Fig. 1.

Schematic representation of the neural control of interlimb coordination. Each limb is controlled by its own spinal locomotor central pattern generator (CPG). Left-right coordination at cervical and lumbar levels is mediated by commissural interneuronal pathways. Descending and ascending propriospinal pathways, with homolateral and diagonal projections, coordinate cervical and lumbar CPGs. The propriospinal pathways can be composed of neurons with long or short axonal projections. Supraspinal inputs and somatosensory feedback from the limbs access the spinal CPGs via commissural and propriospinal pathways. The arrows can represent an excitatory or inhibitory influence. E, extensor; F, flexor; LF, left forelimb; LH, left hindlimb; RF, right forelimb; RH, right hindlimb.