Block of conduction in mammalian myelinated nerve fibres by low temperatures.

Abstract

Low temperatures are used extensively for blocking various respiratory and cardiovascular reflexes on the presumption that cold must have a differential effect on the nerve fibres of different diameters. However, there is no unanimity of opinion regarding the nature of this differential effect (Paintal, 1963). One group of studies, in which the compound action potential has been used as a guide, has indicated that the smaller myelinated fibres are blocked at a higher temperature than that needed to block conduction in the larger fibres (Dodt, 1953; Douglas & Malcolm, 1955). On the other hand, Torrance & Whitteridge (1948), Whitteridge (1948), and Widdicombe (1954), who recorded impulses in individual fibres, have arrived at the opposite conclusion. Some support for the latter conclusion was obtained recently by comparing the distribution of the blocking temperatures of pulmonary afferent fibres with the distribution of their conduction velocities (cf. Fig. 8 in Paintal, 1963). Experiments were begun with the expectation that this conclusion would be easily confirmed but it turns out, as shown in this paper, that there is no relation between the conduction velocities of myelinated nerve fibres and their blocking temperatures. In the following paper, the results of a systematic study of the effects of different temperatures on conduction in nerve fibres will be presented (Paintal, 1965).