Basal Ganglia

In this paper, I will be discussing the normal physiology of the basal ganglia, or basal nuclei, how the different structures within are involved with motor functions, and how dysfunctions within the basal ganglia lead to movement disorders.

The basal ganglia are a group of interconnected subcortical structures composed primarily of the striatum, pallidum, substantia nigra, and the subthalamic nucleus. These structures span across the diencephalon, telencephalon, and the midbrain, and lie under the cerebral cortex. The striatum is the primary afferent, or input, structure, consisting of two parts, the medial caudate and the lateral putamen. The primary output structures of the basal ganglia are the medial globus pallidus and substantia nigra pars reticula. The basal
The first step in the circuit starts with the cortico-striatal projection, in which the striatum sends projections to the medial globus pallidus and substantia nigra, but these can be sent directly or indirectly. In both pathways, it begins with all neural activity through the cortex stimulating the striatum. The direct pathway goes straight from the projection to the medial globus pallidus and the substantia nigra para reticula and inhibits them. When the projections are sent indirectly, they are first sent to the lateral globus pallidus and then to the MGP and SNr. The indirect pathway results in a much larger projection being sent to the subthalamic nucleus. This in turn leads to inhibition of globus pallidus neurons which then results in disinhibition of the subthalamic nucleus, increase of the excitatory drive on the output nuclei, and increase of inhibition of efferent targets within the thalamus. The subthalamic nucleus eventually sends a signal back to the medial globus pallidus and the substantia nigra pars reticula which in return sends a projection to the lateral globus pallidus which results in a possible negative feedback loop. The striatum also sends