Instinct and the unconscious (II) / by Charles S. Myers.

  • Charles Samuel Myers
Date:
[1919?]
Catalogue details

Licence: In copyright

Credit: Instinct and the unconscious (II) / by Charles S. Myers. Source: Wellcome Collection.

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    adaptation may be set up within wide limits of such swing. The “ afferent impulses which cause (or are set up by) reflex contraction of a group of muscles governed by one centre of the double reflex simultaneously cause inhibition of contraction in the antagonistic group of muscles governed by the other centre of the same reflex. It is the special role of such reciprocal graded inhibition to procure an exact adjustment between the strengths of incoming stimuli and outgoing discharge1.” The ‘all-or-none’ and ‘graded monophasic’ reflexes are characteristic of the spinal cord; each reflex element is easily fatigable and shows a well-marked ‘refractory period/ during which the movements produced by it are inexcitable. The full-blown ‘graded diphasic’ reflex, on the other hand, occurs in the decerebrate animal, in which the spinal cord retains its connexion with the bulb, pons and mid-brain; it is devoid of refractory period: its activity is continuous and, within certain limits, it is indefatigable. The outgoing impulses, instead of being periodically cut short, outlast the stimulus, so as to produce continuous, instead of intermittent, reflex muscular contraction. Moreover, prolonged excita¬ tion of one member of the double reflex, accompanied by prolonged inhibition of the other member, tends to give way to a reversal of these processes: the balance, when disturbed, swings sooner or later in the opposite direction. It is not difficult to imagine that far more complex groupings of reflexes occur in higher regions of the central nervous system, giving rise, for example, to what may be described as (iv) the ‘graded poly- phasic ’ reaction, where one complex reflex action may be followed by one or other of a variety of complex, not necessarily wholly antagonistic, reactions, according to the condition of the centres concerned. My object in such classification of the reflexes was to point out (а) that the ‘heat and cold spot’ systems of cutaneous sensibility bear a striking analogy to the first class of reflex actions, in respect of the ‘all-or-none’ principle, the absence of adaptation, the easy fatigability of the spots and the different degrees of sensitivity of different spots; (б) that in the ‘warmth and cool’ system of cutaneous sensibility (and in the paired ‘blue and yellow,’ ‘red and green’ systems of retinal sensibility) we can find an equally striking analogy with the third class of reflex actions, in which gradation, adaptation and (in vision) reversal are such characteristic features; (c) that auditory sensations—where neither the fatigability and ‘all-or-none’ principle of (a) occur, nor the bi-polaritv and adaptability of (6),—may be likened to the second class 1 This Journal, 1913, vi. 146-7.