Movements in the Myelin Schwann Sheath of the Vertebrate Axon

Abstract

THE demonstration in our laboratory that radioactive amino-acid and uridine label the myelin lamellae of vertebrate peripheral nerve and penetrate into the axon^1–3 raised the problem of the route and mechanism of transport of these materials through the layered sheath⁴. Two mechanisms seemed salient: direct transfer through the battery of stacked myelin membranes, governed by the forces involved in transport across membranes; and transport within the Schwann cytoplasm into the depths of the myelin via the Schmidt–Lanterman clefts, perhaps propelled by movements of the Schwann cell body. These speculations, particularly the second one, led us to examine the myelin sheaths of living nerve fibres with lapsed-time microcinematography. We report our findings on movements in the myelin sheath, with particular reference to the clefts.