Correlation between Threshold and Conduction Rate in Myelinated Nerves

Abstract

In observing the effects of stimulating a nerve in the body, it is possible to lead off the cut end of the nerve into the oscillograph and thus correlate the potential form with the functional result of stimulation. Since the different fibers of a nerve are stimulated at different threshold strengths, if the difference in thresholds of different fibers were known, the oscillograph or other potential recorder could be dispensed with except for an occasional observation of threshold for the most irritable fibers, and the experimental procedure thus simplified. With this end in view, we have examined the ratios between the threshold of the first fibers stimulated in a nerve and that of other fibers, taking as criteria the thresholds of the first fibers in the various potential waves which represent fiber size groups. Gasser and Erlanger 1 have shown that the conduction rates of different fibers tend to vary as the fiber diameters, and by correlating the thresholds and conduction rates of different waves it should be possible to find the relationship between threshold and fiber size.

For the potential waves of 4 bullfrog sciatic nerves, the averages of the ratios of the α/β and β/γ conduction rates are 1.64 and 1.60, respectively. The same ratios for similar nerves for which the data are obtained from the table in Gasser and Erlanger's 2 paper are 1.62 and 1.60. This is approximately the ratio of fiber diameters shown in Gasser and Erlanger's charts of size distribution. The β/δ ratios of conduction rate for 2 nerves available are 1.45 and 1.40. The ratio of average thresholds for β/α for the first 4 nerves above is 1.63, but the γ/β ratio is 2.3. No data are available for δ.