Diencephalon

diencephalon (dī'ənsĕf`əlŏn): see brain.

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diencephalon [¦dī·en′sef·ə‚län]

(embryology)

The posterior division of the embryonic forebrain in vertebrates.

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Diencephalon 

the section of the brain that consists of the most anterior (in man, the topmost) part of the brain stem, over which the cerebral hemispheres are located.

Inferiorly and posteriorly, the diencephalon borders on the mesencephalon (midbrain). The central portion of the diencephalon, around which the other parts are grouped, is the thalamus. These other parts are the epithalamus, which includes the epiphysis; the hypothalamus, which is connected to the pituitary, or hypophysis; and the subthalamic nucleus. The formations of the diencephalon perform a number of very important functions: they participate in the organization of the body’s sensory processes (sensitivity), motor functions, and autonomic (visceral) activities. The diencephalon plays a very important role in processes related to emotional reactivity and the states of sleep and wakefulness, as well as in the autoregulatory processes of the brain, which are reflected in the overall electrical activity of its higher areas, as recorded in the electroencephalogram. The diencephalon processes and switches the currents of neural impulses that enter from the various sense organs and signal shifts in the body’s external and internal environments. It does the same with impulses from various brain structures and directs them to other areas of the brain, including the cerebral cortex.

L. P. LATASH

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Diencephalon 

the section of the brain at the base of the large hemispheres that is the extreme anterior part (in humans the superior part) of the brain stem. The different portions of the diencephalon are the thalamus, hypothalamus, and subthalamus. Together they have very important functions; for example, they participate in the organization of the sensory processes of brain analyzers and in the performance of autonomic functions. Other bodily functions they affect are sleep, memory, instinctive behavior, and emotional and motivational processes. The structures of the diencephalon are associated with the perception of pain sensations and with the integration of the processes that maintain homeostasis. The functions of the glands of internal secretion are regulated through releasing hormones (releasing factors) produced by the neurosecretory cells of the hypothalamus. Aldosterone is produced, for example, by the adrenal cortex with the participation of a special polypeptide from the hypothalamus.

L. P. LATASH