The external globus pallidus (GPe or lateral globus pallidus) combines with the

internal globus pallidus The internal globus pallidus (GPi or medial globus pallidus) is one of the two subcortical nuclei that provides inhibitory output in the basal ganglia, the other being the substantia nigra pars reticulata. Together with the external globus pallid ...

(GPi) to form the

globus pallidus The globus pallidus (GP), also known as paleostriatum or dorsal pallidum, is a major component of the Cerebral cortex, subcortical basal ganglia in the brain. It consists of two adjacent segments, one external (or lateral), known in rodents simpl ...

, an anatomical subset of the

basal ganglia The basal ganglia (BG) or basal nuclei are a group of subcortical Nucleus (neuroanatomy), nuclei found in the brains of vertebrates. In humans and other primates, differences exist, primarily in the division of the globus pallidus into externa ...

Globus pallidus The globus pallidus (GP), also known as paleostriatum or dorsal pallidum, is a major component of the Cerebral cortex, subcortical basal ganglia in the brain. It consists of two adjacent segments, one external (or lateral), known in rodents simpl ...

means "pale globe" in Latin, indicating its appearance. The external globus pallidus is the segment of the

that is relatively further (lateral) from the midline of the brain. The GPe is predominantly composed of inhibitory

GABAergic In molecular biology and physiology, something is GABAergic or GABAnergic if it pertains to or affects the neurotransmitter gamma-aminobutyric acid (GABA). For example, a synapse is GABAergic if it uses GABA as its neurotransmitter, and a GABAergic ...

neurons that project

axon An axon (from Greek ἄξων ''áxōn'', axis) or nerve fiber (or nerve fibre: see American and British English spelling differences#-re, -er, spelling differences) is a long, slender cellular extensions, projection of a nerve cell, or neuron, ...

s to the subthalamic nucleus (in the

diencephalon In the human brain, the diencephalon (or interbrain) is a division of the forebrain (embryonic ''prosencephalon''). It is situated between the telencephalon and the midbrain (embryonic ''mesencephalon''). The diencephalon has also been known as t ...

), the

striatum The striatum (: striata) or corpus striatum is a cluster of interconnected nuclei that make up the largest structure of the subcortical basal ganglia. The striatum is a critical component of the motor and reward systems; receives glutamat ...

, internal globus pallidus (GPi) and

substantia nigra pars reticulata The pars reticulata (SNpr) is a portion of the substantia nigra and is located lateral to the pars compacta. Most of the neurons that project out of the pars reticulata are inhibitory GABAergic neurons (i.e., these neurons release GABA, which is a ...

. The GPe is particular in comparison to the other elements of the set by the fact that it does not work as an output base of the basal ganglia (not sending axons to the thalamus) but as the main regulator of the basal ganglia system. It is sometimes used as a target for

deep brain stimulation Deep brain stimulation (DBS) is a type of neurostimulation therapy in which an implantable pulse generator is stereotactic surgery, surgically implanted subcutaneous tissue, below the skin of the chest and connected by Lead (electronics), leads ...

as a treatment for

Parkinson's disease Parkinson's disease (PD), or simply Parkinson's, is a neurodegenerative disease primarily of the central nervous system, affecting both motor system, motor and non-motor systems. Symptoms typically develop gradually and non-motor issues become ...

Function

Indirect pathway

The

functions to tonically inhibit movement, mainly in the absence of

motor cortex The motor cortex is the region of the cerebral cortex involved in the planning, motor control, control, and execution of voluntary movements. The motor cortex is an area of the frontal lobe located in the posterior precentral gyrus immediately ...

command, via

inhibition of the

ventral lateral nucleus The ventral lateral nucleus (VL) is a nucleus in the ventral nuclear group of the thalamus. Inputs and outputs It receives neuronal inputs from the basal ganglia which includes the substantia nigra and the globus pallidus (via the thalamic fas ...

and

ventral anterior nucleus The ventral anterior nucleus (VA) is a nucleus in the ventral nuclear group of the thalamus. It acts with the anterior part of the ventral lateral nucleus to modify signals from the basal ganglia. Inputs and outputs The ventral anterior nucleus ...

of the

thalamus The thalamus (: thalami; from Greek language, Greek Wikt:θάλαμος, θάλαμος, "chamber") is a large mass of gray matter on the lateral wall of the third ventricle forming the wikt:dorsal, dorsal part of the diencephalon (a division of ...

, as well as the

superior colliculus In neuroanatomy, the superior colliculus () is a structure lying on the tectum, roof of the mammalian midbrain. In non-mammalian vertebrates, the Homology (biology), homologous structure is known as the optic tectum or optic lobe. The adjective f ...

and mesopontine tegmentum of the brain stem. When movement is required, the

cerebral cortex The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. It is the largest site of Neuron, neural integration in the central nervous system, and plays ...

sends commands to the

, which directly inhibits the

medial globus pallidus The internal globus pallidus (GPi or medial globus pallidus) is one of the two subcortical nuclei that provides inhibitory output in the basal ganglia, the other being the substantia nigra pars reticulata. Together with the external globus pallid ...

and

, decreasing thalamus and brainstem inhibition. As the pathway from the

to the

is monosynaptic (containing one

synapse In the nervous system, a synapse is a structure that allows a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or a target effector cell. Synapses can be classified as either chemical or electrical, depending o ...

), it is called the

direct pathway The direct pathway, sometimes known as the direct pathway of movement, is a neural pathway within the central nervous system (CNS) through the basal ganglia which facilitates the initiation and execution of voluntary movement. It works in conjunc ...

. The

indirect pathway The indirect pathway, sometimes known as the indirect pathway of movement, is a neuronal circuit through the basal ganglia and several associated nuclei within the central nervous system (CNS) which helps to prevent unwanted muscle contractions f ...

, which contains the GPe and the subthalamic nucleus, functions to modulate the effects of the direct pathway. The GPe acts as an inhibitory "control device", adjusting subthalamic nucleus neuronal activity via GABAergic output. When movement adjustment is required, striatal inhibitory

axons are sent to the GPe, decreasing inhibition of the subthalamic nucleus. The subthalamic nucleus'

glutamatergic Glutamatergic means "related to glutamate". A glutamatergic agent (or drug) is a chemical that directly modulates the excitatory amino acid (glutamate/aspartate) system in the body or brain. Examples include excitatory amino acid receptor agonist ...

neurons then stimulate the GPi and

. This multisynaptic indirect striatopallidal pathway allows for regulated excitatory input from the subthalamic nucleus to the GPi and

. This combines with direct pathway inhibition in the GPi, allowing for fine tuned basal ganglia output, and more controlled movement.

Related pathology

Lateral globus pallidus dysfunction has been observed in the following conditions: *

Huntington's disease Huntington's disease (HD), also known as Huntington's chorea, is an incurable neurodegenerative disease that is mostly Genetic disorder#Autosomal dominant, inherited. It typically presents as a triad of progressive psychiatric, cognitive, and ...

Dystonia Dystonia is a neurology, neurological Hyperkinesia, hyperkinetic Movement disorders, movement disorder in which sustained or repetitive muscle contractions occur involuntarily, resulting in twisting and repetitive movements or abnormal fixed po ...

References

Basal ganglia {{neuroanatomy-stub