The Journal of Neurophysiology Vol. 80 No. 1 July 1998, pp. 249-254
Copyright ©1998 The American Physiological Society

Comparison of Static Fusimotor Innervation in Cat Peroneus Tertius and Longus Muscles

Françoise Emonet-Dénand, Yves Laporte, and Julien Petit

Laboratoire de Neurophysiologie, Collège de France, 75231 Paris Cedex 05, France

Emonet-Dénand, Françoise, Yves Laporte, and Julien Petit. Comparison of static fusimotor innervation in cat peroneus tertius and longus muscles. J. Neurophysiol. 80: 249-254, 1998. Static fusimotor innervation was compared in cat peroneus longus and tertius muscles because the  to spindle ratio is considerably higher in the longus (~60  axons for 17 spindles) than in the tertius (~24  axons for 14 spindles). Single  axons were identified as static (s) by their typical effects on the response of primary ending to ramp stretch. The intrafusal muscle fibers that single s axons activated in the spindles they supplied were identified by the features of cross-correlograms between Ia impulses and stimuli, at 100 Hz, and by those of primary ending responses during stimulation at 30 Hz. In each experiment, a large proportion of the  population was tested on about nine spindles. A statistical analysis was used to estimate the number of spindles supplied by single s axons and the proportion of s axons that supply only one spindle among those the stimulation of which had activated either bag₂ or chain fibers alone in a single spindle. In peroneus longus, nearly all s axons supply one or two spindles, whereas in peroneus tertius, the majority of s axons supply from three to six spindles. The proportion of nonspecifically distributed s axons, i.e., of axons that supply both bag₂ fibers and chain fibers either in the same or in different spindles, is much lower (56%) in the longus than in the tertius (83%) as previously observed on a population of s axons that supplied from three to six spindles. Correspondingly, the proportion of specific axons is much higher in the longus (44%) than in the tertius (17%). In none of the two muscles was a strict relationship observed between the conduction velocity of s axons and their intrafusal distribution (specific bag₂, specific chain fibers, nonspecific). However, s supplying bag₂ fibers either specifically or in combination with chain fibers tended to have faster conduction velocities, which suggests that, in various motor acts, the proportion of activated bag₂ and chain fibers may be related to the proportions of activated fast and slow s axons.

This article has been cited by other articles:

				F. Emonet-Denand, Y. Laporte, and J. Petit Comparison of the Effects of Stimulating Groups of Static {gamma} Axons With Different Conduction Velocity Ranges on Cat Spindles J Neurophysiol, July 1, 2001; 86(1): 533 - 535. [Abstract] [Full Text] [PDF]

				J. Petit, R. W. Banks, and Y. Laporte Testing the Classification of Static gamma  Axons Using Different Patterns of Random Stimulation J Neurophysiol, June 1, 1999; 81(6): 2823 - 2832. [Abstract] [Full Text] [PDF]