Peripheral factors contributing to the volitional control of firing rates of the human motor units.
Human subjects can volitionally control discharge frequencies of isolated motor units at several frequencies. If the tonic firing rates such as 10 Hz are mainly dependent on the gamma-loop and if Xylocaine blocks gamma-fibers before blocking alpha-fibers, application of Xylocaine would preferentially disturb the tonic rates. After application of Xylocaine to the nerve innervating the motor units the tonic discharges at 10 Hz became irregular, while the phasic discharges at 1 Hz could still be performed volitionally. These results suggest that volitional control of tonic discharges of the motor units are dependent upon gamma activity, while the phasic discharges may be controlled by the impulses along the pyramidal tracts.
Fukushima
K
K
Department of Physiology, Hokkaido University School of Medicine Sapporo 060 Japan.
Taniguchi
K
K
Kamishima
Y
Y
Kato
M
M