Diencephalon and Limbic System

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THE DIENCEPHALON AND LIMBIC SYSTEM THE DIENCEPHALON Comprises the thalamus, hypothalamus and the pineal gland. THALAMUS Location and relations: It forms part of the floor of the lateral ventricle and the dorsolateral wall of the third ventricle. Its relations include: • Dorsally the fornix. • Anterosuperiorly the caudate nucleus • Laterally the internal capsule. • Posterosuperiorly the splenium of the corpus callosum. • Anteroinferiorly the hypothalamus (separated from the thalamus by the hypothalamic sulcus). • Inferiorly the midbrain. Parts: Divided by the internal and external medullary laminae (bands of myelinated fibers) into medial and lateral nuclear groups. The thalamus has a posterior projection, the pulvinar that has lateral and medial geniculate bodies. Blood supply to the thalamus. • Posteromedial central arteries (Thalamoperforating arteries). • Posterolateral central arteries (Ganglionic/ Thalamogeniculate arteries) • Anterior choroidal • Posterior choroidal Venous drainage is via the deep system via the thalamostriate and basal veins. The medial and lateral nuclear groups are themselves subdivided as shown in the diagram below. Their connection are also indicated. Functions of the thalamus • Integration of both sensor and motor impulses. • Relay station for sensory impulses to the cortex • Maintenance and regulation of consciousness, attention and alertness. • Integration of the emotional correlates that accompany sensation. HYPOTHALAMUS Location and relations The hypothalamus lies in the inferior part of the lateral wall of the lateral ventricle connected to the pituitary by the infundibular stalk. It projects into the interpeduncular fossa, by the tuber cinereum and the mamillary bodies. Its relations include: • Posterosuperiorly the thalamus (separated from it by the hypothalamic sulcus)
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