查看Ch14 The Autonomic Nervous System的源代码

=== ANS 具有多级反射环 ===
<b style=color:#0ae>The ANS has multiple levels of reflex loops</b>

The human nervous system is built in a hierarchy that mirrors phylogenetic evolution (see pp. 269–274). Each of the successively more primitive components is capable of independent, organized, and adaptive behavior. In turn, the activity of each of the more primitive levels is modulated by rostral, more phylogenetically advanced components. N14-8

人类神经系统建立在反映系统发育进化的层次结构中（参见第 269-274 页）。每个连续的更原始的组件都能够实现独立、有组织和自适应的行为。反过来，每个更原始的水平的活动都受到喙部、系统发育更高级的成分的调节 [N14-8]。

The enteric nervous system of humans is homologous to the most primitive nervous system, the neural net of jellyfish. In both cases, the component neurons control motility and nutrient absorption and respond appropriately to external stimuli.

人类的肠道神经系统与最原始的神经系统，即水母的神经网络同源。在这两种情况下，组成神经元都控制运动和营养吸收，并对外部刺激做出适当的反应。


The autonomic ganglia are homologous to ganglionic nervous systems, such as those of annelid worms. Autonomic ganglia were previously considered a simple relay station for signals from the CNS to the periphery, but it is now clear that they integrate afferent input from the viscera and have substantial independent control mechanisms. The largest of the sympathetic ganglia, the superior cervical ganglion, contains about 1 million neurons. In addition to postganglionic cell bodies, autonomic ganglia also contain interneurons. Axons from interneurons, sensory receptors located in the end organs, and preganglionic neurons converge with postganglionic neuron dendrites to form a dense network of nerve fibers, or a neuropil, within the ganglion. This neuropil confers considerable computational capability on the ganglia. Whereas feedback from skeletal muscle occurs only in the CNS, the peripheral synapses of visceral afferents result in substantial integration of autonomic activity at peripheral sites. This integration is enhanced by the variety of neurotransmitters released, for example, by interneurons in autonomic ganglia (see Table 14-3). Thus, although fast neurotransmission from preganglionic neurons to postganglionic neurons is an important role of the autonomic ganglia, the ganglia are not simply relays.

自主神经节与神经节神经系统同源，例如环节动物蠕虫的神经系统。自主神经节以前被认为是从 CNS 到外周信号的简单中继站，但现在很明显，它们整合了来自内脏的传入输入，并具有大量独立的控制机制。最大的交感神经节是颈上神经节，包含约 100 万个神经元。除了节后细胞体外，自主神经节还包含中间神经元。来自中间神经元的轴突、位于终末器官的感觉受体和节前神经元与节后神经元树突会聚，在神经节内形成致密的神经纤维网络或神经细胞。这种神经细胞赋予神经节相当大的计算能力。虽然骨骼肌的反馈仅发生在 CNS 中，但内脏传入神经的外周突触导致外周部位自主神经活动的大量整合。这种整合通过释放的各种神经递质得到增强，例如，自主神经节中的中间神经元（见表 14-3）。因此，尽管从节前神经元到节后神经元的快速神经传递是自主神经节的重要作用，但神经节不仅仅是中继。


The spinal cord, which coordinates activity among different root levels, first appeared with the evolution of chordates. The CNS of amphioxus, a primitive chordate, is essentially just a spinal cord. In humans who experience transection of the low cervical spinal cord—and in whom the outflow of the respiratory system is spared (see Chapter 32)—the caudal spinal cord and lower autonomic ganglia can still continue to maintain homeostasis. However, these individuals are incapable of more complex responses that require reflexes mediated by the cranial nerve afferents and cranial parasympathetic outflow. In many patients, this situation can lead to maladaptive reflexes such as autonomic hyper-reflexia, in which a full bladder results in hypertension and sweating (Boxes 14-3 and 14-4).

协调不同根水平之间活动的脊髓首先随着脊索动物的进化而出现。两栖动物的 CNS 是一种原始的脊索动物，本质上只是一条脊髓。在经历颈低位脊髓横断的人类中，呼吸系统流出幸免于难（见第 32 章），尾部脊髓和下自主神经节仍然可以继续维持体内平衡。然而，这些个体无法产生更复杂的反应，这些反应需要由颅神经传入神经和颅副交感神经流出介导的反射。在许多患者中，这种情况会导致适应不良反射，例如自主神经反射亢进，其中膀胱充盈会导致高血压和出汗（框 14-3 和 14-4）。


All vertebrates have a brain that is segmented into three parts (see p. 261): the prosencephalon, mesencephalon, and rhombencephalon. With evolution, the more rostral parts took on a more dominant role. The brain of the ammocoete larva of the lamprey is dominated by the medulla, which is also the most vital part of the human brain; in contrast to destruction of more rostral structures, destruction of the medulla leads to instant death in the absence of life support. The medulla coordinates all visceral control and optimizes it for survival. In humans, normal body homeostasis can continue indefinitely with only a medulla, spinal cord, and peripheral ANS.

所有脊椎动物都有一个分为三个部分的大脑（见第 261 页）：前脑、中脑和菱脑。随着进化，更多的喙部占据了更主导的角色。七鳃鳗的 ammocoete 幼虫的大脑以髓质为主，髓质也是人脑中最重要的部分;与破坏更多的喙部结构相反，髓质的破坏会导致在没有生命支持的情况下立即死亡。延髓协调所有内脏控制并对其进行优化以求生存。在人类中，正常的身体稳态可以无限期地持续，只有髓质、脊髓和外周 ANS。


In fish, the midbrain became the dominant CNS structure in response to the increasing importance of vision. The brain of primitive reptiles is only a brainstem and paleocortex, without a neocortex; the corpus striatum is the dominant structure. Thus, the brainstem is sometimes referred to as the reptilian brain. Finally, the neocortex appeared in mammals and became dominant. The phylogenetically advanced portions of the CNS rostral to the medulla— including the hypothalamus, limbic system, and cortex— coordinate activity of the ANS with complex behaviors, motivations, and desires, but they are not required for normal homeostasis.

在鱼类中，中脑成为占主导地位的 CNS 结构，以应对视觉的重要性日益增加。原始爬行动物的大脑只是脑干和古皮层，没有新皮层;纹状体是主要结构。因此，脑干有时被称为爬行动物的大脑。最后，新皮层出现在哺乳动物中并成为主导。中枢神经系统喙部到延髓的系统发育高级部分——包括下丘脑、边缘系统和皮层——将 ANS 的活动与复杂的行为、动机和欲望协调起来，但它们不是正常体内平衡所必需的。

As a result of this hierarchy, impulses from most visceral afferents never reach the cortex, and we are not usually conscious of them. Instead, they make synapses within the enteric plexuses, autonomic ganglia, spinal cord, and brainstem, and they close reflex loops that regulate visceral output at each of these levels.

由于这种等级制度，来自大多数内脏传入神经的冲动永远不会到达皮层，我们通常不会意识到它们。相反，它们在肠丛、自主神经节、脊髓和脑干内形成突触，并关闭调节每个水平内脏输出的反射回路。

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