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Our Telephone Exchange And Its Cables

Source: A Handbook Of Health

The Brain. We are exceedingly proud of our brain and inclined to
regard it as the most important part of our body. So it is, in a sense;
for it is the part which, through its connecting wires, called the
nerves, ties together all the widely separated organs and regions in
our body, and helps them to work in harmony with one another. We speak
of it as the master and controller of the body; but this is only
partially true.

The brain is not so much the President of our Cell Republic as a great
central telephone exchange, where messages from all over the body are
received, sifted, and transmitted in more or less modified form, to
other parts of the body. Three-fourths of the work of the brain consists
in acting as middle-man, or transmitter, of messages from one part of
the body to another. In fact, the brain is far more the servant of the
body than its ruler; and depends for its food supply, its protection,
its health, and its very life, upon the rest of the body. The best way
to keep the brain clear and vigorous is to keep the muscles of the
stomach, the liver, the heart, and the entire body in good health.

What the Brain Does. The brain is the very wonderful organ with which
we do what we are pleased to call our thinking, and also a number of
other more important things of which we are not conscious at all. It is
a large organ, weighing nearly three pounds when full grown. In shape it
is like an oval loaf of bread split lengthwise by a great groove down
the centre, and with a curiously wrinkled or folded surface. The two
halves of the brain, called hemispheres (though more nearly the shape
of a coffee-bean), are alike; and each one, by some curious twist, or
freak, of nature, receives messages from, and controls, the opposite
half of the body--the right half controlling the left side of the body,
while the left half controls the right side of the body. Thus an injury
or a hemorrhage on the left side of the brain will produce paralysis of
the right side, which is the side on which a stroke of paralysis most
commonly occurs.

All the nerve fibres in each half or hemisphere of the upper brain run
downward and inward like the sticks of a fan, to meet in a strap-like
band, or stalk, which connects it with the base of the brain and the
spinal cord. A very small amount of damage at this central part, or
base, of the brain will produce a very large amount of paralysis. We may
have large pieces of the bones of the skull driven into the outer
surface of the brain, or considerable masses of our upper brain removed,
or destroyed by tumors or disease, without very serious injury. But any
disease or injury which falls upon the base of the brain, where these
stalks run and big nerve-knots (ganglia) lie, will cause very serious
damage, and often death.

The whole upper brain is a department of superintendence, which has
grown up from the lower brain to receive messages, compare them with
each other, and with the records of previous messages which it has
stored up, thus giving us the powers which we call memory, judgment, and
thought. Unfortunately, however, long and carefully as we have studied
the brain, we really know little about the way in which it carries out
these most important processes of memory, of judgment, and of thought,
or even of the particular parts of it in which each of these is carried

No part of the brain, for instance, seems to be specially devoted to, or
concerned in, memory or reason or imagination, still less to any of the
emotions, such as anger, joy, jealousy or fear; so all those systems
which pretend to tell anything about our mental powers and our
dispositions by feeling the shapes of our heads, or the bumps on them,
are pure nonsense.

The most important and highest part of the brain is its surface, a thin
layer of gray nerve-stuff, often spoken of as the gray matter (the
cortex, or bark), which is thrown into curious folds, or wrinkles,
called convolutions. This gray matter is found in the parts of the
nervous system where the most important and delicate work is done. The
rest of the nervous system is made up of what is called white matter,
from its lighter color; and this is chiefly mere bundles of telephone
wires carrying messages from one piece of gray matter to another, or to
the muscles.

We also know that a certain rather small strip of the upper
brain-surface, or cortex, about the size of two fingers, running upward
and backward from just above the ear, controls the movements of the
different parts of the body. One little patch of it for the hand,
another for the wrist, another for the arm, another for the shoulder,
another for the foot, and so on. We can even pick out the little patch
which controls so small a part of the body as the thumb or the eyelids.
So when we have a tumor of the brain or an injury to the skull in this
region, we can tell, by noticing what groups of muscles are paralyzed,
almost exactly where that injury or tumor is. Then we can drill a hole
in the skull directly over it and remove the tumor, lift up the splinter
of bone, or tie the ruptured blood vessel.

Three other patches, or areas, running along the side of the brain, each
of them about two inches across, are known to be the centres for smell,
hearing, and sight, that for sight lying furthest back. Damage to one of
these areas will make the individual more or less completely blind, or
deaf, or deprived of the sense of smell, as the case may be.

At the lower part of the area which controls the muscles of the
different parts of the body, above and a little in front of the tip of
the ear, lies a very important centre, which controls the movements of
the tongue and lips, and is known as the speech centre. If this should
be injured or destroyed, the power of speech is entirely lost. This,
curiously enough, lies upon the left side of the brain, and is the only
one-sided centre in the body. Why this is so is somewhat puzzling,
except that as speech is made up both of sound and of gesture, and our
gestures are usually made with the right hand, it is not unreasonable to
suppose that the speech centre should have grown up on that side of the
brain which controls the right hand, which is, as you remember, the left
hemisphere. What makes this more probable is that in persons who are
left-handed, the speech centre lies upon the opposite or right side
of the brain. So it is waste of time and does more harm than good to try
to break any child of left-handedness.

The Spinal Cord. Running downward from the base of the brain, like the
stalk of a flower, is a great bundle of nerve-fibres, the central cable
of our body telephone system, the spinal cord. This, you will remember,
runs through a bony tube formed by the arches of the successive
vertebrae; and as it runs down the body, like every other cable it gives
off and receives branches connecting it with the different parts of the
body through which it passes. These branches are given off in pairs, and
run out through openings between the little sections of bone, or
vertebrae, of which the spinal column is made up. They are called the
spinal nerves, and each pair supplies the part of the body which lies
near the place where it comes out of the cord.

The spinal nerves contain nerve wires of two sorts--the inward, or
sensory, and the outward, or motor, nerves. The sensory, or ingoing,
nerves come from the muscles and the skin and bring messages of heat and
cold, of touch and pressure, of pain and comfort, to the spinal cord
and brain. The outward, or motor, nerves running in the same bundle go
to the muscles and end in curious little plates on the surface of the
tiny muscle fibres, and carry messages from the spinal cord and brain,
telling the muscles when and how to contract.

As the spinal cord runs down the body, it becomes gradually smaller, as
more and more branches are given off, until finally, just below the
small of the back and opposite the hip bones, it breaks up by dividing
into a number of large branches which go to supply the hips and lower

While most of the spinal cord is made up of bundles of white fibres,
carrying messages from the body to the brain, its central portion, or
core, is made of gray matter. The reason for this is that many of the
simpler messages from the surface of the body and the movements that
they require are attended to by this gray matter, or ganglia, of the
spinal cord without troubling the brain at all.

For instance, if you were sound asleep, and somebody were to tickle the
sole of your bare foot very gently, the nerves of the skin would carry
the message to the gray matter of the spinal cord, and it would promptly
order the muscles of the leg to contract, and your foot would be drawn
away from the tickling finger, without your brain taking any part in the
matter, though, if you had been awake, you would of course have known
what was going on.

This sort of reply to a stimulus, or stirring up, without our knowing
anything about it, is known as a reflex movement. Not only are many of
these reflexes carried out without any help from the will, or brain, but
they are so prompt and powerful that the brain, or will, can hardly stop
them if it tries, as, for instance, in the case of tickling the feet.
You can, if you make up your mind to it, prevent yourself from either
wriggling, pulling your foot away, or giggling, when the sole of your
foot is tickled; but if you happen to be at all ticklish, it will take
all the determination you have to do it, and some children are utterly
unable to resist this impulse to squirm when tickled.

This extraordinary power of your reflexes has developed because only the
promptest possible response, by jerking your hand away or jumping, will
be quick enough to save your life in some accidents or emergencies, when
it would take entirely too long to telephone up to the brain and get its
decision before jumping. When you are badly frightened, you often jump
first and discover that you are frightened afterwards; and this jump,
under certain circumstances, may save your life. On the other hand, like
all instinctive or impulsive movements, it may get you into more trouble
than if you had kept still.

As you will see by the picture, the spinal nerves, which are given off
from the cord in the lower part of the neck and between the shoulder
blades, are gathered together into a great loose bundle to form the long
nerve-wires needed to supply the shoulders and arms. Those given off
from the small of the back just above the hips also run together to
form, first a network and then a big single nerve-cord, called the
sciatic nerve, which many of you have probably heard of from the
frightfully painful disease due to an inflammation of it, called
sciatica. It is the largest nerve-cord in the body, running down the
middle of the back of the thigh to supply the muscles of two-thirds of
the leg.[26]

The substance of both the spinal cord and the brain is made up of
millions of delicate, tiny cells, called neurons, most of which, with
very long branches, are arranged in chains for carrying messages,
forming the white matter; while the others lie in groups, or ganglia,
for sorting and deciding upon messages, forming the gray matter.

Just at the top of the spinal cord, where it passes into the skull and
joins with the brain, it swells out into a sort of knob, about the size
of a queen olive or the head of a gold-headed cane, which is known as
the medulla, or pith. This is the most vital single part of the
entire brain and nervous system; and the smallest direct injury to it
will produce instant death, partly because all the messages which pass
between the brain and the body have to go through it, and partly because
in it are situated the centres which control breathing and the beat of
the heart, and another quite important but less vital centre,--that for

How Messages are Received and Sent. Now to learn how smoothly and
beautifully this nerve telephone system of ours works, and how simple it
really is, although it has such a large number of lines and so many
telephones on each line, and such a large central exchange, let us see
how it deals with a message from the outside world. Suppose you are
running barefoot and step on a thorn. Instantly the tiny nerve bulbs in
the skin of the sole of your foot are stimulated, or set in vibration,
and they send these vibrations up the sciatic nerve, into and up the
whole length of the spinal cord, through the medulla, which switches
them over to the other side of the brain up through the brain stalk,
and out to the part of the surface (cortex) of the brain which controls
the movements of the foot. All this takes only a fraction of a second,
but it is not until the message reaches the brain-surface that you feel
pain. If you were to cut the sciatic nerve, or even tie a string tightly
around it, you could prick or burn the sole of your foot as much as you
pleased, and you would not feel any pain at all.

As soon as the surface of the brain has recognized the pain and where it
comes from, it promptly sends a return message back down the same cable,
though by different nerve-wires, to the muscles of the foot and leg,
saying, Jerk that foot away! As a matter of fact, this message will
arrive too late, for the centres in the spinal cord will already have
attended to this part of the matter, often almost before you know that
you are hurt.

However, there is plenty of other work for the brain to do; and its next
step, quicker than you can think, is to wake up a dozen muscles all over
the body with the order, Sit down! And you promptly sit down. At the
same time, the brain central has ordered the muscles of your arms and
hands to reach down and pick up the foot, partly to protect it from any
further scratch, and partly to pull the thorn out of it. Next it rushes
a hurry call to the muscles controlling your lungs and throat, and says,
Howl! and you howl accordingly. Another jab at the switchboard, and
the eyes are called up and ordered to weep, while at the same time the
muscles of the trunk of your body are set in rhythmic movement by
another message, and you rock yourself backward and forward.

This weeping and rocking yourself backward and forward and nursing your
foot seem rather foolish,--indeed you have perhaps often been told that
they are both foolish and babyish,--but, as you say, you can't help
it, and there is a good reason for it. The howl is a call for help; and
if the hurt were due to the bite of a wolf or a bear, or the cut had
gone deep enough to open an artery, this dreadfully unmusical noise
might be the means of saving your life; while the rocking backward and
forward and jerking yourself about would also send a message that you
needed help, supposing you were so badly hurt that you couldn't call
out, to anyone who happened to be within sight of you. So that it isn't
entirely babyish and foolish to howl and squirm about when you are
hurt--though it is manly to keep both within reasonable limits.

If the message about the thorn had been brought by your eyes,--in other
words, if you had seen it before you stepped on it,--then a similar but
much simpler and less painful reflex would have been carried out. The
image of the thorn would fall on the retina of the eye and through its
optic nerve the message would be flashed to the brain: There is
something slim and sharp in the path,--looks like a thorn. When this
message reached the brain, and not till then, would you see the thorn,
just as in the case of the pain message from the foot. Then the brain
would take charge of the situation just as before, flashing a hasty
message to the muscles of the legs, saying, Jump! while its message to
the throat and lungs, instead of Yell, would be merely, Say,
'Goodness!' or 'Whew!' and you would say it and run on.

If the thing in the grass, instead of a thorn, happened to be a snake,
and you heard it rustle, then the warning message would come through
your ears to the brain, and you would jump just the same; though, as it
is not so easy to tell by a hearing message exactly where the sound is
coming from, you might possibly jump in the wrong direction and land on
top of the danger.

This is the way in which you see, hear, and form ideas of things. Your
eye telegraphs to the brain the colors; your ear, the sounds; and your
nose, the smells of the particular object; and then your brain puts
these all together and compares them with its records of things that it
has seen before, which looked, or sounded, or smelt like that, and
decides what it is; and you say you see an apple, or you hear a
rooster crow, or you smell pies baking. Remember that, strange as it
may seem, you don't see an orange, for instance, but only a circular
patch of yellowness, which, when you had seen it before, and felt of it
with your hand, you found to be associated with a feeling of roundness
and solidness; and when you lifted it toward your nose, with the
well-known smell of orange-peel; so you called it an orange. If the
yellow patch were hard, instead of elastic, to the touch, and didn't
have any aromatic smell when you brought it up to your nose, you would
probably say it was a gourd, or an apple, or perhaps a yellow croquet
ball. This is the way in which, we say, our senses may deceive us, and
is one of the reasons why three different people who have seen something
happen will often differ so much in their accounts of it.

It is not so much that our senses deceive us, but that we draw the wrong
conclusions from the sights, sounds, and smells that they report to our
brains, usually from being in too great a hurry and not looking
carefully enough, or not waiting to check up what we see by touching,
hearing, or tasting the thing that we look at.

This message-and-answer system runs all through our body. For instance,
if we run fast, then the muscle cells in our legs burn up a good deal of
sugar-fuel, and throw the waste gas, or smoke, into the blood. This is
pumped by the heart all over the body, in a few seconds. When this
carbon dioxid reaches the breathing centre in the medulla, it stirs it
up to send promptly a message to the lungs to breathe faster and deeper,
while, at the same time, it calls upon the circulation centre close to
it, to stir up the heart and make it beat harder and faster, so as to
give the muscles more blood to work with. If some poisonous or very
irritating food is swallowed, as soon as it begins to hurt the cells
lining the stomach, these promptly telegraph to the vomiting centre in
the brain, we begin to feel sick at the stomach, the brain sends the
necessary directions to the great muscles of the abdomen and the
diaphragm, they squeeze down upon the stomach, and its contents are
promptly pumped back up the gullet and out through the mouth, thus
throwing up the poisons.

And so on all over the body--every tiniest region or organ in the body,
every square inch of the skin, has its special wire connecting it with
the great telephone exchange, enabling it to report danger, and to call
for help or assistance the moment it needs it.


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