SCIENCE AND SANITY - online book

An Introduction To Non-aristotelian Systems And General Semantics.

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ON ORDER
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these chain reflexes are usually not simple reflexes as diagrammed, but complex elements of the types next to be described. . . . The chain reflex ... is a very common and a very important type. Most of the ordinary nets in the routine of daily life employ it in one form or another, the completion of one stage of the process serving as the stimulus for the initiation of the next. . . .
'Figure 1, C illustrates another method of compounding reflexes so that the stimulation of a single sense organ may excite either or both of two responses. If the two effectors, 1 and 2, can cooperate in the pcrformance of an adaptive response, the case is similar to that of Fig. 1, A, with the possibility of a more complex type of reaction. This is an allied reflex. If, however, the two effectors produce antagonistic movements, so that both cannot act at the same time, the result is a physiological dilemma. Either no reaction at all results, or there is a sort of physiological resolution (sometimes called physiological choice), one motor pathway being taken to the exclusion of the other. Which path will be chosen in a given case may be determined by the physiological state of the organs. If, for instance, one motor system, 2, is greatly fatigued and the other rested, the threshold of 2 will be raised and the motor discharge will pass to 1.
'Figure 1, D illustrates the converse case, where two receptors discharge into a single center, which, in turn, by means of a final common path (FCP) excites a single effector (). If the two receptors upon stimulation normally call forth the same response, they will reinforce each other if simultaneously stimulated, the response will be utrengthened, and we have another type of allied reflex. But there are cases in which the stimulation of Rl and R2 (Fig. 1, D) would naturally call forth antagonistic reflexes. Here, if they are simultaneously stimulated, a physiological dilemma will again arise which can be resolved only by one or the other afferent system getting control of the final common path.
'Figure 1, E illustrates still another form of combination of reflexes. Here there are connecting tracts (A, A) between the two centers so arranged that stimulation of either of the two receptors (Rl and R2) may call forth a response in either one of two effectors (1 and 2). These responses may be allied or antagonistic, and much more complicated reflexes are here possible than in any of the preceding cases. . . .
'It must be kept in mind that in higher vertebrates all parts of the nervous system are bound together by connecting tracts (internunaal pathways).... These manifold connections are so elaborate that every