Licence: In copyright
Credit: The nature of nervous processes / by W. McDougall. Source: Wellcome Collection.
Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.
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![I suggest that this cutting off of the stream of impulses in a, is effected by a diversion of that stream to bj, the resistance of the synapse bj—bj being reduced by the charging of the neurones bj and bj to a lower point than the resistance of the synapse a,—aj. Again, if stimuli of moderate strength are continuously applied to both a, and b,, the effect, as Prof. Sherrington has shown, is commonly an alternation of contractions of the flexors and extensors, each being relaxed or inhibited while the other contracts. This alternation is, I suggest, determined by synaptic fatigue. Suppose F to contract first while E remains relaxed,—that means, in terms of the drainage hypothesis of inhibition, that the energy liberated in both a, and bj is discharged through synapse a^—aj. There are many good reasons for believing that the synapse is liable to a fatigue which rapidly comes on and rapidly passes away again, and which expresses itself as a rise of the resistance of the synapse. If that is the case the resistance of synapse aj—a^ must very soon increase to such a point that ff,—bg becomes the channel of less resistance; both streams of energy, from a, and b,, will then be diverted to bg, and the flexors will relax while the extensors contract. And this will continue to be the case until increasing fatigue of synapse bg—b, and recovery of synapse a^—a, render —a^ once more the path of less resistance. In support of this hypothesis of inhibition by drainage I have produced some positive experimental evidence, and I have also tried to show— (1) that it explains well all the varieties of inhibition observable or inferrible in the central nervous system, from the spinal cord to the highest levels of the brain ; (2) that no other hypothesis of the nature of inhibition is adequate for the explanation of all the varieties of inhibitory phenomena in the central nervous system. This involves a long critical argument, which I cannot attempt to put before you in this brief space of time. This [28] E](https://iiif.wellcomecollection.org/image/b22471492_0015.jp2/full/800%2C/0/default.jpg)
