Basal ganglia

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The basal ganglia are a group of cerebral and diencephalic nuclei made of gray matter. Because they are important for movement sequences, among other things, they are part of the extrapyramidal motor system. The basal ganglia receive their impulses from both the cerebral cortex and the periphery. Read everything you need to know about the basal ganglia, their function and what a failure means!

What are the basal ganglia?

The basal ganglia are collections of gray matter inside the hemispheres of the brain called gray nuclei. In every hemisphere there are these nuclei on the same side.

Caudate nucleus

The caudate nucleus (tail nucleus) is arched with a thick head and a tapering tail that runs along and delimits the lateral ventricle. The head forms the side wall of the anterior horn of the lateral ventricle.

Nucleus lentiformis

The nucleus lentiformis (lens nucleus) consists of two parts: putamen and globus pallidus (or pallidum):

The putamen (shell) is the outer part of the nucleus lentiformis. It is red-brown in color and larger than the pallidum, which it surrounds like a bowl.

The Globus pallidus ("bright core") owes its name to its faint, yellow-gray color. It is divided into an inner and an outer part.

The nucleus lentiformis lies next to the nucleus caudatus and is almost completely separated from it by a capsule. On the front side, however, the two cores are connected and there are gray connecting stripes at the rear end. Because of these stripes, both nuclei are referred to as stripe bodies, corpus striatum, or striatum.

The striatum is the uppermost center of the extrapyramidal motor system. This is where the impulses coming from the thalamus and those coming from the vegetative centers of the diencephalon converge and thus combine the stimuli that come from the environment with those that come from the body.

Nucleus accumbens

Another core of the basal ganglia is the nucleus accumbens, which creates a connection between the putamen and the caudate nucleus. It also consists of a core and a shell region.

Substantia nigra

The substantia nigra are gray nuclei in the midbrain that are connected to the cerebrum and the pallidum, among other things. The cells together with other areas form a so-called black system.

Messenger substances of the basal ganglia

The most important transmitters in the basal ganglia are:

• Dopamine: an excitatory neurotransmitter; the "happiness hormone"
• Acetylcholine: a transmitter that plays a central role in both the central and peripheral nervous systems
• Gamma-amino-butyric acid (GABA): the most important inhibitory neurotransmitter in the central nervous system

What is the function of the basal ganglia?

The basal ganglia initiate physiological and cognitive processes. They inhibit the spontaneous activity of the organism by choosing what is of the greatest importance to it. The important processes are uninhibited, unimportant ones are inhibited. The basal ganglia receive their information from all areas of the cortex and pass on information via the thalamus to the premotor and frontal cortex. This path serves the fast and coordinated regulation of processes of unconscious, automated, fine motor movements.

The striatum regulates all reaction and expression movements that do not go through the cerebral cortex. This includes everything that belongs to facial expressions and gestures.

Connections via the caudate nucleus to the frontal lobe serve an abstract planning that does not lead directly to movements. Cell activities in the globus pallidus are responsible for the expenditure of force and the direction of movement.

The nucleus accumbens is an essential part of the brain's reward system and is therefore important for the development of addiction. There are many dopamine receptors here, the stimulation of which causes a feeling of happiness through stimulating, relaxing or pain-relieving effects. Drugs like opiates, cannabis (THC), cocaine or stimulants like amphetamines stimulate these receptors. From there, information is passed on to the limbic system and hypothalamus, where it is processed and evokes a vegetative response.

Where are the basal ganglia?

The basal ganglia are located inside the endbrain. They lie on the same side in each hemisphere in the white matter under the cerebral cortex. The caudate nucleus lies with its head on both sides next to the anterior horn and its tail above the posterior horn of the lateral ventricle. Putamen and globus pallidus lie to the side of the thalamus. The striatum connects the caudate nucleus with the putamen.

What problems can the basal ganglia cause?

Diseases or damage to the basal ganglia primarily cause movement disorders - in the sense of dystonia or hyperkinesis.

Dystonia manifests itself through an involuntary contraction of muscles, which leads to "dislocated" postures and misalignments of individual parts of the body. These include, for example, a spastic torticollis (torticollis spasticus) - a fixed, incorrect posture of the head that is turned sideways.

A failure of the impulses coming from the striatum leads to a freezing of facial expressions and a general lack of movement due to the failure of automated movements. If, for example, postures are brought about passively, there is a freeze in this posture.

Destruction of the striatum leads to Huntington's disease. This hereditary chronic disease begins with abnormally increased movement activity (hyperkinesis), grimacing and slurred speech. Chewing and swallowing movements become more and more difficult for those affected over time.

Ballism is a rarer form of hyperkinesis. Those affected carry out uncontrolled slingshot movements. The cause is disorders in the globus pallidus as a result of circulatory disorders or bleeding in the brain (stroke). Brain tumors or metastases in the basal ganglia can also cause this clinical picture.

Parkinson's syndrome is also caused by degenerative processes in the basal ganglia. When dopamine-producing cells are destroyed, it leads to a lack of dopamine at the receptors. The result is muscle rigidity, immobility and muscle tremors.

Disorders of the basal ganglia also cause mental illnesses such as obsessive-compulsive disorder, depression and anxiety disorders.

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