The Globus Pallidus

In primates the globus pallidus is divided into two anatomical segments: internal (GPi) and external (GPe). Although these segments are separated by the medial medullary lamina, the pallidal neurons from each segment are extremely similar, and for the most part morphologically indistinguishable (Carpenter 1981). In nonprimates the anatomical structures usually have a larger separation and are referred to as the pallidum and entopeduncular nucleus (corresponding to the GPe and GPi respectively). In humans the external segment constitutes 70% of the total volume of the globus pallidus.

Cytology
There is a variety of neuron types in the globus pallidus. The majority are large ovoid neurons (20-60µm maximum soma diameter) with four to five thick dendrites radiating outwards (see above). The dendrites can extend up to 1000µm in length. On a single neuron some dendrites may be smooth while others exhibit spines (Difiglia et al. 1982). In rodents the dendrites form a discoidal dendritic field with the longest axis lying perpendicular to the incoming striatal afferents (i.e. parallel to the lateral medullary lamina separating the globus pallidus from the putamen). This positions the dendritic fields so as to intercept maximal numbers of striatal afferents (Park et al. 1982).

References

Carpenter, M. (1981). Anatomy of the corpus striatum and brainstem integrating systems. Handbook of Physiology --- The Nervous System 2. 947-995

DiFiglia, M., Pasik, P. and Pasik, T. (1982). A Golgi and ultrastructural study of the monkey globus pallidus. J. Comp. Neurol. 212. 53-75

Park, M., Falls, W. and Kitai, S. (1982). An intracellular HRP study of the rat globus pallidus: I. Responses and light microscope analysis. J. Comp. Neurol. 211. 284-294