The cyclical flexion and extension motions of a leg during walking result from activity at which level of the nervous system

The spinal cord is the locus of complex patterns of rhythmical motions such as to-and-fro movement of the limbs for walking, plus reciprocal motions on opposite sides of the body or of the hindlimbs versus the forelimbs in four-legged animals.All these programs of the cord can be commanded into action by higher levels of motor control, or they can be inhibited while the higher levels take over control.Ref: Guyton; 13th edition; Chapter 57 Contributions of the Cerebellum and Basal Ganglia to Overall Motor Control