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Basal ganglia

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The basal ganglia, also known as basal nuclei, are a group of subcortical nuclei found in the brains of vertebrates. These nuclei are clusters of neurons located deep within the brain. They sit at the base of the forebrain and the top of the midbrain.

Anatomy of the basal ganglia
Anatomy of the basal ganglia

The basal ganglia act as a vital control center for many brain functions. They help regulate voluntary motor movements and facilitate smooth physical actions. Beyond movement, they are involved in procedural learning, habit formation, and conditional learning. They also play roles in eye movements, cognition, and emotion.

Basal-ganglia-coronal-sections-large
Basal-ganglia-coronal-sections-large

This system works through a complex process of action selection. The basal ganglia help the brain choose which specific behaviors to execute. They do this by regulating motor and premotor cortical areas. This regulation allows for smooth, voluntary movements.

basal-ganglia-classic
basal-ganglia-classic

A key part of this process is inhibitory influence. The basal ganglia exert an inhibitory effect on many motor systems. When this inhibition is released, a motor system becomes active. This allows for "behavior switching" based on signals from other brain regions. The prefrontal cortex, which handles executive functions, helps influence these switches.

The basal ganglia consist of several distinct functional components. The largest component is the striatum. The striatum is divided into the dorsal striatum and the ventral striatum. The dorsal striatum contains the caudate nucleus and the putamen. The ventral striatum includes the nucleus accumbens and the olfactory tubercle.

Blausen 0076 BasalGanglia
Blausen 0076 BasalGanglia

Other important parts include the globus pallidus and the ventral pallidum. The system also contains the substantia nigra and the subthalamic nucleus. Each of these parts has its own unique neurochemical and anatomical structure.

These components interact through specific pathways to control movement. The striatum receives input from many brain areas. However, it only sends its output to other parts of the basal ganglia. The globus pallidus receives input from the striatum. It then sends inhibitory output to various motor-related areas.

basal-ganglia-classic
basal-ganglia-classic

The subthalamic nucleus receives input from the striatum and the cerebral cortex. It then projects its signals to the globus pallidus. The substantia nigra is essential because it provides dopamine to the striatum. This neurotransmitter, or chemical messenger, is vital for the function of the entire circuit.

The development of these structures begins in the early embryo. The central nervous system forms from three primitive brain vesicles. These are the prosencephalon, the mesencephalon, and the rhombencephalon.

As the embryo grows, these vesicles divide into smaller, more specialized segments. During this time, cells migrate to form the basal ganglia. This migration is directed by the lateral and medial ganglionic eminences. This organized journey ensures the nuclei reach their correct positions in the adult brain.

Dysfunction in the basal ganglia can lead to serious neurological conditions. When these structures do not work correctly, it affects movement and behavior. Movement disorders are very common results of this dysfunction. Parkinson's disease is a major example. It involves the degeneration of dopamine-producing cells in the substantia nigra.

Motor loop
Motor loop

Huntington's disease is another condition that primarily causes damage to the striatum. Other movement disorders include dystonia and hemiballismus. Behavioral disorders can also occur. These include Tourette syndrome, obsessive-compulsive disorder, and addiction.

The limbic sector of the basal ganglia is specifically tied to reward and emotion. This sector includes the nucleus accumbens, the ventral pallidum, and the ventral tegmental area (VTA). The VTA uses a mesolimbic pathway to send dopamine to the nucleus accumbens. This pathway is central to reward learning and cognition.

basal-ganglia-classic
basal-ganglia-classic

Because of this, highly addictive drugs like cocaine, amphetamine, and nicotine can affect this system. These substances work by increasing the efficacy of the dopamine signal. Scientists also believe that overactivity in the VTA's dopamine projections may be linked to schizophrenia.

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🖼️ Images & Media (8)
Anatomy of the Basal Ganglia.ogv
File:Basal-ganglia-coronal-sections-large.png
Basal-ganglia-coronal-sections-large.png
File:Anatomy of the basal ganglia.jpg
Anatomy of the basal ganglia.jpg
File:Blausen 0076 BasalGanglia.png
Blausen 0076 BasalGanglia.png
File:basal-ganglia-classic.png
basal-ganglia-classic.png
File:Motor loop.png
Motor loop.png
File:The conditional routing model.jpg
The conditional routing model.jpg
File:Basal ganglia circuits.svg
Basal ganglia circuits.svg
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