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Intermediate brain
Last reviewed: 04.07.2025
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The diencephalon is not visible on a whole brain preparation, as it is entirely hidden under the cerebral hemispheres. Only on the base of the cerebrum can the central part of the diencephalon, the hypothalamus, be seen.
The gray matter of the diencephalon consists of nuclei related to the subcortical centers of all types of sensitivity. The diencephalon contains the reticular formation, the centers of the extrapyramidal system, the vegetative centers (regulate all types of metabolism), and the neurosecretory nuclei.
The white matter of the diencephalon is represented by ascending and descending pathways, providing two-way communication of subcortical formations with the cerebral cortex and nuclei of the brainstem and spinal cord. In addition, two endocrine glands adjoin the diencephalon - the pituitary gland, which participates together with the corresponding nuclei of the hypothalamus in the formation of the hypothalamic-pituitary system, and the pineal gland of the brain (pineal body).
The diencephalon's boundaries at the base of the brain are the anterior edge of the posterior perforated substance and the optic tracts at the back, and the anterior surface of the optic chiasm at the front. On the dorsal surface, the posterior boundary is the groove separating the superior colliculi of the midbrain from the posterior edges of the thalami. The anterolateral boundary separates the diencephalon and the telencephalon on the dorsal side. It is formed by the terminal strip (stria terminalis), corresponding to the boundary between the thalamus and the internal capsule.
The diencephalon includes the following sections: the thalamic region (the area of the optic thalamus, the optic brain), which is located in the dorsal areas; the hypothalamus, which unites the ventral sections of the diencephalon; the third ventricle.
Thalamic region
The thalamic region includes the thalamus, metathalamus and epithalamus.
Hypothalamus
The hypothalamus forms the lower sections of the diencephalon and participates in the formation of the floor of the third ventricle. The hypothalamus includes the optic chiasm, the optic tract, the gray tubercle with the funnel, and the mammillary bodies.
Third ventricle
The third (III) ventricle (ventriculus tertius) occupies a central position in the diencephalon. The ventricular cavity has the appearance of a sagittally located narrow slit, limited by 6 walls: two lateral, upper, lower, anterior and posterior. The lateral walls of the III ventricle are the medial surfaces of the thalami facing each other, as well as the medial parts of the subthalamic region located below the hypothalamic groove.