Microanatomy of the ganglionic roots of the abdominal cord of the crayfish, Orconectes virilis (Hagen).

Abstract

AbstractLow magnification electron micrographs were used to construct montage maps of cross sections of the three roots of the second abdominal ganglion of the crayfish Orconectes virilis. Arbitrary fiber diameter size ranges were established within the total size range of 0.2 μ to 55 μ. Fibers within each of the ranges were counted and their positions noted. The first root contains 2,451 fibers and is divided internally into distinct anterior and posterior halves. The posterior half contains 98.2% of the roots total number of fibers below 1 μ in diameter and these are contained primarily in 13 bundles. The second root is divided internally into five subregions and contains a total of 2,741 fibers. The size distribution of the fibers within each of the subregions is noted and compared with the fiber size distribution of the peripheral branches. The subregions are assigned functions based on their similarity to root branches of known activity. The third root contains two distinct elements, a phasic branch containing 13 fibers ranging from 6 μ to 55 μ and a tonic branch containing six fibers ranging from 3.5 μ to 21 μ.