Edited 3-19-09 Subluxations of the vertebrae can and do occur, and that as
a result of this displacement sufficient pressure is brought
to bear upon the nerves passing through the intervertebral
foramina, by the displaced margins of the foramina, to seriously
impair their function.
We will consider the manner in
which this disturbance of the functional activity is brought
about.
The Function of the Nervous System. — By virtue of its
continuity the nervous system puts into connection all the
other systems of the body. Its branches form pathways over
which nerve-impulses pass from the brain to every part of the
body, and from the periphery to the brain. All incoming im-
pulses must react in the central nervous system. It is a fact
of the utmost importance that until the incoming impulses
have reached the brain and spinal cord, they do not give rise
to the outgoing impulses. It must be remembered that nearly
all outgoing impulses are generated as a result of stimulation
of the cerebral or spinal centres by an incoming impulse.
For example, the sight of food excites an afferent impulse to
the brain which in turn excites an efferent impulse in the
cerebral centres which send nerve-fibres to the salivary glands,
and a flow of saliva results. In like manner every action per-
formed by any part of the body is produced as a result of an
outgoing impulse which was generated in the brain or spinal
cord in response to an impulse from the periphery.
By means of the central nervous system reactions are
established in parts of the body not directly affected by the
changing external conditions. In this way harmony between
the activities of the various systems of the body is maintained.
Also the body as a whole, in relation to all things outside it
and forming its environment, is under the guidance of the
nervous system.
The Conduction Process. — In order to appreciate properly
the effects of pressure upon the nerve we must first look into
the nature of the transmission of impulses along the nerves,
namely the conduction process. Many views have been ad-
vanced as to the nature of the conduction process among
which are, that the whole nerve moves like a bell-rope; that
the nerve is a tube and a biting acid flows through it; that
the nerve contains a fluid which moves in waves ; that it con-
ducts an electric current like a wire; that it is composed of
definitely arranged electro-motor molecules which exert an
electro-dynamic influence on each other ; that it is made up of
chemical particles each of which excites its neighbor; lastly,
that the molecules of the nerve-substance undergo a form of
vibration like that of light.
None of these theories has been proven as the only cor-
rect one, and it is likely that the conduction process is simply
a property of the living substance of the cell. It is a state of
activity which spreads like a wave in all directions through
the living substance. It is markedly changed by chemical
and physical influences. Protoplasmic continuity is absolutely
essential to conduction. Hence, as will be shown further on,
any pressure upon the nerve which breaks this protoplasmic
continuity impedes the transmission of impulses along that
nerve.
The Nerve-impulse. — The neurones form pathways along
which nerve-impulses travel. It is through the power of con-
ductivity possessed by the neurones that the impulses travel
along the nerves. The impulses which arrive at the cell-
body produce there chemical changes. These changes, when
they reach a given volume, cause a nerve-impulse which
leaves the cell-body by way of the axone.
As will be pointed out, the impulses travel either toward
the central system, or from it. The former class of impulses
are called afferent, and by means of them the proper relation-
ship of all parts of the body, individually and collectively, to
their environment is maintained. The latter class of impulses
are known as efferent, and it is through them that the func-
tional activity and organic integrity of every part of the body
are governed and maintained.
The amount of nerve influence generated by the brain
must always be commensurate with the amount of work re-
quired of the parts supplied by the nerves. This is excellently
illustrated by the following: We have the power of de-
termining beforehand the amount of nervous influence neces-
sary for the production of a certain degree of movement. Thus
when we lift a vessel, the force which we employ in lifting it
depends upon the idea which we have formed of its contents,
when we are not certain what it contains. If it should, there-
fore, contain something much lighter than we had estimated,
useless force would be expended, and it would be lifted with
exceptional ease ; but if it contain something much heavier
than we had anticipated, we would very likely drop it, because
insufificient force was expended to accomplish the end de-
sired in Roxborough Chiropractors
Just as the response of muscles is proportionate to the
amount of nerve-force received by them, so also are the
functional activities of all parts of the body dependent on the
amount or strength of the nerve-impulses received by them.
If, therefore, anything interferes with the power of conduc-
tion of the nerve, the impulses which it normally conveys to
the parts which it supplies are not forthcoming, and these
parts will suffer. There will be either functional derange-
ment, or changes in its structure.
Irritability of Nerves. — Irritability is that property of liv-
ing protoplasm which causes it to undergo characteristic
physical and chemical changes when it is subjected to cer-
tain influences, called irritants. The term irritants, when
speaking of nerves includes anything which causes the nerve-
cell to send an impulse along its branches. The irritability
of cell-protoplasm is very dependent upon its physical and
chemical constitution, and even slight alterations of this con-
stitution, such as may be induced by mechanical conditions,
may modify the finely-adjusted molecular structure upon
which the normal response to irritants depends.
Without going into this subject in detail, the fact must be
stated that, when a nerve is experimentally subjected to slight
pressure, it is found that it will not conduct impulses ; when
the pressure is removed, it again conducts the impulses. A
frog in which the sciatic nerve and gastrocnemius muscle
are dissected and prepared, and then connected with an elec-
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trie current, will show this. When the nerve is stimulated
by the current, contractions of the muscle occur; when pres-
sure is brought to bear upon the nerve, the muscular con-
tractions cease ; when the pressure is removed and the nerve
again electrically excited, the contractions of the muscle again
occur. This proves conclusively that the pressure which was
applied prevented the conduction of the impulses, for it is
the nervous impulses that caused the muscle to contract. It
also shows and demonstrates another important fact, namely,
that sufficient pressure may be applied to a nerve to prevent
it from conducting impulses without destroying the nerve
itself, because, in the experiments mentioned, as soon as the
pressure was removed, the muscular contractions again oc-
curred.
The Effect of Pressure upon a Nerve. — In a future chapter
the effects of vertebral subluxations are given in detail, but
the physiological efTect of pressure on nerves in general must
be considered at this time.
The effect of pressure to lessen the conduction power of
nerves is one which everyone may demonstrate upon himself.
For example, if pressure be brought to bear on the ulnar
nerve where it crosses the elbow, the region supplied by the
nerve becomes numb, "goes to sleep," as it were.
In like manner, mechanical applications to nerves first
increase and later destroy their irritability. Thus pressure
gradually applied first increases and later reduces the power
to respond to irritants.
As stated above, sufficient pressure may be applied to a
nerve to destroy its irritability and conductivity without in-
juring the nerve itself structurally. Such pressure is exer-
cised upon the nerves passing through the intervertebral for-
amina by the displaced margins of the foramen when a ver-
tebra is subluxated. The pressure does not crush or otherwise
injure the nerve, but it is sufficient to block the impulses
which pass along that nerve. As a result, the organs which
are deprived of these impulses undergo functional or organic
aberrations, and disease results in the part supplied. The
nature of the disease depends upon other contributory factors
which may be present at the time of the subluxation, or may
appear later. In any event the subluxation, by promoting
conditions in the organ which make disease possible in that
organ, are the primary cause of that disease.
For example, a subluxation is produced in the lower dorsal
or upper lumbar region of the vertebral column ; no untoward
effects may follow at once. But years later, perhaps, the in-
dividual develops typhoid fever. The reason that this occurs
is simply that the intestines which are the atrium of the in-
fection in this disease are in such a state of diminished re-
sistance that they form a favorable culture-medium for the
multiplication of the typhoid bacilli and the elaboration of
their toxins. It is for this reason that the fever subsides so
rapidly when these subluxations are corrected — because the
elaboration of the toxins, which are the cause of the fever,
is arrested, favorable conditions for the activity of the bacilli
having been eliminated.
The Effect of Blood-supply on Nerves. — In addition to the
direct effect of pressure upon the nerves, owing to a subluxa-
tion, there is also an indirect effect, as a result of the occlusion
of the blood-vessels which pass through the intervertebral
foramen.
The nerve-fibre requires a constant supply of blood for
the maintenance of its irritability. The irritability of the
nerve cannot long continue without oxygen, and a nerve which
has been removed from the body is found to remain irritable
longer in oxygen than in air, and in air than in an atmosphere
which contains no oxygen.
It will be learned further on that one of the effects of
a subluxation is pressure upon the arteries and veins. These
arteries supply the structures of the corresponding segment
of the spine with nourishment, and the veins carry away the
waste materials. When the circulation of the blood is im-
peded, there will consequently be an impoverishment of the
nerves, and an accumulation of waste materials, both of which
have a deleterious effect on the nerves.
Another function of the blood in respect to the nerves
is that it distributes heat. A nerve which is deprived of this
heat loses its power of irritability and conductivity. This
can be demonstrated by dipping the elbow in ice-water, and
allowing it to remain there until the cold has had time to
penetrate ; at first there will be pain, but as the effect of the
cold becomes greater, the pain is replaced by numbness,
both the irritability and power of conduction of the nerve
being reduced.
In like manner obstruction of the arteries passing through
the intervertebral foramina, by pressure upon them of the
displaced margins of the foramen, diminish the blood-supply
to the nerves, and hence the heat which the blood normally
conveys to them. Impulses to be transmitted by that nerve
will accordingly be impeded, or fail to reach their destination,
and disorders in the parts thus deprived of their necessary
nerve-control will follow.
Further, the blood has the power to neutralize the acids
which are produced by the cells during action, and so main-
tain the alkalinity essential to the life and activity of the
cell; also, by virtue of the salts which it contains it secures
the osmotic relations which are necessary to the preserva-
tion of the normal chemical constitution of the protoplasm
of the nerve.
The irritability of nerve protoplasm is markedly influenced
by even slight changes in its constitution. If, experimentally,
a nerve be allowed to lie in a liquid of a different composition
from its own fluid, and especially if such a liquid be injected
into its blood-vessels, an interchange of materials takes place
which results in an alteration of the tissue and a change of its
irritability.
If, therefore, the venous flow is obstructed, the acid waste
materials of the activities of nerves remain within them, and
a change in the constitution of their protoplasm impairs their
irritability and conductivity. This effect the pressure of the
displaced margins of an intervertebral foramen produces by
obstructing the circulation of the blood in the veins which
it transmits.
The Effects of Lymphatics on Nerves. — The last of the
physiological effects resulting from a subluxation of a verte-
bra with consequent narrowing of the corresponding inter-
vertebral foramen is the influence which it exercises upon
the lymphatics, and their effect on the nerves which they
supply.
The lymphatics which pass through the intervertebral
foramina have much to do with the metabolism of each seg-
ment of the spinal cord. If the nutrition of a certain segment
is faulty as a result of an insufficient supply of lymph, the
reflex excitability of that segment will be diminished. Con-
sequently any incoming impulses to that segment will not
result in a reflex action with the production of an outgoing
impulse, and the tissues thus deprived of these necessary
impulses will fail to function properly.
