Motor Activity and Caliber of Myelinated Axons: A Morphometric Study on the Sciatic NerveThe author wishes to thank Prof. Dr. C. Stang-Voss for critical discussion and Miss W. Brunner for skilful technical assistance.
14 March 2008 (online)
Japanese waltzing mice (JWM), which exhibit a genetically determined motor activity, are considered as a motor model. The myelinated fibers of the sciatic nerve of JWM and normal mice (NM) were compared, thereby determining the diameter of axons (without myelin sheath) and fibers (including the sheath). The following results were obtained: (1) at the light- and electron-microscopic level, no structural differences are discernable between the nerve fibers of NM and JWM; (2) JWM generally possess thicker axons and fibers than NM; (3) the average d/D ratio is the same in both animals; (4) in JWM, myelin sheath thickness is not related in all cases to the axonal caliber, but distinct fibers are assumed to be hypermyelinated. The latter result is considered to depend on the existence of an extraordinarily high number of spindles in JWM muscles, hence the hypermyelinated fibers are assumed to be predominantly in the service of the muscle spindles. The problem of genetic determination or adaptability by training of the peripheral nervous system leading to improved motor conditions is discussed.
myelinated nerves - sciatic nerve - diameter of axons - myelin sheath thickness - motor activity - Japanese waltzing mouse