Along with the sympathetic nerves, the parasympathetic nerves make up the autonomic nervous system. Some of them originate from the brain, while others originate from the sacral cord of the spinal cord. Looking from above, the parasympathetic nerves leave the midbrain and reach the eyes through the oculomotor nerve, a cranial nerve. Some of the nerves that leave the medulla oblongata enter the facial nerve and glossopharyngeal nerve and are distributed to the lacrimal and salivary glands. The largest parasympathetic nerve that leaves the medulla oblongata is called the vagus nerve. "Vagus" comes from the Latin word vagus and the English word wandering, meaning "to wander around," and as its name suggests, it is widely distributed to the internal organs. It first travels down both sides of the neck, enters the chest, and is distributed to the esophagus, heart, bronchi, and lungs. It then travels along the esophagus to the abdomen, where it is distributed to the stomach, liver, pancreas, kidneys, spleen, small intestine, and large intestine. Those that leave the sacral cord are distributed to the rectum, bladder, and reproductive organs. It has dual control over many organs along with the sympathetic nerves, and also has a functional antagonistic effect. Parasympathetic nervous activity constricts the pupils, slows the heart, and stimulates the digestive and urinary systems, creating conditions favorable for the body to recover. Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information |
交感神経とともに自律神経系を構成する末梢神経で,脳から出るものと脊髄の仙髄から出るものとがある。上からみていくと,中脳を出た副交感神経は,脳神経である動眼神経を通って眼に達する。延髄を出たものの一部は顔面神経と舌咽神経に入って涙腺と唾液腺に分布する。延髄から出る最大の副交感神経は迷走神経と名づけられている。「迷走」はラテン語の vagus,英語の wanderingで,「さまよい歩く」という意味であり,その名のとおり広く内臓諸器官に分布している。まず頸の両側を下って胸部に入り食道,心臓,気管支,肺に分布する。さらに食道に沿って腹部に出て,胃,肝臓,膵臓,腎臓,脾臓,小腸,大腸に分布している。仙髄から出たものは,直腸,膀胱,生殖器に分布する。多くの臓器に対して交感神経とともに二重支配し,機能的にも拮抗作用を示す。副交感神経の活動により,瞳孔は縮小し,心臓は抑制され,消化器系,泌尿器系は促進される。こうして身体の機能回復に適した状態がつくられる。
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