查看Ch14 The Autonomic Nervous System的源代码

== 内脏的中枢神经系统控制 ==
<b style=color:#f80>CENTRAL NERVOUS SYSTEM CONTROL OF THE VISCERA</b>

=== 交感神经输出可以是大量和非特异性的，如战斗或逃跑反应，或对特定靶器官有选择性 ===
<b style=color:#0ae>Sympathetic output can be massive and nonspecific, as in the fight-or-flight response, or selective for specific target organs</b>

In 1915, Walter Cannon N14-6 proposed that the entire sympathetic division is activated together and has a uniform effect on all target organs. In response to fear, exercise, and other types of stress, the sympathetic division produces a massive and coordinated output to all end organs simultaneously, and parasympathetic output ceases. This type of sympathetic output is used to ready the body for life-threatening situations—the so-called fight-or-flight response. Thus, when a person is presented with a fearful or menacing stimulus, the sympathetic division coordinates all body functions to respond appropriately to the stressful situation. This response includes increases in heart rate, cardiac contractility, blood pressure, and ventilation of the lungs; bronchial dilatation; sweating; piloerection; liberation of glucose into the blood; inhibition of insulin secretion; reduction in blood clotting time; mobilization of blood cells by contraction of the spleen; and decreased GI activity. This mass response is a primitive mechanism for survival. In some people, such a response can be triggered spontaneously or with minimal provocation; each individual episode is then called a panic attack.

1915 年，Walter Cannon[N14-6] 提出整个交感神经系统一起被激活，对所有靶器官产生统一的作用。为了应对恐惧、运动和其他类型的压力，交感神经系统同时向所有末梢器官产生大量且协调的输出，副交感神经输出相反作用。这种类型的交感神经输出用于让身体为危及生命的情况做好准备 —— 所谓的战斗或逃跑反应。因此，当一个人受到恐惧或威胁性的刺激时，交感神经部门会协调所有身体功能，以适当地应对压力情况。这种反应包括心率、心脏收缩力、血压和肺通气量的增加、支气管扩张、出汗、竖毛、将葡萄糖释放到血液中、抑制胰岛素分泌、减少血液凝固时间、通过脾脏收缩动员血细胞、和 GI 活性降低。这种大量反应是一种原始的生存机制。在一些人中，这种反应可以自发触发，也可以在最小程度的挑衅下触发；每个单独的发作都称为恐惧袭击。


The fight-or-flight response is an important mechanism for survival, but under normal nonstressful conditions, output of the sympathetic division can also be more discrete and organ specific. In contrast to Cannon’s original proposal, the sympathetic division does not actually produce uniform effects on all visceral targets. Different postganglionic sympathetic neurons have different electrophysiological properties and release other neurotransmitters in addition to norepinephrine. This specific distribution of neuroactive chemicals among neurons is called chemical coding. For example, depolarization of guinea pig postganglionic sympathetic neurons in the lumbar sympathetic chain ganglia causes a brief burst of action potentials in 95% of the neurons and release of norepinephrine together with ATP and neuropeptide Y. These neurons are thought to innervate arteries and to induce vasoconstriction (see Fig. 14-10). In contrast, depolarization of postganglionic sympathetic neurons in the inferior mesenteric ganglion causes sustained firing in 80% of the neurons and release of norepinephrine together with somatostatin. These neurons appear to control gut motility and secretion. Thus, sympathetic neurons have cellular properties that are substantially variable. This variability permits the sympathetic division to produce different effects on targets with different functions.

战斗或逃跑反应是生存的重要机制，但在正常的非应激条件下，交感神经部门的输出也可能更加离散和器官特异性。与 Cannon 最初的提议相反，交感神经划分实际上并没有对所有本能目标产生一致的影响。不同的节后交感神经神经元具有不同的电生理特性，除去甲肾上腺素外 (NA)，还释放其他神经递质。神经活性化学物质在神经元中的这种特定分布称为化学编码。例如，腰交感神经节中豚鼠节后交感神经元的去极化导致 95% 的神经元动作电位短暂爆发，并释放去甲肾上腺素以及 ATP 和神经肽 Y。这些神经元被认为支配动脉并诱导血管收缩（见图 14-10）。相比之下，肠系膜下神经节中节后交感神经元的去极化导致 80% 的神经元持续放电，并释放去甲肾上腺素和生长抑素。这些神经元似乎控制着肠道的运动和分泌。因此，交感神经元具有基本可变的细胞特性。这种可变性允许交感神经分裂对具有不同功能的目标产生不同的影响。

<br>

=== 副交感神经元参与许多简单的不自主反射 ===
<b style=color:#0ae>Parasympathetic neurons participate in many simple involuntary reflexes</b>

As opposed to neurons in the sympathetic division, neurons in the parasympathetic division function only in a discrete, organ-specific, and reflexive manner. Together with specific visceral afferents and a small number of interneurons, parasympathetic neurons mediate simple reflexes involving target organs. For example, the output of the baroreceptor reflex (see pp. 537–539) is mediated by preganglionic parasympathetic neurons in the dorsal motor nucleus of the vagus. Other examples include urination in response to bladder distention (see pp. 736–737); salivation in response to the sight or smell of food (see p. 895); vagovagal reflexes (see p. 857) in the GI tract, such as contraction of the colon in response to food in the stomach; and bronchoconstriction in response to activation of receptors in the lungs (see pp. 717– 718). The pupillary light reflex is an example of an involuntary parasympathetic reflex that can be tested at the bedside (see p. 362).

与交感神经部的神经元相反，副交感神经部的神经元仅以离散的、器官特异性和反射性的方式发挥作用。副交感神经元与特定的内脏传入神经和少量中间神经元一起介导涉及靶器官的简单反射。例如，压力感受器反射的输出（见第 537-539 页）是由迷走神经背侧运动核中的节前副交感神经元介导的。其他例子包括对膀胱膨胀的反应排尿（见第 736-737 页）；对食物的视觉或气味产生流涎（见第 895 页）；胃肠道中的阴道反射（见第 857 页），例如结肠对胃中食物的反应收缩和响应肺部受体激活的支气管收缩（见第 717-718 页）。瞳孔对光反射是可以在床边测试的非自主副交感神经反射的一个例子（见第 362 页）。

<br>

=== 各种脑干核提供对 ANS 的基本控制 ===
<b style=color:#0ae>A variety of brainstem nuclei provide basic control of the ANS</b>

In addition to nuclei that contain parasympathetic preganglionic neurons (see Fig. 14-5), a variety of other brainstem structures are also involved in visceral control. These structures include the nucleus tractus solitarii, area postrema, ventrolateral medulla, medullary raphé, reticular formation, locus coeruleus, and parabrachial nucleus. These nuclei within the lower part of the brainstem mediate autonomic reflexes, control specific autonomic functions, or modulate the general level of autonomic tone. In some cases, these nuclei play a well-defined role in one specific autonomic function. For example, stimulation of a group of neurons in the rostral portion of the ventrolateral medulla increases sympathetic output to the cardiovascular system—without affecting respiration or sympathetic output to other targets. In other cases, these nuclei are linked to more than one autonomic function. For example, the medullary raphé contains serotonergic neurons that project to cardiovascular, respiratory, and GI neurons, the reticular activating system, and pain pathways. Therefore, these neurons can affect the background level of autonomic tone. The specific functions of some nuclei are not known, and their involvement in autonomic control is inferred from their anatomical connections, a correlation between neuron activity and activity in autonomic nerves, or the effect of lesions.

除了包含副交感神经节前神经元的细胞核（见图 14-5）外，各种其他脑干结构也参与内脏控制。这些结构包括孤束核、极后区、腹外侧延髓、髓质、网状结构、蓝斑和臂旁核。这些位于脑干下部的细胞核介导自主神经反射，控制特定的自主神经功能，或调节自主神经张力的一般水平。在某些情况下，这些细胞核在一种特定的自主神经功能中发挥着明确的作用。例如，刺激腹外侧延髓喙部的一组神经元会增加心血管系统的交感神经输出，而不会影响呼吸或对其他靶标的交感神经输出。在其他情况下，这些细胞核与多个自主神经功能有关。例如，髓质包含血清素能神经元，这些神经元投射到心血管、呼吸和胃肠道神经元、网状激活系统和疼痛通路。因此，这些神经元可以影响自主神经音调的背景水平。一些细胞核的具体功能尚不清楚，它们参与自主神经控制的参与是从它们的解剖学联系、神经元活动与自主神经活动之间的相关性或病变的影响中推断出来的。


One of the most important lower brainstem structures is the nucleus tractus solitarii (NTS) in the medulla. The NTS contains second-order sensory neurons that receive all input from peripheral chemoreceptors (see pp. 710–713) and baroreceptors input (see p. 537), as well as non-nociceptive afferent input from every organ of the thorax and abdomen. Visceral afferents from the vagus nerve make their first synapse within the NTS, where they combine with other visceral (largely unconscious) afferent impulses derived from the glossopharyngeal (CN IX), facial (CN VII), and trigeminal (CN V) nerves. These visceral afferents form a large bundle of nerve fibers—the tractus solitarius—that the NTS surrounds. Afferent input is distributed to the NTS in a viscerotopic manner, with major subnuclei devoted to respiratory, cardiovascular, gustatory, and GI input. The NTS also receives input and sends output to many other CNS regions (Table 14-4), including the brainstem nuclei described above as well as the hypothalamus and the forebrain. These widespread interconnections allow the NTS to influence and to be influenced by a wide variety of CNS functions. Thus, the NTS is the major lower brainstem command center for visceral control. It integrates multiple inputs from visceral afferents and exerts control over autonomic output, thereby participating in autonomic reflexes that maintain the homeostasis of many basic visceral functions.

最重要的下脑干结构之一是延髓中的孤束核 （NTS）。NTS 包含二阶感觉神经元，它们接收来自外周化学感受器（见第 710-713 页）和压力感受器输入（见第 537 页）的所有输入，以及来自胸部和腹部每个器官的非伤害性传入输入。来自迷走神经的内脏传入神经在 NTS 内形成第一个突触，在那里它们与来自舌咽神经 （CN IX）、面部 （CN VII） 和三叉神经 （CN V） 的其他内脏（大部分是无意识的）传入冲动结合。这些内脏传入神经形成一大束神经纤维——孤立束——NTS 围绕着它。传入输入以内脏定向方式分布到 NTS，主要亚核专门用于呼吸、心血管、味觉和 GI 输入。NTS 还接收输入并将输出发送到许多其他 CNS 区域（表 14-4），包括上述脑干核以及下丘脑和前脑。这些广泛的互连使 NTS 能够影响各种 CNS 功能并受其影响。因此，NTS 是内脏控制的主要下脑干指挥中心。它整合了来自内脏传入神经的多个输入，并控制自主神经输出，从而参与维持许多基本内脏功能的稳态的自主神经反射。

<br>

=== 前脑可以调节自主神经输出，反过来，整合在脑干中的本能感觉输入可以影响甚至压倒前脑 ===
<b style=color:#0ae>The forebrain can modulate autonomic output, and reciprocally, visceral sensory input integrated in the brainstem can influence or even overwhelm the forebrain</b>

Only a subset of the nervous system is necessary to maintain autonomic body homeostasis under most conditions. The necessary structures include (1) the brainstem nuclei discussed in the preceding section, (2) the brainstem nuclei that contain the parasympathetic preganglionic neurons, (3) the spinal cord, and (4) the peripheral ANS. These components are capable of acting autonomously, even without input from higher (i.e., rostral) forebrain regions. However, forebrain regions do play a role in coordinating and modulating activity in the lower centers. Many rostral CNS centers influence autonomic output; these centers include the hypothalamus, amygdala, prefrontal cortex, entorhinal cortex, insula, and other forebrain nuclei.

在大多数情况下，维持自主体稳态只需要神经系统的一个子集。必要的结构包括 （1） 上一节中讨论的脑干核，（2） 包含副交感神经节前神经元的脑干核，（3） 脊髓，以及 （4） 外周 ANS。这些组件能够自主行动，即使没有来自高级（即嘴部）前脑区域的输入。然而，前脑区域确实在协调和调节下部中心的活动中发挥作用。许多喙部 CNS 中心影响自主神经输出;这些中枢包括下丘脑、杏仁核、前额叶皮层、内嗅皮层、岛叶和其他前脑核。


The hypothalamus, especially the paraventricular nucleus, is the most important brain region for coordination of autonomic output. The hypothalamus projects to the parabrachial nucleus, medullary raphé, NTS, central gray matter, locus coeruleus, dorsal motor nucleus of the vagus, nucleus ambiguus, and intermediolateral cell column of the spinal cord. Thus, the hypothalamus can initiate and coordinate an integrated response to the body’s needs, including modulation of autonomic output as well as control of neuroendocrine function by the pituitary gland (see p. 978). The hypothalamus coordinates autonomic function with feeding, thermoregulation, circadian rhythms, water balance, emotions, sexual drive, reproduction, motivation, and other brain functions and thus plays a dominant role in the integration of higher cortical and limbic systems with autonomic control. The hypothalamus can also initiate the fight-orflight response[N14-7].

下丘脑，尤其是脑室旁核，是协调自主神经输出的最重要大脑区域。下丘脑投射到臂旁核、髓质、NTS、中央灰质、蓝斑、迷走神经背运动核、模糊核和脊髓中间外侧细胞柱。因此，下丘脑可以启动和协调对身体需求的综合反应，包括自主神经输出的调节以及垂体对神经内分泌功能的控制（见第 978 页）。下丘脑将自主神经功能与进食、体温调节、昼夜节律、水平衡、情绪、性驱动、生殖、动机和其他大脑功能协调起来，因此在高级皮质和边缘系统与自主神经控制的整合中起主导作用。下丘脑也可以启动战斗或逃跑反应[N14-7]。


The hypothalamus often mediates interactions between the forebrain and the brainstem. However, a number of forebrain regions also have direct connections to brainstem nuclei involved in autonomic control. Most of these forebrain regions are part of the limbic system rather than the neocortex. The paucity of direct neocortical connections probably explains why individuals trained to control autonomic output by biofeedback can generally produce only relatively minor effects on overall autonomic activity rather than regulate output to specific organs. Most individuals are incapable of even limited cortical control over the ANS. However, even though we may have only minimal conscious control of autonomic output, cortical processes can strongly modulate the ANS. Emotions, mood, anxiety, stress, and fear can all alter autonomic output (Table 14-5, top section). The pathways for these effects are unknown, but they could be mediated by direct connections or through the hypothalamus.

下丘脑通常介导前脑和脑干之间的相互作用。然而，许多前脑区域也与参与自主神经控制的脑干核有直接联系。这些前脑区域中的大多数是边缘系统的一部分，而不是新皮层的一部分。缺乏直接的新皮层连接可能解释了为什么受过生物反馈控制自主神经输出训练的个体通常只能对整体自主神经活动产生相对较小的影响，而不是调节对特定器官的输出。大多数人甚至无法对 ANS 进行有限的皮层控制。然而，即使我们对自主神经输出的意识控制可能很小，皮层过程也可以强烈调节 ANS。情绪、情绪、焦虑、压力和恐惧都会改变自主神经输出（表 14-5，顶部）。这些影响的途径尚不清楚，但它们可能通过直接连接或通过下丘脑介导。


Not only does forebrain function influence the ANS, visceral activity also influences forebrain function. Visceral afferents reach the neocortex. However, because these afferents are not represented viscerotopically, they cannot be well localized. Nevertheless, visceral afferents can have profound effects on cortical function. Visceral input can modulate the excitability of cortical neurons (Box 14-2) and, in some cases, can result in such overpowering sensory stimuli that it is not possible to focus cortical activity on anything else (see Table 14-5, bottom section).

不仅前脑功能会影响 ANS，内脏活动也会影响前脑功能。内脏传入神经到达新皮层。然而，由于这些传入神经没有在内脏位上表示，因此无法很好地定位。然而，内脏传入神经会对皮质功能产生深远的影响。本能输入可以调节皮层神经元的兴奋性（框 14-2），并且在某些情况下，会导致如此强大的感觉刺激，以至于不可能将皮层活动集中在其他任何东西上（见表 14-5，下半部分）。

<br>

=== CNS 控制中心监督本能反馈回路并协调前馈响应以满足预期需求 ===
<b style=color:#0ae>CNS control centers oversee visceral feedback loops and orchestrate a feed-forward response to meet anticipated needs</b>

The ANS maintains physiological parameters within an optimal range by means of feedback loops made up of sensors, afferent fibers, central autonomic control centers (discussed in the preceding section), and effector systems. These feedback loops achieve homeostasis by monitoring input from visceral receptors and adjusting the output of both the sympathetic and parasympathetic divisions to specific organs so that they maintain activity at a set-point determined by involuntary CNS control centers. As we have already noted, the sympathetic and parasympathetic divisions usually act in opposite ways to make these adjustments. Blood pressure control is an example of a visceral feedback loop in which the CNS monitors current blood pressure through afferents from baroreceptors, compares it with an internally determined set-point, and appropriately adjusts output to the heart, blood vessels, adrenal gland, and other targets. An increase in blood pressure (see pp. 537–539) causes a reflex decrease in sympathetic output to the heart and an increase in parasympathetic output.

ANS 通过由传感器、传入纤维、中枢自主神经控制中心（在上一节中讨论）和效应系统组成的反馈回路将生理参数保持在最佳范围内。这些反馈回路通过监测来自内脏受体的输入并调整交感神经和副交感神经对特定器官的输出来实现体内平衡，以便它们将活动维持在由非自愿 CNS 控制中心确定的设定点。正如我们已经指出的，交感神经和副交感神经的划分通常以相反的方式进行这些调整。血压控制是本能反馈回路的一个例子，其中 CNS 通过压力感受器的传入神经监测当前血压，将其与内部确定的设定点进行比较，并适当调整到心脏、血管、肾上腺和其他目标的输出。血压升高（见第 537-539 页）导致心脏交感神经输出的反射性减少和副交感神经输出增加。


Instead of merely responding through feedback loops, the ANS also anticipates the future needs of the individual. For example, when a person begins to exercise, sympathetic output increases before the increase in metabolic need to prevent an exercise debt from occurring (see p. 1214). Because of this anticipatory response, alveolar ventilation rises to such an extent that blood levels of CO2 (a byproduct of exercise) actually drop at the onset of exercise. This response is the opposite of what would be expected if the ANS worked purely through feedback loops, in which case an obligatory increase in CO2 levels would have preceded the increase in respiratory output (see pp. 716–717). Similarly, a trained athlete’s heart rate begins to increase several seconds before the starting gun fires to signal the beginning of a 100-m dash. This anticipation of future activity, or feedforward stimulation prior to (and during) exercise, is a key component of the regulation of homeostasis during stress because it prevents large changes in physiological parameters that could be detrimental to optimal function. This type of response probably resulted in an evolutionary advantage that permitted the body to respond rapidly and more efficiently to a threat of danger. A system relying solely on feedback could produce a response that is delayed or out of phase with respect to the stimulus. The central neuronal pathways responsible for this anticipatory or feed-forward response are not known.

ANS 不仅通过反馈循环做出响应，还预测个人的未来需求。例如，当一个人开始锻炼时，交感神经输出在防止运动债务发生的新陈代谢需求增加之前增加（见第 1214 页）。由于这种预期反应，肺泡通气量上升到如此程度，以至于血液中的 CO2（运动的副产品）水平实际上在运动开始时下降。这种反应与 ANS 纯粹通过反馈回路工作时的预期相反，在这种情况下，CO2 水平的强制性增加会在呼吸输出增加之前（见第 716-717 页）。同样，训练有素的运动员的心率在发令枪响前几秒钟开始增加，以发出 100 米冲刺的开始。这种对未来活动的预期，或在运动前（和运动中）的前馈刺激，是压力期间调节体内平衡的关键组成部分，因为它可以防止可能对最佳功能有害的生理参数发生巨大变化。这种类型的反应可能导致一种进化优势，使身体能够快速、更有效地对危险的威胁做出反应。仅依赖反馈的系统可能会产生与刺激有关的延迟或异相响应。负责这种预期或前馈反应的中枢神经元通路尚不清楚。

<br>

=== 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。

<br>