Thalamus

thalamus (thăl`əməs), mass of nerve cells centrally located in the brain just below the cerebrum and resembling a large egg in size and shape. The thalamus is a routing station for all incoming sensory impulses except those of smell, transmitting them to higher (cerebral) nerve centers. In addition, it connects various brain centers with others. Thus the thalamus is a major integrative complex, enabling sensory stimuli to evoke appropriate physical reactions as well as to affect emotions. With the hypothalamus, the thalamus establishes levels of sleep and wakefulness. It is also vital to the neural feedback system controlling brain wave rhythms.

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thalamus [′thal·ə·məs]

(anatomy)

Either one of two masses of gray matter located on the sides of the third ventricle and forming part of the lateral wall of that cavity.

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thalamus, thalamium

In early Greek architecture, an inner room or chamber, esp. the women’s apartment.

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Thalamus 

a conglomerate of the nuclei of gray matter (nerve cells) in the brain, located between the mesencephalon and the cerebral cortex; it is the main part of the diencephalon.

The thalamus developed for the first time in bony fish. In ontogenesis it develops from the prosencephalon sac. The thalamus is a nucleus in which afferent nerve impulses coming from all the sense organs (except the olfactory organs) gather. Each type of sensory pathway has its own specific nuclei (lateral group) in which the impulses are transmitted from one nerve cell to another and are transferred to the appropriate zone of the cerebral cortex. Associative nonspecific nuclei (medial group) receive stimuli from specific nuclei of the thalamus and from nonspecific structures of the diencephalon, mesencephalon, and medulla oblongata and transmit them to various subcortical and cortical neurons. The thalamus is involved in primary analysis and synthesis of all stimuli entering the brain from the neuroreceptors. In lower vertebrate animals the thalamus ensures performance of all necessary reflexes; in mammals and man the higher center of integration is the cerebral cortex. Under the thalamus lies the hypothalamus.

IU. A. FADEEV