The Nervous System

How come that you can walk, run, work, cook, sing and dance?



To do that you must be able to move your arms, legs and your head. How does your body do that?

Well, If you decide to lift your left arm, your brain sends a message through an electric current down through your nervous system to your left shoulder to tighten the muscle in your shoulder. Try putting your right hand on your left shoulder as you lift your arm to feel the muscle move.

Moreover, if you want to bend your left arm, your brain sends another electric current to the muscle in your upper arm, which makes it contract and therefore bend, so on and so forth.

You can think of nerves as small electrical wires running throughout your body, connecting your limbs and organs to your brain. muscles however are just soft tissue connected by a network of these slim electric wires, that are able to contract and expand. Now, Take your left hand and feel this for yourself on the upper part of your right arm.

So, as you can see and feel, nerves are incredibly important for us to be able to walk, run, work, cook, sing and dance. But this is just the surface of what your nerves do, because they’re abundant in every part of your body they work in very intricate ways. For instance, if you bite your finger, an impulse will immediately be sent to your brain, and your brain will by means of your nerves make the muscles of your finger remove the finger from your mouth. Try it, but be careful.

Look at all your of nervous system, impressive, isn’t it?

The Muscle System

We have many of the same sort of muscles as the ones of the shoulder, the arm and the fingers, approximate 400 in fact. They are situated in the forehead, in the eyelids, around the mouth, in the stomach, in the thigh and in many other parts of your body. Look for yourself:

Click here to see the muscle system part 1 Click here to see the muscle system part 2


Sometimes your muscles will not do, what your head wants them to do. They are tired. The reason is, that they are short of energy. It´s like a fire. As long as there is wood to burn, you can have fire and be able to cook.

When the wood has burnt to ashes, there is no more fire and you will have to fetch some more wood. It´s the same with muscles; when they are tired they need new energy from food and oxygen, but they also should rest for a while. You and your friends can see it for yourselves by making some push-ups on the floor.


To be able to walk, run work, cook, sing and dance we need muscles and nerves. And muscles and nerves need energy from food and from oxygen

Our Bloodveins

The muscles and the rest of the body for that matter get energy from the blood. Within the blood there is oxygen and some of the food we have eaten, only it is broken down into very, very tiny parts, so that it can be transported inside the blood veins. Think of that next time you see a drop of blood.

It´s not just the muscles, that need energy from the blood. Every part of the body does. That’s why we have blood veins throughout our body, in our fingers, our legs, our ears, our stomach, our skin etc. etc. To make the blood circulate in the veins we have this incredible pump called the heart. The heart is itself a muscle, that works – without the head having to think about it at all – from the day we lie in our mother´s stomach till the day we die. Try to put the palm of your right hand to your stomach, where you think your heart is situated. Can you feel it pumping? And you don´t even need to ask it to do so.

But how does food and oxygen get into the blood veins?

The Digestive System

Let´s start with the food:

Firstly, we put vegetables or rice or meat into our mouth

After chewing the food, we swallow it and it goes down a thin pipe called the gullet, which is 20-25 cm long. Try to measure 25 cm from your mouth downwards to your stomach.

At the end of the gullet the food lands in the stomach, where it – without us knowing about it – is mixed with acids, that the stomach produces itself. Then the stomach turns the food round and round for four hours, until it´s liquid.

Then the food enters a flexible pipe (called small intestine) through an opening in the stomach. The small intestine is six meters long. Think about how a six meters long intestine can be inside your body.

Four hours later the food has been dissolved into very, very tiny parts by means of insulin and juice from an organ called pancreas, yellowish-green juice from the liver and the small intestine´s own bacteria.

Then the very, very tiny parts of the dissolved food can pass through the wall of the small intestine into the blood veins

Some of the food cannot be dissolved this way. That goes for instance for cherry stones, plum stones, olive stones and grape seed and even pebbles accidently mixed up in a rice dish. Instead of passing into the blood, the rest of the food pass into the large intestine, where it stays for 7-16 hours, until it leaves your body as stools.

If you find this a bit difficult to understand, watch this video:

How lungs work

Now you know how the food gets into your blood. It´s time to find out how the oxygen gets into your blood. That´s not difficult.

Oxygen comes into our lungs through our mouth and nose. Try to breathe through your nose while closing your mouth and then through your mouth holding your nose. The air that we breathe mostly consists of oxygen. We need the oxygen, and we need it quite desperately. Try to see how long time you can close your mouth and hold your nose at the same time. Not for long, I guess. Your body must have new oxygen all the time. From your mouth and nose, the oxygen gets into your lungs.

Inside your lungs the oxygen gets into some very, very fine tiny sort of windpipes, that allows the oxygen into your blood. Look here:

Click here to see the bloodveins

The red veins contain oxygen from inhalation

The blue veins contain carbon dioxide from exhalation (we get back to that later)

If you want to check your understanding of how the oxygen gets into your blood, watch this video:



Your muscles and the rest of your body gets energy from the blood. The energy gets into your blood when you have eaten food and when you have breathed oxygen.


To be able to walk, run, work, cook, sing and dance, we need a lot of muscles, we need nerves throughout our body and we need our blood to circulate in our veins to make sure, that all parts of our body have the energy they need to perform. You already know that a minor part of what we eat pass into the large intestine, until it leaves your body as stools. But when your body uses energy, some more waste will occur. It´s the same as you can observe with a fire; when the wood is burnt, there is no more fire and all there is left is ashes.

Carbon Dioxide

The waste (the ashes) from our body is carbon dioxide and water. The waste gets out of our body by means of the blood streams. “How is that done?” you might think.

Well, do you remember this little fellow?

Click here to see the bloodveins

His red veins contain oxygen from inhalation.

His blue veins contain carbon dioxide for exhalation

When the blood filled with oxygen from the lungs comes back to the lungs from its journey throughout your body it´s filled with carbon dioxide instead of oxygen. We get rid of the carbon dioxide by exhaling from our lungs through our mouth and nose.

Your blood is purified when passing through your liver and your kidneys. From the liver and the kidneys, the waste (water) is directed to the urinary bladder. You empty your bladder when you pee, you can pee 1 to 1½ l a day. You also get rid of water when you sweat and when you exhale steam from your mouth and nose. Try to exhale on a mirror and you can see it.


Our lungs clean our blood for carbon dioxide and we exhale the carbon dioxide through our mouth and nose.

Our liver and kidneys purify our blood for water. We get rid of the water by peeing, by sweating and by exhaling steam through our mouth and nose


  • Now you know how your body works, when you want to walk, run, work, cook, sing and dance.

It´s time to think about how you can support your body, so that it stays healthy. Go to chapter 2