Measurements and mapping of 282,420 nerve fibers in the S1-5 nerve roots.
OBJECTIVE
The study aims to analyze nerve fiber types in the sacral nerve roots as a prerequisite for stimulation.


METHODS
One-micrometer cross-sections of human ventral and dorsal S1-5 roots were stained with osmium and toluidine blue. The total fiber diameter and myelin sheath were measured in 282,420 nerve fibers.


RESULTS
The analysis revealed the following 3 main nerve fiber types: Aalpha fibers (diameter 6-14 microm), Agamma fibers (diameter 2-4 microm), and B fibers (diameter < 2 microm). The B fibers were absent in S-1, present in some S-2 fascicles, and abundant from S-3 to S-5. The Aalpha fibers dominated the S-1 roots and most fascicles of S-2 roots. In the S3-5 roots, only a few Aalpha fibers were present. The relative occurrence of Agamma fibers increased from S-1 to S-5. In dorsal roots, Agamma fibers represented approximately 70% of all nerve fibers in every root and fascicle.


CONCLUSIONS
The B fibers represented efferent parasympathetic fibers. These fibers were concentrated in certain areas of the nerve roots, not randomly distributed. The Aalpha fibers innervate lower-extremity muscles and sphincters. The inverse correlation of Aalpha and Agamma fibers in the ventral roots from S-1 to S-5 is surprising. In dorsal roots, Agamma fibers may conduct pain, touch, and temperature signals. Highly selective fiber stimulation specific for type, location, and direction may improve sacral nerve stimulation for a spastic bladder in paraplegic individuals.
Hauck
Erik F
EF
Department of Neurosurgery, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA. erikhauck@gmx.de
Schwefer
Markus
M
Wittkowski
Werner
W
Bothe
Hans W
HW
D000368:Aged; D017776:Autonomic Pathways / Q000033:anatomy & histology / Q000502:physiology; D001837:Body Weights and Measures; D002102:Cadaver; D005260:Female; D006801:Humans; D008160:Lumbosacral Plexus / Q000033:anatomy & histology* / Q000502:physiology*; D008297:Male; D042282:Microdissection; D009412:Nerve Fibers / Q000502:physiology* / Q000648:ultrastructure*; D013126:Spinal Nerve Roots / Q000502:physiology* / Q000648:ultrastructure*; D001743:Urinary Bladder / Q000294:innervation