查看Ch14 The Autonomic Nervous System的源代码

=== 交感神经和副交感神经分支对大多数内脏目标具有相反的作用 ===
<b style=color:#0ae>The sympathetic and parasympathetic divisions have opposite effects on most visceral targets</b>

All innervation of skeletal muscle in humans is excitatory. In contrast, many visceral targets receive both inhibitory and excitatory synaptic inputs. These antagonistic inputs arise from the two opposing divisions of the ANS, the sympathetic and the parasympathetic.

人类骨骼肌的所有神经支配都是兴奋性的。相比之下，许多内脏靶标同时接受抑制性和兴奋性突触输入。这些对立的输入来自 ANS 的两个对立部分，即交感和副交感。


In organs that are stimulated during physical activity, the sympathetic division is excitatory and the parasympathetic division is inhibitory. For example, sympathetic input increases the heart rate, whereas parasympathetic input decreases it. In organs whose activity increases while the body is at rest, the opposite is true. For example, the parasympathetic division stimulates peristalsis of the gut, whereas the sympathetic division inhibits it.

在体力活动期间受到刺激的器官中，交感神经支是兴奋性的，而副交感神经支是抑制性的。例如，交感神经输入会增加心率，而副交感神经输入会降低心率。在身体处于静止状态时活动增加的器官中，情况正好相反。例如，副交感神经部门刺激肠道蠕动，而交感神经部门抑制肠道蠕动。


Although antagonistic effects of the sympathetic and parasympathetic divisions of the ANS are the general rule for most end organs, exceptions exist. For example, the salivary glands are stimulated by both divisions, although stimulation by the sympathetic division has effects different from those of parasympathetic stimulation (see p. 894). In addition, some organs receive innervation from only one of these two divisions of the ANS. For example, sweat glands, piloerector muscles, and most peripheral blood vessels receive input from only the sympathetic division.

尽管 ANS 交感神经和副交感神经分支的拮抗作用是大多数终末器官的一般规则，但也存在例外。例如，唾液腺受到两种部门的刺激，尽管交感神经部门的刺激与副交感神经刺激的效果不同（见第 894 页）。此外，一些器官仅从 ANS 的这两个分支之一获得神经支配。例如，汗腺、竖毛肌和大多数外周血管仅接收来自交感神经部的输入。


Synapses of the ANS are specialized for their function. Rather than possessing synaptic terminals that are typical of somatic motor axons, many postganglionic autonomic neurons have bulbous expansions, or varicosities, that are distributed along their axons within their target organ (Fig. 14-7). It was once believed that these varicosities indicated that neurotransmitter release sites of the ANS did not form close contact with end organs and that neurotransmitters needed to diffuse long distances across the extracellular space to reach their targets. However, we now recognize that many varicosities form synapses with their targets, with a synaptic cleft extending ~50 nm across. At each varicosity, autonomic axons form an “en passant” synapse with their end-organ target. This arrangement results in an increase in the number of targets that a single axonal branch can influence, with wider distribution of autonomic output.

ANS 的突触专门用于其功能。许多节后自主神经神经元不具有典型的体细胞运动轴突的突触末端，而是具有球状扩张或静脉曲张，这些扩张或静脉曲张分布在其靶器官内的轴突上（图 14-7）。曾经有人认为，这些静脉曲张表明 ANS 的神经递质释放位点不与终末器官形成密切接触，神经递质需要跨细胞外空间长距离扩散才能到达目标。然而，我们现在认识到许多静脉曲张与其靶标形成突触，突触裂隙延伸 ~50 nm。在每个静脉曲张处，自主神经轴突与其终末器官靶标形成一个“en passant”突触。这种安排导致单个轴突分支可以影响的目标数量增加，自主神经输出的分布更广。

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