The internal globus pallidus (GPi or medial globus pallidus; in rodents its homologue is known as the entopeduncular nucleus) and the

external globus pallidus The external globus pallidus (GPe or lateral globus pallidus) combines with the internal globus pallidus (GPi) to form the globus pallidus, an anatomical subset of the basal ganglia. Globus pallidus means "pale globe" in Latin, indicating its appe ...

(GPe) make up the

globus pallidus The globus pallidus (GP), also known as paleostriatum or dorsal pallidum, is a subcortical structure of the brain. It consists of two adjacent segments, one external, known in rodents simply as the globus pallidus, and one internal, known in rod ...

. The GPi is one of the output nuclei of the

basal ganglia The basal ganglia (BG), or basal nuclei, are a group of subcortical nuclei, of varied origin, in the brains of vertebrates. In humans, and some primates, there are some differences, mainly in the division of the globus pallidus into an extern ...

(the other being the

substantia nigra The substantia nigra (SN) is a basal ganglia structure located in the midbrain that plays an important role in reward and movement. ''Substantia nigra'' is Latin for "black substance", reflecting the fact that parts of the substantia nigra app ...

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 ...

). The

GABAergic In molecular biology and physiology, something is GABAergic or GABAnergic if it pertains to or affects the neurotransmitter GABA. For example, a synapse is GABAergic if it uses GABA as its neurotransmitter, and a GABAergic neuron produces GABA. A ...

neurons of the GPi send their axons to the

ventral anterior nucleus The ventral anterior nucleus (VA) is a nucleus 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 receives neuronal inputs from t ...

(VA) and 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 fascicu ...

(VL) in the dorsal

thalamus The thalamus (from Greek θάλαμος, "chamber") is a large mass of gray matter located in the dorsal part of the diencephalon (a division of the forebrain). Nerve fibers project out of the thalamus to the cerebral cortex in all directions, ...

, to the centromedian complex, and to the

pedunculopontine The pedunculopontine nucleus (PPN) or pedunculopontine tegmental nucleus (PPT or PPTg) is a collection of neurons located in the upper pons in the brainstem. It lies caudal to the substantia nigra and adjacent to the superior cerebellar pedunc ...

complex. The efferent bundle is constituted first of the

ansa Ansa (Latin for "handle") or ANSA may refer to: Organizations * Agenzia Nazionale Stampa Associata, Italian news agency ** Ansa Mediterranean or ANSAmed, section of the above * Applied Neuroscience Society of Australasia * Association of Norw ...

and

lenticular fasciculus The lenticular fasciculus is a tract connecting the globus pallidus (internus) to the thalamus and is a part of the thalamic fasciculus. It is synonymous with field H2 of Forel. The thalamic fasciculus (composed of both the lenticular fasciculus a ...

, then crosses the

internal capsule The internal capsule is a white matter structure situated in the inferomedial part of each cerebral hemisphere of the brain. It carries information past the basal ganglia, separating the caudate nucleus and the thalamus from the putamen and the g ...

within and in parallel to the Edinger's comb system then arrives at the laterosuperior corner of the

subthalamic nucleus The subthalamic nucleus (STN) is a small lens-shaped nucleus in the brain where it is, from a functional point of view, part of the basal ganglia system. In terms of anatomy, it is the major part of the subthalamus. As suggested by its name, the ...

and constitutes the field H₂ of Forel, then H, and suddenly changes its direction to form field H₁ that goes to the inferior part of the thalamus. The distribution of axonal islands is widespread in the lateral region of the thalamus. The innervation of the central region is done by collaterals. The internal globus pallidus contains

neurons, which allow for its inhibitory function. As the GPi, along with the

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 ...

, forms the output of the basal ganglia, these neurons extend to the thalamus, the centromedian complex and the pedunculopontine complex.

Function

The GPi acts to tonically inhibit the

and

of the

. As these two nuclei are needed for movement planning, this inhibition restricts movement initiation and prevents unwanted movements.

Direct pathway

The GPi receives inhibitory

signals from the

striatum The striatum, or corpus striatum (also called the striate nucleus), is a nucleus (a cluster of neurons) in the subcortical basal ganglia of the forebrain. The striatum is a critical component of the motor and reward systems; receives glutamate ...

by way of

striatopallidal fibres The striatopallidal fibres, also Wilson's pencils, pencil fibres of Wilson, and pencils of Wilson, are prominent myelinated fibres that connect the striatum to the globus pallidus. Their distinctive appearance allows the putamen to be identified o ...

, when a movement requirement is signaled from 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. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting of ...

. As the GPi is one of the direct output centers of the

, this causes disinhibition of the

, increasing overall ease of initiating and maintaining movement. As this pathway only contains one

synapse In the nervous system, a synapse is a structure that permits a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or to the target effector cell. Synapses are essential to the transmission of nervous impulses from ...

(from the striatum to the internal globus pallidus), it is known as 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 direct pathway is modulated by stimulation of the GPi by the

and

, via 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 ...

Clinical significance

Dysfunction of the internal globus pallidus has been correlated to

Parkinson's disease Parkinson's disease (PD), or simply Parkinson's, is a long-term degenerative disorder of the central nervous system that mainly affects the motor system. The symptoms usually emerge slowly, and as the disease worsens, non-motor symptoms becom ...

Tourette syndrome Tourette syndrome or Tourette's syndrome (abbreviated as TS or Tourette's) is a common neurodevelopmental disorder that begins in childhood or adolescence. It is characterized by multiple movement (motor) tics and at least one vocal (phonic) ...

, and

tardive dyskinesia Tardive dyskinesia (TD) is a disorder that results in involuntary repetitive body movements, which may include grimacing, sticking out the tongue or smacking the lips. Additionally, there may be rapid jerking movements or slow writhing movemen ...

. The internal globus pallidus is the target of

deep brain stimulation Deep brain stimulation (DBS) is a neurosurgical procedure involving the placement of a medical device called a neurostimulator, which sends electrical impulses, through implanted electrodes, to specific targets in the brain (the brain nucleu ...

(DBS) for these diseases. Deep brain stimulation sends regulated electrical pulses to the target. In patients with tardive dyskinesia treated with DBS, most people reported more than a 50% improvement in symptoms. Tourette syndrome patients have also benefited from this treatment, showing over 50% improvement in

tic A tic is a sudden, repetitive, nonrhythmic motor movement or vocalization involving discrete muscle groups.American Psychiatric Association (2000)DSM-IV-TR: Tourette's Disorder.''Diagnostic and Statistical Manual of Mental Disorders'', 4th ed., ...

severity (compulsive disabling motor tics are symptoms of Tourette patients). The GPi is also considered a "highly effective target for neuromodulation" when using deep brain stimulation on Parkinson's disease patients. There is seen to be only some involvement in

Huntington's disease Huntington's disease (HD), also known as Huntington's chorea, is a neurodegenerative disease that is mostly inherited. The earliest symptoms are often subtle problems with mood or mental abilities. A general lack of coordination and an unst ...

with mostly the

being affected.

References

{{Authority control Basal ganglia