Studies in the Osteopathic
The Nerve Centers: Volume
Louisa Burns, M.S., D.O., D.Sc.O.
THE SPINAL CENTERS (Continued)
Lower Thoracic Group
centers of the lower thoracic cord lie in the gray matter of the seventh,
eighth, ninth, tenth, eleventh and twelfth thoracic and the first lumbar
segments. In part the cells of the uppermost of these centers extend
into the sixth and fifth thoracic segments, and in part the cells of the
lowermost of them may extend below the level of the second lumbar segment.
gray matter of the lower thoracic spinal cord is rather small in extent.
The posterior horns are long and rather slender. The lateral
horns are well marked. The dorsal nucleus (Clarke’s column) is a
conspicuous cell mass in the root of the posterior horn. The anterior
horn is small.
anterior horn includes the cell columns of the mesial groups. Their
axons leave the cord at its anterior roots, and pass without relay to the
dorsi, multifidus spinae, accessories, latissimus dorsi, quadratus lumborum,
pyramidalis, cremaster, psoas major and minor, the corresponding intercoastal
and interchondral muscles, and the abdominal muscles.
spinal centers controlling the activities and the nutrition of these muscles
are influenced by impulses from the following sources:
Somatic and visceral sensory impulses affect the tone of the muscles through
reflex action. The contraction of the abdominal muscles in the presence
of inflammation involving the abdominal viscera is a familiar example of
this reaction. Less well recognized is the contraction of the deeper
spinal muscles under the same conditions.
Descending impulses from the medullary centers affect these muscles.
This reaction is noticed in the respiratory movements, and in the movements
of vomiting, etc.
Descending impulses from the cerebellum, vestibular nuclei, pontine centers,
olive, etc., assist in maintaining the tone of these muscles, and in coordinating
their action. This seems to have special reference to the needs of
the body in maintaining the equilibrium of the erect position of the body.
Descending impulses from the precentral cerebral convolutions bring these
muscles under a certain amount of volitional control. This control
is not nearly absolulte.
Descending impulses from the red nucleus are carried by way of the rubro-spinal
tract. In this way the movements of the lower thoracic groups of
somatic muscles are brought under the control of the instinctive and emotional
muscles are peculiarly subject to a loss of their normal tone. This lack
of tone may be due to a number of causes already recognized, such as excessive
fat, pregnancy, tumors which greatly increase the size of the abdomen, etc.