LINEAR RELATIONSHIP BETWEEN FIBER DIAMETER AND VELOCITY OF CONDUCTION IN GIANT AXON OF SQUID

Abstract

Sixty-nine measurements of conduction velocity were made on 45 "ultimate" giant stellar axons after minimal dissection and without removing the nerves from the body. Largely because of various technical improvements, velocities were found to be considerably higher than those reported in the earlier literature. Fibers 260-543 [mu] in diam. had velocities of 18.2-34.8 m. per sec. The data reveal a linear relationship between fiber diam. and conduction velocity for: (1) As the axon tapers in its course distally, the conduction rate decreases exactly in proportion to the reduction in diameter and (2) a straight line through the origin connects the diam. and velocity measurements from all of the expts. The slope of this line indicates an increase of 6.5 m./sec. in conduction velocity for every increase of 100 [mu] in diam. In contrast to the square-root relation previously offered, the linear correlation found between velocity and diam. in this invertebrate and unmyelinated axon is in conformity with the accepted one-to-one relationship of velocity and diam. in vertebrate myelinated and unymelinated fibers. The suggestion may thus be entertained that the rate of conduction and fiber diam. are related in a generally consistent fashion in nerves of different types and of diverse species.