FOREBRAIN: CHARACTERISTICS, DEVELOPMENT AND DIFFERENTIATION - GEOGRAFÍA - 2025

The forebrain is a part of the primitive brain that is located in the anterior portion of the brain. It is a structure that develops during the embryonic phase and later divides into more structures.

The forebrain is thus a basic structure to understand the development of the human brain. During the development of the embryo, it is made up of three main structures: forebrain, midbrain, and rhombencephalon.

Main structures of the nervous system in human embryo

Subsequently, the three main structures of the brain develop and divide into more brain regions. In this sense, differentiation appears, that is, the process by which the structures of the embryo and fetus become increasingly complex and developed.

Forebrain characteristics

The forebrain is one of the first brain structures to form in the embryo. In fact, the brain originates through a dilation or vesicle that appears at the cephalic end of the neural tube. This dilation is what is known as the forebrain.

Certain authors choose to name this region of the brain as the forebrain, but both nomenclatures refer to the anterior portion of the brain during the development phase of the embryo.

More specifically, in an embryo the fetal brain can be divided into three basic and main structures: the forebrain, the midbrain and the rhombencephalon.

The forebrain encompasses the region of the brain that is located in the anterior portion, the rhombencephalon constitutes the hindbrain and the midbrain refers to the midbrain.

In this sense, the forebrain is one of the main structures of the brain of embryos and is a main region when it comes to allowing the development of the central nervous system.

The main characteristic of the forebrain is the differentiation process to which it is subjected. That is, the forebrain is not a structure that remains in the human brain, but is only present during the embryonic phase.

As the embryo develops, the forebrain carries out a developmental process that modifies the brain's organization.

Morphological and histological development of the central nervous system

Main subdivisions of the brain of a vertebrate embryo. I, Nrets / CC BY-SA (http://creativecommons.org/licenses/by-sa/3.0/)

During the development phase of the embryo, the brain of the fetus has a reduced and very simple structure that is far from the complex structures that make up the human brain.

In fact, today the human brain has an infinity of regions and structures with different functions and anatomical properties. In contrast, during the development of the embryo, the brain has only three structures.

These three structures are the forebrain itself that encompasses the anterior portion of the brain, the midbrain that makes up the midbrain, and the rhombencephalon that makes up the hindbrain.

Thus, from a histological point of view, the forebrain is the anterior part of the brain that will later be divided into many other regions and structures.

In general, the main morphological changes that give rise to the morphological and histological development of the central nervous system are:

Forebrain

The forebrain is the main division that the central nervous system undergoes during its embryonic development.

However, in the human brain no structure called the forebrain is connoted, since it acquires two main subdivisions: the telencephalon and the diencephalon.

In this sense, the morphological development of the central nervous system motivates the subdivision of the forebrain into two large brain structures: the telencephalon and the diencephalon.

On the other hand, the brain region called the forebrain is the structure that gives rise, through its development, to the appearance of the third ventricle (referring to the diencephalon) and the lateral ventricles (referring to the telencephalon).

Finally, it should be noted that the main structures derived from the forebrain in the human brain are: the cerebral cortex, the basal ganglia, the thalamus and the hypothalamus.

Midbrain

The midbrain is another of the three major regions through which the brain divides during the embryonic development phase. Unlike the forebrain, this structure does not undergo any subdivision, so the presence of the midbrain is still connoted in the adult brain.

However, the morphological and histological development of this brain region gives rise to the appearance of structures and ventricles that are not present at first. These are: the aqueduct of Silvio and the tectum.

Rhombencephalon

Finally, the rhombencephalon defines the third major structure of the central nervous system during the development phase of the embryo.

In the same way as the forebrain, the rhombencephalon undergoes a subdivision and gives rise to the appearance of two main brain structures: the metencephalon and the myelencephalon.

Likewise, the morphological and histological development of this brain region motivates the development of the fourth ventricle and highly relevant structures such as the cerebellum, the pons, or the medulla oblongata.

Differentiation process

Differentiation is the process by which the structures of the embryo and fetus develop and acquire more and more extensive and complex properties.

In this sense, the first step in the differentiation of the brain is the formation of a neural tube of three vesicles at the end of the primitive brain.

These three vesicles are vital when it comes to starting brain development. Specifically, the anterior vesicle forms the forebrain or forebrain, the second vesicle forms the midbrain or midbrain, and the third vesicle forms the hindbrain or rhombencephalon.

Likewise, the rhombencephalon develops in such a way that it establishes a connection with the rest of the primitive neural tube and ends up being transformed into the spinal cord.

Prosencephalon subdivision

The forebrain is a structure that motivates the constitution of brain elements important for the development of the central nervous system. Specifically, the forebrain gives rise to:

-Two optic vesicles that through the evolutionary process separate from the forebrain and constitute the two retinas of the eye (one in the right eye and one in the left eye). This fact reveals two main elements: the forebrain plays a major role in the development of vision, and the retina, contrary to what it may seem, is a tissue that is part of the central nervous system.

-The telencephalic vesicles which acquire a slow and gradual development. When these vesicles complete their development, they originate the cerebral hemispheres.

-The diencephalon, which is a unique structure that in turn differentiates into multiple important brain regions such as the thalamus or the hypothalamus.

Structures developed from the forebrain

The forebrain is a simple and underdeveloped brain structure. However, it constitutes a basic brain region since it gives rise to the formation of highly important structures of the brain.

The forebrain causes the development of the telencephalon, the uppermost region of the brain. The telencephalon contains important structures such as the basal nuclei or the nucleus accumbens, which are responsible for interconnecting the cerebral cortex with subcortical regions.

Likewise, the forebrain causes the development of the diencephalon, a region of the brain that contains important structures such as the hypothalamus, the thalamus or the epithalamus.

-Diencephalon

Diencephalon

The forebrain develops until it is finally subdivided into diencephalon and telencephalon. The diencephalon is the part of the brain that lies between the midbrain (midbrain) and the telencephalon.

The most important anatomical regions that this region of the brain presents are: hypothalamus, subthalamus, thalamus, epithalamus and metathalamus.

Hypothalamus

Hypothalamus (orange)

It is a small organ that is located inside the intermediate temporal lobe of the brain. It forms the base of the thalamus, the place where the pituitary gland is located, and performs functions related to the regulation of the hormonal system, autonomous visceral activities, sexual impulses, and feelings of hunger and thirst.

Subthalamus

It is a small structure that contains the red nucleus and the gray matter of the brain.

Thalamus

It is the most important region of the diencephalon. It is made up of two voluminous masses located under the cerebral hemispheres and constitutes the route of entry for all sensory stimuli except smell.

Epithalamus

It is a structure of the diencephalon that is located on the thalamus and includes the hypophysis (neuroendocrine gland), the habenular nuclei and the medullary striae.

Metathalamus

It is a region that contains the medial geniculate body, a structure that acts as a relay station for nerve impulses between the lower peduncle and the auditory cortex.

-Tencephalon

The telencephalon is the uppermost region of the brain, which is located above the diencephalon. This region derived from the forebrain contains two main structures: the striatum and the amygdala.

Striated body

It is a structure that contains the basal nuclei (caudate and putamen), which are responsible for interconnecting the diencephalon with the cerebral cortex. Likewise, it is a structure related to body movement and reinforcement.

Amygdala

Tonsil (blue)

It is a structure that is part of the limbic system along with the thalamus, the hypothalamus, the hippocampus and the corpus callosum. Its main function lies in the processing of emotions.

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