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First of all, the tone of my muscle cells must hold my skeleton together so that it neither collapses in upon my organs nor dislocates at its joints. It is tone, just as much as it is connective tissues or bone, that is responsible for my basic structural shape and integrity. Secondly, my muscle tone must superimpose upon its own stability the steady, rhythmical expansion and contraction of respiration. Third, it must support my overall structure in one position or another—lying, sitting standing, and so on. Finally, it must be able to brace and release any part of the body in relation to the whole, and to do this with spontaneity and split-second timing, so that graceful, purposeful action may be added to my stability, my posture, and my rhythmic respiration. It is no wonder we find that such large portions of our nervous systems are so continually engaged in controlling the maintenance and adjustments of this tone. The entire system of spindle cells, with both their contractile parts and their anulospiral receptors, the Golgi tendon organs, the reflex arcs, much of the internuncial circuitry of the spinal column, and most of the oldest portion of our brains—including the reticular formation and the basal ganglia—all work together to orchestrate this complex phenomenon. We have, as it were, a brain within our brain and a muscle system within our muscle system to monitor the constantly shifting values of background tonus, to provide a stable yet flexible framework which we are free to use how we will. Nor is it a wonder that these elements and processes are normally controlled below my level of consciousness—if this were not the case, walking across the room to get a glass of water would require more diversified and minute attention than my conscious awareness could possibly muster. It is the old brain, along with the even more ancient spinal cord, that are given the bulk of this task, because they have had so many more generations in which to grapple with the problems and refine the solutions. Millions upon millions of trials and errors have resulted in genetically constant motor circuits and sensory feedback loops which handle the fundamental life-supporting jobs of muscle tone for me automatically. Firm structure, posture, respiratory rhythms, swallowing, elimination, grasping, withdrawing, tracking with the eyes—all these intact and fully functional activities and more are given to each of us as new-born infants, the legacy of the development of our ancestors.
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