Supraspinal Control of Slow and Fast Spinal Motoneurons of the Cat

Abstract

This chapter presents the investigations to clarify whether cortical stimulation produces differential effects on tonic and phasic or slow and fast (or type S and type F) spinal motoneurons such as those seen in the case of rubral stimulation. The chapter also presents the investigation to find the relations between slow and fast pyramidal tract (PT) cells and slow and fast spinal motoneurons. It investigates the control of slow and fast spinal motoneurons by the extrapyramidal system. Though rubral effects on slow and fast spinal motoneurons have been investigated in detail, differential controls of slow and fast spinal motoneurons by the medial longitudinal fasciculus and Deiters' nucleus are not known. The patterns of PSPs produced by repetitive stimulation of the contralateral pericruciate cortex of cats are found to be inhibitory to slow and excitatory to fast spinal motoneurons, and not inhibitory and excitatory to extensor and flexor motoneurons respectively. The experiments with decorticated cats show that axons of fast PT cells degenerate. The experiments with decorticated cats reveal that slow PT cells exert almost exclusively excitatory effects on both slow and fast spinal motoneurons, while fast PT cells preferentially influence inhibitory and excitatory effects on slow and fast spinal motoneurons respectively.