The basal ganglia plays an integral role in movement. It is composed of the following nuclei: the caudate nucleus, putamen, and the globus pallidus. Inputs from the cerebral cortex, especially the primary motor strip and primary somatosensory cortex, are received in the basal ganglia and the substantia nigra. The outputs of these two areas are the primary motor cortex, supplementary motor area, the motor nuclei of the brain stem, and via the thalamus, the premotor cortex. The location of these nuclei and pathway for movement is a circular loop which enables the basal ganglia to receive information about planned movements and motion that is performed by the primary motor cortex as seen on below . With this knowledge, the basal ganglia controls the motor cortex. The diagram below illustrates the planned and executed aspects of movement(Eccles, 134).
The inputs from the primary motor cortex and the primary somatosensory cortex are projected to the the putamen. Next, the signal is sent to the caudate and then to globus pallidis, which has two different outputs: the motor nuclei of the brain stem and the subthalamic nucleus. From the globus pallidus, the signal is then projected to the motor cortex via the ventrolateral thalamus. The feedback loop is complete when information from the primary motor and primary somatosensory cortex are sent to the putamen.
Specifically, the loop is maintained by two neurotransmitters: glutamate and GABA. The substantia nigra via dopamine sends both excitatory and inhibitory signals to the caudate, which innervates different areas of the putamen. The inhibitory signal has been received in the putamen, and it is relayed to the external globus pallidus. As a result, an IPSP is produced at the subthalmic nucleus. This inhibition results in an EPSP at the internal globus pallidus. Consequently, an inhibitory signal is sent to the thalamus, which produces an EPSP. This excitatory message is then projected to the motor cortex, which results in motor movement. The excitatory input from the substantia nigra has a somewhat similar pathway. Like the inhibitory pathway, an IPSP is produced at the globus pallidus, but at a different location, the internal globus pallidus. From this area, the mechanism is like the one previously described. The diagram below illustrates the corto-basal ganglia loop (Carlson, 244). The red arrows indicate inhibitory pathways; the black arrow are excitatory connections.