[Activity of fusimotor neurons during reflex muscle contraction]

The influence of fusimotor activity, via the gamma-loop, on the reflex response of motor neurons to stretch or vibration of triceps surae muscles was investigated in decerebrated cats. Action potentials of single fusimotor neurons were recorded from fine branches cut from nerves innervating triceps surae muscles leaving their main nerve supply intact. Most of the examined fusimotor neurons were found to be coactivated with motor neurons during reflex contraction of the muscles. Week autogenetic inhibitory influence on the discharge of fusimotor neurons was established at the beginning of the reflex tension rise in the muscles. A decrease of the reflex motor signal leading to the so-called silent period may, on the ground of this finding, results partially from the transiently lowered fusimotor outflow to the contracting muscles. Investigation of the changes in fusimotor spike occurrence during the rising phase of reflex muscle contraction seemed to be valuable in the estimation of both the autogenetic reflex influence on these motoneurons and conditions required for servoassistance.