14 julio, 2024

Subthalamus: what it is, structure, functions and diseases

What is the subthalamus?

He subthalamus It is a region of the diencephalon that is associated with motor functions. As its name indicates, it is located below the thalamus, between the latter and the tegmentum of the midbrain. Despite its small size, it is enormously complex, containing different groups of nerve cells.

The subthalamus is shaped like a biconvex lens (like two convex surfaces, being thinner at the ends than at the center). Its most important and studied part is the subthalamic nucleus, which establishes connections with other brain regions. For example, it has fundamental connections with the striatum to regulate muscle activity.

Different somatic and sensory pathways traverse the subthalamus. Mainly, they target the cerebellum, thalamus, and basal ganglia.

On the other hand, the subthalamus also includes many essential tracts that travel from the tegmentum to the thalamic nuclei. Some of them are the cranial ends of the medial, spinal, and trigeminal lemnisci.

Location of the subthalamus

The subthalamus is located in a transition area between the brainstem and the cerebral hemispheres.

It is located in the ventral part of the thalamus, and is limited posteriorly by the midbrain. The hypothalamus is located anterior to the subthalamus. It lies medial to the internal capsule.

Towards its caudal part it is limited by the tegmentum of the midbrain, and includes the rostral extension of the substantia nigra and the red nucleus.

In the area ventrolateral to the subthalamus are the descending fibers of the internal capsule towards the cerebral peduncle.

During embryonic development, the subthalamus is an extension of the hypothalamus. They are only separated by a few white matter fibers mainly from the internal capsule. Caudally, it is separated from the thalamus by the intrathalamic limiting zone (ILZ).

Parts of the subthalamus (structure)

The subthalamus is a brain region made up of several nuclei of gray matter and white matter. Anatomically, it is considered a prolongation of the midbrain integrated into the interior of the diencephalon.

The subthalamus consists mainly of two structures: the subthalamic nucleus and the uncertain zone. The subthalamic nucleus is located ventral to the latter.

Subthalamic nucleus, or nucleus of Luys

The subthalamic nucleus consists of an ovoid mass of gray matter that is located in the central part of the uncertain zone. It is separated from it by the Forel H2 field.

In its lateral part is the internal capsule, and caudally it is associated with the substantia nigra.

It is a group of gray matter made up of neurons of medium size and various shapes.

This nucleus regulates motor activities through its interconnections with the basal ganglia. Its neurons secrete and receive glutamate, a substance that exerts excitatory effects. Thus, they activate neurons of the globus pallidus and the substantia nigra.

uncertain zone

It is a thin sheet of gray matter, located parallel to the hypothalamic sulcus. It is separated from the latter by the H1 and H de Forel fields. Dorsolateral to it is the reticular nucleus of the thalamus. At its medial end there is a group of neurons that constitute the nucleus of the tegmental field.

This region joins the diencephalon with the midbrain to coordinate vision with our movements, being involved in the extrapyramidal pathway. To do this, it receives information from the motor cortex.

Some authors consider it as a continuation of the reticular formation of the midbrain.

Between the neuronal groups of the subthalamus, the cranial ends of the red nuclei and the substantia nigra are observed.

Within the subthalamus is also the subthalamic fasciculus, a structure composed of fibers that connect the globus pallidus with the subthalamic nucleus.

On the other hand, the Forel fields are also included, which are made up of three specific areas of white matter called “H fields”. These are:

– The H1 field, an area of ​​white matter made up of the lenticular loop, the lenticular fasciculus and cerebello-thalamic tracts. They are projections that reach the thalamus from the basal ganglia and the cerebellum.

– The H2 field, or lenticular fasciculus, which carries projections from the globus pallidus to the thalamus and the subthalamic nucleus.

– The H or H3 field is a large area of ​​gray and white matter, a mixture of the pallidothalamic tracts of the lenticular fasciculus and the lenticular loop.

connections

The subthalamus establishes efferent connections (that is, it sends information) with the striatum (caudate nucleus and putamen), the dorsal thalamus, the substantia nigra, and the red nucleus.

While it receives information or maintains afferent connections with the substantia nigra and the striatum. Also, exchange information with the pale globe.

Functions of the subthalamus

The subthalamus is known as the motor region of the diencephalon. This area has the nuclei of the extrapyramidal motor system, which is the one that directs the involuntary motor functions, which are, among others:

– The reflections,

– locomotion,

– postural control,

– regulation of impulses from the optic nerves and vestibular nerves (those responsible for balance and orientation),

– transmission of these impulses to the globus pallidus.

Diseases

Lesions or degenerations of the subthalamus by certain diseases produce motor disorders. Specifically, a relationship has been found between damage to the subthalamic nucleus and the appearance of chorea. Chorea, or dyskinesia, is a neurological disorder characterized by involuntary movements of the extremities.

They are due to non-rhythmic, non-repetitive irregular contractions that seem to travel from one muscle to the next. The movements resemble playing the piano or doing a dance.

Disorders of the subthalamic nucleus can be linked to two kinds of chorea:

Huntington’s chorea: Also called Huntington’s disease, it has a hereditary origin and is chronic. It is characterized by a progressive appearance of motor and cognitive alterations, in addition to psychiatric symptoms.

At first the motor restlessness or chorea is not observed, but little by little it becomes more noticeable. It is also accompanied by problems with motor control, coordination, language articulation, and swallowing.

Sydenham’s Chorea: or minor chorea, is an infectious disease that produces uncontrollable and aimless movements in the face, shoulders, arms, hands, legs and trunk. They are observed as spasms that disappear when the patient sleeps.

This disease arises from the attack of bacteria Streptococcus pyogenes to the central nervous system.

References

Fields of Forel. Retrieved from en.wikipedia.org.
Issa, N. Hypothalamus, Subthalamus, and Epithalamus. Retrieved from docneuro.com.

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