Chapter 4. THE ROLE OF THE BASAL GANGLIA IN THE MOTOR SYSTEM
PHYLOGENETIC ASPECTS
The basal ganglia are a part of the motor system. The principal nuclei of the basal ganglia are the caudate nucleus, the putamen, and the globus pallidus, all of which lie in the subcortical white matter of the telencephalon. These nuclei are connected to each other, and to the motor cortex, in complex regulatory circuits. They exert both excitatory and inhibitory effects on the motor cortex. They play an important role in the initiation and modulation of movement and in the control of muscle tone. Lesions of the basal ganglia, and of other, functionally related nuclei, such as the substantia nigra and the subthalamic nucleus, can produce either an excess or a deficiency of movement-related impulses, and/or pathological alterations of muscle tone. The most common disease of the basal ganglia is Parkinson disease, which is characterized by the clinical triad of rigidity, akinesia, and tremor.
Preliminary Remarks on Terminology
The hierarchically uppermost center for the control of movement is the cerebral cortex, whose signals are transmitted by the pyramidal pathway to the motor cranial nerve nuclei and to the anterior horn cells of the spinal cord (pyramidal system). A number of other structures in the central nervous system participate in the initiation and modulation of movement. The most important of these "accessory motor centers" are the basal ganglia, a set of subcortical nuclei located within the deep white matter of the telencephalon. The pyramidal system was long regarded as the "major" system for the control of movement, as it provides the most direct and most rapid connection between the cortex and the motor neurons of the brainstem and spinal cord. All other structures playing a role