The diencephalon and the telencephalon form the brain, which corresponds to the forebrain. The brain is the most developed part of the brain and occupies about 80% of the cranial cavity. The diencephalon is an odd structure that is only seen in the lower portion of the brain. The diencephalon comprises the following parts: thalamus, hypothalamus, epithalamus and subthalamus, all related to the III ventricle.

Diencephalon Division

III Ventricle:

 It is an odd diencephalon cavity 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 median sagittal plane, the lateral walls of the III ventricle are exposed widely; There is then a depression, the hypothalamic groove, which extends from the cerebral aqueduct to the interventricular foramen. The portions of the wall above this groove belong to the thalamus; and those below belong to the hypothalamus.

In the floor of the III ventricle, from anterior to posterior, there are the following formations: optic chiasm, infundibulum, tubercle and nipple bodies, belonging to the hypothalamus. Joining the two thalamus, a structure formed by gray matter, the adherence is often observed. intetalamica, which appears only sectioned.

 Diencephalon - Medial View
Source: NETTER, Frank H .. Atlas of Human Anatomy. 2 ed. Porto Alegre: Artmed, 2000.

The very small posterior wall of the ventricle is formed by the epithalamus, which is located above the hypothalamic sulcus. Leaving either side of the epithalamus and traversing the highest part of the sidewalls, there is a bundle of nerve fibers, the medullary striae of the thalamus, where the choroidal mesh forming the roof of the III ventricle is inserted. From the choroidal screen, the ventricular lumen of the III ventricle is invaginated in the ventricular lumen, which are arranged in two parallel lines and are continuous, through the respective interventricular foramina, with the choroidal plexus of the lateral ventricles.

The anterior wall of the III ventricle is formed by the terminal lamina, thin lamina of nervous tissue, which joins the two hemispheres and is arranged between the optic chiasm and the anterior commissure. The anterior commissure, the terminal lamina, and the adjacent parts of the lateral walls of the III ventricle belong to the telencephalon. The light of the III ventricle travels to form four recesses in the infundibulum region:

 Infundibulum recessabove the optic chiasm;

 Optical Recess;

 Pineal Recesson the pineal gland stem;

 Suprapineal recessabove the pineal body.


Thalamus - Medial ViewThe thalamus, about 3 cm long, making up 80% of the diencephalon, consists of two paired ovulated masses of gray matter, organized in nuclei, with white matter tracts inside. In general, a gray matter connection, called intermediate mass (intertalamic adhesion), joins the right and left parts of the thalamus. The anterior end of each thalamus has an eminence, the anterior thalamus tubercle, which participates in the delimitation of the interventricular foramen.

The posterior extremity, considerably larger than the anterior, presents a great eminence, the pulvinar, that projects over the lateral and medial geniculate bodies.

The medial geniculate body is part of the auditory pathway, and the lateral one of the optic pathway, and both are considered by some authors as a division of the diencephalon called the metathalamus.

Source: NETTER, Frank H .. Atlas of Human Anatomy. 2 ed. Porto Alegre: Artmed, 2000.

Medial and lateral geniculate body

The lateral portion of the superior aspect of the thalamus is part of the floor of the lateral ventricle and is covered by ependymal epithelium (epithelium that covers this part of the thalamus and is called the fixed lamina). The medial portion of the thalamus forms the lateral wall of the III ventricle, whose roof consists of the fornix and corpus callosum, telencephalic formations. The transverse fissure is occupied by a sink bottom sack which then enters the constitution of the choroidal screen. The lateral surface of the thalamus is separated from the telencephalon by the inner capsule, a compact bundle of fibers that connects the cerebral cortex to subcortical nerve centers. The underside of the thalamus continues with the hypothalamus and subthalamus.

Source: NETTER, Frank H .. Atlas of Human Anatomy. 2 ed. Porto Alegre: Artmed, 2000.

Some nuclei transmit impulses to the sensory areas of the brain:

 Medial Geniculate Body - transmits auditory impulses;

 Lateral Geniculate Body - transmits visual impulses;

 Posterior Ventral Body - transmits impulses to taste and somatic sensations such as touch, pressure, vibration, heat, cold and pain.

Thalamic cores can be divided into five groups:

 Previous Group

 Later Group

 Side group

 Median Group

 Medial group

Thalamus nuclei
Thalamus Cores
Source: NETTER, Frank H .. Atlas of Human Anatomy. 2 ed. Porto Alegre: Artmed, 2000.

The thalamus serves as an intermediate station for most fibers that run from the lower brain and spinal cord to the sensitive areas of the brain. The thalamus classifies the information, giving us an idea of the sensation we are experiencing, and directs it to specific areas of the brain for more accurate interpretation.

Thalamus Functions:


 Motor skills;

 Emotional Behavior;

 Cortex Activation;

 Plays some role in the wake mechanism, or alertness.

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Hypothalamus It is a relatively small area of the diencephalon, located below the thalamus, with important functions mainly related to visceral activity.
The hypothalamus is part of the diencephalon and is located on the walls of the III ventricle, below the hypothalamic sulcus, which separates
the thalamus. It has some visible anatomical formations on the underside of the brain: the optic chiasm, the tubercle, the infundibulum, and the nipple bodies. It is a very small area (4 g) but, nonetheless, the hypothalamus, by its numerous and varied functions, is one of the most important areas of the nervous system.

Nipple Bodies
: are two rounded eminences of gray matter evident on the anterior part of the interpeduncular fossa.

Optic Chiasma: It is located in the anterior part of the ventricular floor. It receives myelinic fibers from the optic nerve, which cross it in part and continue into the optic tract that travels to the lateral geniculate bodies after circumventing the brain peduncles.

Téber Cinéreo: This is a slightly gray, medium area behind the chiasm and optic tract between the nipple bodies. In the cinereal tube, the pituitary is attached by means of the infundibulum.

Infundibulum: It is a funnel-shaped nerve formation that attaches to the cinereal tube, containing small extensions of the ventricular cavity, the infundibulum recess. The upper extremity of the infundibulum dilates to constitute the median eminence of the cineal tube, while the lower extremity continues with an infundibular process, or pituitary lobe. The pituitary is contained in the turgical saddle of the sphenoid bone.

Hypothalamus - Medial View

 Hypothalamus - Medial View
Source: NETTER, Frank H .. Atlas of Human Anatomy. 2 ed. Porto Alegre: Artmed, 2000.

The hypothalamus is fundamentally made up of gray matter that is grouped into nuclei. Across the hypothalamus there are also varied fiber systems, such as the fornix. It runs up and down each half of the hypothalamus, ending in its nipple body. Impulses from neurons whose dendrites and cell bodies are located in the hypothalamus are driven by their axons to neurons located in the spinal cord, and then many of these impulses are then transferred to muscles and glands throughout the body.

Hypothalamus Functions:

 Autonomic nervous system control;

 Body temperature regulation;

 Regulation of emotional behavior;

 Sleep and wake regulation;

 Regulation of food intake;

 Regulation of water intake;

 Diuresis regulation;

 Regulation of the endocrine system;

 Generation and regulation of circadian rhythms.


Epithalamus It subsequently limits the III ventricle, above the hypothalamic sulcus, already in transition with the midbrain. Its most evident element is the pineal gland, the piriform, odd and median endocrine gland, which rests on the mesencephalic ceiling. The base of the pineal body attaches anteriorly to two transverse bundles of fibers that cross a median plane, the posterior commissure and the commissure of the habenulae, between which a small extension of the ventricular cavity, the pineal recess, penetrates into the pineal gland.

The posterior commissure is located at the extension in which the cerebral aqueduct connects to the III ventricle and is considered as the limit between the midbrain and the diencephalon. The commissure of the habituids interposes between two small triangular eminences, the trigons of the habenula. These are located between the pineal gland and the thalamus and continue anteriorly on each side with the thalamic spinal cord. The chorioid mesh of the III ventricle inserts laterally into the medullary striae of the thalamus and, subsequently, into the commissure of the habituids, thus closing the III ventricle.

 Epithalamus - Medial View
Source: NETTER, Frank H .. Atlas of Human Anatomy. 2 ed. Porto Alegre: Artmed, 2000.

Therefore, the epithalamus is formed by:

Haben's Trine - triangular area at the posterior end of the thalamus tapeworm near the pineal body.

Pineal body - is a gland-like structure, approximately 8 mm long, which lies between the upper colliculi. Although its physiological role is not yet fully understood, the pineal gland secretes the hormone melatonin, thus being an endocrine gland. Melatonin is considered the sleep promoter and also seems to contribute to the body's biological clock adjustment.

Later Commissioner - is a rounded fiber bundle that crosses the midline at the junction of the aqueduct with the third anterior ventricle and superior to the superior colliculus. Marks the boundary between the midbrain and diencephalon.

 Epithalamus - Top View
Source: NETTER, Frank H .. Atlas of Human Anatomy. 2 ed. Porto Alegre: Artmed, 2000.

Except for the posterior commissure, all nonendocrine epithelial formations belong to the limbic system and are thus related to the regulation of emotional behavior.


It comprises the transition zone between the diencephalon and the midbrain integument. Its visualization is better in frontal sections of the brain. It is found to be located below the thalamus, limited laterally by the inner capsule and medially by the hypothalamus. The subthalamus has white and gray matter formations, the most important being the subthalamic nucleus. Subtalamic nucleus damage causes a syndrome known as hemibalism, characterized by abnormal movements of the extremities.

Structures of
Nervous system
Nervous tissue

Spinal cord




Meninges and CSF

Brain Vascularization

Peripheral Nervous System


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