Chapter IV: The Muscles

It has already been stated that there are at least two muscles attached to a bone to move it in opposite directions. Since there are two hundred and six bones, you are not surprised to learn that to move the bones and accomplish the various purposes just stated, there are five hundred and twenty-six (526) skeletal muscles.

=Two Kinds of Muscles.=--All muscles are controlled by means of the nervous system. Some of them are directed by parts of the brain that work consciously; others are controlled by the spinal cord and the parts of the brain that work unconsciously. Those of the first kind are _usually controlled by the will_, but they sometimes act involuntarily. _They are called voluntary muscles._ They move the bones and are located in the limbs and near the surface of the trunk (Fig. 44). The other kind of muscles are _never controlled by the will, and are called involuntary muscles_. We cannot cause them to act, nor can we prevent them from acting. They contract more slowly than the voluntary muscles. Most of them are tubular and found in the cavity of the trunk. The involuntary muscles _belong to the internal organs_, and relieve the will of the responsibility and trouble of the activity of these organs; otherwise, the mind would have no time for voluntary actions.

=Gross Structure of Voluntary Muscles.=--A beefsteak is seen to be chiefly red, although parts of it are white or yellowish. The white or yellowish flesh is fat; the red, lean flesh is voluntary muscle. If a piece of beef is thoroughly boiled, it may be easily separated into _bundles the size of large cords_. These bundles may, by the use of needles, be picked apart and separated into _threadlike fibers_ (Fig. 40).

=Microscopic Structure of Muscles.=--These threadlike fibers may, under a magnifying glass, be separated into _fine strands called fibrils. These last are the true muscle cells_; they are shown by the microscope to be crossed by many dark lines (Fig. 48). Hence _voluntary muscles are called striated or striped muscles_. Prolonged boiling and patient picking with a needle are needed to dissect muscle, because the bundles are held together by thin, glistening sheets of connective tissue by which they are surrounded. This connective tissue surrounds and holds in place the separate fibers of each bundle (Fig. 40).

The fibrils of involuntary muscles are _spindle-shaped_ (see Fig. 42). There are no cross lines on the fibrils; hence involuntary muscles are called _smooth or unstriped muscles_. The heart fibers are exceptional; they are the only involuntary muscle fibers that are striped (Fig. 41).

THOUGHT QUESTIONS. =Classification of Some of the Muscles.=--Copy the
following list and mark _I_ for involuntary and _V_ for voluntary
after the appropriate muscles.

Muscles for chewing. Muscles of gullet. Muscles of the heart. Muscles
that move arms. Muscles for breathing. Muscles in the skin that cause
the hair to stand on end. Muscles that move eyelids. Muscles that
contract pupil of eye. Muscles for talking. Muscles that contract and
expand the arteries (in blushing and turning pale). Muscles that move
eyeball. Muscles that give expression to the face.

=Tendons.=--_The connective tissue which binds the fibers of muscles into bundles, and forms sheaths for the bundles, extends beyond the ends of the muscles and unites to form tough, inelastic white cords called tendons._ Some muscles are without tendons, and are attached directly to bones. Study the figures and find examples of this (see Figs. 44, 75). To realize the toughness of tendons, feel the tendons under the bent knee or elbow, where they feel almost as hard as wires. _The tendons save space_ in places where there is not room enough for the muscles, and permit the bulky muscles to be located where they are out of the way. Wherever the tendons would rise out of position when a joint is bent, as at the wrist and ankle, they are bound down by a ligament.

=Arrangement of Voluntary Muscles.=--_Circular_ muscles, called _sphincter muscles_, are found around the mouth and eyes. Muscles that extend straight along the limb either bend it and are called _flexors_, or straighten it and are called _extensors_. Most of the voluntary muscles are arranged in pairs and cause motion in opposite directions; they are said to be _antagonists_. The biceps (Fig. 43) bends the arm. Its antagonist is the triceps on the back of the arm. By feeling them swell and harden as they shorten, locate on your own body the muscles mentioned in Fig. 44.

=How a Muscle grows Stronger; its Blood Supply.=--Nature has provided that any part of the body shall receive more blood when it is working than when it is resting. _When it works the hardest, the blood tubes expand the most and its blood supply is greatest._ So whenever a muscle is used a great deal, an unusual amount of material is carried to it by the blood, the cells enlarge and multiply, and the muscle grows. The walls of the capillaries are so thin that the food which is in the blood readily passes from them to the muscle. Because of the oxidation taking place, a working muscle is warmer than one at rest. _By use a muscle grows large, firm, and of a darker red_; by disuse, it becomes small, flabby, and pale. But if muscles are worked too constantly, especially in youth, their cells do not have time to assimilate food and oxygen, and their growth is stunted.

Unless the meal has been a very light one, vigorous exercise should not be taken after eating, as the blood will be drawn from the food tube to the muscles and the secretion of the digestive fluids will be hindered. Persons whose entire circulation is weak may find that light exercise after a meal, such as walking slowly, may help circulation and digestion.

=Why the Muscles work in Harmony.=--_When a boy throws a stone, almost every part of the body is concerned in the action._ His arms, his legs, his eyes, the breathing, the beating of the heart, are all modified to assist in the effort. As the boy wills to throw the stone, nerve impulses are sent to all the organs that can assist, and they are excited to just the amount of action needed.

Draw a dotted line from each function mentioned on margin to the muscle or muscles having that function.

Bows the head?

Straightens the elbow?

Straightens the fingers?

Swings leg outward?

Bends the knee?

Straightens the knee?

Crosses the leg?

Straightens toes?

Draws shoulder back?

Lifts the whole arm outward and upward?

Draws whole arm downward and forward?

Bends the elbow?

Bends the fingers?

Raises the body on the toes?

Raises toes?

FIG. 44.--SUPERFICIAL MUSCLES AFTER THE STATUE OF “THE DIGGER” (Lami).]

=The Nerve Impulse and the Contraction.=--Each nerve that goes to a muscle is composed of many fibers; the fibers soon separate and go to all parts of the muscle, _and each muscle fiber receives its nerve fiber_ (see Fig. 45). In the brain each fiber is stimulated at once, and all the fibers shorten and thicken together. This change is spoken of as contraction; but since the muscle does not become smaller, the word may be misleading. When the muscle shortens, it thickens in proportion and occupies as much space as it did when relaxed.

=Where does Muscular Energy come from?=--_The nerve does not furnish the energy which the muscle uses when contracting. The muscle cells have already stored up energy from the food and oxygen brought to them by the blood_, and the process called oxidation sets free the energy. Activity of muscle may increase the carbon dioxid output fivefold. Mental work has practically no effect upon it.

=How a Muscle stays Contracted.=--The muscle relaxes at once after contraction; and in order to keep it contracted, nerve impulses must be sent in quick succession, causing in fact many contractions; the effect of this is sometimes visible, as the trembling of the muscle. Figure 47 shows an easy standing posture.

=What causes Fatigue.=--Fatigue or exhaustion is due to the using up of the living material in the nerve cells and muscle cells by oxidation. Rest is necessary to give cells opportunity to repair themselves. Why is it less fatiguing to walk for an hour than to stand perfectly still for ten minutes?

=Degeneration of Muscles= begins with habitual disuse. We dare not furnish a substitute for the work of a muscle, if we wish the muscle to remain sound. A belt or a stay at the waist will cause the muscles of the trunk to become flabby and the abdomen to relax and protrude.

=How Muscular Activity helps the Health.=--Life is change, stagnation is death. _Muscular activity uses up the food, gives a good appetite, and sets the digestive organs to work; it uses up the oxygen and sets the lungs to work; but most of all, every contraction of a muscle helps the blood to flow._ As a muscle contracts, it presses upon the veins and lymphatics, and, by this pressure, forces the blood and lymph along (Fig. 48). In any ordinary activity, dozens of muscles are being used. That the effect upon the circulation is very powerful, is shown by the rosy skin, deep breathing, and rapid heart beat. The many benefits of an active circulation of the blood and lymph will be discussed in the next chapter. See page 67.

A grave danger from athletics is that of developing the muscles, including the heart, to an enormous extent by training; then _when training ceases the muscles undergo fatty degeneration from disuse_. Heart disease and other diseases may follow. Many athletes die young, killed by trying to turn their bodies into mere machines for running, boxing, or rowing, instead of living complete lives. _The athletic ideal is not the highest ideal of health_; general activity, resembling the occupations of hunting and farming by which the early race supported itself, is best for health. Many kinds of factory work use only one set of muscles. The savage did not lead a monotonous life, and monotony is bad for both muscles and nerves.

=Advantages of Work and Play over Gymnastic Exercises.=--The interest
that comes from doing something useful, makes muscular exertion
doubly beneficial to the health. The lifting of dumbbells, Indian
clubs, and pulley weights, and letting them down again, tends to
become very irksome, even though done with the knowledge that the
exercise will benefit the health. _Useful labor and games place
definite objects in view and do not require so great an effort of the
will nor exhaust the nerves so much as mere exercise._ The interest
in the work or the game serves to arouse all the nerves and muscles
to work in harmony.

=An Advantage of Gymnastics over Work and Play.=--Gymnastics can
furnish any required variety of exercises and _can develop exactly
the muscles that need development and leave those idle that have
become overdeveloped_ by doing constantly one kind of work or playing
continually the same game. The _deformity of a flat chest_ (and round
shoulders which always accompany it) does not so often indicate a
weak chest or small lungs as it indicates weak or relaxed muscles
of the back and the habit of sitting in a relaxed position at work
(Figs. 49, 50, 51). _Gymnastic exercise is not wholly an artificial
custom._ Cats stretch themselves, stretching each leg in succession;
many animals gambol and play. A gymnastic drill, taken to music and
with large numbers of pupils in the drill, is interesting as work or
play, and should not be neglected for any study, however important.

=Environment of Early Man and Modern Man.=--A well-developed man
of one hundred and fifty pounds weight should have sixty pounds of
muscles. The proportion is often different in the puny bodies of the
average civilized men, such as clerks, merchants, lawyers, and other
men with sedentary occupations; their bodies are as likely to be
lean and scrawny or fat and flabby as to be correctly proportioned.
Why does a normal man have sixty pounds of muscles instead of twenty
pounds of puny strings such as would have sufficed for a clerk,
student, or a writer? This is because, in his native condition, he
had to seek his food by roaming through the forest, contending with
wild beasts or with other savage men, often traveling many miles a
day, climbing trees, etc.

=Too Rapid Change of Environment; Destructive Tendencies of
Civilization.=--_It is impossible for the human body to change
greatly in a few hundred years._ The body of man served him for many
ages for the manner of life outlined above. It was suited for these
conditions, and the muscles and the organs that support them cannot
accommodate themselves to changed conditions in a few generations. It
has only been a few hundred years since the ancestors of the Britons
and Germans, for instance, were running wild in the German forests,
clad in the skins of wild beasts. Yet _civilized man lets his muscles
fall into disuse_, he takes a trolley car or horse vehicle to go
half a mile, an elevator to climb to the height of thirty feet. He
neglects all his muscles except those that move the tongue and the
fingers of the right hand. He never makes enough exertion to cause
him to draw a deep breath, and his lungs contract and shrivel. He
seldom looks at anything farther than a few inches from his nose, and
his eyes become weak. At the same time that he neglects his muscles
and his lungs, he overworks his brain and his stomach; yet he expects
his body to undergo the rapid changes to suit the demands of his
life. Such rapid changes in the human race are impossible. A man that
does not see that _sound health is the most valuable thing in the
world, except a clear conscience_, is in danger both of wrecking his
own happiness _and of failing in his duty to others_.

THOUGHT QUESTIONS. =Shoes.=--=1.= What the faults of shoes may be
in size; shape; sole; heel; toe; instep. =2.= Name deformities
resulting to skin of foot; nails; joints; arch; ankle; spine. =3.=
State effects of uncomfortable shoes on muscular activity; mind and
disposition. =4.= State effect of aversion to walking on muscles;
circulation. =5.= If a shoe is too loose, it slips up and down at
the heel and chafes the skin there; if too tight, there is pressure
on the toes, which causes a corn or ingrowing nail. Have your shoes
been correct, or have they been too loose or too tight? According to
this test, what proportion of people wear shoes that are too tight?
=6.= How many sprained ankles have you known among boys; girls? =7.=
Why is it that people who grow up in warm climates have high, arched
insteps, and short, broad, elastic feet, but people of the same race
who pass their childhood in cold climates often have long narrow feet
with low arches and sometimes have the deformity called “flat foot”?

=Instinct as a Guide for using the Muscles.=--The instinctive feeling
called _fatigue tells us when to rest_. There is also a _restless,
uneasy feeling that comes over a normal human being when confinement
and restraint of the muscles have reached an unhealthy limit. This
feeling should not be repressed_ for long at a time. Many, ruled by
avarice, ambition, interest in sedentary work, a silly notion of
respectability, or a false conception of duty, have repressed this
feeling and have lost it. There is then a feeling of languor, and a
disinclination to the very activity which health demands. An unheeded
instinct is as useless as an alarm clock that has been habitually
disregarded.

=Exercise and Climate.=--In our warmest states and in the tropics,
one hour’s vigorous physical labor a day, combined with the ordinary
activities of life, will keep a person in good condition. In the
colder states, muscular exertion for several hours is needed daily.

=Complete Living.=--Numberless people have devoted themselves to
an intellectual occupation, and planned to keep their bodies sound
by gymnastics and special exercises. Because of the monotony of
exercises, they are soon given up in nearly every instance. _The
safest way is never to allow all the energies to be devoted to a
one-sided occupation, but so to plan one’s life and work that a
part of the time is devoted to some physical work_, whether it be
in a garden, workshop, or orchard; in walking a long distance to
the office; at bookbinding, cooking, wood carving, or any one of
various other useful occupations. The result of manual training shows
_that not only strength of body, but strength of mind, is promoted
by physical labor_. Problems of war and of the chase kept active
both the body and mind of the savage. Hence he led a more nearly
complete life than his civilized descendants, and his body was strong
accordingly. We should admit the hopelessness of having permanent
good health without muscular activity and should determine that
muscular exertion shall be as much a habit and pleasure as eating and
sleeping.

=Alcohol and Muscular Strength.=--Benjamin Franklin, one of the
wisest and greatest of Americans, was a printer when he was a young
man. In his autobiography he gives an account of his experience as a
printer in London. He says: “I drank only water; the other workmen,
fifteen in number, were great drinkers of beer. On occasion I carried
up and down stairs a large form of types in each hand, when others
carried but one in both hands. They wondered to see, from this and
several instances, that the Water-American, as they called me, was
stronger than themselves, who drank strong beer. My companion at the
press drank every day a pint before breakfast, a pint at breakfast
with his bread and cheese, a pint between breakfast and dinner, a
pint at dinner, a pint in the afternoon about 6 o’clock, and another
when he had done his day’s work. I thought it a detestable custom,
but it was necessary, he supposed, to drink strong beer that he might
be strong to labor.”

EXERCISES IN WRITING.--The Right and the Wrong Way to ride a Bicycle.
Pay Day at a Factory. A Graceful Form: how Acquired; how Lost. A
Drinking Engineer and a Railway Wreck.

PRACTICAL QUESTIONS.--=1.= Can we always control the voluntary
muscles? Do we shiver with the voluntary or involuntary muscles?
=2.= If a man had absolute control over his muscles of respiration,
what might he do that he cannot now do? =3.= Why is one who uses
alcoholic drinks not likely to be a good marksman? =4.= Why should a
youth who wishes to excel in athletic contests abstain from the use
of tobacco? =5.= Is there any relation between the amount of bodily
exertion necessary for a person’s health and the amount of wealth
or the amount of intelligence he possesses? =6.= Can you relax the
chewing muscles so that the lower jaw will swing loosely when the
head is shaken? Can you relax your arm so that it falls like a rope
if another person raises it and lets it fall? =7.= The average man
has sixty pounds of muscle and two pounds of brain; one half of the
blood goes through the muscles and less than one fifth goes through
the brain. What inference may you draw as to the kind of life we
should lead? =8.= Why is a slow walk of little value as exercise?
=9.= How can we best prove that we have admiration and respect for
our wonderful bodies? =10.= Why is the ability to relax the muscles
thoroughly of great benefit to the health? How is this ability
tested? (Question 6.) =11.= Why is it as correct to say that the
muscles support the skeleton as the reverse?

1. Head arteries (carotid).

2. Nameless arteries (innominate).

3. Collar bone (subclavian) artery.

4. Great bend of the aorta.

5. Pulmonary arteries.

6. Thoracic aorta.

7, 10. Abdominal aorta.

8. Artery to liver (hepatic).

9. Artery to spleen (splenic).

11. Artery to intestine (mesenteric).

12. Artery to kidney (renal).

13. Descending vena cava.

14. Nameless vein (innominate, 15 and 16 before branching).

15. Collar bone vein (subclavian).

16. Jugular vein.

17. Pulmonary vein.

18. Ascending vena cava.

19. Vein from liver (hepatic).

20. Vein from stomach (gastric).

21. Vein from spleen.

22. Vein from intestine.

23. Vein to liver (portal).

24. Vein from kidney.

25. Right auricle.

26. Left auricle.

27. Right ventricle.

28. Left ventricle.

29. Thoracic duct.

30. Stomach.

31. Spleen.

32. Liver.

33. Kidneys.

34. Duodenum.

35. Ascending colon.

36. Descending colon.

37. Lymphatic glands of mesentery.]