Globus pallidus

Where is the globus pallidus?

It lies on the medial side of the putamen, and the curve of the internal capsule borders it further in. (StatPearls, Globus Pallidus)

With the putamen it forms the lentiform, or lenticular, nucleus beneath the insula. (OpenStax A&P 2e, 13.2; StatPearls, Globus Pallidus)

What are the two parts of the globus pallidus?

A sheet of white matter, the medial medullary lamina, divides it into an internal segment (GPi), the medial one, and an external segment (GPe), the lateral one. (OpenStax A&P 2e, 13.2; StatPearls, Globus Pallidus)

Its name is Latin for “pale globe”. Its myelinated axons make it look lighter than the striatum beside it. (StatPearls, Globus Pallidus)

What does the globus pallidus do?

The internal segment, with the substantia nigra pars reticulata, is the target of the striatum’s direct pathway, and it projects to the thalamus. (OpenStax A&P 2e, 13.2; StatPearls, Basal Ganglia)

The external segment lies on the indirect pathway, which runs from the striatum to it, then to the subthalamic nucleus, then to the internal segment. (OpenStax A&P 2e, 13.2; StatPearls, Basal Ganglia)

The output to the thalamus is inhibitory and uses GABA. The direct pathway lifts that inhibition from the thalamus; the indirect pathway keeps or strengthens it. (OpenStax A&P 2e, 13.2; StatPearls, Basal Ganglia)

The internal segment is the final output of both pathways. (StatPearls, Globus Pallidus)

What connects to the globus pallidus?

Most of its inhibitory GABA input comes from the striatum, the caudate nucleus and putamen. Its output nucleus, the internal segment, sends mainly to the thalamus. (StatPearls, Globus Pallidus; OpenStax A&P 2e, 13.2)

The reticular nucleus of the thalamus receives disinhibitory input from the globus pallidus, which allows voluntary movement to begin. (StatPearls, Thalamus)