The caliber of central and peripheral neurites of spinal ganglion cells and variations in fiber size at different levels of dorsal spinal roots

The question as to whether the proximal and the distal neurite of a ganglion cell have the same or a different caliber has not yet been adequately answered. Cajal ('09) mentions that just at the point of separation of the central and peripheral neurite the former is in many instances thinner than the latter, but one can also find the reverse condition, or also neurites of the same size. Further information is not available. Nor has the possibility of a variation in fiber size at different levels of the spinal nerve root been investigated systematically. Both questions have, however, a considerable neurophysiological interest. Dorsal roots are often studied as representative for peripheral sensory nerve fibers. Both ventral and dorsal roots present physiological gradients of various kinds, which might in one way or another be connected with the size of the root fibers. In a former work (Rexed, '44) it was pointed out that varying fiber size at different levels might present a source of error in comparing roots from different individuals. This paper contains some material collected from man in connection with the previous study in addition to some results on the cat.