Ch12 Physiology of Neurons

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=== 神经信息从树突流向胞体，从轴突流向突触 ===
 
=== 神经信息从树突流向胞体，从轴突流向突触 ===
 
<b style=color:#0ae>Neural information flows from dendrite to soma to axon to synapse</b>
 
<b style=color:#0ae>Neural information flows from dendrite to soma to axon to synapse</b>
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Numerous dendrites converge on a central soma, or cell body, from which a single axon emerges and branches multiple times (see Fig. 10-1). Each branch culminates at a presynaptic terminal that contacts another cell. In most neurons, dendrites are the principal synaptic input sites, although synapses may also be found on the soma, on the axon hillock (the region of the soma neighboring the axon), or even directly on the axons. In some primary sensory neurons, the dendrites themselves are transducers of environmental energy. Regardless of their source, signals—in the form of voltage changes across the membrane—typically flow from dendrites to soma to axon and finally to synapses on the next set of cells. Under some circumstances electrical signals may also propagate in the opposite direction, from the soma outward along dendrites to their tips.
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许多树突聚集在一个中央体细胞或细胞体上，单个轴突从中出现并多次分枝（见图 10-1）。每个分支在与另一个细胞接触的突触前末端结束。在大多数神经元中，树突是主要的突触输入位点，尽管突触也可能出现在体细胞、轴突小丘（与轴突相邻的胞体区域）甚至直接在轴突上。在一些初级感觉神经元中，树突本身是环境能量的传感器。无论它们的来源如何，信号（以跨膜电压变化的形式）通常从树突流向胞体，再流向轴突，最后流向下一组细胞上的突触。在某些情况下，电信号也可能沿相反方向传播，从胞体沿着树突向外传播到它们的尖端。
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Excitatory input to a neuron usually generates an inward flow of positive charge (i.e., an inward current) across the dendritic membrane. Because the interior of a resting neuron is polarized negatively with respect to the external environment, this inward current, which makes the membrane voltage more positive (i.e., less negative), is said to depolarize the cell. Conversely, inhibitory input to a neuron usually generates an outward current and, thus, hyperpolarization.
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神经元的兴奋性输入通常产生穿过树突状膜的向内正电荷流（即向内电流）。因为静息神经元的内部相对于外部环境呈负极化，所以这种使膜电压更正（即负更小）的向内电流被称为细胞去极化。相反，对神经元的抑制性输入通常会产生向外的电流，从而产生超极化。
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If the neuron receives its input from a neighboring cell through a chemical synapse, neurotransmitters trigger currents by activating ion channels. If the cell is a sensory neuron, environmental stimuli (e.g., chemicals, light, mechanical deformation) activate ion channels and produce a flow of current. The change in membrane potential (Vm) caused by the flow of charge is called a postsynaptic potential (PSP) if it is generated at the postsynaptic membrane by a neurotransmitter and a receptor potential if it is generated at a sensory nerve ending by an external stimulus. In the case of synaptic transmission, the postsynaptic Vm changes may be either positive or negative. If the neurotransmitter is excitatory
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如果神经元通过化学突触接收来自邻近细胞的输入，神经递质就会通过激活离子通道来触发电流。如果细胞是感觉神经元，环境刺激（例如化学物质、光、机械变形）会激活离子通道并产生电流。由电荷流动引起的膜电位 （Vm） 变化如果由神经递质在突触后膜产生，则称为突触后电位 （PSP），如果它是在感觉神经末梢由外部刺激产生的，则称为受体电位。在突触传递的情况下，突触后 Vm 变化可能是阳性或阴性的。如果神经递质是兴奋性的
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and produces a depolarizing PSP, we refer to the PSP as an excitatory postsynaptic potential (EPSP; see p. 210). On the other hand, if the neurotransmitter is inhibitory and produces a hyperpolarizing PSP, the PSP is an inhibitory postsynaptic potential (IPSP). In all cases, the stimulus produces a Vm change that may be graded from small to large depending on the strength or quantity of input stimuli (see p. 174). Stronger sensory stimuli generate larger receptor potentials; similarly, more synapses activated together generate larger PSPs. A graded response is one form of neural coding whereby the size and duration of the input are encoded as the size and duration of the change in the dendritic Vm.
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并产生去极化 PSP，我们将 PSP 称为兴奋性突触后电位 （EPSP;见第 210 页）。另一方面，如果神经递质具有抑制性并产生超极化 PSP，则 PSP 是抑制性突触后电位 （IPSP）。在所有情况下，刺激都会产生 Vm 变化，根据输入刺激的强度或数量，该变化可以从小到大分级（见第 174 页）。更强的感觉刺激产生更大的受体电位;同样，更多的突触一起激活会产生更大的 PSP。分级反应是神经编码的一种形式，其中输入的大小和持续时间被编码为树突状 Vm 变化的大小和持续时间。
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The synaptic (or receptor) potentials generated at the ends of a dendrite are communicated to the soma, usually with substantial attenuation of the signal (Fig. 12-1A). Extended cellular processes such as dendrites behave like leaky electrical cables (see pp. 201–203). As a consequence, dendritic potentials usually decline in amplitude before reaching the soma. As an EPSP reaches the soma, it may also combine with EPSPs arriving via other dendrites on the cell; this behavior is a type of spatial summation and can lead to EPSPs that are substantially larger than those generated by any single synapse (see Fig. 12-1B, C). Temporal summation occurs when EPSPs arrive rapidly in succession; when the first EPSP has not yet dissipated, a subsequent EPSP tends to add its amplitude to the residual of the preceding EPSP (see Fig. 12-1D).
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树突末端产生的突触（或受体）电位被传达给胞体，通常信号会大幅衰减（图 12-1A）。延伸的细胞过程，如树突，表现得像泄漏的电缆（见第 201-203 页）。因此，树突状电位通常在到达胞体之前振幅下降。当 EPSP 到达胞体时，它也可能与通过细胞上其他树突到达的 EPSP 结合;这种行为是一种空间求和，可导致 EPSP 比任何单个突触产生的 EPSP 大得多（参见图 12-1B、C）。当 EPSP 连续快速到达时，就会发生时间求和;当第一个 EPSP 尚未消散时，随后的 EPSP 倾向于将其振幅添加到前一个 EPSP 的残差中（见图 12-1D）。
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The tendency for synaptic and receptor potentials to diminish with distance along a dendrite puts significant limitations on their signaling abilities. If nothing else happened, these depolarizing potentials would simply dwindle back to the resting membrane potential as they spread through the soma and down into the axon. At best, this passive signal might be carried a few millimeters, clearly inadequate for commanding a toe to wiggle when the axon of the motor neuron stretching from the spinal cord to the muscles moving the foot might be 1000 mm long. Some amplification is therefore necessary for certain inputs to generate effective signals to and from the central nervous system (CNS). Amplification is provided in the form of regenerating action potentials. If the Vm change in the soma is large enough to reach the threshold voltage (see p. 173), the depolarization may trigger one or more action potentials between the soma and axon, as shown in Figure 12-1B to D. Action potentials are large, rapid fluctuations in Vm. As described in Chapter 7, an action potential is an efficient, rapid, and reliable way to carry a signal over long distances. However, notice that generation of action potentials entails another transformation of neuronal information: the neuron converts the graded-voltage code of the dendrites (i.e., the PSPs) to a temporal code of action potentials in the axon. The initiation site for action potentials in many types of neurons is the axon initial segment, the first stretch of unmyelinated axon past the soma.
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突触电位和受体电位随树突距离的增加而减弱的趋势对它们的信号传导能力造成了重大限制。如果没有其他事情发生，这些去极化电位在通过胞体扩散并向下扩散到轴突时，只会减少回静息膜电位。充其量，这个被动信号可能被携带了几毫米，当从脊髓延伸到移动脚部的肌肉的运动神经元的轴突可能长达 1000 毫米时，显然不足以命令脚趾摆动。因此，某些输入需要一些放大才能产生进出中枢神经系统 （CNS） 的有效信号。放大以再生动作电位的形式提供。如果胞体中的 Vm 变化足够大以达到阈值电压（参见第 173 页），则去极化可能会触发胞体和轴突之间的一个或多个动作电位，如图 12-1B 至 D 所示。如第 7 章所述，动作电位是一种长距离传输信号的有效、快速和可靠的方式。然而，请注意，动作电位的产生需要神经元信息的另一种转换：神经元将树突的分级电压代码（即 PSP）转换为轴突中动作电位的时间代码。在许多类型的神经元中，动作电位的起始位点是轴突初始段，即通过体细胞的第一段无髓轴突。
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Action potentials are fixed in amplitude, not graded, and have uniform shape. So how is information encoded by action potentials? This question has no simple answer and is still hotly debated. Because one axonal spike looks like another (with slight exceptions), neurons can vary only the number of spikes and their timing. For a single axon, information may be encoded by the average rate of action potential firing, the total number of action potentials, their temporal pattern, or some combination of these mechanisms. Figure 12-1 illustrates that as the synaptic potential in the soma increases in size, the resultant action potentials occur more frequently, and the burst of action potentials in the axon lasts longer. Notice also that by the time the signal has propagated well down the axon, the transformation has become complete—the graded potential has waned and vanished, whereas the action potentials have retained their size, number, and temporal pattern. The final output of the neuron is entirely encoded by these action potentials. When action potentials reach axonal terminals, they may trigger the release of a neurotransmitter at the next set of synapses, and the cycle begins again.
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动作电位的振幅是固定的，没有分级，并且具有均匀的形状。那么动作电位是如何编码信息的呢？这个问题没有简单的答案，至今仍备受争议。因为一个轴突尖峰看起来与另一个轴突尖峰相似（除了轻微的例外），神经元只能改变尖峰的数量及其时间。对于单个轴突，信息可能由动作电位的平均放电速率、动作电位的总数、它们的时间模式或这些机制的某种组合进行编码。图 12-1 表明，随着胞体中突触电位的大小增加，产生的动作电位发生得更频繁，轴突中动作电位的爆发持续时间更长。还要注意，当信号沿着轴突传播时，转化已经完成——分级电位已经减弱和消失，而动作电位则保留了它们的大小、数量和时间模式。神经元的最终输出完全由这些动作电位编码。当动作电位到达轴突末梢时，它们可能会触发下一组突触处神经递质的释放，循环再次开始。
  
 
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2024年12月25日 (三) 17:11的版本

神经元生理学

本页英文内容取自：经典教材医学生理学（第三版） (Medical Physiology, 3rd Edtion, Walter F Boron, published in 2016)

中文内容由 BH1RBH (Jack Tan) 粗糙翻译

蓝色 【注】 后内容为 BH1RBH (Jack Tan) 所加之注释

目录

1 Overview

1.1 神经元接收、组合、转换、存储和发送信息

Neurons receive, combine, transform, store, and send information

Neurons have arguably the most complex job of any cell in the body. Consequently, they have an elaborate morphology and physiology. Each neuron is an intricate computing device. A single neuron may receive chemical input from tens of thousands of other neurons. It then combines these myriad signals into a much simpler set of electrical changes across its cellular membrane. The neuron subsequently transforms these ionic transmembrane changes according to rules determined by its particular shape and electrical properties and transmits a single new message through its axon, which itself may contact and inform hundreds of other neurons. Under the right circumstances, neurons also possess the property of memory; some of the information coursing through a neuron’s synapses may be stored for periods as long as years.

神经元可以说是体内任何细胞中最复杂的工作。因此，它们具有复杂的形态和生理学。每个神经元都是一个复杂的计算设备。单个神经元可以接收来自数以万计的其他神经元的化学输入。然后，它将这些无数信号组合成一组更简单的细胞膜电变化。神经元随后根据其特定形状和电特性决定的规则转换这些离子跨膜变化，并通过其轴突传递一条新信息，轴突本身可以接触并通知数百个其他神经元。在适当的情况下，神经元也具有记忆的特性;通过神经元突触传输的一些信息可以存储长达数年。


This general scheme of neuronal function applies to most neurons in the vertebrate nervous system. However, the scheme is endlessly variable. For example, each region of the brain has several major classes of neurons, and each of these classes has a physiology adapted to perform specific and unique functions. In this chapter, the general principles of neuronal function are outlined, and the almost unlimited variability contained within the general schema is discussed.

这种神经元功能的一般方案适用于脊椎动物神经系统中的大多数神经元。然而，这个方案是无穷无尽的。例如，大脑的每个区域都有几大类神经元，每类神经元都有适应于执行特定和独特功能的生理学。在本章中，概述了神经元功能的一般原理，并讨论了一般图式中包含的几乎无限的可变性。


1.2 神经信息从树突流向胞体，从轴突流向突触

Neural information flows from dendrite to soma to axon to synapse

Numerous dendrites converge on a central soma, or cell body, from which a single axon emerges and branches multiple times (see Fig. 10-1). Each branch culminates at a presynaptic terminal that contacts another cell. In most neurons, dendrites are the principal synaptic input sites, although synapses may also be found on the soma, on the axon hillock (the region of the soma neighboring the axon), or even directly on the axons. In some primary sensory neurons, the dendrites themselves are transducers of environmental energy. Regardless of their source, signals—in the form of voltage changes across the membrane—typically flow from dendrites to soma to axon and finally to synapses on the next set of cells. Under some circumstances electrical signals may also propagate in the opposite direction, from the soma outward along dendrites to their tips.

许多树突聚集在一个中央体细胞或细胞体上，单个轴突从中出现并多次分枝（见图 10-1）。每个分支在与另一个细胞接触的突触前末端结束。在大多数神经元中，树突是主要的突触输入位点，尽管突触也可能出现在体细胞、轴突小丘（与轴突相邻的胞体区域）甚至直接在轴突上。在一些初级感觉神经元中，树突本身是环境能量的传感器。无论它们的来源如何，信号（以跨膜电压变化的形式）通常从树突流向胞体，再流向轴突，最后流向下一组细胞上的突触。在某些情况下，电信号也可能沿相反方向传播，从胞体沿着树突向外传播到它们的尖端。


Excitatory input to a neuron usually generates an inward flow of positive charge (i.e., an inward current) across the dendritic membrane. Because the interior of a resting neuron is polarized negatively with respect to the external environment, this inward current, which makes the membrane voltage more positive (i.e., less negative), is said to depolarize the cell. Conversely, inhibitory input to a neuron usually generates an outward current and, thus, hyperpolarization.

神经元的兴奋性输入通常产生穿过树突状膜的向内正电荷流（即向内电流）。因为静息神经元的内部相对于外部环境呈负极化，所以这种使膜电压更正（即负更小）的向内电流被称为细胞去极化。相反，对神经元的抑制性输入通常会产生向外的电流，从而产生超极化。


If the neuron receives its input from a neighboring cell through a chemical synapse, neurotransmitters trigger currents by activating ion channels. If the cell is a sensory neuron, environmental stimuli (e.g., chemicals, light, mechanical deformation) activate ion channels and produce a flow of current. The change in membrane potential (Vm) caused by the flow of charge is called a postsynaptic potential (PSP) if it is generated at the postsynaptic membrane by a neurotransmitter and a receptor potential if it is generated at a sensory nerve ending by an external stimulus. In the case of synaptic transmission, the postsynaptic Vm changes may be either positive or negative. If the neurotransmitter is excitatory

如果神经元通过化学突触接收来自邻近细胞的输入，神经递质就会通过激活离子通道来触发电流。如果细胞是感觉神经元，环境刺激（例如化学物质、光、机械变形）会激活离子通道并产生电流。由电荷流动引起的膜电位 （Vm） 变化如果由神经递质在突触后膜产生，则称为突触后电位 （PSP），如果它是在感觉神经末梢由外部刺激产生的，则称为受体电位。在突触传递的情况下，突触后 Vm 变化可能是阳性或阴性的。如果神经递质是兴奋性的


and produces a depolarizing PSP, we refer to the PSP as an excitatory postsynaptic potential (EPSP; see p. 210). On the other hand, if the neurotransmitter is inhibitory and produces a hyperpolarizing PSP, the PSP is an inhibitory postsynaptic potential (IPSP). In all cases, the stimulus produces a Vm change that may be graded from small to large depending on the strength or quantity of input stimuli (see p. 174). Stronger sensory stimuli generate larger receptor potentials; similarly, more synapses activated together generate larger PSPs. A graded response is one form of neural coding whereby the size and duration of the input are encoded as the size and duration of the change in the dendritic Vm.

并产生去极化 PSP，我们将 PSP 称为兴奋性突触后电位 （EPSP;见第 210 页）。另一方面，如果神经递质具有抑制性并产生超极化 PSP，则 PSP 是抑制性突触后电位 （IPSP）。在所有情况下，刺激都会产生 Vm 变化，根据输入刺激的强度或数量，该变化可以从小到大分级（见第 174 页）。更强的感觉刺激产生更大的受体电位;同样，更多的突触一起激活会产生更大的 PSP。分级反应是神经编码的一种形式，其中输入的大小和持续时间被编码为树突状 Vm 变化的大小和持续时间。


The synaptic (or receptor) potentials generated at the ends of a dendrite are communicated to the soma, usually with substantial attenuation of the signal (Fig. 12-1A). Extended cellular processes such as dendrites behave like leaky electrical cables (see pp. 201–203). As a consequence, dendritic potentials usually decline in amplitude before reaching the soma. As an EPSP reaches the soma, it may also combine with EPSPs arriving via other dendrites on the cell; this behavior is a type of spatial summation and can lead to EPSPs that are substantially larger than those generated by any single synapse (see Fig. 12-1B, C). Temporal summation occurs when EPSPs arrive rapidly in succession; when the first EPSP has not yet dissipated, a subsequent EPSP tends to add its amplitude to the residual of the preceding EPSP (see Fig. 12-1D).

树突末端产生的突触（或受体）电位被传达给胞体，通常信号会大幅衰减（图 12-1A）。延伸的细胞过程，如树突，表现得像泄漏的电缆（见第 201-203 页）。因此，树突状电位通常在到达胞体之前振幅下降。当 EPSP 到达胞体时，它也可能与通过细胞上其他树突到达的 EPSP 结合;这种行为是一种空间求和，可导致 EPSP 比任何单个突触产生的 EPSP 大得多（参见图 12-1B、C）。当 EPSP 连续快速到达时，就会发生时间求和;当第一个 EPSP 尚未消散时，随后的 EPSP 倾向于将其振幅添加到前一个 EPSP 的残差中（见图 12-1D）。


The tendency for synaptic and receptor potentials to diminish with distance along a dendrite puts significant limitations on their signaling abilities. If nothing else happened, these depolarizing potentials would simply dwindle back to the resting membrane potential as they spread through the soma and down into the axon. At best, this passive signal might be carried a few millimeters, clearly inadequate for commanding a toe to wiggle when the axon of the motor neuron stretching from the spinal cord to the muscles moving the foot might be 1000 mm long. Some amplification is therefore necessary for certain inputs to generate effective signals to and from the central nervous system (CNS). Amplification is provided in the form of regenerating action potentials. If the Vm change in the soma is large enough to reach the threshold voltage (see p. 173), the depolarization may trigger one or more action potentials between the soma and axon, as shown in Figure 12-1B to D. Action potentials are large, rapid fluctuations in Vm. As described in Chapter 7, an action potential is an efficient, rapid, and reliable way to carry a signal over long distances. However, notice that generation of action potentials entails another transformation of neuronal information: the neuron converts the graded-voltage code of the dendrites (i.e., the PSPs) to a temporal code of action potentials in the axon. The initiation site for action potentials in many types of neurons is the axon initial segment, the first stretch of unmyelinated axon past the soma.

突触电位和受体电位随树突距离的增加而减弱的趋势对它们的信号传导能力造成了重大限制。如果没有其他事情发生，这些去极化电位在通过胞体扩散并向下扩散到轴突时，只会减少回静息膜电位。充其量，这个被动信号可能被携带了几毫米，当从脊髓延伸到移动脚部的肌肉的运动神经元的轴突可能长达 1000 毫米时，显然不足以命令脚趾摆动。因此，某些输入需要一些放大才能产生进出中枢神经系统 （CNS） 的有效信号。放大以再生动作电位的形式提供。如果胞体中的 Vm 变化足够大以达到阈值电压（参见第 173 页），则去极化可能会触发胞体和轴突之间的一个或多个动作电位，如图 12-1B 至 D 所示。如第 7 章所述，动作电位是一种长距离传输信号的有效、快速和可靠的方式。然而，请注意，动作电位的产生需要神经元信息的另一种转换：神经元将树突的分级电压代码（即 PSP）转换为轴突中动作电位的时间代码。在许多类型的神经元中，动作电位的起始位点是轴突初始段，即通过体细胞的第一段无髓轴突。


Action potentials are fixed in amplitude, not graded, and have uniform shape. So how is information encoded by action potentials? This question has no simple answer and is still hotly debated. Because one axonal spike looks like another (with slight exceptions), neurons can vary only the number of spikes and their timing. For a single axon, information may be encoded by the average rate of action potential firing, the total number of action potentials, their temporal pattern, or some combination of these mechanisms. Figure 12-1 illustrates that as the synaptic potential in the soma increases in size, the resultant action potentials occur more frequently, and the burst of action potentials in the axon lasts longer. Notice also that by the time the signal has propagated well down the axon, the transformation has become complete—the graded potential has waned and vanished, whereas the action potentials have retained their size, number, and temporal pattern. The final output of the neuron is entirely encoded by these action potentials. When action potentials reach axonal terminals, they may trigger the release of a neurotransmitter at the next set of synapses, and the cycle begins again.

动作电位的振幅是固定的，没有分级，并且具有均匀的形状。那么动作电位是如何编码信息的呢？这个问题没有简单的答案，至今仍备受争议。因为一个轴突尖峰看起来与另一个轴突尖峰相似（除了轻微的例外），神经元只能改变尖峰的数量及其时间。对于单个轴突，信息可能由动作电位的平均放电速率、动作电位的总数、它们的时间模式或这些机制的某种组合进行编码。图 12-1 表明，随着胞体中突触电位的大小增加，产生的动作电位发生得更频繁，轴突中动作电位的爆发持续时间更长。还要注意，当信号沿着轴突传播时，转化已经完成——分级电位已经减弱和消失，而动作电位则保留了它们的大小、数量和时间模式。神经元的最终输出完全由这些动作电位编码。当动作电位到达轴突末梢时，它们可能会触发下一组突触处神经递质的释放，循环再次开始。


2 树突中的信号传导

SIGNAL CONDUCTION IN DENDRITES

2.1 树突减弱突触电位

Dendrites attenuate synaptic potentials


2.2 树突状膜具有电压门控离子通道

Dendritic membranes have voltage-gated ion channels


3 躯体中尖峰模式控制

CONTROL OF SPIKING PATTERNS IN THE SOMA

3.1 神经元可以将简单的输入转换为各种输出模式

Neurons can transform a simple input into a variety of output patterns


3.2 本征发射模式由动力学相对较慢的各种离子流决定

Intrinsic firing patterns are determined by a variety of ion currents with relatively slow kinetics


4 轴突传导

AXONAL CONDUCTION

4.1 轴突专门用于快速、可靠和高效的电信号传输

Axons are specialized for rapid, reliable, and efficient transmission of electrical signals


4.2 动作电位通常在初始节段启动

Action potentials are usually initiated at the initial segment


4.3 有髓轴突的传导速度随直径线性增加

Conduction velocity of a myelinated axon increases linearly with diameter


4.4 脱髓鞘轴突缓慢、不可靠或根本不传导动作电位

Demyelinated axons conduct action potentials slowly, unreliably, or not at all


5 Reference


来自“http://wiki.jackslab.org/index.php?title=Ch12_Physiology_of_Neurons&oldid=18012”
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