Muscles

Huuuuuuuuuh! I want to be as strong as you, Seamus! I’ll build every muscle in my entire body. I won’t miss a single one! Well, Leon… I don’t think that’s possible.

You can’t build up all your muscles. You can’t even control every muscle. HUH? Whadya mean can’t control? That’s right.

Not all muscles can be controlled. When we talk about building muscles, we normally mean skeletal muscles. It’s skeletal muscles that enable us to move: everything from running fast, and lifting heavy things, to blinking an eyelid. The muscles are attached to the skeleton, and to the skin, with tendons. There are more than 600 skeletal muscles in the body.

Each one consists of bundles of threadlike cells -- muscle fibres. The muscle fibres have this special property: they can get shorter -- contract. The more, and the thicker the fibres in a muscle, the more strongly it can contract. Look here. When we want to bend an arm, the fibres in the biceps muscle contract. ...but when we want to extend the arm again, the biceps can’t do that work.

Instead it’s the triceps, on the other side of the arm, that contract. Muscles often work like this, in pairs. Sometimes there are even more of them working together, which makes the movement smoother and more controllable. We can control our skeletal muscles voluntarily - consciously, that is. But there are two kinds of muscle that we can’t voluntarily control.

One type are called smooth muscles. Smooth muscles are found in the intestines, airways, and blood vessels. You can’t decide to.. expand your blood vessels, can you? Your body controls the smooth muscles in several ways: Parts of the brain that we cannot control consciously send out electrical signals through the nerves, to the smooth muscles.

The smooth muscles are also affected by chemical signals, from substances that the body produces itself -- hormones… One hormone is adrenaline - also called epinephrine - which is produced in the adrenal glands, and released when we exert a lot of effort… ...and when we are scared, or angry. Adrenaline affects the muscles around the blood vessels, sending more blood to the large muscles, and less to other parts, like the liver for example. The second kind of muscle that you can’t control voluntarily is a really strong muscle, one that works all the time, your entire life. You have figured it out, haven’t you? That’s right - the heart!

Or, the cardiac muscle. The contractions of the heart are controlled by electricity. But this is a special kind of muscle. The electrical impulses that trigger every heartbeat come from inside the heart. The heart doesn’t need the brain to trigger the beats.

However, signals from the brain and from other places in the body can change how hard and how fast the heart beats. For muscles to work, they need energy, which they get from fat or glucose - a type of sugar. The muscles also use oxygen, in order to metabolize the sugar. As well as helping us move, muscles do several other things. They support the skeleton… ...protect internal organs… ...help keep us warm, by generating heat… ...and they can store energy, in the form of sugar molecules.

By working and using your muscles, you make them stronger and healthier. But for muscles to get strong, they also need proper food.. ..And they need to take a break, too. It’s when muscles are resting - between the periods of work - that they recover and get stronger. If you only work out and never rest, your muscles deteriorate instead. So what do you say, should we have another go with those rocks?

Naah, we’ll see. I’ve got some other muscles to exercise. The smooth muscles. In my intestines.