There exist neuronal networks in the spinal cord that can generate rhythmic movements without descending control and sensory afferent input. The neural networks generating locomotion are called central pattern generators（CPGs). Electrophysiological studies show that there are distinct flexor and extensor centers within the CPGs that can generate flexor and extensor rhythms independently. Within the flexor and extensor centers of CPG，there are interneurons that may act as pacemaker cells for rhythmogenesis. Pharmacological studies indicate that NMDA receptors play a critical role in determining the pacemaker property of these cells. Activation of Non-NMDA receptors modulates the frequency of rhythmicity. Other mechanisms of rhythmogenesis，such as calcium activated potassium channels and persistent sodium channels，have been proposed since the role of NMDA receptors in generating locomotor activity has not been indicated in all experimental conditions. Descending pathways from the basal ganglia and the brainstem control the selection and initiation of locomotor behavior. Mesencephalic locomotor region in the brainstem and the ventrolateral funiculus in the spinal cord appear to contain the key elements of the descending control pathways for locomotion. Sensory inputs from the moving parts of the body，as well as inputs from the visual，auditory，and vestibular receptors，have a powerful impact on the modulation of locomotor activity and make it highly adaptable to the ever changing environment of the external world. Impairments of motor functions in conditions such as spinal cord injury diminish the quality of life. Promise and progress have been made in therapeutic strategies targeted at reactivating CPGs below the spinal lesion，fostering neuroplasticity of CPGs，promoting functional recovery and rehabilitation through intensive training，and restoring neural connections through neural regeneration facilitated by surgical，pharmacological，immunological，and transplantational approaches.