Studies in the Osteopathic
The Nerve Centers: Volume
Louisa Burns, M.S., D.O., D.Sc.O.
THE SPINAL CENTERS
The spinal cord is to be considered in regard to two chief functions.
From the standpoint of the lower vertebrates, the spinal cord is chiefly
a series of neuron groups, which are centers for the control of all of
the skeletal and visceral structures of the corresponding segment.
Later development shows a progressive development of long tracts.
These long tracts serve several purposes, all concerned in increasing the
efficiency of the central nervous system in its duties in unifying the
parts of the body. The long tracts may be afferent, in which case
they supply the higher centers with the nerve impulses needful in their
functions; or they may be efferent, in which case they carry to the spinal
centers the impulses sent out from the higher centers in answer to the
action of the impulses transmitted by the afferent tracts; or they may
be associational, in which case they enable the different centers, both
in the cord and in certain of the higher centers, to act in unity.
The spinal centers have retained in great degree their original functions
in controlling the structures of the corresponding segments of the body,
through all the great development of the long tracts.
spinal centers are not to be considered, with their present development,
at least, to be separate and distinct from an anatomical standpoint.
It is not possible to select from the cells of the cord the exact groups
concerned in any reaction. It is not possible, at present, to say
certainly whether the same nerve cell or group of cells may be concerned
in the coordination of the nerve impulses of more than one different function.
There are no facts of interest in this connection except the symptoms produced
by certain degenerative processes in the cord, and the results of these
observations are, so far, very contradictory.
is not possible to determine the exact extent of any nerve center.
For if any center should extend through several segments of the cord, or
if it should be very limited in extent, but should receive axons or collaterals
from the sensory roots of several segments, the relations would be identical
from a functional standpoint.
the symptoms observed in cases of disease following injury to the cells
in the gray matter of the cord, it appears that the viscero-motor centers
extend through several segments of the cord. Yet it is possible that
they merely receive association fibers from several adjacent segments.
It is possible, then, only to locate these centers rather vaguely—that
is to say, that any one is found between a certain spinal segment and another
lower spinal segment.
The Spinal Cord
spinal cord includes that part of the central nervous system which lies
within the vertebral canal. Its uppermost extremity is marked by
the lower limit of the decussation of the pyramids, and by the uppermost
fibers of the origin of the first cervical nerve. It terminates at
the lower border of the first lumbar vertebra. The entire length
of the cord is about seventeen or eighteen inches, according to the varying
heights of individuals.
the limit of the cord lies an extension continuous with it, the filum
terminale. This resembles the cord for a short distance; it contains
fibers and gray matter resembling embryonic nerve tissues. Vestiges
of the coccygeal nerve roots are sometimes to be found. The filum
terminale reaches down into the sacral region, where it terminates by becoming
continuous with the connective tissue cord formed from the rudimentary
meninges, and is attached to the sacrum.
spinal cord varies in diameter in different regions; it is a little more
than a half inch in its largest diameter, and a little less than a half
inch in its smallest diameter. Its weight is about one and one-half
form the spinal cord is an irregular cylinder. It presents two swellings.
The upper of these is called the cervical enlargement, which corresponds
to the area of origin of the nerve roots which supply the arms and shoulder
girdle. The lower is the lumbar enlargement, which gives rise to
those nerves which supply the pelvic girdle and the legs.
spinal cord contains at its approximate center a canal called the sixth
ventricle, or the neural canal, or the central canal of the cord.
It is lined with epithelium, which is ciliated in the embryo.
The Spinal Gray Matter
gray matter of the cord surrounds this central canal. It is arranged
in the form of a very irregular H, whose arms vary in length and breadth
in the different areas of the cord. Throughout the thoracic region,
and to slight extent in certain other regions, there is found a slight
swelling upon the central part of each lateral arm of the H-shaped gray
matter. This is called, when present, the lateral horn of the cord.
(Figs. 35, 36, 37.)
part of the gray matter which extends forward is called the anterior horn,
that which extends backward is called the posterior horn.
anterior horn includes two classes of cells. The large multipolar
cells, which are so conspicuous a feature in cord sections, are the motor
cells of the first order; their axons pass by way of the anterior roots
to the skeletal muscles and carry the nerve impulses which cause the movements
of the skeleton. (Fig. 44.) Associated
closely with these cells are others, smaller and also multipolar, whose
axons branch very freely close to the cell, and do not leave the gray matter.
These cells (Golgi Type II) are functional in assisting in the coordination
and transmission of impulses concerned in reflex actions.
cells of the lateral horn send axons by way of the anterior roots and the
white rami communicantes to the sympathetic ganglia. They carry impulses
which are concerned in the control of the viscera and the blood vessels.
(Figs. 39, 40, 41, 45.)
posterior horn includes cells of several functions. In this part
of the gray matter are found cells whose axons terminate by branching among
the cells of the other parts of the gray matter. These are associational
in function. Others of the posterior cells send axons upward and
downward through the gray matter or through the tracts of white matter
at the edge of the gray, to upper or lower segments. They terminate
by entering the cord and forming synapses with different cells at that
nucleus dorsalis (Clarke’s column) is found only in the thoracic cord.
It sends axons by way of the anterior ascending cerebello-spinal tract
and by way of the posterior ascending cerebello-spinal tract to the cortex
of the superior vermis of the cerebellum, or to its central nuclei.
This tract carries the impulses concerned in muscular sense. Axons
from this column of cells probably make up the spino-thalamic tract, which
carries impulses concerned in pain and the temperature sense to the optic
white matter of the cord is composed of ascending, descending, and mixed
The descending tracts are as follows:
The direct pyramidal tract extends from the medulla to the mid-dorsal region.
It terminates by forming synapses with the cells in the central region
of the opposite spinal crescent. It is composed of axons of the large
pyramidal cells of the precentral convolutions of the same side of the
cerebral cortex, and it carries impulses concerned in the voluntary movements
of the arms and shoulder muscles.
42. Control of the brachial circulation. Anterior root;
Anterior horn; Sensory cell; Sensory; Axon; Posterior root; Gray fiber;
Sympathetic; Cell; White fiber; Anterior root; Anterior horn; Lateral horn;
Sensory; Cell; Sensory; Axon.
The crossed pyramidal tract extends through the entire length of the cord.
It terminates by forming synapses with the cells of the gray matter of
the central part of the crescent of the same side. The tract is composed
of the axons of the large pyramidal cells of the precentral convolution
of the opposite side of the cerebral cortex, and it carries the impulses
concerned in the voluntary movements of the lower part of the body.
The rubro-spinal tract extends through the length of the cord. It
is composed of fibers which are axons of the cells of the red nucleus,
and probably the substantia nigra and the sub-thalamic region, and it terminates
by forming synapses with the cells of the lateral horns and the central
gray matter. Perhaps the fibers may pass in part to the anterior
horns directly, but this is not certainly known. This tract carries
impulses concerned in the emotional and instinctive movements of the skeletal
muscles, and in the visceral activities associated with emotional states.
The anterior longitudinal bundle (tecto-spinal tract) extends through the
length of the cord. Its fibers are axons of cells in the colliculi,
and it terminates with the pyramidal fibers. It is supposed to be
concerned in maintenance of the muscular tone, and certainly transmits
impulses functional in the coordination of those reflex movements associated
with sights and sounds.
The olivo-spinal tract is not well known. Its fibers are the axons
of cells in the inferior olive, and the impulses are supposed to be concerned
in the coordination of the more complex movements of the body. It
is closely related to the cerebellum in function.
The ponto-spinal tracts extend the length of the cord. They are composed
of the axons of cells in the reticulum of the pons, which are distributed
to the gray matter with the pyramidal tracts. The impulses carried
by these tracts are probably concerned in the coordination of the muscular
movements and in the maintenance of the tone of the skeletal muscles.
The lateral ponto-spinal tract is decussated, the medial tract is not decussated.
The vestibulo-spinal tract has its origin in the vetibular nuclei.
It is rudimentary structure in the higher vertebrates, but represents a
connection of great importance in fishes. It forms synapses either
with the anterior horn cells, or with cells closely related to these.
The impulses carried by this tract are concerned in the maintenance of
muscular tone, and the coordination of the movements associated with equilibrium.
The descending cerebello-spinal tract extends through the length of the
cord. Its fibers terminate by forming synapses with the cells of
different regions of the gray matter of the cord at different levels.
Its fibers are axons from the cerebellum. It is not known whether
they are axons of the Purkinje cells or of the cells of the dentate nucleus.
The impulses carried by this tract are concerned in maintaining the tone
of both skeletal and visceral muscles, and in securing the coordinate activity
of the skeletal muscles, especially those concerned in equilibrium.
It is not known whether these impulses are greatly concerned in the visceral
activities or not. The phylogenetic history of the relations seems
to indicate the possibility that this function may be included.
The comma tract, though a descending tract, is derived from the sensory
neurons. The entering axons of the sensory neurons divide into two
branches, the shorter of which passes downward in the posterior funiculi
for a distance of one or two spinal segments, and terminates by forming
synapses with the cells of the lower levels. The impulses thus transmitted
are probably concerned in the more complex reflexes, and in securing more
perfect coordination of the movements of the skeletal and visceral muscles.
The ascending tracts of the cord include the following:
The fasciculus gracilis (tract or column of Goll) lies near the posterior
median septum. It is composed chiefly of the axons of the sensory
ganglion cells, and a smaller number of axons from the posterior horn cells
from below the mid-dorsal region. The fibers pass to the nucleus
gracilis in the medulla, where they terminate by forming synapses with
the cells of that nucleus. A few fibers of this tract pass directly
to the cerebellum by way of the restiform body.
The fasciculus cuneatus (tract or column of Burdach) is composed chiefly
of the axons of the cells of the sensory ganglia, and partly of a smaller
number of axons of cells of the posterior horns. These fibers pass
upward to the nucleus cuneatus in the medulla, and form synapses with the
cells of that nucleus. A few of the fibers of this tract pass directly
into the restiform body and into the cerebellum.
There is some reason to consider the existence of a long sensory tract
situated in the posterior gray commissure of the cord. This has been
called Ciaglinski’s tract. Its relations are not known.
The anterior ascendidng cerebello-spinal tract (Gower’s tract) is composed
of axons of the cells of the dorsal nucleus, chiefly of the opposite side.
With it are carried the fibers of the spino-thalamic tract, which have
the same origin. These tracts pass together into the region of the
brachium conjunctivum, where the cerebellar part of the tract turns backward
to enter the cerebellum, while the spino-thalamic tract passes onward to
the optic thalamus.
The posterior ascending cerebello-spinal tract (direct cerebellar) is composed
of axons of the cells of the dorsal nucleus, chiefly of the same side.
These fibers pass by way of the restiform body to the cerebellum, where
they terminate either in the cortex of the superior vermis, or in the central
gray matter of the cerebellum, by which the impulses are transmitted to
the cortex of the superior vermis.
The median longitudinal bundle is composed of axons of the cells of the
anterior horns, and it terminates in the cranial nerve nuclei and the thalamus.
It is concerned in the more complex reflex actions.
The antero-lateral fasciculus proprius lies next to the anterior horn on
its lateral aspect. Its fibers are from the cells of the gray matter,
and they pass both upward and downward, thus connecting the different levels
of the same side of the cord.
The antero-median fasciculus proprius lies next to the anterior horn on
its central aspect. Its fibers pass both upward and downward to a
certain extent, but chiefly they decussate in this passing, so that these
fibers are concerned in connecting the contra-lateral segments of gray
matter, both of the same and of neighboring levels. Within this tract
lies the median longitudinal bundle.
The posterior fasciculus proprius is made of axons which connect the different
levels of the cord. They are mostly short fibers, only a few segments
in length. The cornu-commissural tract is the postero-lateral bundle
of fibers, which include also fibers concerned in connecting the contra-lateral
gray matter, as well as the different homolateral levels of the cord.
The Upper Cervical Group
of the upper cervical cord lie within the gray matter of the first, second,
third and fourth cervical segments. The gray matter of this portion
of the cord presents certain peculiarities.
segments occupy the upper part of the cervical enlargement. The posterior
horn is capped by the substantia gelatinosa, among whose cells the descending
branches of the fifth cranial nerve terminate. The ophthalmic division
of the fifth supplies this region especially freely.
nucleus dorsalis (Clarke’s column) is wanting. The intermedio-lateral
cell group (lateral horn) is displaced anteriorly, probably because of
the development of somatic functions and relations on the part of the cells
whose axons make up the spinal part of the eleventh cranial nerve, and
of those whose axons make up the phrenic nerve. The trapezius and
the sterno-mastoid are innervated by the eleventh cranial, and the diaphragm
by the phrenic. These muscles are especially subject to abnormal
reflex contractions as the result of excessive viscero-sensory impulses
from viscera, which are affected by pathological conditions.
anterior horn is large and broad. It includes several groups of cells.
The mesial cell column is homologous with a similar group of cells through
the whole extent of the cord, and it innervates the trunk muscles; in the
case of the upper cervical group, the superior and inferior oblique, the
rectus capitis posticus major and minor, the complexus and trachelo-mastoid,
the splenius and semispinalis, the multifidus spinae, the transversalis
cervicalis, cervicalis ascendens, by the posterior primary divisions, the
splenius, platysma, scalene, longus colli, rectus capitis anticus major
and minor, rectus capitus lateralis, and the sterno-mastoid in part by
the anterior primary divisions. The hyoid muscles also are innervated
from these segments, probably from a small cell group in the antero-lateral
cell groups are intricately associated with the cell groups of the posterior
horns, and with the gray matter of neighboring segments. The muscles
named above are thus affected by many of the sensory impulses reaching
the segments. They are found abnormally contracted in many disorders
of viscera, limb structures, and cranial structures.
antero-lateral cell group is not represented in the thoracic cord, but
is well marked in the upper and lower cervicals; the axons of these cells
innervate the limb muscles. These cell groups seem to represent a
later phylogenetic development than the antero-mesial group; they are larger
cells, have long axons, and are poorly associated with the other cell groups
of the gray matter. This is, no doubt, the reason why the visceral
reflexes have so little effect upon the limb muscles, though they are not
altogether free from visceral reflexes, as is commonly supposed.
They are very well supplied with association fibers from the sensory neurons
innervating the limb muscles, skin and joint surfaces. The muscles
innervated by the anterior lateral group are, Levator scapulae, teres major
and minor, supraspinatus, and rhomboid.
somatic sensory cells of this group lie in the ganglia on the posterior
roots of the corresponding nerves. The dendrites of these cells are
distributed as follows:
over the back of the neck and the head to the vertex, including the mastoid
process and part of the ear; the skin of the neck as far upward as the
lower line of the mandible; the muscles innervated by the motor neurons
of the same segments; the articular surfaces of the first, second, third,
fourth and fifth vertebrae; and the sterno-clavicular and the acromio-clavicular
articulations; the meninges of the corresponding spinal segments.
viscero-sensory neurons are found in these segments, but the viscero-sensory
neurons of the fifth, eighth, ninth and tenth cranial nerves send collaterals
and terminals to these segments. The sensory portion of the seventh
is not known to send fibers to the cervical cord.
efferent impulses from these centers are influenced by both inhibiting
and stimulating impulses from the following sources:
The impulses from the skin, muscles and joint surfaces innervated by the
somatic sensory neurons of the same segments affect the efferent impulses
from these centers. By this relation the direct reflexes are governed.
Under slightly abnormal conditions, such as slight malpositions of the
articular surfaces mentioned, the contraction of the muscles may become
excessive and constant, and these reflex muscular contractions may in turn
send in sensory impulses which increase or decrease the abnormal position
of the structural tissues, and the stream of sensory impulses may be further
Impulses from the sensory nuclei of the fifth, eighth, ninth and tenth
cranial nerves are carried to the upper cervical centers. By this
relationship abnormal conditions in the area of distribution of these nerves
may cause excessive contractions of the muscles innervated by the upper
cervical segments. Thus are produced the tension of these muscles
during toothache, or gastritis, or pharyngitis, or otitis media, or conjunctivitis,
Impulses from the nucleus gracilis and nucleus cuneatus reach the upper
cervical segments. At a result of this relationship abnormal sensory
impulses from diseased viscera may cause abnormal tension of the upper
cervical muscles. The tension of the upper cervical muscles so often
found associated with diseased pelvic or abdominal organs is thus produced.
Impulses from the cerebellum, the vestibular nuclei, the quadrigeminates,
and probably the nuclei of the pontine reticulum, reach the nuclei of the
upper cervical segments. By this means the movements of the upper
cervical muscles are coordinated, and their normal tone is maintained.
The fibers of the direct pyramidal tract form synapses with the cells of
the lateral cell mass of the opposite side, and these in turn send axons
to the large motor cells of the anterior horn. Thus the impulses
from the precentral cerebral convolution are enabled to carry the impulses
concerned in the volitional control of the upper cervical muscles.
The rubro-spinal tract carries impulses from the red nucleus and the neighboring
basal ganglia to these segments. By this means the upper cervical
muscles are brought under the control of the emotional impulses.
Descending impulses from the viscero-motor centers in the medulla reach
the upper cervical segments. By this means the movements of the diaphragm,
scaleni, etc., in respiration, and in the modified respiratory movements,
as coughing, sneezing, the respiratory factors in speech, etc., are controlled;
the diaphragmatic movements in vomiting, defecation, and similar actions
Lower Cervical Group
This group of centers includes those situated in the fifth, sixth, seventh
and eighth cervical segments, and the first thoracic segment of the
cord. The gray matter in these segments presents certain peculiarities.
The segments named include the lower part of the cervical enlargement.
posterior horn is capped by the substantia gelatinosa. In this region
it is less conspicuous than in the upper cervical group, and it contains
fewer nerve cells. There is a difference among neurologists concerning
the place of the descending fibers of the fifth; by some authors it is
given as reaching as low as the sixth cervical segment, while others consider
the evidence insufficient to show fifth-nerve fibers below the second cervical
segment. Reflexes initiated by the stimulation of the fifth nerve
affect the action of the centers of the cord as low as the upper thoracic
segment, but this may be due to the existence of closely-related association
neurons. The lower cervical group evidently receives impulses from
the fifth, whether by direct fiber paths or by means of interpolated neurons
is not yet apparent.
nucleus dorsalis (Clarke’s column) is found only in the seventh cervical
and first thoracic segments. The viscero-motor column is scarcely
to be found. A few fibers enter the phrenic from the upper part of
the group, and a few assist in forming the spinal portion of the eleventh
cranial nerve. Otherwise the column is not represented. The
significance of these nerves is discussed in connection with the upper
first thoracic and perhaps the seventh cervical segments contain a few
cells of the cilio-spinal center.
anterior horns of this region are broad and large. The cells are
arranged in groups, part of which are placed mesially and a part of which
are placed laterally.
mesial group is homologous with a similar column of cells through the extent
of the cord. Its fibers innervate the muscles of the trunk, including
the semispinalis and multifidus spinae, the trachelomastoid, scaleni, longus
colli, cervicalis ascendans, transversalis cervicis, complexus, and splenius.
The cells in this group represent the older structure, phylogenetically,
than the lateral group of cells; their central relations are complex, and
they receive impulses from many sources, viscero-sensory, somatic sensory,
and descending. The muscles named as being innervated from these
cells are, therefore, subject to abnormal contractions as the result of
excessive stimulation of the centers from other structures. It is
especially noted that these contractions follow visceral disturbances of
the cervical and cranial regions, as well as in the upper thorax.
lateral group of cells includes several groups, whose exact functions have
not been certainly worked out. This column is not found in the thoracic
region of the cord. Its cells send axons which innervate the muscles
of the shoulder girdle and the arms, including the following:
major and minor, supraspinatus and infraspinatus, rhomboid, anconeus, subscapularis,
serratus magnus, pectoralis major and minor, coracobrachialis, deltoid,
biceps, triceps, brachialis anticus, supinators longus and brevis, latissimus
dorsi, the pronators, extensors and flexors of the wrists and fingers,
the lumbricales and interossei, and the thenar and palmar muscles.
cell groups represent the newer structure, phylogenetically; their central
connections are not very freely associated with other cell groups, and
the muscles named are not especially subject to abnormal contractions from
sensory stimulations in other parts of the body.
somatic sensory cells lie in the sensory ganglia on the corresponding posterior
roots. Their dendrites are distributed to the following structures:
over the arms, hands and fingers, and a small area over the anterior and
posterior aspect of the thorax, innervated by the first thoracic nerve.
muscles innervated by the motor neurons of the same segments.
articular surfaces of the fifth, sixth and seventh cervical and the first
thoracic vertebrae, the clavicle, the first costo-sternal, the scapula,
the humerus, radius and ulna, and all the articulations of the wrist, hands
meninges of the corresponding spinal segments.
viscero-sensory neurons are found in these segments, and the only sources
of viscero-sensory impulses is by way of the descending fibers of the cranial
nerves, and the association neurons of the thoracic segments.
efferent impulses from these centers are affected by both stimulatory and
inhibitory impulses from the following sources:
The somatic sensory impulses from the skin, articular surfaces, and muscles
innervated from these segments affect the efferent impulses through simple
and complex reflex action. Under slightly abnormal conditions, such
as malpositions of the articular surfaces, or skin lesions, the contractions
of the muscles may become constant and excessive. These muscular
contractions may also affect efferent impulses. Since the structures
innervated from the brachial plexus are phylogenetically of comparatively
recent origin, the central associations are comparatively less complex
and the reflexes are less severe and less frequent than in the case of
certain other structures.
Impulses from the cerebellum, the vestibular nucleus, the olive, the quadrigeminates,
and probably the nuclei of the pontine reticulum, reach the lower cervical
segments by way of the tracts named after their origin. By these
connections the normal tone of the muscles innervated from the brachial
plexus are maintained, and their movements are coordinated.
Fibers from the direct pyramidal tract of the cord form synapses with the
cells of the opposite side of the cord. By this means the voluntary
impulses from the precentral convolutions reach the muscles of the opposite
The rubro-spinal tract carries impulses from the red nucleus and adjacent
ganglia to these segments. Thus the arm movements are controlled
by the emotional reactions.
impulses from the viscero-motor centers in the medulla, and perhaps the pons
and midbrain, reach these segments. The most conspicuous function thus
mediated is that of respiration.