
0:41:20 > 0:41:25when they're experiencing strong emotion or in social interactions.
0:41:26 > 0:41:31That's all very well - but what if you're left-handed, like me?
0:41:31 > 0:41:33Now, I'm a natural left-hander.
0:41:33 > 0:41:37Does that mean that my brain is wired up in a different way?
0:41:37 > 0:41:40There's about 10% of the population that is left-handed
0:41:40 > 0:41:44and within that 10%, about a third have the exact
0:41:44 > 0:41:48reversal of the brain that us right-handers have so...
0:41:48 > 0:41:50So, is it like a flipped-over brain?
0:41:50 > 0:41:55Yeah, exactly, so in the remaining 70% of left-handers,
0:41:55 > 0:42:00actually the brain is organised in the same way as right-handers.
0:42:00 > 0:42:03It's likely that there's transference of signals
0:42:03 > 0:42:06between the hemispheres before information passes to the hand.
0:42:08 > 0:42:12Though our brain may be wired to our hands in different ways,
0:42:12 > 0:42:14Gillian's work suggests that all of us
0:42:14 > 0:42:19may be using our non-dominant hand more than we realised.
0:42:19 > 0:42:22It responds to our emotional side
0:42:22 > 0:42:26and may play an important part in our social lives.
0:42:36 > 0:42:41We've looked in forensic detail at the mechanics of the hand,
0:42:41 > 0:42:45what gives it its strength and phenomenal range of movement,
0:42:45 > 0:42:49but there's one final secret we've yet to uncover.
0:42:49 > 0:42:53Hidden beneath our fingertips are the workings of one of the most
0:42:53 > 0:42:59complex and vital systems in our body - our sense of touch.
0:43:00 > 0:43:02Our sense of touch is, for me,
0:43:02 > 0:43:05the pinnacle of what the hand can achieve.
0:43:05 > 0:43:09And there's a fascinating way to show just how powerful it can be.
0:43:11 > 0:43:14Sarah McLean was born blind.
0:43:14 > 0:43:17She's been reading Braille since she was five years old.
0:43:18 > 0:43:21So, Sarah, the ends of your fingertips must be very
0:43:21 > 0:43:24- sensitive indeed. - Yeah, I guess they are.
0:43:24 > 0:43:27I mean, touch is essential to everyone, but for me,
0:43:27 > 0:43:29it's kind of like two senses in one, I guess.
0:43:29 > 0:43:32It's how I read and how I perceive things so, yeah, they will be.
0:43:32 > 0:43:37This machine here can actually print and...read Braille out, if you like.
0:43:37 > 0:43:40Yeah, you can read off it via the wee keypad at the bottom.
0:43:40 > 0:43:43And how does it work?
0:43:43 > 0:43:48Well, these are just the raised dots. And Braille is a six-dot system.
0:43:48 > 0:43:51So all the alphabet, all the letters and words,
0:43:51 > 0:43:54are made up of different combinations of these six dots.
0:43:54 > 0:43:57- So, can you read off this pad now? - Yes.
0:43:57 > 0:44:01I'm going to read an extract from A Christmas Carol by Charles Dickens.
0:44:01 > 0:44:03OK.
0:44:03 > 0:44:05"Marley was dead, to begin with.
0:44:05 > 0:44:07"There is no doubt whatever about that.
0:44:07 > 0:44:11"The register of his burial was signed by the clergyman, the clerk,
0:44:11 > 0:44:15"the undertaker, and the chief mourner. Scrooge signed it
0:44:15 > 0:44:18"and Scrooge's name was good upon change,
0:44:18 > 0:44:21"for anything he chose to put his hand to.
0:44:21 > 0:44:24"Old Marley was as dead as a door-nail."
0:44:24 > 0:44:25HE CHUCKLES
0:44:25 > 0:44:28- I should have a try at this, do you think?- Yeah, why not?
0:44:28 > 0:44:31Have you got anything I can read?
0:44:31 > 0:44:35Yes. There are some words on there.
0:44:35 > 0:44:38OK, so I'll just run my fingers over it
0:44:38 > 0:44:42and I can feel a little series of raised dots there.
0:44:42 > 0:44:46- Mm-hm. - And there's a shorter series there.
0:44:48 > 0:44:53'I can feel dots but I'm also using my eyes to help.
0:44:53 > 0:44:56'How Sarah gets a language out of this series of bumps is
0:44:56 > 0:44:59'really impressive.'
0:44:59 > 0:45:02- Are you going to reveal what the word was?- Yes, hidden secret, yes.
0:45:02 > 0:45:07OK, so the top one says G-E-O-R-G-E
0:45:07 > 0:45:10and then that tiny dot there is to show it's a capital,
0:45:10 > 0:45:14cos obviously it's your name, and then that one says Sarah,
0:45:14 > 0:45:19so my name obviously, and then this is a sentence and it just says,
0:45:19 > 0:45:22"Hello, this is Braille."
0:45:22 > 0:45:24- I'm blown away, actually. - It's a great invention.
0:45:26 > 0:45:29Sarah's sense of touch is incredibly refined.
0:45:32 > 0:45:36But all humans have this unique capacity of feeling.
0:45:39 > 0:45:41Our sense of touch is the most sophisticated
0:45:41 > 0:45:45connection our hand has with the brain.
0:45:45 > 0:45:49And it's our front-line contact with the world around us.
0:45:52 > 0:45:55To understand this ultimate ability of the hand,
0:45:55 > 0:46:00we're about to embark on the final part of our dissection,
0:46:00 > 0:46:04our most complicated yet - the nerves.
0:46:04 > 0:46:08Quentin's exposed and cleaned every single nerve here so that we can see
0:46:08 > 0:46:11that all of this front of the hand, which is the crucial one,
0:46:11 > 0:46:15especially for touch, is supplied by these two major nerves.
0:46:15 > 0:46:18You can see the median nerve and the ulnar nerve here
0:46:18 > 0:46:21and this median nerve, if we look at it and follow it through,
0:46:21 > 0:46:23it goes through the tunnel, comes out at this end
0:46:23 > 0:46:27- and if I now pick it up, you get an idea...- It's like a little tree.
0:46:27 > 0:46:33Precisely, how it gives branches to every single part of the hand.
0:46:33 > 0:46:35All we are seeing here are the main trunks.
0:46:35 > 0:46:38If this were a road network, these would be the motorways
0:46:38 > 0:46:43and then there are smaller roads and smaller roads and little lanes
0:46:43 > 0:46:46so that everything is reached.
0:46:46 > 0:46:51What strikes me is the incredible intricacy of all those nerves.
0:46:51 > 0:46:53I mean it must be really hard to dissect.
0:46:53 > 0:46:55Well, this is probably the most difficult part
0:46:55 > 0:46:58in the hand to dissect. It also makes them the most exciting.
0:46:58 > 0:47:01It's really quite good fun to try and challenge ourselves to get
0:47:01 > 0:47:06the smallest branch possible held in place.
0:47:09 > 0:47:13Nerves work by sending and receiving electrical impulses.
0:47:13 > 0:47:16When we touch a surface with our fingertips,
0:47:16 > 0:47:21sensory information is converted into electrical signals.
0:47:21 > 0:47:25These are sent all the way up to the brain via the spinal cord.
0:47:26 > 0:47:31The brain sends responses back, instructing the hand what to do.
0:47:37 > 0:47:40To get to the culmination of nerves within the hand, we have to open up
0:47:40 > 0:47:46the last untouched part of our specimen - the ends of the fingers.
0:47:46 > 0:47:49But as you get towards the end of the finger,
0:47:49 > 0:47:52we're getting a real concentration of all the smallest
0:47:52 > 0:47:55branches in the fat pad of the fingertip
0:47:55 > 0:47:57and it's in this area that we're going to have
0:47:57 > 0:48:00the highest concentration of sensation
0:48:00 > 0:48:02for pretty much anywhere in the body.
0:48:03 > 0:48:06If I make a cut through the middle of the fat pad...
0:48:09 > 0:48:13..then we'll see where all of these nerves are ending.
0:48:15 > 0:48:20It's at the microscopic level that we can properly see these nerves.
0:48:23 > 0:48:26The green strands are the nerve fibres.
0:48:26 > 0:48:30Over 20,000 of these terminate in each fingertip.
0:48:34 > 0:48:39It's at these nerve ends that we take in sensory information.
0:48:45 > 0:48:50Dr Francis McGlone is a specialist on sensation.
0:48:50 > 0:48:53He's going to show me just how sensitive my fingertips are
0:48:53 > 0:48:56compared with other parts of my body.
0:48:56 > 0:49:01We can demonstrate just how acute the fingertips are at detecting
0:49:01 > 0:49:04objects that are placed on them with a little experiment here, George.
0:49:04 > 0:49:09If you want to pop this blindfold on, I can give you a little test.
0:49:09 > 0:49:12- So, that is two layers of blindfold.- OK.
0:49:12 > 0:49:15I'm going to put some objects here on the forearm
0:49:15 > 0:49:18and here on the fingertip and I want you to have
0:49:18 > 0:49:22a bit of a guess at what I'm putting on your body.
0:49:23 > 0:49:25Any idea what that is?
0:49:25 > 0:49:28Well, it's quite cool, it's quite smooth.
0:49:30 > 0:49:33Mmm, a piece of...plastic pipe or something?
0:49:33 > 0:49:37OK, let's try it across the fingertips now.
0:49:37 > 0:49:41- Ah. Oh, it's a banana. - Very good. Perfectly.
0:49:41 > 0:49:44Let's try another one, a little more difficult, possibly.
0:49:45 > 0:49:48And again, I'll put it on your forearm and tell me
0:49:48 > 0:49:52- what you think that is. - I really...have no idea.
0:49:52 > 0:49:54Now, let's try and put it on your fingertips
0:49:54 > 0:49:58and have a go at telling me what you think that is now.
0:49:58 > 0:49:59Oh, it's a coin.
0:49:59 > 0:50:04Very good. Could you go one step further and say what coin it is?
0:50:04 > 0:50:05Can you maybe guess it?
0:50:05 > 0:50:07- Oh, it's a pound coin. - Excellent.
0:50:07 > 0:50:09THEY CHUCKLE
0:50:09 > 0:50:12That's astonishing. I can tell so much more with my fingertips.
0:50:14 > 0:50:16But that's not just down to nerves.
0:50:17 > 0:50:22Our sense of touch also relies on tiny receptors just under our skin.
0:50:24 > 0:50:25Welcome back.
0:50:28 > 0:50:32This is a section of skin from the fingertip seen under the microscope.
0:50:33 > 0:50:37The receptors are joined to the end of the black nerve fibres.
0:50:38 > 0:50:42Some respond to pain, some temperature.
0:50:42 > 0:50:45Others react to pressure and vibration.
0:50:45 > 0:50:48These are the most important for our sense of touch.
0:50:50 > 0:50:53There are more of these receptors in our fingertips
0:50:53 > 0:50:55than anywhere else in our body.
0:50:55 > 0:50:57They take in information as we touch
0:50:57 > 0:51:00and move our finger across a surface.
0:51:02 > 0:51:07What we've got here is a section through the skin and here,
0:51:07 > 0:51:11beautifully, we can see one of these receptors, a Meissner's corpuscle.
0:51:11 > 0:51:14This Meissner's corpuscle picks up transients,
0:51:14 > 0:51:17very fast events that are happening on the surface of the skin
0:51:17 > 0:51:18like fine texture,
0:51:18 > 0:51:21and we can just about see the beginnings of a ghost
0:51:21 > 0:51:24of another one here and this is a Merkel's disc
0:51:24 > 0:51:27and the Merkel's disc is looking at pressure.
0:51:27 > 0:51:30So if you indent the fingertip,
0:51:30 > 0:51:32these will send information to the brain
0:51:32 > 0:51:35all the time that indentation is there and it's
0:51:35 > 0:51:39because of these little receptors that you are able to detect
0:51:39 > 0:51:43the very fine detail of those objects that I placed in your hand.
0:51:49 > 0:51:52We're still at the early stages of understanding
0:51:52 > 0:51:56how the relationship between touch receptors and the brain works.
0:52:00 > 0:52:03But that hasn't stopped one group of scientists attempting
0:52:03 > 0:52:06a hugely ambitious project.
0:52:09 > 0:52:14To replicate our sense of touch - artificially.
0:52:14 > 0:52:17What if I could touch these clothes remotely
0:52:17 > 0:52:19without even being here at all?
0:52:19 > 0:52:21Well, the idea that we could physically interact
0:52:21 > 0:52:26with objects in a virtual world may seem far-fetched but actually,
0:52:26 > 0:52:28it might be closer than we think.
0:52:34 > 0:52:39At Exeter University, Dr Ian Summers is developing technology
0:52:39 > 0:52:41that simulates touch.
0:52:41 > 0:52:43This is our tactile stimulator.
0:52:43 > 0:52:46As incredible as it sounds, Ian claims he's designed
0:52:46 > 0:52:51a machine that lets you feel what you're seeing on a computer screen.
0:52:51 > 0:52:53- So, would you like to have a go? - Yes, please.
0:52:53 > 0:52:56- So, I just put my finger on here? - That's right.
0:52:56 > 0:52:59You rest your finger on it, you move it around like a mouse...
0:53:00 > 0:53:03..and what you see on the screen
0:53:03 > 0:53:06is a green rectangle that represents your fingertip
0:53:06 > 0:53:11and also on the screen, you see the surface of the textile and...
0:53:11 > 0:53:14That is a piece of corduroy
0:53:14 > 0:53:18and I'm actually feeling virtual corduroy on my finger.
0:53:18 > 0:53:22That's the idea. And you've got a piece of corduroy on the table,
0:53:22 > 0:53:26- real corduroy, so you can compare the two.- Very similar, very similar.
0:53:26 > 0:53:31That's really rough across the way as you'd expect and then up
0:53:31 > 0:53:34and down, it's not nearly as rough cos that's with
0:53:34 > 0:53:36the grain of the corduroy.
0:53:36 > 0:53:39So, Ian, how is this possible? What's actually happening here?
0:53:39 > 0:53:41Well, what we're trying to do
0:53:41 > 0:53:44is replicate what happens in a real touch situation.
0:53:44 > 0:53:46So if you imagine, for example,
0:53:46 > 0:53:49my finger running over the surface of this piece of hessian
0:53:49 > 0:53:54and then what happens is the interaction with the surface
0:53:54 > 0:53:59deforms the skin and vibrations travel through the tissue underneath
0:53:59 > 0:54:02to the underlying touch receptors.
0:54:02 > 0:54:04So, we're trying to reproduce that.
0:54:04 > 0:54:06So the job of our tactile stimulator
0:54:06 > 0:54:09is to deliver those kind of vibrations
0:54:09 > 0:54:12to the touch receptors in the finger.
0:54:12 > 0:54:17The machine works by making pins on top of the computer mouse vibrate
0:54:17 > 0:54:20to trick the touch receptors in my fingertip.
0:54:21 > 0:54:23By changing the strength of the vibration,
0:54:23 > 0:54:27Ian can replicate the feel of different materials.
0:54:27 > 0:54:32'As a general rule, rougher materials generate strong vibrations
0:54:32 > 0:54:35'whereas smoother materials generate weak vibrations.'
0:54:35 > 0:54:38- So, would you like to try another surface?- Yes, please.
0:54:38 > 0:54:41Right, we've got something a bit smoother, some kind of silk,
0:54:41 > 0:54:44- I think, so we'll try switching to that one.- So there's silk.
0:54:44 > 0:54:48So, that's a nice silk texture. Very smooth.
0:54:49 > 0:54:51Let's see how that feels.
0:54:51 > 0:54:56Yes, it's good, it's not as great as the corduroy but it's good.
0:54:56 > 0:54:58Yeah, I think that with smooth surfaces,
0:54:58 > 0:55:01you're very aware of just the feel of the stimulator
0:55:01 > 0:55:02whereas for rougher surfaces,
0:55:02 > 0:55:06maybe you're more aware of what's coming out of the stimulator.
0:55:06 > 0:55:10Ian has so far simulated over 70 types of material.
0:55:10 > 0:55:12In studies, volunteers guess
0:55:12 > 0:55:16what around 60% of the virtual versions are supposed to be.
0:55:17 > 0:55:22What were the challenges you faced in making virtual touch work?
0:55:22 > 0:55:25I think the sticking point at the moment is not really
0:55:25 > 0:55:28the technology, in terms of the stimulator
0:55:28 > 0:55:31and moving over the surface and whatever,
0:55:31 > 0:55:37it's that we don't know enough about the nature of the real interaction
0:55:37 > 0:55:40between a real finger and a real surface
0:55:40 > 0:55:43and so we don't really have enough information to know
0:55:43 > 0:55:46what are the right signals to put through our virtual system.
0:55:46 > 0:55:50Because we understand so little about touch,
0:55:50 > 0:55:54Ian is still some way off having a reliable system
0:55:54 > 0:55:58but if he's successful, it does have many potential uses.
0:55:58 > 0:56:01From online shopping and gaming
0:56:01 > 0:56:05to helping surgeons perform operations remotely.
0:56:06 > 0:56:08I'm genuinely surprised by Ian's work.
0:56:08 > 0:56:10I would never have thought that we were
0:56:10 > 0:56:14so close to being able to touch things in a virtual world
0:56:14 > 0:56:18but what strikes me most is that even with all our technology,
0:56:18 > 0:56:23we struggle to replicate the complexities of human touch and
0:56:23 > 0:56:28that just demonstrates how amazingly sophisticated our hands really are.
0:56:33 > 0:56:35I've discovered so much I didn't know
0:56:35 > 0:56:38about what makes our hands unique.
0:56:39 > 0:56:42Over the course of our dissection,
0:56:42 > 0:56:45I've seen the incredible natural engineering
0:56:45 > 0:56:47that lies behind every action,
0:56:47 > 0:56:51the muscles that give our hands their strength,
0:56:51 > 0:56:53the tendons that channel their power,
0:56:53 > 0:56:58how the thumb gives us unrivalled movement,
0:56:58 > 0:57:03the co-ordination and intricate control of the fingers,
0:57:03 > 0:57:08the sensitivity of our fingertips that connects us to the world.
0:57:11 > 0:57:15And what I find most impressive is the way it all works together
0:57:15 > 0:57:20to give us such a versatile and powerful instrument.
0:57:23 > 0:57:27If you'd asked me before we started what defines us as human,
0:57:27 > 0:57:30I think, like most people, I'd have said our brain
0:57:30 > 0:57:33but now I'd have to include the hand.
0:57:33 > 0:57:36Having taken it apart, bit by bit,
0:57:36 > 0:57:40and seen the incredible natural engineering inside, I've got
0:57:40 > 0:57:45a new-found respect and admiration for this part of our anatomy.
0:57:45 > 0:57:48Without hands, we wouldn't be who we are.
0:57:52 > 0:57:55Next time, we take apart a human foot.
0:57:55 > 0:58:01That is the first time I have ever seen inside the foot.
0:58:01 > 0:58:04We'll uncover the extraordinary inner workings that drive
0:58:04 > 0:58:07every step we take.
0:58:09 > 0:58:13And I'll meet people with unique talents...
0:58:13 > 0:58:16I should get you making a paper aeroplane, really, shouldn't I?
0:58:16 > 0:58:18Oh, come on, Tom, come on.
0:58:19 > 0:58:23..to discover what gives us a rare and crucial ability...
0:58:23 > 0:58:25Oh! Jesus.
0:58:25 > 0:58:28..to stand and walk upright.