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第32行： − Because the electric field is the gradient of the voltage distribution, rapid changes in voltage within a small region imply a strong electric field; on the converse, if the voltage remains approximately the same over a large region, the electric fields in that region must be weak. A strong electric field, equivalent to a strong voltage gradient, implies that a strong force is exerted on any charged particles that lie within the region.+ − − 因为电场是电压分布的梯度，电压在小区域内迅速变化表明存在强电场；而电压在较大区域大致保持不变，则说明该区域电场较弱。强电场，即强电压梯度，意味着较强的作用力被施加到该区域的带电粒子。 第40行：
第38行： − − Ions cross the cell membrane under two influences: [[diffusion]] and [[electric field]]s. A simple example wherein two solutions—A and B—are separated by a porous barrier illustrates that diffusion will ensure that they will eventually mix into equal solutions. This mixing occurs because of the difference in their concentrations. The region with high concentration will diffuse out toward the region with low concentration. To extend the example, let solution A have 30 sodium ions and 30 chloride ions. Also, let solution B have only 20 sodium ions and 20 chloride ions. Assuming the barrier allows both types of ions to travel through it, then a steady state will be reached whereby both solutions have 25 sodium ions and 25 chloride ions. If, however, the porous barrier is selective to which ions are let through, then diffusion alone will not determine the resulting solution. Returning to the previous example, let's now construct a barrier that is permeable only to sodium ions. Now, only sodium is allowed to diffuse cross the barrier from its higher concentration in solution A to the lower concentration in solution B. This will result in a greater accumulation of sodium ions than chloride ions in solution B and a lesser number of sodium ions than chloride ions in solution A. − − This means that there is a net positive charge in solution B from the higher concentration of positively charged sodium ions than negatively charged chloride ions. Likewise, there is a net negative charge in solution A from the greater concentration of negative chloride ions than positive sodium ions. Since opposite charges attract and like charges repel, the ions are now also influenced by electrical fields as well as forces of diffusion. Therefore, positive sodium ions will be less likely to travel to the now-more-positive B solution and remain in the now-more-negative A solution. The point at which the forces of the electric fields completely counteract the force due to diffusion is called the equilibrium potential. At this point, the net flow of the specific ion (in this case sodium) is zero. − + − + − − Every cell is enclosed in a [[plasma membrane]], which has the structure of a [[lipid bilayer]] with many types of large molecules embedded in it. Because it is made of lipid molecules, the plasma membrane intrinsically has a high electrical resistivity, in other words a low intrinsic permeability to ions. However, some of the molecules embedded in the membrane are capable either of actively transporting ions from one side of the membrane to the other or of providing channels through which they can move.<ref name="lieb_1986">{{cite book |vauthors=Lieb WR, Stein WD | year = 1986 | chapter = Chapter 2. Simple Diffusion across the Membrane Barrier | title = Transport and Diffusion across Cell Membranes | publisher = Academic Press | location = San Diego | isbn = 978-0-12-664661-0 | pages = 69–112}}</ref> − − 每个细胞都被包裹在质膜中，质膜具有脂双分子层的结构，其中包含很多种类的大分子。因为它是由脂分子组成的，所以质膜本身具有很高的电阻率，换句话说，对离子的固有渗透性很低。然而，嵌入膜中的一些分子能够将离子从膜的一侧有效地转运到另一侧，或者提供离子移动的通道。<ref name="lieb_1986" /> − In electrical terminology, the plasma membrane functions as a combined [[resistor]] and [[capacitor]]. Resistance arises from the fact that the membrane impedes the movement of charges across it. Capacitance arises from the fact that the lipid bilayer is so thin that an accumulation of charged particles on one side gives rise to an electrical force that pulls oppositely charged particles toward the other side. The capacitance of the membrane is relatively unaffected by the molecules that are embedded in it, so it has a more or less invariant value estimated at about 2 μF/cm<sup>2</sup> (the total capacitance of a patch of membrane is proportional to its area). The conductance of a pure lipid bilayer is so low, on the other hand, that in biological situations it is always dominated by the conductance of alternative pathways provided by embedded molecules. Thus, the capacitance of the membrane is more or less fixed, but the resistance is highly variable.+ − 电学上讲，质膜在功能上是电阻和电容的组合。电阻的产生是因为质膜阻碍电荷的跨膜运动。电容是这样产生的：脂双分子层非常之薄，以至于膜的一侧积聚的粒子产生电场力，将带相反电荷的粒子拉向膜的另一侧。膜的电容相对而言不受嵌入其中的分子的影响，因此它的数值相对恒定，约为 2 μF/cm<sup>2</sup> 左右（膜片的总电容与其面积成正比）。另一方面，纯的脂双分子层的电导率非常之低，在生物体中通常由嵌入分子提供的支路的电导率决定。因此，膜的电容相对是固定的，但电阻是高度可变的。+ − The thickness of a plasma membrane is estimated to be about 7-8 nanometers. Because the membrane is so thin, it does not take a very large transmembrane voltage to create a strong electric field within it. Typical membrane potentials in animal cells are on the order of 100 millivolts (that is, one tenth of a volt), but calculations show that this generates an electric field close to the maximum that the membrane can sustain—it has been calculated that a voltage difference much larger than 200 millivolts could cause [[dielectric breakdown]], that is, arcing across the membrane.+ − 质膜的厚度估计约为 7-8 纳米。膜非常薄，因此不需要很大的跨膜电压就以在其中产生强电场。动物细胞中典型的膜电位大约为 100 毫伏（即十分之一伏特），但计算表明，这种电位产生的电场接近膜所能承受的最大电场——据计算，大于 200 毫伏的电压差可能导致介质击穿，即产生跨膜电弧。+ − + − The resistance of a pure lipid bilayer to the passage of ions across it is very high, but structures embedded in the membrane can greatly enhance ion movement, either [[active transport|actively]] or [[passive transport|passively]], via mechanisms called [[facilitated transport]] and [[facilitated diffusion]]. The two types of structure that play the largest roles are ion channels and [[ion transporter|ion pump]]s, both usually formed from assemblages of protein molecules. Ion channels provide passageways through which ions can move. In most cases, an ion channel is permeable only to specific types of ions (for example, sodium and potassium but not chloride or calcium), and sometimes the permeability varies depending on the direction of ion movement. Ion pumps, also known as ion transporters or carrier proteins, actively transport specific types of ions from one side of the membrane to the other, sometimes using energy derived from metabolic processes to do so.+ − − 纯的脂双分子层对横穿的离子有很大的阻力，但是嵌入膜中的结构能极大地增强离子运动，通过主动的易化转运或被动的易化扩散的机制。最重要的两种结构是离子通道和离子泵，它们通常都是由蛋白质分子装配而成。离子通道提供了离子可以移动的通道。在大多数情况下，一种离子通道只对特定的离子种类（例如钠离子和钾离子而非氯离子或钙离子）有通透性，某些情况下通透性因离子的运动方向而不同。离子泵，亦称离子转运蛋白或载体蛋白，主动将特定的例子种类从膜的侧运输到另一侧，有时需要消耗新陈代谢过程产生的能量。 − + − + − 离子泵是一类内在膜蛋白，其执行主动运输，即利用细胞能量（ATP）将离子逆浓度梯度用“泵”输送<ref name="hodgkin_1955" />。这种离子泵将离子从膜的一侧摄入（而减少浓度），释放到膜的另一侧（增加浓度）。+ − The ion pump most relevant to the action potential is the [[Na+/K+-ATPase|sodium–potassium pump]], which transports three sodium ions out of the cell and two potassium ions in.<ref name="caldwell_1960">{{cite journal | vauthors = Caldwell PC, [[Alan Lloyd Hodgkin|Hodgkin AL]], [[Richard Keynes|Keynes RD]], Shaw TI | year = 1960 | title = The effects of injecting energy-rich phosphate compounds on the active transport of ions in the giant axons of ''Loligo'' | journal = J. Physiol. | volume = 152 | issue = 3 | pages = 561–90 | pmid = 13806926 | pmc = 1363339 | doi = 10.1113/jphysiol.1960.sp006509 }}</ref> As a consequence, the concentration of [[potassium]] ions K<sup>+</sup> inside the neuron is roughly 20-fold larger than the outside concentration, whereas the sodium concentration outside is roughly ninefold larger than inside.<ref name="steinbach_1943">{{cite journal |vauthors=Steinbach HB, Spiegelman S | year = 1943 | title = The sodium and potassium balance in squid nerve axoplasm | journal = J. Cell. Comp. Physiol. | volume = 22 | issue = 2 | pages = 187–96 | doi = 10.1002/jcp.1030220209}}</ref><ref name="hodgkin_1951">{{cite journal | author = Hodgkin AL | year = 1951 | title = The ionic basis of electrical activity in nerve and muscle | journal = Biol. Rev. | volume = 26 | issue = 4 | pages = 339–409 | doi = 10.1111/j.1469-185X.1951.tb01204.x| s2cid = 86282580 | author-link = Alan Lloyd Hodgkin }}</ref> In a similar manner, other ions have different concentrations inside and outside the neuron, such as [[calcium]], [[chloride]] and [[magnesium]].<ref name="hodgkin_1951" />+ − − 对于动作电位最重要的离子泵是钠钾泵（sodium–potassium pump），其一次可将三个钠离子输出细胞，两个钾离子输入细胞。<ref name="caldwell_1960" /> 结果就是，钾离子浓度在神经元胞内约是胞外的 20 倍，而钠离子浓度在神经元胞外大约是胞内的 9 倍。<ref name="steinbach_1943" /><ref name="hodgkin_1951" /> 类似地，钙离子、氯离子和镁离子等离子也在神经元胞内和胞外有不同的浓度。<ref name="hodgkin_1951" /> − − If the numbers of each type of ion were equal, the sodium–potassium pump would be electrically neutral, but, because of the three-for-two exchange, it gives a net movement of one positive charge from intracellular to extracellular for each cycle, thereby contributing to a positive voltage difference. The pump has three effects: (1) it makes the sodium concentration high in the extracellular space and low in the intracellular space; (2) it makes the potassium concentration high in the intracellular space and low in the extracellular space; (3) it gives the intracellular space a negative voltage with respect to the extracellular space. − − 如果每种离子的数量相等，钠钾泵就是电中性的，但是，由于这种三对二的交换，每个循环都会产生一个正电荷从细胞内向细胞外的净移动，从而产生正电压差。钠钾泵有三个效应：（1）它使细胞外钠离子浓度高而细胞内的钠离子浓度低；（2）它使细胞内的钾离子浓度高而细胞外的钾离子浓度低；（3）它使细胞内相对于细胞外有负电位。 第92行：
第74行： − Another functionally important ion pump is the [[sodium-calcium exchanger]]. This pump operates in a conceptually similar way to the sodium-potassium pump, except that in each cycle it exchanges three Na<sup>+</sup> from the extracellular space for one Ca<sup>++</sup> from the intracellular space. Because the net flow of charge is inward, this pump runs "downhill", in effect, and therefore does not require any energy source except the membrane voltage. Its most important effect is to pump calcium outward—it also allows an inward flow of sodium, thereby counteracting the sodium-potassium pump, but, because overall sodium and potassium concentrations are much higher than calcium concentrations, this effect is relatively unimportant. The net result of the sodium-calcium exchanger is that in the resting state, intracellular calcium concentrations become very low.+ − − − + 第119行：
第99行： − + − 泄漏通道是最简单的离子通道类型，因为它们的渗透率几乎是恒定的。在神经元中，钾离子通道和氯离子通道是泄漏通道中最重要的类型。即使它们的性质也不是完全恒定的: 首先，它们中的大多数是电压依赖性的，因为它们在一个方向上比在另一个方向上导电更好(换句话说，它们是整流器) ; 其次，它们中的一些能够被化学配体关闭，即使它们不需要配体来操作。+ 第129行：
第109行： − 配体门控离子通道是当某种类型的化学配体与蛋白结构结合时，其通透性大大增加的通道。动物细胞含有成百上千种这样的通道。很大一部分是作为神经递质受体的一个很大的子集功能ーー它们发生在突触后位点，而与它们相关的化学配体是由突触前轴突末端释放的。这种类型的一个例子是 AMPA 受体，一种神经递质谷氨酸的受体，当激活时允许钠离子和钾离子通过。另一个例子是 GABA < sub > a 受体，一种神经递质 GABA 的受体，当被激活时允许氯离子通过。+ − 神经递质受体被出现在细胞外区的配体激活，但是还有其他类型的配体门控通道是由细胞内的相互作用控制的。+ − + − 电压依赖性通道，也称为电压依赖性离子通道，是一种通道，其通透性受膜电位的影响。它们形成了另一个非常大的基团，每个成员具有特定的离子选择性和特定的电压依赖性。其中许多还与时间有关ー换句话说，它们不会立即对电压变化作出反应，而只是在延迟之后才作出反应。+ − 这个小组最重要的成员之一是一种作为动作电位基础的电压门控钠通道ーー这些通道有时被称为 Hodgkin-Huxley 钠通道，因为在他们获得诺贝尔奖的动作电位生理学研究中，他们最初是拥有属性艾伦·劳埃德·霍奇金和 Andrew Huxley。通道在静息电压水平处关闭，但当电压超过一定阈值时突然打开，从而允许大量钠离子流入，使膜电位发生非常迅速的变化。从动作电位中恢复部分依赖于一种在静息电压水平关闭但在动作电位产生巨大电压变化时打开的电压门控钾离子通道。+ − + − 一个离子的翻转电位电位(或平衡电位)是一个跨膜电压的值，在这个电压下扩散力和电力相互抵消，因此没有净离子流过这个跨膜电位。这意味着跨膜电压完全对抗离子的扩散力，使得跨膜离子的净电流为零且不变。翻转电位是重要的，因为它提供了作用于离子可渗透通道的电压---- 换句话说，它提供了离子浓度梯度作为电池时产生的电压。+ − + 第170行：
第150行： − + − + − + − + − + − + − +
无编辑摘要
用数学术语来说，电压的定义从电场的概念开始，电场 {{math|'''E'''}} 是一个向量场，它为空间中的每一点指定一个大小和方向。在许多情况下，电场是一个保守场，这意味着它可以表示为一个标量函数的梯度，{{math|<VAR>V</VAR>}}，即 {{math|'''E''' {{=}} –∇<VAR>V</VAR>}}。这个标量场 {{math|<VAR>V</VAR>}} 称为电压分布。注意，这个定义允许任意的积分常数——这就是为什么电压的绝对值没有意义。一般来说，只有在磁场对电场影响不大的情况下，电场才能被认为是保守的，不过这种情况通常适用于生物组织。
用数学术语来说，电压的定义从电场的概念开始，电场 {{math|'''E'''}} 是一个向量场，它为空间中的每一点指定一个大小和方向。在许多情况下，电场是一个保守场，这意味着它可以表示为一个标量函数的梯度，{{math|<VAR>V</VAR>}}，即 {{math|'''E''' {{=}} –∇<VAR>V</VAR>}}。这个标量场 {{math|<VAR>V</VAR>}} 称为电压分布。注意，这个定义允许任意的积分常数——这就是为什么电压的绝对值没有意义。一般来说，只有在磁场对电场影响不大的情况下，电场才能被认为是保守的，不过这种情况通常适用于生物组织。
因为电场是电压分布的梯度，电压在小区域内迅速变化表明存在强电场；而电压在较大区域大致保持不变，则说明该区域电场较弱。强电场，即强电压梯度，意味着该区域的带电粒子会受到较强的作用力。
===离子和驱动离子运动的力===
===离子和驱动离子运动的力===
生物体的电信号通常是离子驱动的。<ref name=":3">Johnston and Wu, p. 9.</ref> 动作电位最重要的阳离子是钠离子（Na<sup>+</sup>）和钾离子（K<sup>+</sup>）。<ref name="bullock_140_141">[[Theodore Holmes Bullock|Bullock]], Orkand, and Grinnell, pp. 140–41.</ref> 两者都是带一个正电荷的单价阳离子。动作电位也可能需要钙离子（Ca<sup>2+</sup>），<ref name=":4">[[Theodore Holmes Bullock|Bullock]], Orkand, and Grinnell, pp. 153–54.</ref> 一种带有两个正电荷的二价阳离子。氯离子（Cl<sup>−</sup>）在某些藻类的动作电位中起主要作用，<ref name="mummert_1991">{{cite journal |vauthors=Mummert H, Gradmann D | year = 1991 | title = Action potentials in Acetabularia: measurement and simulation of voltage-gated fluxes | journal = Journal of Membrane Biology | volume = 124 | pages = 265–73 | pmid = 1664861 | doi = 10.1007/BF01994359 | issue = 3| s2cid = 22063907 }}</ref> 然而在大多数动物的动作电位中的作用微不足道。<ref name=":5">[[Knut Schmidt-Nielsen|Schmidt-Nielsen]], p. 483.</ref>
生物体的电信号通常是离子驱动的。<ref name=":3">Johnston and Wu, p. 9.</ref> 动作电位最重要的阳离子是钠离子（Na<sup>+</sup>）和钾离子（K<sup>+</sup>）。<ref name="bullock_140_141">[[Theodore Holmes Bullock|Bullock]], Orkand, and Grinnell, pp. 140–41.</ref> 两者都是带一个正电荷的单价阳离子。动作电位也可能需要钙离子（Ca<sup>2+</sup>），<ref name=":4">[[Theodore Holmes Bullock|Bullock]], Orkand, and Grinnell, pp. 153–54.</ref> 一种带有两个正电荷的二价阳离子。氯离子（Cl<sup>−</sup>）在某些藻类的动作电位中起主要作用，<ref name="mummert_1991">{{cite journal |vauthors=Mummert H, Gradmann D | year = 1991 | title = Action potentials in Acetabularia: measurement and simulation of voltage-gated fluxes | journal = Journal of Membrane Biology | volume = 124 | pages = 265–73 | pmid = 1664861 | doi = 10.1007/BF01994359 | issue = 3| s2cid = 22063907 }}</ref> 然而在大多数动物的动作电位中的作用微不足道。<ref name=":5">[[Knut Schmidt-Nielsen|Schmidt-Nielsen]], p. 483.</ref>
离子的跨膜运动受两个因素的影响：扩散作用和电场。举个简单的例子，带孔的隔板隔开两种溶液 A 和 B，扩散作用会使两者最终混合成等浓度的溶液。这种混合是因两者存在浓度差而发生的，高浓度区域向低浓度区域扩散。扩展这个例子，让溶液 A 有 30 个钠离子和 30 个氯离子；另外让溶液 B 只含有 20 个钠离子和 20 个氯离子。假设隔板允许两种类型的离子通过，那么将达到一个稳态，即两种溶液均有 25 个钠离子和 25 个氯离子。然而，如果带孔隔板是选择性的让离子通过，那么最终的溶液将不会仅由扩散作用决定。回到前面的例子，让我们现在构造一个只能透过钠离子的隔板。现在，只有钠可以从溶液 A 中较高的浓度扩散到溶液 B 中较低的浓度。这将导致 B 溶液中积聚多于氯离子的钠离子，而 A 溶液中钠离子少于氯离子。
离子的跨膜运动受两个因素的影响：扩散作用和电场。举个简单的例子，带孔的隔板隔开两种溶液 A 和 B，扩散作用会使两者最终混合成等浓度的溶液。这种混合是因两者存在浓度差而发生的，高浓度区域向低浓度区域扩散。扩展这个例子，让溶液 A 有 30 个钠离子和 30 个氯离子；另外让溶液 B 只含有 20 个钠离子和 20 个氯离子。假设隔板允许两种类型的离子通过，那么将达到一个稳态，即两种溶液均有 25 个钠离子和 25 个氯离子。然而，如果带孔隔板是选择性的让离子通过，那么最终的溶液将不会仅由扩散作用决定。回到前面的例子，让我们现在构造一个只能透过钠离子的隔板。现在，只有钠可以从溶液 A 中较高的浓度扩散到溶液 B 中较低的浓度。这将导致 B 溶液中积聚多于氯离子的钠离子，而 A 溶液中钠离子少于氯离子。
这意味着在溶液 B 中存在净正电荷，这是由于带正电荷的钠离子比带负电荷的氯离子浓度高。同样，在溶液 A 中，由于带负电荷的氯离子的浓度比带正电荷的钠离子的浓度大，所以存在净负电荷。由于异性电荷相互吸引，同性电荷相互排斥，因此离子现在除了扩散作用也受到电场力的影响。因此，带正电的钠离子较不可能移到现在带更多正电的溶液 B，而留在现在带更多负电的溶液 A。电场完全抵消扩散作用的点称为平衡电位。此时，特定离子（本例中是钠离子）净流量为零。
这意味着在溶液 B 中存在净正电荷，这是由于带正电荷的钠离子比带负电荷的氯离子浓度高。同样，在溶液 A 中，由于带负电荷的氯离子的浓度比带正电荷的钠离子的浓度大，所以存在净负电荷。由于异性电荷相互吸引，同性电荷相互排斥，因此离子现在除了扩散作用也受到电场力的影响。因此，带正电的钠离子较不可能移到现在带更多正电的溶液 B，而留在现在带更多负电的溶液 A。电场完全抵消扩散作用的点称为平衡电位。此时，特定离子（本例中是钠离子）净流量为零。
===Plasma membranes 细胞质膜===
===细胞质膜===
[[File:Cell membrane detailed diagram en.svg|thumb|right|500px|The cell membrane, also called the plasma membrane or plasmalemma, is a [[semipermeable membrane|semipermeable]] lipid bilayer common to all living cells. It contains a variety of biological molecules, primarily proteins and lipids, which are involved in a vast array of cellular processes.|链接=Special:FilePath/Cell_membrane_detailed_diagram_en.svg]]
[[File:Cell membrane detailed diagram en.svg|thumb|right|500px|The cell membrane, also called the plasma membrane or plasmalemma, is a [[semipermeable membrane|semipermeable]] lipid bilayer common to all living cells. It contains a variety of biological molecules, primarily proteins and lipids, which are involved in a vast array of cellular processes.
细胞膜，也称质膜（plasma membrane 或 plasmalemma），是所有活细胞都有的半透脂双层。其含有各种生物分子，主要是蛋白和脂类，参与大量的细胞活动。|链接=Special:FilePath/Cell_membrane_detailed_diagram_en.svg]]
每个细胞都包裹在质膜中。质膜具有脂双分子层的结构，其中嵌入很多种类的大分子。质膜由脂分子组成的，因而本身具有很高的电阻率，即离子的固有渗透性很低。然而，嵌入膜中的一些分子能够主动地将离子从膜的一侧转运到另一侧，或者为离子提供移动的通道。<ref name="lieb_1986">{{cite book |vauthors=Lieb WR, Stein WD | year = 1986 | chapter = Chapter 2. Simple Diffusion across the Membrane Barrier | title = Transport and Diffusion across Cell Membranes | publisher = Academic Press | location = San Diego | isbn = 978-0-12-664661-0 | pages = 69–112}}</ref>
从电学的角度看，质膜在功能上是电阻和电容的组合。电阻的产生是因为质膜阻碍电荷的跨膜运动。电容是这样产生的：脂双分子层非常之薄，以至于膜的一侧积聚的带电粒子产生电场力，将带相反电荷的粒子拉向膜的另一侧。膜电容相对而言不受内嵌的分子的影响，因此其数值相对恒定，约为 2 μF/cm<sup>2</sup> 左右（一片质膜的总电容与其面积成正比）。另一方面，纯的脂双分子层的电导率非常之低，在生物体中通常由内嵌的分子提供的支路的电导率决定。因此，膜的电容相对是固定的，但电阻是高度可变的。
质膜厚约 7-8 纳米，非常薄，因此无需很大的跨膜电压就可在其中产生强电场。动物细胞中典型的膜电位大约为 100 毫伏（即十分之一伏特），但计算表明，这种电位产生的电场接近膜所能承受的最大电场——据计算，大于 200 毫伏的电压差可能导致介质击穿，即产生跨膜电弧。
===Facilitated diffusion and transport易化扩散和转运 ===
===易化扩散和易化转运 ===
[[File:Scheme facilitated diffusion in cell membrane-en.svg|thumb|300px|right|细胞膜上的易化扩散，显示了离子通道和载体蛋白（carrier protein）|链接=Special:FilePath/Scheme_facilitated_diffusion_in_cell_membrane-en.svg]]
[[File:Scheme facilitated diffusion in cell membrane-en.svg|thumb|300px|right|细胞膜上的易化扩散，显示了离子通道和载体蛋白（carrier protein）|链接=Special:FilePath/Scheme_facilitated_diffusion_in_cell_membrane-en.svg]]
离子横穿纯的脂双分子层会遇到很大的阻力，但嵌入膜中的结构能极大地增强离子运动，通过主动的易化转运（facilitated transport）或被动的易化扩散（facilitated diffusion）的机制。最重要的两种结构是离子通道（ion channels）和离子泵（ion pumps），它们通常都是由蛋白质分子装配而成的。离子通道提供了允许离子移动的通道。多数情况下，一种离子通道只对特定的离子种类（例如钠离子和钾离子而非氯离子或钙离子）有通透性，某些情况下通透性因离子的运动方向而不同。离子泵，亦称离子转运蛋白或载体蛋白，主动将特定的例子种类从膜的侧运输到另一侧，有时需要消耗新陈代谢过程产生的能量。
===Ion pumps 离子泵===
===离子泵===
[[File:Scheme sodium-potassium pump-en.svg|thumb|right|350px|钠-钾泵利用 ATP 产生的能量，将钠离子与钾离子跨膜交换。|链接=Special:FilePath/Scheme_sodium-potassium_pump-en.svg]][[Ion transporter|Ion pumps]] are [[integral membrane protein]]s that carry out [[active transport]], i.e., use cellular energy (ATP) to "pump" the ions against their concentration gradient.<ref name="hodgkin_1955">{{cite journal | author = [[Alan Lloyd Hodgkin|Hodgkin AL]], [[Richard Keynes|Keynes RD]] | year = 1955 | title = Active transport of cations in giant axons from ''Sepia'' and ''Loligo'' | journal = J. Physiol. | volume = 128 | pages = 28–60 | pmid = 14368574 | issue = 1 | pmc = 1365754 | doi=10.1113/jphysiol.1955.sp005290}}</ref> Such ion pumps take in ions from one side of the membrane (decreasing its concentration there) and release them on the other side (increasing its concentration there).
[[File:Scheme sodium-potassium pump-en.svg|thumb|right|350px|钠-钾泵利用 ATP 产生的能量，将钠离子与钾离子跨膜交换。|链接=Special:FilePath/Scheme_sodium-potassium_pump-en.svg]]离子泵是一类内在膜蛋白，其执行主动运输（active transport），即利用细胞能量（ATP）将离子逆浓度梯度“泵”送。<ref name="hodgkin_1955">{{cite journal | author = [[Alan Lloyd Hodgkin|Hodgkin AL]], [[Richard Keynes|Keynes RD]] | year = 1955 | title = Active transport of cations in giant axons from ''Sepia'' and ''Loligo'' | journal = J. Physiol. | volume = 128 | pages = 28–60 | pmid = 14368574 | issue = 1 | pmc = 1365754 | doi=10.1113/jphysiol.1955.sp005290}}</ref> 这种离子泵从膜的一侧摄入离子（减少其浓度），释放到膜的另一侧（增加其浓度）。
对于动作电位最重要的离子泵是钠钾泵（sodium–potassium pump），其一次可转运三个钠离子到胞外，两个钾离子到胞内。<ref name="caldwell_1960">{{cite journal | vauthors = Caldwell PC, [[Alan Lloyd Hodgkin|Hodgkin AL]], [[Richard Keynes|Keynes RD]], Shaw TI | year = 1960 | title = The effects of injecting energy-rich phosphate compounds on the active transport of ions in the giant axons of ''Loligo'' | journal = J. Physiol. | volume = 152 | issue = 3 | pages = 561–90 | pmid = 13806926 | pmc = 1363339 | doi = 10.1113/jphysiol.1960.sp006509 }}</ref> 结果就是，钾离子浓度在神经元胞内约为胞外的 20 倍，而钠离子浓度在神经元胞外约是胞内的 9 倍。<ref name="steinbach_1943">{{cite journal |vauthors=Steinbach HB, Spiegelman S | year = 1943 | title = The sodium and potassium balance in squid nerve axoplasm | journal = J. Cell. Comp. Physiol. | volume = 22 | issue = 2 | pages = 187–96 | doi = 10.1002/jcp.1030220209}}</ref><ref name="hodgkin_1951">{{cite journal | author = Hodgkin AL | year = 1951 | title = The ionic basis of electrical activity in nerve and muscle | journal = Biol. Rev. | volume = 26 | issue = 4 | pages = 339–409 | doi = 10.1111/j.1469-185X.1951.tb01204.x| s2cid = 86282580 | author-link = Alan Lloyd Hodgkin }}</ref> 类似地，钙离子、氯离子和镁离子等也在神经元胞内和胞外有不同的浓度。<ref name="hodgkin_1951" />
如果交换的每种离子数量上相等，那钠钾泵就是电中性的，但是，三对二的交换使每个循环都向细胞外净移动一个正电荷，从而产生正的电位差。钠钾泵有三个效应：（1）它使细胞外钠离子浓度高而细胞内的钠离子浓度低；（2）它使细胞内的钾离子浓度高而细胞外的钾离子浓度低；（3）它使细胞内相对于细胞外有负电位。
The sodium-potassium pump is relatively slow in operation. If a cell were initialized with equal concentrations of sodium and potassium everywhere, it would take hours for the pump to establish equilibrium. The pump operates constantly, but becomes progressively less efficient as the concentrations of sodium and potassium available for pumping are reduced.
The sodium-potassium pump is relatively slow in operation. If a cell were initialized with equal concentrations of sodium and potassium everywhere, it would take hours for the pump to establish equilibrium. The pump operates constantly, but becomes progressively less efficient as the concentrations of sodium and potassium available for pumping are reduced.
离子泵仅通过建立细胞内外的离子浓度对来影响动作电位。动作电位主要是离子通道的开关，而非离子泵。若去除其能量来源，或加入哇巴因（ouabain）之类的抑制剂来关闭离子泵，轴突仍然可以在其幅值开始明显衰减前发放数十万动作电位。<ref name="hodgkin_1955" /> 特别是，离子泵在动作电位后细胞膜的复极化过程中未有明显作用。<ref name="bullock_140_141" />
离子泵仅通过建立细胞内外的离子浓度对来影响动作电位。动作电位主要是离子通道的开关，而非离子泵。若去除其能量来源，或加入哇巴因（ouabain）之类的抑制剂来关闭离子泵，轴突仍然可以在其幅值开始明显衰减前发放数十万动作电位。<ref name="hodgkin_1955" /> 特别是，离子泵在动作电位后细胞膜的复极化过程中未有明显作用。<ref name="bullock_140_141" />
另一个有重要功能的离子泵是钠钙交换体（sodium-calcium exchanger）。这种泵的工作原理与钠钾泵相似，只是在每个循环中，它将 3 个胞外钠离子与 1 个胞内钙离子交换。因为净电流是向胞内的，这个泵实际上是顺着电位梯度，因而除了膜电位之外不需要任何能量来源。其最重要的作用是将钙离子泵出胞外ーー还允许钠离子内流从而抵消钠钾泵产生的钠外流，但由于总的钠钾浓度远高于钙浓度，这种作用相对来说并不重要。钠钙交换体的最终结果是在静息状态下，胞内钙离子浓度变得非常低。
另一个有重要功能的离子泵是钠钙交换体（sodium-calcium exchanger）。这种泵的工作原理与钠钾泵相似，只是在每个循环中，它将 3 个胞内钠离子与 1 个胞外钙离子交换。因为净电流是向胞内的，这个泵实际上是走“下坡”，因而除了膜电位之外不需要任何能量来源。其最重要的作用是将钙离子泵出胞外ーー还允许钠离子内流从而抵消钠钾泵产生的钠外流，但由于总的钠钾浓度远高于钙浓度，这种作用相对来说并不重要。钠钙交换体的最终结果是在静息状态下，胞内钙离子浓度变得非常低。
===Ion channels离子通道===
===离子通道===
[[File:Action potential ion sizes.svg.png|thumb|Despite the small differences in their radii,<ref name=":6">''CRC Handbook of Chemistry and Physics'', 83rd edition, {{ISBN|0-8493-0483-0}}, pp. 12–14 to 12–16.</ref> ions rarely go through the "wrong" channel. For example, sodium or calcium ions rarely pass through a potassium channel.
[[File:Action potential ion sizes.svg.png|thumb|Despite the small differences in their radii,<ref name=":6">''CRC Handbook of Chemistry and Physics'', 83rd edition, {{ISBN|0-8493-0483-0}}, pp. 12–14 to 12–16.</ref> ions rarely go through the "wrong" channel. For example, sodium or calcium ions rarely pass through a potassium channel.
离子通道可以根据它们对环境的反应来分类.<ref name="goldin_2007" /> 。例如，与动作电位有关的离子通道是电压敏感通道，它们随着跨膜电压的变化而开闭。配体门控通道形成另一个重要类别，这些离子通道开放和关闭响应配体分子的结合，如神经递质。其他离子通道的开启和关闭都受到机械力的作用。还有一些离子通道(如感觉神经元的通道)在其他刺激(如光、温度或压力)的作用下开关。
离子通道可以根据它们对环境的反应来分类.<ref name="goldin_2007" /> 。例如，与动作电位有关的离子通道是电压敏感通道，它们随着跨膜电压的变化而开闭。配体门控通道形成另一个重要类别，这些离子通道开放和关闭响应配体分子的结合，如神经递质。其他离子通道的开启和关闭都受到机械力的作用。还有一些离子通道(如感觉神经元的通道)在其他刺激(如光、温度或压力)的作用下开关。
====Leakage channels====
====泄露通道====
[[Leakage channel]]s are the simplest type of ion channel, in that their permeability is more or less constant. The types of leakage channels that have the greatest significance in neurons are potassium and chloride channels. Even these are not perfectly constant in their properties: First, most of them are voltage-dependent in the sense that they conduct better in one direction than the other (in other words, they are [[rectifier]]s); second, some of them are capable of being shut off by chemical ligands even though they do not require ligands in order to operate.
[[Leakage channel]]s are the simplest type of ion channel, in that their permeability is more or less constant. The types of leakage channels that have the greatest significance in neurons are potassium and chloride channels. Even these are not perfectly constant in their properties: First, most of them are voltage-dependent in the sense that they conduct better in one direction than the other (in other words, they are [[rectifier]]s); second, some of them are capable of being shut off by chemical ligands even though they do not require ligands in order to operate.
泄漏通道（leakage channels）是最简单的离子通道类型，因为它们的渗透率几乎是恒定的。在神经元中，钾离子通道和氯离子通道是泄漏通道中最重要的类型。即使它们的性质也不是完全恒定的：首先，它们中的大多数是电压依赖性的，因为他们的渗透性具有方向性（即作为整流器）；第二，其中一些能被化学配体关闭，尽管他们不需要配体来起作用。
====Ligand-gated channels 配体门控离子通道====
====Ligand-gated channels 配体门控离子通道====
[[Ligand-gated ion channel]]s are channels whose permeability is greatly increased when some type of chemical ligand binds to the protein structure. Animal cells contain hundreds, if not thousands, of types of these. A large subset function as [[neurotransmitter receptor]]s—they occur at [[postsynaptic]] sites, and the chemical ligand that gates them is released by the presynaptic [[axon terminal]]. One example of this type is the [[AMPA receptor]], a receptor for the neurotransmitter [[glutamic acid|glutamate]] that when activated allows passage of sodium and potassium ions. Another example is the [[GABAA receptor|GABA<sub>A</sub> receptor]], a receptor for the neurotransmitter [[GABA]] that when activated allows passage of chloride ions.
[[Ligand-gated ion channel]]s are channels whose permeability is greatly increased when some type of chemical ligand binds to the protein structure. Animal cells contain hundreds, if not thousands, of types of these. A large subset function as [[neurotransmitter receptor]]s—they occur at [[postsynaptic]] sites, and the chemical ligand that gates them is released by the presynaptic [[axon terminal]]. One example of this type is the [[AMPA receptor]], a receptor for the neurotransmitter [[glutamic acid|glutamate]] that when activated allows passage of sodium and potassium ions. Another example is the [[GABAA receptor|GABA<sub>A</sub> receptor]], a receptor for the neurotransmitter [[GABA]] that when activated allows passage of chloride ions.
配体门控离子通道（ligand-gated ion channels）是当某种类型的化学配体与蛋白结构结合时，其通透性大大增加的通道。动物细胞含有成百上千种这样的通道。很大一部分是作为神经递质受体发挥作用ーー它们存在于突触后位点，而与它们相关的化学配体是由突触前轴突末端释放的。这种类型的一个例子是 AMPA 受体，一种神经递质谷氨酸的受体，当激活时允许钠离子和钾离子通过。另一个例子是 GABA<sub>A</sub> 受体，一种神经递质 GABA 的受体，当被激活时允许氯离子通过。
Neurotransmitter receptors are activated by ligands that appear in the extracellular area, but there are other types of ligand-gated channels that are controlled by interactions on the intracellular side.
Neurotransmitter receptors are activated by ligands that appear in the extracellular area, but there are other types of ligand-gated channels that are controlled by interactions on the intracellular side.
神经递质受体被出现在细胞外的配体激活，但是还有其他类型的配体门控通道是由细胞内的相互作用控制的。
====Voltage-dependent channels====
====电压依赖性通道 Voltage-dependent channels====
[[Voltage-gated ion channel]]s, also known as ''voltage dependent ion channels'', are channels whose permeability is influenced by the membrane potential. They form another very large group, with each member having a particular ion selectivity and a particular voltage dependence. Many are also time-dependent—in other words, they do not respond immediately to a voltage change but only after a delay.
[[Voltage-gated ion channel]]s, also known as ''voltage dependent ion channels'', are channels whose permeability is influenced by the membrane potential. They form another very large group, with each member having a particular ion selectivity and a particular voltage dependence. Many are also time-dependent—in other words, they do not respond immediately to a voltage change but only after a delay.
电压门控离子通道（Voltage-gated ion channels），也称为电压依赖性离子通道（Voltage-dependent channels），是一种通道，其通透性受膜电位的影响。它们形成了另一个非常大的基团，每个成员具有特定的离子选择性和特定的电压依赖性。其中许多还与时间有关ー换句话说，它们不会立即对电压变化作出反应，而只是在延迟之后才作出反应。
One of the most important members of this group is a type of voltage-gated sodium channel that underlies action potentials—these are sometimes called ''Hodgkin-Huxley sodium channels'' because they were initially characterized by [[Alan Lloyd Hodgkin]] and [[Andrew Huxley]] in their Nobel Prize-winning studies of the physiology of the action potential. The channel is closed at the resting voltage level, but opens abruptly when the voltage exceeds a certain threshold, allowing a large influx of sodium ions that produces a very rapid change in the membrane potential. Recovery from an action potential is partly dependent on a type of voltage-gated potassium channel that is closed at the resting voltage level but opens as a consequence of the large voltage change produced during the action potential.
One of the most important members of this group is a type of voltage-gated sodium channel that underlies action potentials—these are sometimes called ''Hodgkin-Huxley sodium channels'' because they were initially characterized by [[Alan Lloyd Hodgkin]] and [[Andrew Huxley]] in their Nobel Prize-winning studies of the physiology of the action potential. The channel is closed at the resting voltage level, but opens abruptly when the voltage exceeds a certain threshold, allowing a large influx of sodium ions that produces a very rapid change in the membrane potential. Recovery from an action potential is partly dependent on a type of voltage-gated potassium channel that is closed at the resting voltage level but opens as a consequence of the large voltage change produced during the action potential.
这个小组最重要的成员之一是一种作为动作电位基础的电压门控钠通道ーー这些通道有时被称为霍奇金赫胥黎钠通道（Hodgkin-Huxley sodium channels），因为在他们获得诺贝尔奖的动作电位生理学研究中，他们最初是拥有属性艾伦·劳埃德·霍奇金和Alan Lloyd Hodgkin and Andrew Huxley 鉴定的。通道在静息电压水平处关闭，但当电压超过一定阈值时突然打开，从而允许大量钠离子流入，使膜电位发生非常迅速的变化。从动作电位中恢复部分依赖于一种在静息电压水平关闭但在动作电位产生巨大电压变化时打开的电压门控钾离子通道。
===Reversal potential===
===逆转电位Reversal potential===
The [[reversal potential]] (or ''equilibrium potential'') of an ion is the value of transmembrane voltage at which diffusive and electrical forces counterbalance, so that there is no net ion flow across the membrane. This means that the transmembrane voltage exactly opposes the force of diffusion of the ion, such that the net current of the ion across the membrane is zero and unchanging. The reversal potential is important because it gives the voltage that acts on channels permeable to that ion—in other words, it gives the voltage that the ion concentration gradient generates when it acts as a [[battery (electricity)|battery]].
The [[reversal potential]] (or ''equilibrium potential'') of an ion is the value of transmembrane voltage at which diffusive and electrical forces counterbalance, so that there is no net ion flow across the membrane. This means that the transmembrane voltage exactly opposes the force of diffusion of the ion, such that the net current of the ion across the membrane is zero and unchanging. The reversal potential is important because it gives the voltage that acts on channels permeable to that ion—in other words, it gives the voltage that the ion concentration gradient generates when it acts as a [[battery (electricity)|battery]].
一个离子的逆转电位（Reversal potential）或平衡电位（equilibrium potential）是跨膜电位值，在这个电压下扩散力和电力相互抵消，因此没有净离子流过这个跨膜电位。这意味着跨膜电压完全对抗离子的扩散力，使得跨膜离子的净电流为零且不变。翻转电位是重要的，因为它提供了作用于离子可渗透通道的电压——换句话说，它提供了离子浓度梯度作为电池时产生的电压。
The equilibrium potential of a particular ion is usually designated by the notation ''E''<sub>ion</sub>.The equilibrium potential for any ion can be calculated using the [[Nernst equation]].<ref name="nernst">Purves ''et al.'', pp. 28–32; [[Theodore Holmes Bullock|Bullock]], Orkand, and Grinnell, pp. 133–134; Schmidt-Nielsen, pp. 478–480, 596–597; Junge, pp. 33–35</ref> For example, reversal potential for potassium ions will be as follows:
The equilibrium potential of a particular ion is usually designated by the notation ''E''<sub>ion</sub>.The equilibrium potential for any ion can be calculated using the [[Nernst equation]].<ref name="nernst">Purves ''et al.'', pp. 28–32; [[Theodore Holmes Bullock|Bullock]], Orkand, and Grinnell, pp. 133–134; Schmidt-Nielsen, pp. 478–480, 596–597; Junge, pp. 33–35</ref> For example, reversal potential for potassium ions will be as follows:
一个特定离子的平衡电位通常用记号 Eion 来表示。任何离子的平衡电位都可以用能斯特方程来计算.<ref name="nernst" /> 。普尔维斯等人。28-32; 布洛克，Orkand 和格林内尔，pp。133–134; Schmidt-Nielsen, pp.478-480,596-597; Junge，pp.33-35例如，钾离子的翻转电位如下:
一个特定离子的平衡电位通常用记号 ''E''<sub>ion</sub> 来表示。任何离子的平衡电位都可以用能斯特方程来计算。<ref name="nernst" /> 例如，钾离子的逆转电位如下:
:<math> E_{eq,K^+} = \frac{RT}{zF} \ln \frac{[K^+]_{o}}{[K^+]_{i}} , </math>
:<math> E_{eq,K^+} = \frac{RT}{zF} \ln \frac{[K^+]_{o}}{[K^+]_{i}} , </math>
其中
其中
*''E''<sub>eq,K<sup>+</sup></sub> 是钾的平衡电位，用伏特为单位
*''E''<sub>eq,K<sup>+</sup></sub> 是钾的平衡电位，用伏特为单位
*''R'' 为通用气体常数，等于 8.314 [[joule]]s·K<sup>−1</sup>·mol<sup>−1</sup>
*''R'' 为通用气体常数，等于 8.314 joules·K<sup>−1</sup>·mol<sup>−1</sup>
*''T'' 为绝对温度，以 K 为单位 in [[kelvin]]s (= K = degrees Celsius + 273.15)
*''T'' 为绝对温度，以 K （℃ + 273.15）为单位
*''z'' 反应中所涉及的离子的基本电荷数
*''z'' 反应中离子的基本电荷数
*''F'' 是法拉第常数，等于 96,485 [[coulomb]]s·mol<sup>−1</sup> is the [[Faraday constant]], equal to 96,485 [[coulomb]]s·mol<sup>−1</sup> or J·V<sup>−1</sup>·mol<sup>−1</sup>
*''F'' 是法拉第常数，等于 96,485 coulombs·mol<sup>−1</sup> or J·V<sup>−1</sup>·mol<sup>−1</sup>
*[K<sup>+</sup>]<sub>o</sub> 为钾离子的胞外浓度 measured in [[Mole (unit)|mol]]·m<sup>−3</sup> or mmol·l<sup>−1</sup>
*[K<sup>+</sup>]<sub>o</sub> 为钾离子的胞外浓度，单位为 [[Mole (unit)|mol]]·m<sup>−3</sup> or mmol·l<sup>−1</sup>
*[K<sup>+</sup>]<sub>i</sub> is 为钾离子的胞内浓度，
*[K<sup>+</sup>]<sub>i</sub> is 为钾离子的胞内浓度
即使两种离子具有相同的电荷（即 K<sup>+</sup> and Na<sup>+</sup> ），只要胞内外浓度不同，它们仍然具有非常不同的平衡电位。以神经元中钾和钠的平衡电位为例，钾离子在胞内为 140 mM，胞外 5 mM，平衡电位为 -84 mV；而钠离子胞内约 12 mM，胞外 140 mM，平衡电位 ''E''<sub>Na</sub> 约为 +66 mV <ref name=":0" group="note">Note that the signs of ''E''<sub>Na</sub> and ''E''<sub>K</sub> are opposite. This is because the concentration gradient for potassium is directed out of the cell, while the concentration gradient for sodium is directed into the cell. Membrane potentials are defined relative to the exterior of the cell; thus, a potential of −70 mV implies that the interior of the cell is negative relative to the exterior.</ref>。
即使两种离子具有相同的电荷（即 K<sup>+</sup> and Na<sup>+</sup>），只要胞内外浓度不同，它们仍然具有非常不同的平衡电位。以神经元中钾和钠的平衡电位为例，钾离子在胞内为 140 mM，胞外 5 mM，平衡电位 ''E''<sub>K</sub> 为 -84 mV；而钠离子胞内约 12 mM，胞外 140 mM，平衡电位 ''E''<sub>Na</sub> 约为 +66 mV <ref name=":0" group="note">Note that the signs of ''E''<sub>Na</sub> and ''E''<sub>K</sub> are opposite. This is because the concentration gradient for potassium is directed out of the cell, while the concentration gradient for sodium is directed into the cell. Membrane potentials are defined relative to the exterior of the cell; thus, a potential of −70 mV implies that the interior of the cell is negative relative to the exterior.</ref>。
===发育中膜电位的变化===
===发育中膜电位的变化===