The Spinal Cord
The spinal cord is the source of most of the nerve supply to the body. Every organ and tissue receives some nerve supply which originates from the spinal cord. The cord is also the point of entry or reception of most of the information from the organs and tissues of the body. Impulses carrying information to the higher centres and the brain pass into and through the cord and are often 'screened' and organized and transmitted in, and by, tissues in the spinal cord. Everything that is happening to the body is constantly monitored and controlled via this vital pathway. Many automatic functions as well as conscious orders are either conveyed by or recoded and dispatched by the cord. Insofar as the musculo-skeletal system is concerned, Korr explains it thus: [4]

The spinal cord is the keyboard on which the brain plays when it calls for activity. But each 'key' in the console sounds not an individual tone' such as the contraction of a particular group of muscle fibres, but a whole "melody' of activity, even a 'symphony' of motion. In other words, built into the cord is a large repetoire of patterns of activity, each involving the complex, harmonious, delicately balanced orchestration of the contractions and relaxation of many muscles. The brain thinks in terms of whole motions, not individual muscles. It calls, selectively, for the pre-programmed patterns in the cord and brain stem, modifying them in countless ways and combining them in an infinite variety of still more complex patterns. Each activity is subject to further modulation refinement, and adjustment by the feedback continually streaming in from the participating muscles, tendons and joints.

One of the most important concepts of osteopathic philosophy and practice is that of the facilitated segment. Described in research writings of the profession over the past thirty years, the concept of the facilitated segment states that because of abnormal afferent or sensory inputs to a particular area of the spinal cord, that area is kept in a state of constant increased excitation. This facilitation allows normally ineffectual, or subliminal stimuli, to become effective in producing efferent output from the facilitated segment, causing both skeletal and visceral organs innervated by the affected segment to be maintained in a state of over-activity. It is probable that the 'osteopathic lesion' or somatic dysfunction with which a facilitated segment is associated, is the direct result of the abnormal segmental activity, as well as being partly responsible for the facilitation. Although the effects of the facilitated segment on various skeletal and visceral functions are well documented, little is understood about the genesis and maintenance of spinal facilitation. Even the question of why some traumas cause facilitation and others do not, remains unanswered.

Facilitation of the sensory pathways in the disturbed lesioned segments means that there is easier access to the nervous system—including the higher centres—through these segments. The lesioned segment is one through which environmental changes—especially noxious or painful stimuli—have exaggerated impact on man. Facilitation of motor pathways leads to sustained muscular tensions, exaggerated responses, postural asymmetries, and limited and painful motion. Since the muscles have rich sensory as well as motor innervation, under these conditions, they and related tendons, ligaments, joint capsules etc. may become the sources of relatively intense and unbalanced streams of impulses. The physiopathological effects of facilitation on local sympathetic pathways depend on the structures which are innerverted by those pathways; that is which viscera? which blood vessels? which glands?