The internal globus pallidus (GPi or medial globus pallidus) is one of the two

subcortical 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 neural integration in the central nervous system, and plays a key ...

nuclei that provides inhibitory

output Output may refer to: * The information produced by a computer, see Input/output * An output state of a system, see state (computer science) * Output (economics), the amount of goods and services produced ** Gross output in economics, the valu ...

in 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 ...

, 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 a ...

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 ...

. Together with the external globus pallidus (GPe), it makes up one of the two segments of 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 ...

, a structure that can decay with certain neurodegenerative disorders and is a target for medical and neurosurgical therapies. The GPi, along with the substantia nigra pars reticulata, comprise the primary output of the basal ganglia, with its outgoing

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 having an inhibitory function in the thalamus, the centromedian complex and the pedunculopontine complex.

Anatomy

The efferent bundle is constituted first of the ansa and lenticular fasciculus, then crosses the

internal capsule The internal capsule is a paired white matter structure, as a two-way nerve tract, tract, carrying afferent nerve fiber, ascending and efferent nerve fiber, descending axon, fibers, to and from the cerebral cortex. The internal capsule is situate ...

within and in parallel to the Edinger's comb system then arrives at the laterosuperior corner of the subthalamic nucleus 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 GPi has outgoing

neurons that connect to the

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 ...

(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 fas ...

(VL) in the dorsal

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 ...

, 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 is involved in voluntary movements, arousal, and provides sensory feedback to the cere ...

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 (: 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 ...

by way of striatopallidal fibres, 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. It is the largest site of Neuron, neural integration in the central nervous system, and plays ...

. 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 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 ...

(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 external globus pallidus and subthalamic nucleus, 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 ...

Neurodegenerative disorders

Dysfunction of the internal globus pallidus has been correlated to

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 ...

Tourette syndrome Tourette syndrome (TS), or simply 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) tic. Common tics are blinkin ...

, and

tardive dyskinesia Tardive dyskinesia (TD) is an iatrogenic disorder that results in involuntary repetitive body movements, which may include grimacing, sticking out the tongue or smacking the lips, which occurs following treatment with medication. Additional mo ...

. The internal globus pallidus is the target of

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 ...

(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 and repetitive motor movement or vocalization that is not rhythmic and involves discrete muscle groups. Tics are typically brief and may resemble a normal behavioral characteristic or gesture. Tics can be invisible to the obs ...

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 an incurable neurodegenerative disease that is mostly Genetic disorder#Autosomal dominant, inherited. It typically presents as a triad of progressive psychiatric, cognitive, and ...

with mostly the external globus pallidus being affected.

Animals

rodent Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and Mandible, lower jaws. About 40% of all mammal specie ...

s its homologue is known as the entopeduncular nucleus.

References

{{Authority control Basal ganglia