External globus pallidus

External Globus Pallidus

The external globus pallidus (GPe) is a subregion of the globus pallidus, which is part of the basal ganglia in the brain. The basal ganglia are a group of nuclei in the brain associated with a variety of functions, including the regulation of voluntary motor movements, procedural learning, routine behaviors or "habits", eye movements, cognition, and emotion.

Anatomy

The external globus pallidus is located lateral to the internal globus pallidus (GPi) and medial to the putamen. It is part of the lentiform nucleus, which also includes the putamen. The GPe is separated from the GPi by the medial medullary lamina, a thin layer of white matter.

Function

The external globus pallidus plays a crucial role in the indirect pathway of the basal ganglia circuitry. It receives inhibitory input from the striatum and sends inhibitory output to the subthalamic nucleus (STN). This pathway is essential for the regulation of movement and the suppression of involuntary movements.

Pathways

The GPe is involved in several important neural pathways:

• **Indirect Pathway**: In this pathway, the GPe receives input from the striatum and projects to the STN. The STN then projects to the GPi and the substantia nigra pars reticulata (SNr), which in turn project to the thalamus and then to the cerebral cortex.
• **Projections to the Subthalamic Nucleus**: The GPe sends inhibitory signals to the STN, which is a critical component of the indirect pathway. This interaction helps modulate the activity of the GPi and SNr.

Clinical Significance

Dysfunction in the external globus pallidus is associated with several neurological disorders, including Parkinson's disease, Huntington's disease, and dystonia. In Parkinson's disease, the loss of dopaminergic neurons in the substantia nigra pars compacta leads to increased activity in the GPe, which disrupts the normal balance of the basal ganglia circuitry and results in motor symptoms such as tremors, rigidity, and bradykinesia.

Research

Ongoing research is focused on understanding the precise role of the GPe in the basal ganglia circuitry and its involvement in various neurological disorders. Advances in neuroimaging and electrophysiological techniques are providing new insights into the function and dysfunction of the GPe.

See Also

• Basal ganglia
• Globus pallidus
• Internal globus pallidus
• Subthalamic nucleus
• Parkinson's disease
• Huntington's disease
• Dystonia