Globus pallidus

The globus pallidus is a pale, subcortical component of the basal ganglia and forms the medial part of the lentiform nucleus, while the putamen forms its lateral part. It is a roughly triangular mass of grey matter situated medial to the putamen and lateral to the internal capsule. Its characteristic pale appearance is produced by the numerous myelinated axons passing through it.

Globus pallidus externum and internum

The medial medullary lamina divides the globus pallidus into two subdivisions: the globus pallidus externus (GPe), which is the larger lateral subdivision, and the globus pallidus internus (GPi), which is the medial subdivision.

Functional correlates

Functionally, the globus pallidus is an important component of basal ganglia circuitry regulating movement. It receives predominantly inhibitory GABAergic input from the striatum.

• The GPe functions mainly as an intrinsic or relay nucleus and participates prominently in the indirect pathway through its connections with the subthalamic nucleus.

• The GPi is a major output nucleus of the basal ganglia and projects mainly to the thalamus.

Through the direct and indirect pathways, pallidal activity regulates thalamocortical activity, helping facilitate desired movements while limiting excessive or inappropriate movements.

The globus pallidus also participates in parallel basal ganglia circuits concerned with cognitive, frontal eye field, and limbic functions, rather than functioning exclusively in motor control.