Diencephalon

Eva Rudolf-Müller is a freelance writer in the medical team. She studied human medicine and newspaper sciences and has repeatedly worked in both areas - as a doctor in the clinic, as a reviewer, and as a medical journalist for various specialist journals. She is currently working in online journalism, where a wide range of medicine is offered to everyone.

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The diencephalon, which lies between the cerebrum (endbrain) and the midbrain. It fulfills extremely diverse and important tasks: it is part of the brain stem, the diencephalon, acts as a “gateway to consciousness”, is important for endocrine and vegetative control, influences the sleep-wake rhythm and much more. Read everything you need to know about the diencephalon: function, division, disorders!

What is the diencephalon?

The diencephalon arises in the embryonic development from a lower expansion of the forebrain vesicle of the neural tube. The cavity that surrounds the diencephalic vesicle then forms the diencephalic part of the 3rd ventricle, which it encloses; the thickened side walls become the thalamus (visual hillock because it is related to the central visual pathway) and the pallidum of the lens nucleus (belongs to the basal ganglia).

The diencephalon is divided into five areas:

Thalamus

The thalamus is a ganglion mass that represents the actual gateway to consciousness. You can read more about this diencephalon section in the article Thalamus.

Hypothalamus

Below the thalamus is the hypothalamus. You can find out more about him in the article Hypothalamus.

Epithalamus

The epithalamus lies in the back of the diencephalon and above the thalamus. It is composed, among other things, of the pineal gland (epiphysis) and the habenulae (epiphyseal stalks), which connect the epiphysis with the thalamus.

Another area of ​​the epithalamus contains numerous nuclei, of which seven nuclei on both sides receive afferents from the retina (retina of the eye).

Subthalamus

The subthalamus consists primarily of the subthalamic nucleus and the pallidum - two basal ganglia that belong to the extrapyramidal motor system.

Metathalamus

The metathalamus comprises the two knee cusps (corpus geniculatum mediale et laterale).

What is the function of the diencephalon?

The diencephalon fulfills a variety of tasks in its various areas:

The thalamus is the collection point for all sensory impressions with the exception of the sense of smell, which are switched here on the way to the cerebral cortex. He decides which sensory impressions from the environment and the organism should penetrate into consciousness.

The control of endocrine functions and the production of neurohormones takes place in the hypothalamus. In this diencephalon area, breathing, circulation, metabolism, food and fluid intake, body temperature, sexual behavior and the sleep-wake cycle are regulated. All emotions related to these diverse functions are also anchored in this area of ​​the diencephalon.

The pineal gland as part of the epithalamus in the back of the diencephalon produces the tissue hormone melatonin. The production is subject to a daily rhythm and controls the day-night rhythm and also a seasonal rhythm. Nuclei in the habenula are switching stations for the olfactory system through which the olfactory brain is connected to the brain stem.

The core area of ​​the epithalamus receives afferents from the retina of the eye (retina). It ensures that the pupils narrow reflexively when light falls.

The subthalamus is primarily responsible for controlling gross motor skills. The subthalamic nucleus is connected to the pallidum and receives signals from it that inhibit movement.

Neurons that come from the dorsal cochlear nucleus run over the diamond pit to the medial knee cusp, and the central auditory pathway runs from here to the auditory cortex. All visual and auditory impressions are switched in the two knees of the diencephalon on the way to the visual and auditory cortex. The function of these switching cores is in particular to modify the patency for incoming excitations in such a way that - with concentrated attention - some sensory impressions are perceived more strongly and others less.

Where is the diencephalon?

Between the two frontal lobes and the two temporal lobes of the cerebrum and the front edge of the bridge (pons) is the lower part of the diencephalon, which rests on the middle fossa. In the front center, between the two cerebral legs and at the base of the brain stem, there are two hemispheres (corpus mamillare).

The epithalamus, the back area of ​​the diencephalon, lies directly on top of the thalamus.

What problems can the diencephalon cause?

A diencephal-autonomic crisis is characterized by atypical epileptic seizures that arise from diseases of the hypothalamus.

Gliomas (tumors originating in the cell tissue of the nervous system) in the diencephalon cause a strong psychological slowdown, general disinterest with a reduction in affects and an increased need for sleep.

Damage to the subthalamic nucleus in the subthalamus leads to the clinical picture of ballism. It is characterized by lightning-fast, spontaneous, flinging movements of the extremities. The disorder usually only occurs on one side, on the opposite side of the damage (hemiballism). Swallowing disorders and language disorders such as word and phrase repetitions, slurred speech also indicate a disorder in this area.

The electrical stimulation of the subthalamic nucleus in the subthalamus is used therapeutically to alleviate the symptoms of Parkinson's disease.

A failure of the pallidum in the thalamus in the diencephalon causes muscle rigidity and, associated with this, a reduction in motor skills. Diseases that are based on such a disorder are Parkinson's disease, Little's disease, and Wilson's disease.

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