THE PROPERTIES OF GROWING NERVE FIBERS

Publisher Website
Google Scholar
Abstract
Prepns. were made of the saphenous nerve and the cervical sympathetic trunk from kittens ranging in ages from a few days to 3 mos. On these preps., detns. were made of the velocity of conduction, the spike duration, the refractory period, and the configuration of the after-potentials. Saphenous nerves of kittens 4 days old showed the A and C elevations in the action potential. As the A fibers grew, their conduction velocities increased in proportion to the length of the leg. Cervical sympathetic nerves showed a single elevation at C velocity in kittens 4 days old. Differentiation into faster groups started at about the 12th day, and the A and B groups were definitely organized at the 20th day. After the groups appeared, the velocities in the constituent fibers increased until adult status was reached. Immature A fibers conducting at B velocities had a positive after-potential with a duration characteristic of A fibers. The amplitude was slightly greater than that characteristic for A, but less than half that characteristic for B. Immature B fibers conducting at C velocity had a positive after-potential differing from that of adult C fibers, but its exact configuration could not be detd. The after-potentials appeared to depend more upon the type than upon the fiber size. The spike durations in the fibers that would possess the fastest velocities in adult nerves had a value falling in the adult range (0.4-0.5 msec.) as soon as the velocities in the immature fibers reached 20 m.p.s. Below this velocity the durations appeared slightly longer, but the measurements were more uncertain. When the absolutely refractory period detns. made upon growing A and B fibers were plotted against the corresponding velocities, the values appeared to scatter about a continuous curve irrespective of fiber type. From 60 to approximately 20 m.p.s. the curve displayed a slight increase of refractory period from 0.40 to 0.45 msec. At about 20 m.p.s. the increase in refractory period became abrupt, so that at a velocity of 10 m.p.s. an avg. value of about 1 msec. and at 1 m.p.s. an avg. value of about 2.6 msec. were found.

This publication has 3 references indexed in Scilit: