Autonomic Nervous System: Sympathetic vs Parasympathetic, Animation · Alila Medical Media
讲解自主神经系统的交感和副交感两大部分，适合练习医学英语和生理学相关词汇。
The autonomic nervous system, or ANS, is the part of the nervous system that regulates activities of internal organs.
自主神经系统（Autonomic Nervous System，简称ANS）是神经系统的一个组成部分，其主要功能是调节内脏器官的活动。
The ANS is largely autonomous, acting independently of the body’s consciousness and voluntary control.
自主神经系统（ANS）在很大程度上具有自主性，其活动独立于人体的意识及自愿控制机制。
It has two main divisions: sympathetic, SNS, and parasympathetic, PSNS.
神经系统主要分为两个部分：交感神经系统（SNS）和副交感神经系统（PSNS）。
In situations that require alertness and energy,
在需要保持警觉性和充沛精力的情况下，
such as facing danger or doing physical activities, the ANS activates its sympathetic division to mobilize the body for action.
例如在面临危险或进行体力活动时，自主神经系统（ANS）会激活其交感神经分支，以使身体为行动做好准备。
This division increases cardiac output, accelerates respiratory rate, releases stored energy, and dilates pupils.
这种生理反应会增加心脏的输出量（即每分钟泵出的血液量），加快呼吸频率，释放体内储存的能量，并使瞳孔扩大。
At the same time, it also inhibits body processes that are less important in emergencies, such as digestion and urination.
同时，它还会抑制那些在紧急情况下不太重要的生理过程，比如消化和排尿。
On the other hand, during ordinary situations, the parasympathetic division conserves and restores.
另一方面，在正常情况下，副交感神经系统会起到保护身体机能并促进其恢复的作用。
It slows heartbeats, decreases respiratory rate, stimulates digestion, removes waste and stores energy.
它能够减缓心跳速度、降低呼吸频率、促进消化、排除体内废物，并储存能量。
The sympathetic division is therefore known as the “fight or flight” response, while the parasympathetic division is associated with the “rest and digest” state.
因此，交感神经系统被称为“战斗或逃跑”反应系统，而副交感神经系统则与“休息与消化”状态相关。
Despite having opposite effects on the same organ, the SNS and PSNS are not mutually exclusive.
尽管交感神经系统（SNS）和副交感神经系统（PSNS）对同一器官的作用截然相反，但它们并非互相排斥、彼此排斥的。
In most organs, both systems are simultaneously active, producing a background rate of activity called the “autonomic tone” - a balance between sympathetic and parasympathetic inputs.
在大多数器官中，这两种神经系统同时处于活跃状态，从而产生一种被称为“自主神经张力”的基础活动水平——这种状态体现了交感神经与副交感神经之间的平衡。
This balance shifts, one way or the other, in response to the body’s changing needs.
这种平衡会随着身体需求的变化而向某个方向发生改变。
Some organs, however, receive inputs from only one system.
然而，有些器官仅接收来自一个系统的信号或输入。
For example, the smooth muscles of blood vessels only receive sympathetic fibers, which keep them partially constricted and thus maintaining normal blood pressure.
例如，血管中的平滑肌仅接收交感神经纤维的支配；这些神经纤维会使血管保持部分收缩状态，从而维持正常的血压。
An increase in sympathetic firing rate causes further constriction and increases blood pressure, while a decrease in firing rate dilates blood vessels,
交感神经的放电频率增加会导致血管进一步收缩，从而升高血压；而放电频率降低则会扩张血管，从而降低血压。
lowering blood pressure.
降低血压。
The autonomic nerve pathways, from the control centers in the central nervous system to the target organs, are composed of 2 neurons,
自主神经通路从中枢神经系统中的控制中心延伸到目标器官，由两个神经元组成。
which meet and synapse in an autonomic ganglion.
这些神经纤维在自主神经节中相遇并形成突触连接。
Accordingly, these neurons are called preganglionic and postganglionic.
因此，这些神经元被称为“节前神经元”（preganglionic neurons）和“节后神经元”（postganglionic neurons）。
In the SNS, the preganglionic neurons arise
在神经系统中，节前神经元（preganglionic neurons）就是在这里形成的。
from the thoracic and lumbar regions of the spinal cord; their fibers exit by way of spinal nerves to the nearby sympathetic chain of ganglia.
这些神经纤维起源于脊髓的胸段和腰段，然后通过脊神经传递到附近的交感神经节链中。
Once in the chain, preganglionic fibers may follow any of 3 routes: some fibers synapse immediately with postganglionic neurons;
一旦进入神经传导链，节前纤维可能会沿着以下三种路径中的任何一种进行传递：部分纤维会立即与节后神经元形成突触连接；
some travel up or down the chain
有些元素会在产业链中向上或向下移动（即在不同环节之间流转）。
before synapsing; some pass through the chain without synapsing - this third group continues as splanchnic nerves to nearby collateral ganglia for synapsing instead.
在形成突触之前，部分神经会直接穿过神经链而不发生突触连接；这类神经属于第三类，它们会继续作为内脏神经（splanchnic nerves）前往附近的神经节进行突触连接。
From the ganglia, long postganglionic fibers run all the way to target organs.
从神经节出发，长长的节后纤维会一直延伸到目标器官。
The SNS has a high degree of neuronal divergence: one preganglionic fiber can synapse with up to 20 postganglionic neurons.
交感神经系统（SNS）具有高度的神经元分支特性：一根节前纤维可以与多达20个节后神经元形成突触连接。
Thus, effects of the SNS tend to be widespread.
因此，交感神经系统（SNS）的作用往往具有广泛的覆盖范围。
In the PSNS, the preganglionic neurons arise from the brainstem and sacral region of the spinal cord.
在 PlayStation Network Service (PSNS) 中，节前神经元起源于脑干以及脊髓的骶部区域。
Preganglionic fibers exit the brainstem via several cranial nerves and exit the spinal cord via spinal nerves before forming the pelvic splanchnic nerves.
节前纤维通过多条颅神经从脑干发出，再通过脊神经从脊髓传出，最终形成盆内脏神经。
Parasympathetic ganglia are located near or within target organs, so postganglionic fibers are relatively short.
副交感神经节位于目标器官附近或内部，因此其节后纤维的长度相对较短。
The degree of neuronal divergence in the PSNS is much lower than that of the SNS.
副交感神经系统（PSNS）中神经元的多样性程度远低于交感神经系统（SNS）。
Thus, the PSNS produces more specific, localized responses compared to the SNS.
因此，与交感神经系统（SNS）相比，副交感神经系统（PSNS）能够引发更为具体、更具局部针对性的生理反应。