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So it is necessary that we have a means of monitoring the tension developed by muscular activity, and equally necessary that the threshold of response for the inhibitory function of that monitor be a variable threshold that can be readily adjusted to suit many purposes, from preventing tissue damage due to overload, to providing a smooth and delicate twist of the tuning knob of a sensitive shortwave receiver. And such a marvelously adaptable tension-feedback system we do have in our Golgi tendon organs, reflex arcs which connect the sensory events in a stretching tendon directly to the motor events which control that degree of stretch, neural feed-back loops whose degree of sensory and motor stimulation may be widely altered according to our intent, our conscious training, and our unconscious habits. This ingenious device does, however, contain a singular danger, a danger unfortunately inherent in the very features of the Golgi reflex which are the cleverest, and the most indispensable to its proper function. The degree of facilitation of the feed-back loop, which sets the threshold value for the “required tension,” is controlled by descending impulses from higher brain centers down into the loop’s internuncial network in the brain stem and the spinal cord. In this way, conscious judgements and the fruits of practice are translated into precise neuromuscular values. But judgement and practice are not the only factors that can be involved in this facilitating higher brain activity. Relative levels of overall arousal, our attitudes towards our past experience, the quality of our present mood, neurotic avoidances and compulsions of all kinds, emotional associations from all quarters—any of these things can color descending messages, and do in fact cause considerable alterations in the Golgi’s threshold values. It is possible, for instance, to be so emotionally involved in an effort—either through panic or through exhilaration—that we do not even notice that our exertions have torn us internally until the excitement has receded, leaving the painful injury behind to surprise us. Or acute anxiety may drive the value of the “required tension” so high that our knuckles whiten as we grip the steering wheel, the pencil suddenly snaps in our fingers, or the glass shatters as we set it with too much force onto the table. On the other hand, timidity or the fear of being rejected can so sap us of “required tension” that it is difficult for us to produce a loud, clear knock upon a door that we tremble to enter.
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