[Types of skeletal muscle motor unit activity during cold tremor].

The impulse activity of 184 single motor units of the sartorius muscle was investigated in anesthetized cats during cold tremor. Motor units whose impulse activity was connected with respiration cycles and motor units functioning independently of respiration were detected. The functions of both types of the motor units are characterized by the same average rate (4-12 imp/s) and low variability of interspike intervals. Additional thermal stimulation of the vascular thermoreceptors and changes in the rate and amplitude of respiratory excursions caused similar responses of the motor units of both types. It is suggested that motor units of both types have the same thresholds and belong to the phasic slow motor units.