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 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 exter ...
(the other being 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 ...
). The
GABAergic 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 fasc ...
(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 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, 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 ...
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 internal globus pallidus contains
GABAergic 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
![Basal-ganglia-classic](https://upload.wikimedia.org/wikipedia/commons/4/45/Basal-ganglia-classic.png)
The GPi acts to tonically inhibit 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 fasc ...
and
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 ...
of the
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, ...
. As these two nuclei are needed for movement planning, this inhibition restricts movement initiation and prevents unwanted movements.
Direct pathway
The GPi receives inhibitory
GABAergic signals from the
striatum 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. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consistin ...
. As the GPi is one of the direct output centers 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 exter ...
, this causes disinhibition of the
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, ...
, increasing overall ease of initiating and maintaining movement. As this pathway only contains one
synapse (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
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 ...
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 ...
.
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 nucleus ...
(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 uns ...
with mostly 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 ...
being affected.
References
{{Authority control
Basal ganglia