“In a sense, therefore, the spinal cord is the keyboard on which the brain plays when it calls for activity or for change in activity. But each “key” in the console sounds, not an individual “tone,” such as the contraction of a particular group of muscle fibers, but a whole) “melody” of activity, even a “symphony” of motion. In other words, built into the cord is a large repertoire of patterns of activity, each involving the complex, harmonious, delicately balanced orchestration of the contractions and relaxations of many muscles. The brain “thinks” in terms of whole motions, not individual muscles. It calls,, selectively, for the preprogrammed patterns in the cord and brainstem, modifying them in countless ways and combining them in an infinite variety of still more complex patterns. Each activity is also subject to further modulation, refinement, and adjustment by the afferent feedback continually streaming in from the participating muscles, tendons, and joints.
Irvin Korr The spinal cord as organizer of disease process : Some preliminary perspectives, JAOA 76 : 35-45, Sep 76