Work of the muscles and single motor neurones during controlled locomotion

1. (1) We have recorded the total electrical activity of the muscles and the action potentials of single motor neurones during locomotion induced in the mesencephalic cat by stimulation of a definite region of the brain stem. 2. (2) The amplitude of the electromyograms both of the flexors and extensors increases with increase in the stimulation of the stem. The motor neurones already involved in locomotion do not change the frequency of their pulsation but new motor neurones are brought into the work. The duration of the packet of the flexor motor neurones may fall while that of the extensor motor neurones remains unchanged if the speed of locomotion is kept constant. 3. (3) Change in the speed of locomotion with constant strength of stimulation of the stem does not affect the electromyogram of the flexors; the amplitude of the electromyogram of the extensors also remains unchanged but the duration of their activity increases with slowing of locomotion. Single extensor motor neurones change the duration of the packet of pulses with change in the speed of locomotion in the same way as the extensors change their total activity. The frequency of the pulses in the packet does not change. Change in the speed of locomotion does not influence the work of the flexor neurones. 4. (4) The frequency of pulses in the packet in motor neurones active in the support phase during controlled locomotion was in the majority of cases 15-45 per sec.