WHAT IS THE DIENCEPHALON?

The diencephalon derives from the forebrain or forebrain, the most frontal part of the brain in early embryonic development. As the forebrain grows, it divides into the diencephalon and the telencephalon until it becomes a bridge between the midbrain and the telencephalon.

It is located below the corpus callosum and fornix, and joins the hemispheres of the telencephalon on the sides. Therefore, it is located in the middle part of the brain.

Structures in the diencephalon have connections with the rest of the nervous system, including the cortical and subcortical areas. Therefore, it is a center that sends and receives nervous signals (afferents and efferents, respectively) and plays a fundamental role in the proper functioning of multiple biological processes.

FACTS ABOUT THE DIENCEPHALON

The diencephalon is the control center that makes our body maintain its internal balance or homeostasis. We show you some of its curiosities:

• It represents only 2% of the total weight of the nervous system.

• The pituitary is connected to the hypothalamus and is involved in processes such as reproduction and growth through the action of hormones.

• Maintains body temperature.

• Regulates appetite and therefore food intake.

• An area of the epithalamus called the habenula is associated with both fear and depression.

• Regulates the endocrine activity of the adenohypophysis (or anterior pituitary).

• It is the main modulator of the functioning of the Vegetative Nervous System.

THE DIENCEPHALON, STRESS AND EMOTIONS

Additionally, the diencephalon takes involved in the neuroendocrine reactions to stress. In fact, a published study on the relationship between the hypothalamic-pituitary-adrenal axis and stress appears in the journal Dialogues in Neuroscience. It indicates that animals, to respond to stress, activate a range of physiological and behavioural responses associated with this axis.

The authors explain stress as a state of real or perceived threat. As the hypothalamus regulates homeostasis, it manages the situation by working in conjunction with the nervous, endocrine and immune systems.

Likewise, the enormous importance of the hypothalamus in the generation of emotional behaviors has been demonstrated. H. Nakao, in a study published in the American Journal of Physiology, proved that the stimulation of the hypothalamus in cats through implanted electrodes led to aggressive responses.

Thanks to the diencephalon, a little known “great administrator”, communication between cortical and subcortical levels is possible. It also allows us to maintain the balance of our body and the regulation of our emotions, always hand in hand with other systems. A fantastic and efficient control centre.

MAIN STRUCTURAL DIVISIONS OF THE DIENCEPHALON

1. Thalamus

2. Hypothalamus

3. Epithalamus

4. Subthalamus

1. THALAMUS

• It is a mass located in both hemispheres brain.

• Easily visible near the third ventricle.

• Its interior is formed by gray matter (nuclei of neurons) with projections to the cerebral cortex.

THALAMUS – FUNCTIONAL CONSIDERATIONS

• Structure located above the hypothalamus, works as a radio station relay of sensory impulses from the periphery, acting as a “filter” that modulates the information that is sent to the cerebral cortex, as well as reaching the consciousness of the individual.

• Participates in the motor information integration network between the nuclei of the base and cerebellum, and as a relay of motor information to the brain.

• Contrary to what was previously thought, the thalamus not only passes on information to cortex, but it processes higher order information, with the participation of active form in functions usually attributed to the cortex.

• Sensory Functions: The thalamus filters, modulates and distributes all inputs sensory to the various cortical areas.

• Motor functions: It has a relay function between the cerebellum-cortical circuits.

• Emotional functions: Some of its nuclei are part of the limbic system with branches to the prefrontal cortex. Reaction mediation functions to anger, fear and defense.

• Cortical activation function: Some of your nuclei make connection between the reticular activating system and the cerebral cortex. Important functions to protect from some danger or in sleep-wake cycles.

CLINICAL PATHOLOGY OF THE THALAMUS

• A stroke in the arteries supplying the thalamus leads to anesthesia or paresthesia of the opposite half of the thalamic lesion in the individual's body. Being this sense of top of the neck to the tip of the toes. There may be motor difficulties.

• Thalamic pain syndrome: Sensation of pain opposite the thalamic area affected, without peripheral injuries to justify it. This pain is caused dysfunction of the pain pathways that pass through the thalamus.

• Fatal familial insomnia: Rare and hereditary disease, manifests as a result of severe damage to the thalamus. With the cells of this structure destroyed, the individual loses the ability to sleep, dying between six and eighteen months.

2. HYPOTHALAMUS

• It is an important structure for regulating the body's homeostasis.

• Controls the autonomic nervous system as well as all functioning body hormone.

• Much of this regulation is done through its influence on the gland pituitary gland, which secretes the main hormones that stimulate the other glands in the body.

HYPOTHALAMUS – FUNCTION OF THE MAIN NUCLEI

• Supraoptic and paraventricular nucleus: Water balance (regulation of diuresis).

• Suprachiasmatic nucleus: Regulation of the circadian cycle (biological clock).

• Posterior hypothalamic area: Controls the body's conservation of heat.

• Anterior hypothalamic area: Controls body heat loss. 

• Medial preoptic nucleus: Controls blood pressure.

• Ventromedial nucleus: Satiety.

• Mammillary body: Feeding.

HYPOTHALAMUS – THE PITUITARY PHYSIS

• It is also known as the pituitary gland. Having dimensions approx. a pea grain, weighing between 0.5 to 1 gram.

• It is located at the base of the brain, below the hypothalamus, being connected to it by the pituitary stalk or infundibulum.

• It is considered a master gland, because it secretes hormones that control the functioning of other glands.

• It is separated into two sections anatomically:

> Neurohypophysis – posterior pituitary. 

> Adenohypophysis – anterior pituitary.

PITUITARY PATHOLOGIES

• Acromegaly: Disorder caused by excess GH, also known as gigantism. There may also be growth hormone deficiency. These conditions affect the body, both physically and cognitively.

• Diabetes insipidus: Caused by reduced production of vasopressin. if characterized by a large increase in the production of urine, which causes thirst, and consequently increase in water intake.

• Hypopituitarism: Endocrine disease characterized by reduced production of one or more pituitary hormones. When there is a reduction in most hormones, this condition is given the term panhypopituitarism. Consequently, the reduction of one or more pituitary hormones will influence the functioning of other glands in the body.

3.EPITHALAMUS

• Structure posterior to the diencephalon, being a central segment of the brain. He has as one of its main structures the pineal gland.

• It is an important communication path between the limbic system, base nuclei and other areas of the brain.

• Thanks to the retina and impulses arriving through the suprachiasmatic nucleus it becomes possible, through light, the production of melatonin. this hormone secreted by the pineal gland is directly responsible for our cycle of sleep/wake.

• Because of this, dark or low light environments stimulate the production of melatonin. While environments with plenty of light inhibit its production.

4.SUBTHALAMUS

• It is a structure that is not easily observable. Being located in the area transition between the diencephalon and the midbrain.

• The subthalamic nucleus plays an important role among the circuits of the cortex cerebral cortex and the basal nuclei, these being fundamental for the regulation of motricity.

• Lesions in this region are responsible for a syndrome known as hemiballismus, which consists of involuntary movements of the extremities of the body. In Parkinson's disease it is one of the pathways affected.

III VENTRICLE

It is a unique cavity in the diencephalon that communicates with the IV ventricle through the cerebral aqueduct and with the lateral ventricles through the respective interventricular foramina.

Third Ventricle When the brain is sectioned in the midsagittal plane, the lateral walls of the third ventricle are exposed widely; the existence of a depression, the hypothalamic sulcus, is then verified, which extends from the cerebral aqueduct to the interventricular foramen.The thalamus is responsible for the portions of the wall above this groove, while the hypothalamus is responsible for the parts of the wall below.

On the floor of the III ventricle, from anterior to posterior, the following formations are found: optic chiasm, infundibulum, cinereous tubercle and mammillary bodies, belonging to the hypothalamus. intethalamia, which appears only sectioned.