The brain stem is generally made up of the diencephalon, midbrain, pons, and medulla oblongata. The brain stem contains ascending and descending pathways connecting the left and right cerebral hemispheres and the spinal cord, numerous cranial nerve nuclei, and many of the basic reflex centers required for survival (reflexes for blood pressure, heart rate, breathing, posture, etc.). In addition, the reticular formation, which is involved in maintaining proper consciousness, is present at all levels of the brain stem. Therefore, direct damage to this area (brain stem tumors and vascular lesions) or indirect damage (cerebral infarction due to pressure on a remote lesion, etc.) can cause impaired consciousness and directly endanger life. If irreversible loss of function occurs in the brain stem, the cerebrum cannot maintain its function either. In the UK, brain stem death is considered to be human death. Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information |
脳の幹をなす部分という意味で,一般に間脳,中脳,脳橋,延髄で構成されている。脳幹には,左右の大脳半球と脊髄を結ぶ上行性および下行性連絡路,多数の脳神経核,生存のための基礎的反射中枢の多く (血圧,心拍,呼吸,姿勢などの反射) が存在する。さらに,意識の適正な持続に関与する網様体が脳幹の全レベルに存在する。そのため,この部に直接的障害 (脳幹部腫瘍や血管性病変) とか,間接的障害 (遠隔病変部の圧迫による脳かんとんなど) があると,意識障害を起し,生命に直接危険が及ぶ。脳幹に不可逆性の機能喪失が起ると,大脳もその機能を保持できなくなる。イギリスではこの脳幹死をもって人間の死としている。
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