We are talking about the “little brother” of the telencephalon.
This structure differentiates into 4 main parts during embryonic development, the forebrain, the midbrain, the hindbrain, and the spinal cord. Of these, the forebrain represents the most developed part in humans, which ends up forming both the diencephalon inside the brain and the telencephalon, which covers it .
In this article we will talk about the diencephalon, an internal brain structure with various functions ranging from movement to emotions or our circadian cycle.
The diencephalon, parts and functions
The diencephalon, unlike the telencephalon that ends up forming the cerebral cortex and other internal structures such as the basal ganglia, forms several internal structures located on both sides of the third cerebral ventricle , one of the 4 cavities filled with cerebrospinal fluid that protect the brain of movement and shock.
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.
Within the different parts of the diencephalon we can highlight the following.
1. The hypothalamus
The hypothalamus is located, as its name suggests, just below the thalamus, another important structure of the diencephalon. It is located in a very central location within the brain, just like the pituitary gland with which it is associated.
The functions of the hypothalamus are several of vital importance for the functioning of the organism, such as homeostasis -the maintenance of normal conditions, such as those of body temperature-, as well as playing a role in sexual desire, hunger and thirst. It is also involved in sleep and memory processes, as well as in the function of sex hormones .
The hypothalamus is considered one of the largest endocrine control centers in the human body . The signals that this part of the diencephalon emits condition a large number of hormones from the endocrine system, thanks to the release of hormones that they cause in the pituitary gland, also known as the pituitary gland.
2. The thalamus
The thalamus corresponds to one of the largest structures in the diencephalon , made up mainly of gray matter, rich in neuronal bodies.
Nerve impulses pass through the thalamus from the central to the peripheral nervous system and vice versa, this being the place where sensory signals are integrated for later 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 familial insomnia is a disease in which the thalamus mainly degenerates, causing the patient to eventually lose their ability to sleep, leading to death. Other damage to the thalamus can 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 tasks related to spatial memory , which allows us to associate events and characteristics with places in our environment.
Other functions of the thalamus also include control of the sleep-wake cycle (also known as the 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 hypophysis, is a small glandular body that is attached to the hypothalamus . It is responsible for translating the neuronal impulses that reach it through the diencephalic structure due to its connection with hypothalamic neurons, into hormonal signals with effects throughout the body and of longer duration than nerve impulses.
It is connected to the limbic system, responsible for 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, responsible for producing sex hormones.
Other functions of the pituitary gland include the 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 habenulae -cell nuclei with limbic and motor functions- and the pineal gland. It has important functions within the limbic system, connecting it to other parts of the brain, including, for example, control of the circadian rhythm through the pineal gland.
Its central position in the brain led some thinkers such as René Descartes to assume -erroneously- a role for 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 photosensing 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 ticks the days and nights according to sunlight. Several factors in our body are regulated by this biological clock, which is not unique to humans or only to organisms that have a brain, since these rhythms have also been observed in plants, fungi and bacteria.
5. The subthalamus
The subthalamus is a complex structure located in the brainstem, made up of both white matter structures rich in neuronal axons and gray matter, composed mainly of neuronal bodies. It is found limiting the thalamic area of the diencephalon with the tegmentum area, which belongs to the midbrain. In addition, it has a lateral connection with the hypothalamus.
The subthalamus 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 posture maintenance.
The subthalamus is also related to the regulation of optical and vestibular information -that which has to do with balance-. Disorders that affect the subthalamus usually present motor symptoms , as is the case with Huntington’s Chorea.
6. Retina and optic nerve
The optic nerve is a part of the diencephalon, since it is attached to this brain structure . Like the retina, these visual structures are formed from cells of the embryonic diencephalon, but they differ from the rest of the neuronal tissue. These structures translate light into nerve impulses, which will then be analyzed in the rest of the brain.
The optic nerve is fixed to the diencephalon and the retina itself is a part of cells from the embryonic diencephalon.
Bibliographic references
- Gray, Henry (1858), Anatomy: Descriptive and Surgical, London: John W. Parker and Son
- Hall, John E. (2011). Treatise on Medical Physiology (Twelfth Edition). Barcelona: Elsevier. pp. 714-716. ISBN 978-84-8086-819-8
- Evarts, E V; Thach, W T (1969). “Motor Mechanisms of the CNS: Cerebrocerebellar Interrelations”. Annual Review of Physiology. 31: 451–98. doi:10.1146/annurev.ph.31.030169.002315.
- Zarranz JJ, Arteagoitia JM, Atares B, Rodriguez-Martinez AB, Martinez-de-Pancorbo M, et al (2007). «The spongiform encephalopathies or prion diseases in the Basque Country». GacMedBilbao 104(2):64–69. PMID 10371520. doi:10.1016/S0304-4858(07)74572-9.
- Burgess, N., Maguire, E., & O’Keefe, J. (2002). The Human Hippocampus and Spatial and Episodic Memory. Neuron, 35(4), 625-641. doi:10.1016/s0896-6273(02)00830-9.
To the classic question “what do you do?” I always answer “basically I am a psychologist”. In fact, my academic training has revolved around the psychology of development, education and community, a field of study influenced my volunteer activities, as well as my first work experiences in personal services.