III. On the restoration of co-ordinated movements after nerve-crossing, with interchange of function of the cerebral cortical centres

Abstract

Restoration of voluntary co-ordinated movements after reunion of a divided nerve is well known to occur, but the exact process by which it is brought about is by no means clear. This favourable result might be due to re-establishment of the old paths for the nervous impulses, or, on the other hand, the phenomenon might be due to the establishment of new paths due to the inevitable imperfect coaptation of the divided nerve ends. Each of the nerve-fibres in a nerve-trunk is supposed to be the path of communication between a central cell and a definite peripheral area. On dividing the nerve-trunk, and reuniting it by suture, it seems to be a difficulty to assume that perfect coaptation has been made of all or even of a majority of the cut fibres. If such an assumption is made, then the difficulty of the problem disappears, but it is clear that an assumption of the kind is unjustifiable. In a former paper (20) I showed from experiments on the sciatic nerve in dogs that the progress of recovery is practically the same whether the nerve is reunited by suture as accurately in the old position as possible, or whether the opposite state of matters is ensured by rotating the peripheral segment through a semicircle before reuniting it to the central segment. It is true that the peripheral segment of the nerve undergoes Wallerian degeneration after the act of division, but it is never­ theless still a necessity for the regeneration of the nerve. Taking the view of regeneration advocated by Ranvier (8, 9), it is a necessity only as a guide for the growth of the young sprouting nerve-fibres to the peripheral terminations, supplying these fibres at most with their envelopes (Strcebe, Notthaft, Howell and Huber). Taking, on the other hand, the view that the peripheral segment regenerates its own young nerve-fibres after the degeneration of the old fibres, which view I prefer (15), then each fibre in the peripheral segment is reproduced from the point of division on to the peripheral ending. In either case careful coaptation of the cut ends of the nerve would seem to be an important element for the re-establishment of the old paths along which nervous impulses were transmitted. If accurate coaptation is impossible, and if the accuracy of coaptation is not an essential condition of restoration of co­-ordinated movements, then the explanation of restoration is either that the central ends are endowed with the capacity of finding their proper peripheral ends, or that the nerve-centres are capable of altering their functions in so far that, when brought into connection with new muscular fibres by the alteration of the paths for nervous impulses, they can call forth muscular contractions in the new muscular fibres, so as to cause perfectly co-ordinated movements.