Presumably different centers connect via internuncial neurons with groups of peripherally disposed motor units. . . . As the severity of effort increases, those involved primarily in one movement may be recruited to assist in the performance of others. Movements, not muscles, are represented in the cortex. Patterns are learned and those patterns are peculiar to every movement. Indeed, they are so repetitive as to warrant designating them patterned movements. . .
Partial patterns emerge secondarily, by virtue of special training, . .
It is highly unlikely that partial or isolated training of movement segments will replicate the unit function in the total action. There will be no integration of the partial practice movement into the total response movement. Central excitations have a tendency to flow always into stretched muscles. Thus, every change in body positioning alters the configuration of the next succeeding efferent response. It affects not only the muscle stretched, but all functionally related muscle groups as well.