Descending motor pathways and the spinal motor system. Limbic and non-limbic components

For a thorough understanding of the descending pathways of the motor system originating in the forebrain, knowledge about the anatomy and function of the structures in the more caudally located parts of the central nervous system is indispensable. In this paper an overview will be presented of these caudal structures in brainstem and spinal cord as far as they concern the motor system, (sections 1 to 3). After that the descending pathways belonging to the so-called somatic motor system are reviewed (section 4). Finally, a summary of the many newly discovered pathways related to the limbic system will be given (section 5). In the Conclusions section a concept will be presented, which subdivides the multitude of motor pathways into three motor systems. In this concept the motoneurons will be considered to belong to the peripheral motor system, (motor unit, which is the motoneuronal cell body-motor axon-muscle). The first motor system consists of the interneurons involved in motor reflex pathways. The second motor system contains the pathways of the so-called somatic motor system, while the third motor system comprises the motor pathways related to the limbic system. The second and third motor systems act upon the neurons of the first motor system and to a limited extent directly on motoneurons, but not on each other. The importance and strength of the third motor system, which, untill recendy, was virtually unknown, will be emphasized