The Muscular System
( Originally Published 1917 )
The Muscles.—There are some five hundred separate muscles in the human body and they make up about half its weight. They are of many different shapes, and of sizes ranging from a large muscle in the back that weighs several pounds to the tiny muscles that move the eyelids. Muscle in an animal is the portion we eat as lean meat.
If a muscle is studied under the microscope, it is found to be composed of a great number of tiny muscle fibers, each an inch or an inch and a half long and 1/2500 to 1/250 of an inch thick (somewhat the shape of a long leather shoe string). Each of these fibers can contract; and when all the fibers of a muscle contract together, the whole muscle shortens. It is this contraction, or shortening, of the muscles which causes movement.
How the Muscles Move the Parts of the Body.—The larger muscles are fixed, at one or both ends, to bones or
other parts of the body, by means of tough whitish strings called tendons. These tendons help to make the machinery of movement simple and efficient. There are, for example, many different muscles which move the fingers. Some of these are relatively large. Instead of running down into the wrist to make it bulky and awkward, the larger muscles stop in the arm and are attached to tendons which extend down to the bones in the hand. You can see these tendons working in the back of your hand when you open and close it. They do not themselves contract but are pulled by the shortening of the muscles in the arm. At or near the point where they are attached to the bones, the tendons are often held in place by ligaments.
When a muscle contracts and pulls on its tendons, the bones or other parts of the body to which the tendons are attached must, of course, move toward each other. Figure 19 shows how the biceps muscle in the upper arm raises the hand. This muscle is attached at one end to the bones of the shoulder and at the other end to the upper part of the forearm. If you hold your arm in position A of the figure and raise your forearm, the biceps muscle shortens and thickens. You can feel it do this if, at the same time, you put your other hand on your upper arm.
When you want to straighten the arm again, there is another muscle on the other side (the triceps) which, by contracting, pulls on the lower end of the forearm and draws it back into line with the upper arm.
Antagonistic Action of Muscles.—The biceps and triceps are good examples of what is called antagonistic action. One muscle pulls the arm up and the other pulls it down; the position of the arm depends on the balance between these two pulls. In this way one of the pair of antagonistic muscles serves as a check upon the other. It prevents the motion from going too far and permits a much more exact control of movement than would otherwise be possible.
Varied Work of the Muscles.—All of the various movements of the body are made by contractions of muscles. Every change in the position of the ribs, the bones of the arms and legs, or the backbone is due to the shortening or lengthening of muscle fibers.
It is not only when we move, however, that the muscles are active. Holding any part of the body still requires the action of a great many muscles, but the antagonistic muscles are then pulling equally hard in opposite directions. If you hold your arm out straight in the air for a few minutes, you will become very tired from the muscular work that you have been doing.
The body, in standing, is held erect by great bands of muscle which run up the back and hold the spinal column straight and the head erect. (See Fig. 7.) A skeleton, such as you may have seen in a museum, would double up and fall over if it were placed upon its feet, for lack of muscles to hold it up. The organs of the trunk are held in place by flat sheets of muscle in the abdominal wall. When we shiver with cold, it is because a chill has upset the normal relation between the tiny muscles of the skin, and they pull first one way and then another, instead of being evenly balanced.
Muscles of the Digestive and Circulatory Systems.—Besides the muscles which move the skeleton, there are a great many other muscles in the body which we do not ordinarily think about, but which are constantly at work to keep the human machine running.
Did you ever wonder what becomes of your food after you have swallowed it? It does not just fall down. It has to move through the esophagus and the stomach and the intestines (see Fig. 23, p. 52) and in order to do this it must be pushed along by the contraction of muscles in the walls of these organs.
It takes a great deal of force to drive the blood through the blood vessels that extend all over the body. This is done mainly by the heart, which is really a powerful muscle. The daily work of this organ is said to be equivalent to the lifting of a hundred-ton locomotive a foot in the air. The walls of all the blood vessels contain layers of muscles which, by their contraction, regulate the size of the blood vessels so that each part of the body gets the necessary supply of blood.
Voluntary and Involuntary Muscles.—The muscles that move the arms and the legs, the skin of the face, the tongue, and many other parts of the body are under the control of the will; they are called voluntary muscles. We can move such muscles when we wish to do so. Most of the organs inside the body, however, like those in the digestive and circulatory systems, work automatically. The muscles which control these movements are called involuntary muscles; we cannot contract them at will.
Keeping the Muscles Strong.—Any one can strengthen his muscles by exercise. When a muscle is used, it grows more powerful. You can tell a baseball pitcher or a black-smith by the big muscles of his arm, and a man who has rowed on a crew by the powerful muscles of his back.
It is not necessary or wise for all boys and girls to take part in athletic competitions which require great development of special sets of muscles. Every boy or girl, however, ought to take enough active exercise to develop all the muscles of the body to a reasonable degree. Nowadays we like to see girls as well as boys strong and vigorous, and able to excel in games.
Effects of Muscular Exercise on the Body as a Whole. Muscular exercise is necessary, not only for the development of the muscles, but also for the health of the body as a whole. When we exercise the muscles, we exercise all the other organs. The heart and the blood vessels work better. The lungs take in deeper draughts of air. The appetite is increased, and the digestive system does better work. The waste products of the body are carried away more rapidly. The brain is clearer and the spirit more cheerful.
The natural love of play gives most young people plenty of exercise, but as they grow older many of them become so busy or so lazy that they forget to give their muscles enough to do. Really vigorous health requires active muscular exercise.
Exercise to Develop Special Parts of the Body.—If any particular part of the body is weak, special kinds of exercise may be used to develop it. A child who does not use his lungs properly can take special breathing exercises. There are special exercises for developing the muscles of the legs, the arms, the chest, the back, the trunk, and other parts of the body. Certain exercises, such as dancing, are especially valuable, not so much for developing the muscles them-selves, as for training the power of balancing or properly coordinating the action of various muscles.
One of the best things about the Greek people in the great days of their country was their admiration for the perfect and graceful human body. In their wonderful statues they showed the ideal body of an athlete, and each Greek boy and girl was expected to reach this ideal, as far as possible, by training and developing the body.
The Best Kinds of General Exercise.—The best exercises (aside from those used to correct special defects) are those which develop as many as possible of the different muscles of the body. Such exercises are brisk walking and running, rowing, riding, swimming, and playing tennis, baseball, and football.
It is better to exercise in the open air than indoors, but merely being outdoors is not enough. Leisurely walking is not exercise. You must use your muscles vigorously, so as to make the heart beat faster and the chest expand fully, if you are to get the best results.
Exercise in the form of games has a special value because games train and develop the eye and the brain as well as the muscle. Athletic sports and games that require team play teach young people how to cooperate with others, and to subordinate self to the good of the team.
Every boy and girl should have at least one form of exercise that he or she likes to do and learns to do well. It may be swimming, riding, tennis, basketball, skating, or brisk, hard walking. The important thing is to have the
habit of some kind of outdoor exercise and to love it, so that as you grow older you will turn to that sport for relaxation.
The Gymnasium.—Exercise taken in the form of games cannot, however, take the place of systematic drill in the gymnasium. Such drill, as has been pointed out, develops the special muscles that particularly need developing and trains the balancing or coordinating power of the body. To many people who live in crowded cities, the gymnasium furnishes the only chance for exercise; and even those who are fortunate enough to have opportunities for outdoor sports are made and kept fit for these activities by training in the gymnasium.
The Danger of Over-exercise.—All good things can be abused. Exercise draws the blood to the muscles and the skin. It is unwise, therefore, to take active exercise just before or after a heavy meal, for then the blood is needed in the digestive organs. Exercise at any time should not be carried so far as to tire one unduly. Great harm may be done by severe games, like boat races or Marathon runs for boys, or hard basketball games for girls.
Your object should not be to break records or win games, but to have a strong, healthy body and to play school games and the game of life gallantly, whether you win or lose.
The Effect of Alcohol and Other Poisons on Muscular Efficiency.—Aside from the need for exercise to develop the various muscles and the nerves by which they are made to act together, the most important thing to do in order to have a strong and efficient muscular system is to avoid poisons. The muscles and the other organs of the body may be chemically injured or poisoned in various ways. Sometimes men who work in trades where they have to use poisonous compounds, like certain lead salts, are poisoned by them. Sometimes people who eat too much, or too much of particular things, are poisoned by the results of decay of food in their intestines. Among the commonest injuries of this kind are those due to alcoholic drinks and narcotic drugs. It is recognized to-day that the use of such drugs does very great harm, and a special chapter will be devoted to the subject later. It will be well, however, to consider briefly the effect of alcohol upon the health of the various systems of organs, as they are taken up in turn.
The influence of alcohol on the work of the muscles has been studied by physiologists who devote their lives to finding out all they can about the human body. Hellsten of Sweden, for instance, determined the power of certain muscles and their resistance to fatigue by an instrument called the ergograph. In this machine the finger may be put into a strap which is connected with a weight by a thread over a pulley. The finger is bent downward again and again, each time lifting the weight on the other side of the pulley. The amount of the lift is recorded automatically by a point which traces an up-and-down line on a moving surface of smoked paper. Studies made with apparatus similar to this show that even moderate doses of alcohol cause a loss of about eight per cent in the power to do muscular work.
This conclusion from laboratory experiments is borne out by practical experience. Men on forced marches and those who have to do especially heavy work are no longer given alcoholic drinks, for it has been found that the effect is not to increase but to diminish endurance. College athletes in training for athletic victories are, of course, never allowed to use alcohol or tobacco or any other harmful drugs.
Sir Frederick Treves, a famous English physician, has said in this connection: "As a work-producer, alcohol is exceedingly extravagant, and like all other extravagant measures, leads to a physical bankruptcy. It is also curious that troops cannot work or march on alcohol. I was . . . with the relief column that moved on to Ladysmith, and, of course, it was an extremely trying time by reason of the hot weather. In that enormous column of thirty thousand, the first who dropped out were not the tall men, or the short men, or the big men, or the little men--they were the drinkers, and they dropped out as clearly as if they had been labelled with a big letter on their backs."
QUESTIONS FOR DISCUSSION AND REVIEW
1. What is the special work, or function, of the muscular system?
2. How are muscles attached to bones and other parts of the body?
3. Examine the tendons in a chicken drumstick. How are they arranged?
4. How does a muscle work in moving a part of the body?
5. When a muscle contracts, how does it change its form?
6. Raise your arm with palm up. Clench your hand and bring it slowly to your shoulder. What happens in your upper arm? What happens when you extend your arm again?
7. How is the body held in an erect position?
8. What causes shivering?
9. I know a boy who can drink a glass of water while he hangs head downward from a bar. How is this possible?
10. What is the difference between the action of the muscles of the stomach and those in the hand?
11. What effect does active exercise have upon the muscles?
12. A boy broke his right arm and kept it in splints and bandages for several months. When the splints were removed, this arm was soft and weak, and smaller than the left arm. Why?
13. What are some of the effects of exercise on parts of the body other than the muscles?
14. Why is it a good plan to learn some games and sports which you can continue to play when you are older?
15. You gain speed, accuracy, and quick thinking in games. Of what special value are these in everyday life? Give examples.
16. How does team work learned in games help to make boys and girls better citizens?
17. Jane and Rose are both fond of basketball. Jane plays a brilliant but erratic game, always depending on her own play to win. Rose is steady and uses passes to other players who are in a better position to throw for a basket. Which is the more valuable member of the school team?
18. John had been working hard all the morning and was so hungry that he ate an unusually large dinner. Some of the boys came to see him directly afterward, and they all went swimming. John had been in the water only a short time when he was seized with a cramp in his stomach. What caused the cramp?
19. Is beer a good drink for men on an exploring party? Give reasons for your opinion.