Diencephalon. Anatomical structure that is part of the central portion of the human nervous system . It is located below the corpus callosum and the fornix fusing on the sides with the cerebral hemispheres. It has two parts: the thalamoencephalon and the hypothalamus . Its ependymal cavity is the third ventricle.
Summary
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- 1 Situation and portions
- 2 Thalamus-brain
- 1 Thalamus
- 2 Epithalamus
- 3 Metathalamus
- 3 Internal configuration of the thalamus
- 4 Hypothalamus
- 5 Sources
Situation and portions
The diencephalon is located below the corpus callosum and the fornix, fusing at the sides with the hemispheres of the telencephalon . Two main portions are distinguished: a phylogenetically younger dorsal, the thalamoencephalon, which is a center of afferent pathways and a ventral, phylogenetically older, hypothalamus, which is a superior vegetative center
The ependymal cavity of the diencephalon is the III ventricle which communicates with the IV through the midbrain aqueduct and with the lateral ventricles of the telencephalon through the interventricular holes.
Thalamoencephalon
Structure of the diencephalon.
The thalamus-brain consists of three parts:
Thalamus
It represents a large even accumulation of gray matter on both sides of the III ventricle and is shaped like an egg , with its sharp anterior end called the anterior tubercle and the posterior one enlarged and thickened called the pulvinar of the thalamus . The gray matter of the thalamus is divided into sheets of white matter called medullary sheets, in several nuclei. Its name depends on its topographic location: anterior, central, medial, median, lateral, and a series of ventral nuclei: ventralposterolateral, ventralposteromedial, etc.
Epithalamus
The medullary striae of both thalamus are directed backwards and form on either side a triangular widening called the trine of the habenulas . From each of these, the so-called habenules depart, supporting the pineal body with the opposite side .
Metathalamus
Located behind the thalamus are in the form of two small eminences, the lateral and medial geniculate bodies.
Internal configuration of the thalamus
The thalamus is a very important suprasegmental structure, which develops by forming a functional anatomical complex with the cerebral cortex.very important in the integration of the afferent pathways, as well as the motor systems. The gray matter of the thalamus is divided into groups of nuclei by the medullary laminae. These sheets are made up of white matter and are two: medial medullary lamina and lateral medullary lamina. Thalamic nuclei are classified according to their suprasegmental functional relationships into 3 types: nuclei of specific projection, nuclei of thalamocortical association and nonspecific nuclei. Specific projection nuclei are characterized by receiving specific segmental and suprasegmental inputs and by sending specific inputs to circumscribed areas of the neocortex. This group of nuclei occupies the ventral and lateral portion of the thalamus, as well as the anterior extremity of it.
Thalamocortical association nuclei are characterized by receiving their afferent fibers from the other thalamic nuclei and sending their efference to wide areas of the neocortex and then receiving connections from it (thalamocortical reverberant circuits). These nuclei occupy the dorsal portion and almost the entire posterior extremity of the thalamus. The nonspecific nuclei are made up of the thalamic reticular complex and a group of nuclei that occupies the medial portion of the thalamus in front of the pulvinar and behind the anterior nucleus. These nuclei have diffuse connections with the cerebral cortex.
Hypothalamus
The hypothalamus is made up of structures located below the hypothalamic groove. In correspondence with embryonic development, the hypothalamus is morphologically divided into two parts: an anterior or optic, whose name corresponds to its position after the optic chiasm and is made up of a series of macroscopic structures such as the tuber cinereum , the infundibulum and the neurohypophysis . Another posterior or olfactory one made up of the mamillary bodies, the posterior perforated substance and the subthalamic region. All these structures mentioned, although considered morphologically hypothalamic, are not really the ones that attract attention in the study of the hypothalamus.
What is really interesting and important is the knowledge of the nuclei that are described in their internal configuration which participate in the regulation of important neurohormonal mechanisms of the organism and which will be described in other chapters. Within these nuclei we can mention the supraoptic, the paraventricular, ventromedial, lateral hypothalamus, etc. Physiologically, the hypothalamus is one of the key pieces of the limbic system. It has important functions in the control of the regulation of the autonomic portion of the nervous system , of the regulation of temperature , thirst , hunger and also in the regulation of reproductive function, etc.
