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The tegmentum (from Latin for "covering") is a general area within the brainstem. It is located between the ventricular system and distinctive basal or ventral structures at each level. It forms the floor of the midbrain (mesencephalon) whereas the tectum forms the ceiling.〔http://old.lf3.cuni.cz/physio/Physiology/education/materialy/cns/neuro2.ppt〕 It is a multisynaptic network of neurons that is involved in many unconscious homeostatic and reflexive pathways. The tegmentum area includes various different structures, such as the "rostral (=frontal/cranial/oral) end of the reticular formation, several nuclei controlling eye movements, the periaqueductal gray matter, the red nucleus, the substantia nigra, and the ventral tegmental area."〔 The tegmentum is the location of several cranial nerve (CN) nuclei. The nuclei of CN III and IV are located in the tegmentum portion of the midbrain. The nuclei of CN V to VIII are located in the tegmentum at the level of the pons. The nuclei of CN IX, X, and XII are located in that of the medulla. ==Development== In embryos, the tegmentum is the anterior half of the neural tube. However, for fetuses to adults, tegmentum refers only to the parts of the brain that remain relatively unchanged after development is complete, i.e. at the brain stem especially the midbrain. Other parts, on the other hand, develop further, through folding and thickening, and have different names. Still, it is considered a continuous central region through all levels of the brainstem. Structures that develop to grow ventral or lateral outside this primitive tube as add-ons (e.g., the crus cerebri in the anterior of the midbrain) are not considered part of the ''tegmentum'', as they are not part of the primitive neural tube but grow as projections from the cerebral cortex. However, parts that were inside the primitive neural tube and remained an integral part of it after complete development (e.g., the red nucleus) are considered part of the tegmentum. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Tegmentum」の詳細全文を読む スポンサード リンク
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