Studies in the Osteopathic Sciences
Basic Principles: Volume 1
Louisa Burns, M.S., D.O., D.Sc.O.

Nerve Centers.
             These points have been called “centers” for the functions regulated through their intervention.  Physiologically, the term “center” is applied to a group of nerve cells wherein any function is regulated.  The use of the same term in reference to points upon the surface of the body is not defended, but the term has become so well fixed in usage that it is perhaps better to continue its use than to add another term for the same thing.

            These superficial centers are very closely related with the nerve centers, and owe their effectiveness to that relation.  The nerve centers control the activity of certain organs by coordinating the nerve impulses received from the sensory nerves of those organs, from other tissues associated with these in structure or function, and from higher centers in the brain.  The vaso-motor center, for example, is affected by sensory impulses from the heart, by sensory impulses from all over the body, by descending impulses from the basal ganglia, etc.

Regulation of Nerve Centers.

            The nerve cells of these centers are affected by changes in their environment, as are other living cells.  The respiratory center, for example, is stimulated by increasing venosity of the blood flowing through it; the heart center is affected in the same way.  Both of these centers are subject also to the stream of sensory impulses which are continually being carried to them.  All of the other nerve cells of the body are also affected by the quality of the blood flowing through them.

            The nerve centers are affected continually by the nerve impulses reaching them from all other parts of the body in structural relationship with them.  The action of the nerve centers, and therefore the action of the structures controlled by them, depends upon the character of the sensory impulses reaching the center.  In other words, the action of any given center represents the algebraic sum of the nerve impulses reaching that center.  If  we wish to affect any function, then, we may do so if we can affect the character of the nerve impulses reaching the group of nerve cells controlling that function.

            These groups of nerve cells are placed well within the nervous system, and inclosed in a bony case, hence any direct methods of affecting them are out of the question.  The pathway of impulses from the center to the structure innervated may be directly affected in many cases, as, for example, in the case of the vagus and phrenic nerves, the cervical sympathetic ganglia, and others.

            Since the nerve centers act in accordance with the algebraic sum of the impulses reaching them, it is possible for us to affect their action indirectly by changing the character of the impulses sent to them.  This is done by means of appropriate manipulations of certain superficial areas called centers, also.  Unfortunately, the term center is thus applied both to the group of nerve cells and to the superficial area which is in closest functional relationship with it.


Demonstration of Superficial Centers.

            These superficial centers were first recognized by clinical experience.  Afterward, they were demonstrated by experiments upon animals and persons.

            Clinical evidence has been somewhat inexact, as clinical evidence always must be, since patients nearly always suffer from so many and such complicated abnormal conditions.  In cases of long standing every abnormal effect is itself a cause of other abnormal conditions, and these in turn result in yet other malfunctions, and so on.  For this reason, the evidence afforded by observations upon patients has not been so satisfactory in isolating the individual centers as it has been in demonstrating the success of the therapeutic measures employed.


Areas of Hyperesthesia.

            The existence of hyperesthetic areas and of abnormal muscular contractions in the neighborhood of the roots of the nerves supplying organs of disordered function was first  a matter of clinical observation, and later a matter of experimental demonstration.  In clinical experience, the relief of the muscular contractions and of the hyperesthesias was found to be followed by some relief of the symptoms noted.  This relief was only temporary in some cases, but in acute disorders, and in cases wherein the muscular contraction was the chief factor in perpetuating the abnormal function, the relief secured by relieving the muscular tension and the hyperesethesia was permanent.  These cases, whether acute or chronic, and whether the relief were temporary or permanent, proved the existence of a central relationship between superficial areas and viscera.



            It was also found that slight malpositions of the ribs and vertebrae were usually found present in the neighborhood of the roots of the nerves supplying the affected organ.  The osteopathic conception of the relation of slight mal-positions of bones and articular structures to the malfunction and disease of the various tissues of the body was thus determined.  The fact that the correction of the mal-positions as found was followed by a decrease in the severity of the disease symptoms, and in many cases by either a symptomatic or an absolute recovery, established the relation of cause and effect beyond a reasonable doubt.


Physiology of Superficial Centers.

            The existence of the osteopathic or superficial centers depends upon the fact that all structures innervated from any segment of the spinal cord are affected by all sensory impulses reaching that segment.  Because of this physiological relationship, the viscero-sensory impulses initiate impulses to the skeletal muscles innervated from the same and adjoining segments of the cord, as well as to the viscera innervated from the same area.  Conversely, sensory impulses from the skeletal muscles and other somatic structures initiate changes in the impulses governing the functions of the visceral muscles and glands, as well as the reflex actions usually recognized.  This relation of the somato-visceral and the viscero-somatic reflexes underlies all the physiology of the osteopathic centers.


Structural Nerve Relations.

            The anatomy of the nervous structures concerned in these reflexes is fairly well known.  The axons of the sensory ganglia enter the spinal cord as its posterior roots.  After the Y-division both branches of the axon give off collaterals which penetrate the gray matter and form synapses with the neurons of the anterior, lateral and posterior horns, and of Clarke’s column.  According to Barker, probably every axon sends collaterals to every region of the same, and probably also to every region of adjoining spinal segments.  Thus the structure of the neurons is such as to facilitate the occurrence of both somato-visceral and viscero-somatic reflexes through every segment of the cord.  (Note A.)


Somatic Reflexes.

            The ordinary somatic segmental reflex actions are effected by impulses carried over the somato-sensory neurons either directly or by means of interpolated association neurons to the somato-motor cells of the anterior horns of the cord.  The axons of these  terinate upon the skeletal muscles.


Visceral Reflexes.

            The ordinary segmental visceral reflex actions are effected by impulses carried by the viscero-sensory neurons either directly or by means of interpolated association neurons to the viscero-motor cells of the lateral horns of the cord.  The axons of these cells terminate by forming synapses with the sympathetic neurons, and the axons of the sympathetic neurons terminate upon the visceral and vascular muscles, the glands, etc.  The cells of the lateral horns send their axons outward chiefly with the anterior roots.  It is these fibers which make up most of the white rami communicantes, the splanchnic nerves and the erigentes.  The visceral portion of the third cranial nerve, the vagus and those parts of other cranial nerves which are concerned in visceral activity arise from groups of nerve cells which are homologous with the lateral horn neurons, and, like the splanchnics, terminate around the cells of the peripheral sympathetic ganglia.  According to Howell, there is probably only one relay between the viscero-motor center in the spinal cord or sub-cerebral centers, and the destination of the nerve impulse.

            The viscero-somatic reflexes are effected by means of impulses carried by the viscero-sensory neurons either directly or by means of interpolated association neurons to the somato-motor neurons of the anterior horn, thence to the skeletal muscles.

            The somato-visceral reflexes are effected by means of impulses carried by the somato-sensory neurons either directly or by means of interpolated association neurons to the lateral horns of the cord, thence to the sympathetic ganglia, and thence to the viscera.

            These structural relationships are seen in slides from the various regions of the cord, medulla, pons, and mid-brain.  The functional relationships indicated by these structures have been demonstrated by experiments upon animals and persons, as well as by observations upon sick people.


Superficial Centers in Diagnosis.

            The superficial centers are of value in diagnosis, because the disorder of any visceral structure initiates a reflex muscular tension in the superficial center of that organ.  Both the visceral disorder and the abnormal muscular tension produced by it are a source of increased nerve impulses to that segment of the cord  This abnormal increase of nerve stimulation lowers the threshold of the neurons concerned.  Thereafter the receipt of normal impulses initiates extravagant reactions, both in consciousness and reflexly, because of the lowering of the neuron threshold.  For this reason, the existence of marked muscular tension and of areas of increased sensitiveness along the origin of the nerves to any viscus is evidence of some abnormality of the structure or the function of that viscus.


Superficial Centers in Therapeutics.

            In therapeutics, the same principle is concerned.  Since the visceral activity may be affected by sensory impulses reaching the segment of the cord from which it is innervated, then it is evident that abnormal impulses from abnormal conditions of skin, muscle, articular surfaces, or other structures may exert an abnormal influence upon the visceral activities.  This being true in any given instance, it follows that the removal of the cause of the abnormal sensory impulses, or the removal of that which interferes with the normal flow of sensory impulses, must exert a favorable effect upon the progress of the patient toward a normal condition, unless permanent structural changes have been caused by the persistence of the lesion.

            The therapeutic procedures are indicated by the diagnosis and the etiology.  Whether complete recovery will result from the removal of the original cause of the disease or not depends, it is evident, upon the nature and extent of the secondary changes which have been produced.  In cases of structural mal-adjustment of long standing, certain changes occur in the gross structures, and also in the habits of metabolism of the cells which have been subjected to abnormal conditions of innervation.  Absolute recovery, then, must be slow and uncertain.  The symptoms may often be greatly relieved, in these cases, even when absolute recovery is impossible.


Palliative Measures.

            In cases of acute illness, due to indiscretion, or to temporarily abnormal conditions of the environment, not associated with gross structural changes, it is sometimes possible to relieve the most annoying symptoms by manipulation of the center controlling the disturbed function.  This is merely a palliative measure, but it is a very effective one whenever it is indicated by the condition of the patient.  The efficiency of these measures depends upon the integrity of the neuron systems by means of which the reflex actions are effected.

 Note A.—(Figure 1)—“The outlines of the cord and of the gray matter in it, and of the sensory and sympathetic ganglia, are drawn to scale.  The size of the nerve cells is magnified and their arrangement is diagrammatic.  It would be impossible to secure in a single slide all of these relationships.
            “The fiber “A” is viscero-sensory.  The body of the cell is in the sensory ganglion ‘H.’  The peripheral prolongation, properly called a dendrite, is medullated.  It passes through the sympathetic ganglion ‘F,’ without making any physiological connection with the sympathetic neurons, so far as known, and is distributed with the sympathetic nerves.  These fibers retain their medullary sheaths until they reach the neighborhood of their termination in the viscera.  ‘B’ is a viscero-motor fiber, the axon of a cell in the lateral horn ‘O’ of the spinal cord.  These fibers form the greater part of the white rami communicantes, and they usually pass through one or more ganglia before forming a synapsis with sympathetic neurons.  These fibers are medullated until they reach the ganglion of their termination.  ‘C’ is a viscero-motor fiber, the axon of a cell in the sympathetic ganglion ‘F.’  These fibers are not medullated, usually, and the medullary sheath is extremely thin in the very few instances where it is found at all.  Impulses carried over these fibers are derived from the lateral horn.   “The lateral horn of the spinal cord ‘O’ should be considered as part of the autonomic nervous system, of which the sympathetic nerves also are a part.  The nerve cells of the lateral horn of the cord are smaller than those of the anterior horn, and the axons of these cells are finer.  The axons terminate by forming synapses with sympathetic neurons.  The cells of the lateral horn of the cord receive impulses from several sources, -- from cells in the posterior horn ‘K,’ from cells of the spinal ganglion ‘H,’ by collaterals from their axons ‘L,’ from the red nucleus by way of the rubro-spinal tract ‘X,’ from the vasomotor and other centers in the medulla, and perhaps from other sources.  Impulses are carried to the lateral  horn only from sensory nerves and from centers which coordinate sensory impulses.

            “Probably all the sensory nerves entering the cord send collaterals to the lateral horn of the same spinal segment.  Normally, the sensory impulses carried to the cells of the lateral horn are just sufficient to initiate the viscero-motor impulses necessary to the normal action of the visceral and vascular muscles and the glands of the body.  If these impulses are deficient,--as, for example, if the threshold values of the neurons concerned should be abnormally high,--the outgoing impulses are deficient.  Any abnormal stimulation of the sensory nerves initiates abnormal stimulation of the cells in the lateral horn, and through these, of the sympathetic nerves.  This abnormal stimulation may be received through viscero-sensory nerves as is the case in the presence of indigestible food, etc., or it may be derived from abnormally contracted muscles, from joint structures held in abnormal tension, as in subluxations, or, rarely, from the skin itself.

            “Since collaterals from the sensory axons pass also to cells of the anterior horn, abnormal viscero-sensory impulses may initiate the abnormal contraction of the spinal muscles.  This tension may in time bring about mal-position of the vertebrae.  Both the muscular tension and the mal-position may in turn initiate abnormal sensory impulses which stimulate the cells of the lateral horn in an abnormal manner.  This reflex muscular tension and the exaggeration of the viscero-motor impulses thus produced are of great value to the body under slightly abnormal conditions, but are a source of great misery if the visceral abnormality be continued.  The effects produced from this long-continued muscular tension are probably not to be distinguished from those resulting from accidental structural mal-adjustments of long standing.” -- From “How Osteopathic Lesions Affect Eye Tissues,” The Journal of The American Osteopathic Association, March, 1907.


                Sensory Visceral Areas, in Morat’s “Physiology of the Nervous System,” p. 154, Edition of 1906.

                Chapter XXVII, in “The Nervous System,” by L. F. Barker.