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The sensory roles of the anulospiral receptor and the tendon organ are absolutely central in this process of exerting and adjusting muscle tone. These devices establish the “feel” for length and tension, and it is this feeling which is maintained by the gamma motor system, the reflex arcs, and the alpha skeletal muscles. All of my muscle cells—both alpha and gamma—are continually felt by the mind as they work, whether most of these “feelings” ever reach my conscious awareness or not. And it is primarily these muscular feelings which supply my central nervous system with the constant information necessary to successfully combine the demands of free motion with those of basic structural stability. The sophistication required for this maintenance of structure and flexibility can be appreciated if we remember that almost any simple motion—such as raising the arm out to the side—changes either the length or the tension values in most of the body’s muscle cells. If one is to avoid tipping towards the extended arm, then the feet, the legs, the hips, the back, the neck, and the opposite arm all must participate in a new distribution of balance created by the “isolated” movement of raising the arm. The difficulties experienced by every child learning to sit, to stand erect, and to walk with an even gait attest to the complexity of the demands which these shifts in balance and tone make upon us. The entire musculature must learn to participate in the motion of any of its parts. And to do this, the entire musculature must feel its own activity, fully and in rich detail. Competent posture and movement are among the chief points of sensory self-awareness. The purpose of bodywork is to heighten and focus this awareness. It is the child’s task during this early motor training to experiment by trial and error, and to set the precise lengths and tensions—and changes in length and tension—in all his muscle fibers for these basic skills of standing and walking. This is the education of the basal ganglia and the gamma motor system, as learned reflex responses are added to our inherited ones. The lengths and rates of change of the spindle fibers are set at values which experience has confirmed to be appropriate for the movement desired, and then the sensorimotor reflex arcs of the spindles and the Golgis command the alpha motor nerves, and hence the skeletal muscles, to respond exactly to those specifications that have been established in the gamma system by previous trial and error. And this chain of events holds true not only for the actual limb being moved, but for all other parts of the musculature that must brace, or shift, or compensate in any way. In this complicated process, the child is guided primarily by sensory cues which become more consistent and more predictable with every repetition of his efforts.
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