Journal of Neurophysiology, Vol 38, Issue 6 1390-1394, Copyright © 1975 by APS
Proportion of muscles spindles supplied by skeletofusimotor axons (beta-axons) in peroneus brevis muscle of the cat
F. Emonet-Denand and Y. Laporte
Of 32 cat peroneus brevis spindles, 23 (72%) were found to be supplied by a
least 1 skeletofusimotor or beta-axon. A motor axon was identified as
skeletofusimotor when repetitive stimulation of it elicited both the
contraction of extrafusal muscle fibers and as acceleration of the
discharge of primary ending, which persisted after selective block of the
neuromuscular junctions of extrafusal muscle fibers. The block was obtained
by stimulating single axons at 400-500/s for a few seconds. Of 135 axons
supplying extrafusal muscle fibers, 24 (18%) were shown to be beta-axons;
22 beta-axons had conduction velocities ranging from 45 to 75 m/s. All but
three beta-axons increased the dynamic sensitivity of primary endings.
Beta-innervated spindles may also be supplied by dynamic gamma-axons.
