Spinal functions in sensorimotor control of movements.

The transformation of sensory information to movement patterns in spinal interneuronal systems is far from just being a stereotyped reflex pattern. Information from the different sensory modalities (skin-, muscle, and joint receptors) is integrated at the interneuronal level and transformed into patterns of coordinated movements which are adapted to the current position and the phase of movement of a limb. In addition, spinal interneuronal systems are capable of generating rhythmic motor activities like locomotion or scratching without a sensory feed-back from the periphery and without a corresponding drive from supraspinal structures. The same interneuronal systems which are engaged in the reflexogenic control and generation of movements at the spinal level also convey information for the performance of supraspinally-induced, goal-directed ("voluntary") movements. The inherent convergence between descending and peripheral afferent information onto common interneuronal systems implies an improved coordination and adaptation of movements in dependence on the peripheral conditions. Disturbance of the supraspinal control of these interneuronal systems leads to an impairment of the transformation of sensory inputs into motor acts. Spasticity is probably partly caused by such a disturbed control of the transmission in the interneuronal systems.