A 55 year old man who made an extraordinary wish before he died that his remains be used by me to educate people about human anatomy. I met him several times. He was passionate about science and about the enlightenment of lay people.
Tonight, I will dissect him and unravel the mysteries beneath his skin. Lesson 1. Movement. Wiggling your toes. It seems an almost inconsequential action. Yet the systems which underlie it are amazingly complex.
In this series, we'll be revealing the systems of the human body so that you can see them for yourselves. And in this programme, we'll be beginning with movement. we'll be taking you to the core of the human body to the central controllers of the brain and the spinal cord and how they're connected to our movement machines the muscles and how the muscles transfer their energy energy to the system of levers which is our skeleton.
But to get there we first have to peel away the part of human anatomy that's most familiar. The section has been done since centuries. This picture originates from 1747 and the approach is always the same. At first we have to take off the skin to look at the muscles. And to dissect those I go over here to our specimen which is an upper limb.
right position because this is the position we move our muscles. For reason of anonymity, I've covered the face. We want to start from the back, therefore I want to turn around. Marius, could you be of help? Thank you very much.
To take the skin away takes a while, therefore we have already started, so we are faster. And I start here at the side and I want to take off the skin. skin in one large piece this is a fresh specimen we have not fixed it this way the muscles are more flexible it's easier to show you later on their function If you think of the skin as an organ, the skin is actually our largest continuous organ.
I think you'd be surprised at just quite how big it is when it's actually been fully removed. The skin forms our interface with the external world. It has a number of functions. It conveys sensory information from the outside world to our nervous system.
It's responsible for heat regulation because the sweat... glands are located in our skin. The skin also makes specialised structures such as hair and nails.
And although it is a continuous organ, it does have specialised areas. For example, only our scalp tends to make hair and perfusion. Only the skin near the tips of our fingers and our toes makes nails.
Although the skin itself, when it's removed in this way, is a very large organ, a lot of the material that you see is actually composed of tough connective tissue and subcutaneous fat which also helps to keep us warm. But the actual active portion of the skin is is a small growing layer just between the fat and connective tissue and the surface, which is what rubs off when we're in the bath. This layer is only a single cell thick, probably about a tenth of a millimetre thick, and thinner than a piece of tissue paper, and as easy to tear, or probably easier to tear.
But without that growing layer, we wouldn't actually have a skin to protect us. I want to save the ear and the face and the face. So the skin is loosened and I actually take it now with scissors off the body.
Would you help me a little bit? The color of the subcutaneous fat that you see is exactly the same as the surgeon sees when he's doing an operation. Actually the skin, the largest organ, depending on the amount of subcutaneous tissue between 3 and 30 kg heavy, we want to put it neatly, you know.
It's very important that the specimen looks nice. This now is the skin in its entirety. Here the skin from the head. The right and the left extremity is here the leg. And in fact, although this may seem, and indeed is, strange site.
It has a long history in art. One of the most famous examples of the skin being painted in this state can be found on the roof of the Sistine Chapel where Michelangelo has painted a portrait of himself. as the flayed skin of St. Bartholomew.
To give you an overview about the muscles, they are all covered by loose connective tissue, the muscle sheath, and inside the muscle contracts over the... trunk they are the muscles in a flat shape they move the shoulder plate then move the ribcage they move the hips but as for the extremities The muscles always have a rather round shape and they usually end in tendons in dense connective tissue like here in the lower arm or like here in the biceps. Well, the logic of dissection means that we must start our study of movement from the outside with the muscles. So let's first have a look at some muscles in action. And over here we have Juliet, our resident anatomical artist, who's just drawing some muscles on our model dentist's arm here.
here which we'll come to in a moment. But first let me show you a muscle in action and if I could just ask you to hold that for me. I'll swap it with a ruler and Dennis here has a particularly fine biceps that we can do a useful demonstration of muscle action on.
If you just hold your arm there and I'm just going to extend this ruler so that we can all see. Roughly, here we are, how long the muscle is. And if I put the end of the ruler near the one there, at the edge of Dennis'biceps, if you know how tense your biceps are, Dennis, and you can see that bulge, it's shortened really quite considerably.
Just relax again. Okay, let's do that one more time. So there it is.
And the muscle has actually shortened about half of its length. Thanks. Well, it used to be thought that muscles were some type of spring and that they ping together when they shorten.
perhaps the proteins coiled up, but in fact the modern understanding of muscle was only established in about the 1950s when it was found out using electron microscopy, very high magnification microscopy, that muscles really are constructed like little machines. They are made out of interlacing filaments which overlap in this way, and when the muscle is switched on, actually by an arriving nerve impulse, this causes the filaments to interact in such a way that they slide past one another, and when the muscle is switched off, they then relax again. So muscles really are constructed like a small machine which moves past and back and past and back in shortening and lengthening.
Well if we now have a look at the muscles that Juliet's drawn on Dennis's forearm here, we've mentioned the biceps in the top of the arm, muscles can of course only contract which means that for every group of muscles there has to be a group of muscles on the other side of the bone to pull in the other direction. These muscles