A neuronal system of movement control via muscle spindle secondaries.

A recently discovered spinal interneuronal system of movement control is briefly described. It includes a population of midlumbar interneurones with a predominant monosynaptic input from secondary muscle spindle afferents but supplied with information via several other afferent and descending neuronal systems as well. The neurones are in direct contact with both motoneurones and other interneurones. The evidence in favour for their involvement in locomotion is briefly summarized.