The Diencephalon: Structure and Function of this Brain Region

When it begins to develop, the central nervous system is made up of three sections: the prosencephalon, midbrain, and rhomboid. These initial structures will later give rise to the various parts of the adult brain, including the diencephalon.

In this article we will describe the structure and functions of the diencephalon, which includes such important regions as the thalamus and hypothalamus and allows for the correct functioning of multiple biological processes, such as the secretion of hormones and the regulation of the autonomic system.

This structure is differentiated into 4 main parts during embryonic development, the prosencephalon, the midbrain, the hindbrain and the spinal cord. Of these, the prosencephalon represents the most developed part in humans, that ends up forming both the diencephalon inside the brain and the telencephalon, which covers it.

The diencephalon, parts and functions

Diencephalon Location

This brain region has a central location within the brain, it is located between the cerebral hemispheres and the brain stem, and through it travel most of the fibers that go to the cerebral cortex.

The diencephalon, unlike the telencephalon that ends up forming the cerebral cortex and other internal structures such as the basal ganglia, is found forming several internal structures located on both sides of the brain. third ventricle of the brain .One of the 4 cavities filled with cerebrospinal fluid that protect the brain from movement and impact.

Midsagittal view of the brain. Visible are the structures situated on the medial aspect of the cortex as well as subcortical areas, which include the corpus callosum, septum pellucidum, fornix, diencephalon, and brainstem structures.

These structures are closely related to each other and can collaborate to carry out specific tasks. The diencephalon, moreover, is the part of the brain that integrates most sensory information before transmitting it to the cerebral cortex, where it is analyzed and processed.

Parts of the Diencephalon

1. The hypothalamus

The hypothalamus is, as its name suggests, just below the thalamus, another important structure of the diencephalon. It is in a very central location within the brain, as is the pituitary gland with which it is associated.

The functions of the hypothalamus are several of vital importance to the functioning of the body, such as homeostasis – the maintenance of normal conditions, such as body temperature, as well as plays a role in sexual desire, hunger and thirst. Also participates in sleep and memory processes, as well as in the function of sex hormones.

The hypothalamus is considered one of the largest centers of endocrine control of the human body.. The signals that this part of the diencephalon emits condition a large amount of hormones in the endocrine system, thanks to the release of hormones that they cause in the pituitary gland, also known as the pituitary gland.

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2. The thalamus

The thalamus corresponds to one of the largest structures in the diencephalon.It is made up mainly of grey matter, rich in neuronal bodies.

Nerve impulses pass through the thalamus from the central nervous system to the peripheral and vice versa, this being the place where sensory signals are integrated for subsequent interpretation in other areas of the brain, such as the cortex.

The thalamus is related to important thought processes, such as consciousness, sleep, or alertness. In fact, the hereditary disorder of fatal family insomnia is a disease in which the thalamus mainly degenerates, causing the patient to end up losing his or her ability to sleep, causing death. Other damage to the thalamus may result, for example, in comatose states of varying severity.

It is also related to the hippocampus, a structure of the cerebral cortex with functions related to long-term memory. The thalamus also facilitates work related to spatial memory which allows us to associate events and characteristics to places in our environment.

Other functions of the thalamus also include control of the sleep-wake cycle (also known as circadian rhythm), as well as being key in processes related to attention span, awareness, and emotional regulation.

3. Pituitary gland

The pituitary gland, also known as the pituitary gland, is a small glandular body attached to the hypothalamus. It is in charge of translating the neuronal impulses that arrive through the diencephalic structure by its connection with the hypothalamic neurons, in hormonal signals with effects for the whole organism and of longer duration than the nervous impulses.

It has a connection with the limbic system, in charge of emotional control, in addition to controlling other important parts of the endocrine system, such as the thyroid gland or the adrenal glands, as well as the gonads, in charge of producing sex hormones.

Other functions of the pituitary gland include secretion of hormones that control growth, blood pressure, energy expenditure, osmotic control of the kidneys, temperature control, pain relief, as well as certain processes related to pregnancy and lactation.

4. The epithalamus

The epithalamus is a dorsal part of the diencephalon, which is formed mainly by the habenulas -cellular nuclei with limbic and motor functions- and the pineal gland. It has important functions within the limbic system, connecting it with other parts of the brain, which for example include controlling the circadian rhythm through the pineal gland.

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Its centric position in the brain led some thinkers such as RenĂ© Descartes to erroneously assume a role of this gland as the “seat of the soul”, supposedly having important functions in memory or emotions.

Evolutionarily, the pineal gland is related to the parietal eye.a photosensor organ that can be found in some reptiles and amphibians, which allow them to more accurately detect changes in ambient lighting.

The circadian rhythm is a “biological clock” system that marks days and nights according to sunlight. Several factors of our organism are regulated by this biological clock, which is not unique to humans nor only to organisms with brains, since these rhythms have also been observed in plants, fungi and bacteria.

5. The subtalamus

The subalamus is a complex structure located in the brainstem, formed both of white matter structures rich in neuronal axons and of grey matter, composed mainly of neuronal bodies. It is bordering the thalamic zone of the diencephalon. with the zone of the tegmentum, which belongs to the midbrain. It also has a lateral connection to the hypothalamus.

The subtalamo is responsible for integrating part of the motor information, especially those involuntary aspects, thanks to its joint action with the striatum, part of the telencephalon. These include reflexes or maintaining posture.

The sublamo is also related to the regulation of optical and vestibular information – that which has to do with equilibrium. Disorders affecting the subtalamus often have motor symptoms as is the case with Huntington’s Korea.

6. Retina and optic nerve

The optic nerve is a part of the diencephalon. is attached to this brain structure. Like the retina, these visual structures are formed from cells of the embryonic diencephalon, but differ from the rest of the neuronal tissue. These structures translate light into nerve impulses, which are then analyzed in the rest of the brain.

The optic nerve is attached to the diencephalon and the retina itself is a part of cells from the embryonic diencephalon.

Diencephalon anatomy