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第64行： − 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.+ − − 钠钾泵的工作速度较慢。如果开始时细胞内外是等浓度的钠离子和钾离子，那么需要钠钾泵工作几个小时才能建立平衡。钠钾泵始终在运转，但其泵送效率会随着可用的钠离子和钾离子的浓度下降而逐渐降低。 − − Ion pumps influence the action potential only by establishing the relative ratio of intracellular and extracellular ion concentrations. The action potential involves mainly the opening and closing of ion channels not ion pumps. If the ion pumps are turned off by removing their energy source, or by adding an inhibitor such as [[ouabain]], the axon can still fire hundreds of thousands of action potentials before their amplitudes begin to decay significantly.<ref name="hodgkin_1955" /> In particular, ion pumps play no significant role in the repolarization of the membrane after an action potential.<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" />+ − + − − 尽管它们的半径有很小的差别,<ref name=":6" /><nowiki>，化学和物理的离子很少通过错误的通道。例如，钠离子或钙离子很少通过钾离子通道。| alt = 7个球半径与一价锂、钠、钾、铷、铯离子（分别为0.76、1.02、1.38、1.52和1.67 å）、二价钙离子（1.00 å）和一价氯离子（1.81 å）的半径成正比。</nowiki>|链接=Special:FilePath/Action_potential_ion_sizes.svg.png]] − − [[Ion channel]]s are [[integral membrane protein]]s with a pore through which ions can travel between extracellular space and cell interior. Most channels are specific （selective） for one ion; for example, most potassium channels are characterized by 1000:1 selectivity ratio for potassium over sodium, though potassium and sodium ions have the same charge and differ only slightly in their radius. The channel pore is typically so small that ions must pass through it in single-file order.<ref name="eisenman_theory">{{cite book | author = Eisenman G | year = 1961 | chapter = On the elementary atomic origin of equilibrium ionic specificity | title = Symposium on Membrane Transport and Metabolism | editor = A Kleinzeller |editor2=A Kotyk | publisher = Academic Press | location = New York | pages = 163–79}}{{cite book | author = Eisenman G | year = 1965 | chapter = Some elementary factors involved in specific ion permeation | title = Proc. 23rd Int. Congr. Physiol. Sci., Tokyo | publisher = Excerta Med. Found. | location = Amsterdam | pages = 489–506}}<br />* {{cite journal |vauthors=Diamond JM, Wright EM | year = 1969 | title = Biological membranes: the physical basis of ion and nonekectrolyte selectivity | journal = Annual Review of Physiology | volume = 31 | pages = 581–646 | doi = 10.1146/annurev.ph.31.030169.003053 | pmid = 4885777}}</ref> Channel pores can be either open or closed for ion passage, although a number of channels demonstrate various sub-conductance levels. When a channel is open, ions permeate through the channel pore down the transmembrane concentration gradient for that particular ion. Rate of ionic flow through the channel, i.e. single-channel current amplitude, is determined by the maximum channel conductance and electrochemical driving force for that ion, which is the difference between the instantaneous value of the membrane potential and the value of the [[reversal potential]].<ref name="junge_33_37">Junge, pp. 33–37.</ref> − − 离子通道是一种内在膜蛋白，它有一个孔，离子可以通过这个孔在细胞外液和细胞内部之间穿梭。大多数钾离子通道对单个离子具有特异性（选择性） ; 例如，大多数钾离子通道对钾与钠的选择性比为 1000:1，尽管钾离子和钠离子带同样的电荷，只是半径略有不同。通道孔通常非常小，以至于离子必须以单列顺序通过。<ref name="eisenman_theory" /> 虽然一些通道表现出不同的亚电导水平，但是通道孔可以为离子通过而打开或关闭。当通道打开时，离子通过通道孔，顺着该离子种类的跨膜浓度梯度渗透。离子通过通道的速率，即单通道电流的幅度，是由该离子的最大通道电导和电化学驱动力决定的，即膜电位的瞬时值与逆转电位（reversal potential）值之间的差值 <ref name="junge_33_37" /> − − [[File:Potassium channel1.png|thumb|left|200px|<nowiki>Depiction of the open potassium channel, with the potassium ion shown in purple in the middle, and hydrogen atoms omitted. When the channel is closed, the passage is blocked.左图 | 200px | </nowiki>描绘开放的钾离子通道，中间以紫色显示的钾离子，省略了氢原子。当通道关闭时，通道就被堵塞了。|链接=Special:FilePath/Potassium_channel1.png]] − Schematic stick diagram of a tetrameric potassium channel where each of the monomeric subunits is symmetrically arranged around a central ion conduction pore. The pore axis is displayed perpendicular to the screen. Carbon, oxygen, and nitrogen atom are represented by grey, red, and blue spheres, respectively. A single potassium cation is depicted as a purple sphere in the center of the channel.+ − 四聚体钾离子通道的简图，其中每个单体亚基都对称地排列在中央离子导电孔周围。孔轴与屏幕垂直显示。碳原子、氧原子和氮原子分别用灰色、红色和蓝色球体表示。一个单独的钾离子被描绘成通道中心的一个紫色球体。+ − A channel may have several different states （corresponding to different [[protein structure|conformations]] of the protein）, but each such state is either open or closed. In general, closed states correspond either to a contraction of the pore—making it impassable to the ion—or to a separate part of the protein, stoppering the pore. For example, the voltage-dependent sodium channel undergoes ''inactivation'', in which a portion of the protein swings into the pore, sealing it.<ref>{{cite journal |vauthors=Cai SQ, Li W, Sesti F |title=Multiple modes of a-type potassium current regulation |journal=Curr. Pharm. Des. |volume=13 |issue=31 |pages=3178–84 |year=2007 |pmid=18045167 |doi=10.2174/138161207782341286}}</ref> This inactivation shuts off the sodium current and plays a critical role in the action potential.+ − + − 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 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。+ − − − + 第134行：
第118行： − <nowiki>E_{eq,K^+} = \frac{RT}{zF} \ln \frac{[K^+]_{o}}{[K^+]_{i}} , </nowiki> − : <nowiki>E_{eq,K^+} = \frac{RT}{zF} \ln \frac{[K^+]_{o}}{[K^+]_{i}} ,</nowiki> − − :e _ { eq，k ^ + } = frac { RT }{ zF } ln frac {[ k ^ + ]{ o }{[ k ^ + ]{ i } , − − where − *''E''<sub>eq,K<sup>+</sup></sub> is the equilibrium potential for potassium, measured in [[volt]]s − *''R'' is the universal [[gas constant]], equal to 8.314 [[joule]]s·K<sup>−1</sup>·mol<sup>−1</sup> − *''T'' is the [[absolute temperature]], measured in [[kelvin]]s （= K = degrees Celsius + 273.15） − *''z'' is the number of [[elementary charge]]s of the ion in question involved in the reaction − *''F'' is the [[Faraday constant]], equal to 96,485 [[coulomb]]s·mol<sup>−1</sup> or J·V<sup>−1</sup>·mol<sup>−1</sup> − *[K<sup>+</sup>]<sub>o</sub> is the extracellular concentration of potassium, measured in [[Mole (unit)|mol]]·m<sup>−3</sup> or mmol·l<sup>−1</sup> − *[K<sup>+</sup>]<sub>i</sub> is the intracellular concentration of potassium − 第160行：
第130行： − A [[neuron]]'s resting membrane potential actually changes during the [[Neural development|development]] of an organism. In order for a neuron to eventually adopt its full adult function, its potential must be tightly regulated during development. As an organism progresses through development the resting membrane potential becomes more negative.<ref name=":7">{{Cite journal|last1=Sanes|first1=Dan H.|last2=Takács|first2=Catherine|date=1993-06-01|title=Activity-dependent Refinement of Inhibitory Connections|journal=European Journal of Neuroscience|language=en|volume=5|issue=6|pages=570–574|doi=10.1111/j.1460-9568.1993.tb00522.x|pmid=8261131|s2cid=30714579|issn=1460-9568}}</ref> [[Neuroglia|Glial cells]] are also differentiating and proliferating as development progresses in the [[brain]].<ref name=":8">{{Cite journal|last1=KOFUJI|first1=P.|last2=NEWMAN|first2=E. A.|date=2004-01-01|journal=Neuroscience|volume=129|issue=4|pages=1045–1056|doi=10.1016/j.neuroscience.2004.06.008|issn=0306-4522| pmc=2322935 |pmid=15561419|title=Potassium buffering in the central nervous system}}</ref> The addition of these glial cells increases the organism's ability to regulate extracellular [[potassium]]. The drop in extracellular potassium can lead to a decrease in membrane potential of 35 mV.<ref name=":9">{{Cite book|title=Development of the nervous system|last1=Sanes|first1=Dan H.|last2=Reh|first2=Thomas A|date=2012-01-01|publisher=Elsevier Academic Press|isbn=9780080923208|pages=211–214|oclc=762720374|edition=Third}}</ref>+ − − 神经元的静息膜电位在生物体发育过程中会发生变化。为了让神经元最终发挥其完整的成年期功能，它的潜能必须在发育过程中受到严格的调控。随着生物体的发育，静息膜电位变得更负 <ref name=":7" /> 。随着脑的发育，神经胶质细胞也在分化和增殖 <ref name=":8" />。增加的神经胶质细胞增加了机体调节细胞外钾的能力。细胞外液中的钾的下降可导致膜电位下降 35 mV <ref name=":9" />。 第169行：
第137行： − Many cell types are considered to have an excitable membrane. Excitable cells are neurons, myocytes （cardiac, skeletal, [[Smooth muscle|smooth]]）, vascular [[Endothelium|endothelial cells]], [[pericyte]]s, [[juxtaglomerular cell]]s, [[Interstitial cell of Cajal|interstitial cells of Cajal]], many types of [[Epithelium|epithelial cells]] （e.g. [[beta cell]]s, [[alpha cell]]s, [[delta cell]]s, [[enteroendocrine cell]]s, [[Neuroendocrine_cell#Pulmonary_neuroendocrine_cells|pulmonary neuroendocrine cells]], [[pinealocyte]]s）, [[glia]]l cells （e.g. astrocytes）, [[mechanoreceptor]] cells （e.g. [[hair cell]]s and [[Merkel cell]]s）, [[chemoreceptor]] cells （e.g. [[glomus cell]]s, [[taste receptor]]s）, some [[plant cells]] and possibly [[White blood cell|immune cells]].<ref name=":15">{{Cite journal|last1=Davenport|first1=Bennett|last2=Li|first2=Yuan|last3=Heizer|first3=Justin W.|last4=Schmitz|first4=Carsten|last5=Perraud|first5=Anne-Laure|date=2015-07-23|title=Signature Channels of Excitability no More: L-Type Channels in Immune Cells|journal=Frontiers in Immunology|volume=6|page=375|doi=10.3389/fimmu.2015.00375|pmid=26257741|pmc=4512153|issn=1664-3224|doi-access=free}}</ref> Astrocytes display a form of non-electrical excitability based on intracellular calcium variations related to the expression of several receptors through which they can detect the synaptic signal. In neurons, there are different membrane properties in some portions of the cell, for example, dendritic excitability endows neurons with the capacity for coincidence detection of spatially separated inputs.<ref name=":16">{{Cite journal|last=Sakmann|first=Bert|date=2017-04-21|title=From single cells and single columns to cortical networks: dendritic excitability, coincidence detection and synaptic transmission in brain slices and brains|journal=Experimental Physiology|volume=102|issue=5|pages=489–521|doi=10.1113/ep085776|pmid=28139019|pmc=5435930|issn=0958-0670|doi-access=free}}</ref>+ − 许多细胞类型被认为具有兴奋性膜。兴奋性细胞包括神经元、肌细胞（心肌细胞、骨骼肌细胞、平滑肌细胞）、血管内皮细胞、周细胞、肾小球旁细胞、Cajal 间质细胞、多种类型的上皮细胞（如 β 细胞、α 细胞、δ 细胞、肠内分泌细胞、肺神经内分泌细胞、松果体细胞）、胶质细胞（例如星形胶质细胞）、机械感觉受体细胞（例如毛细胞和 Merkel 细胞）、化学感觉受体细胞（例如血管球细胞、味觉受体细胞）、一些植物细胞，可能还有免疫细胞 <ref name=":15" />。星形胶质细胞表现出一种非电兴奋性，这种兴奋性是基于细胞内钙离子的变化，这种变化与几个受体的表达有关，通过这些受体它们可以检测到突触信号。在神经元中，细胞的某些部分具有不同的膜特性，例如，树突的兴奋性赋予神经元对空间上分离的输入信号进行重合检测的能力 <ref name=":16" />。+ − + − − 第185行：
第151行： − When the membrane potential of a cell goes for a long period of time without changing significantly, it is referred to as a [[resting potential]] or resting voltage. This term is used for the membrane potential of non-excitable cells, but also for the membrane potential of excitable cells in the absence of excitation. In excitable cells, the other possible states are graded membrane potentials （of variable amplitude）, and action potentials, which are large, all-or-nothing rises in membrane potential that usually follow a fixed time course. Excitable cells include [[neuron]]s, muscle cells, and some secretory cells in [[gland]]s. Even in other types of cells, however, the membrane voltage can undergo changes in response to environmental or intracellular stimuli. For example, depolarization of the plasma membrane appears to be an important step in [[apoptosis|programmed cell death]].<ref name=":17">{{cite journal |vauthors=Franco R, Bortner CD, Cidlowski JA |title=Potential roles of electrogenic ion transport and plasma membrane depolarization in apoptosis |journal=J. Membr. Biol. |volume=209 |issue=1 |pages=43–58 |date=January 2006 |pmid=16685600 |doi=10.1007/s00232-005-0837-5|s2cid=849895 |url=https://zenodo.org/record/1232645 }}</ref>+ − 当一个细胞的膜电位长时间不发生明显变化时，它被称为静息电位（resting potential）或静息电压（resting voltage）。这个概念用于非兴奋性细胞的膜电位，也用于兴奋性细胞在未受刺激时的膜电位。兴奋性细胞在静息电位的状态之外，还有幅值可变的级量膜电位，以及动作电位这种幅值较大、全或无出现、有固定时间过程的膜电位上升。兴奋性细胞包括神经元、肌细胞和腺体中的一些分泌细胞。然而，即使在其他类型的细胞中，膜电位也会因为环境或细胞内的刺激而发生变化。例如，质膜去极化似乎是细胞程序性死亡的一个重要步骤。<ref name=":17" />+ − − The interactions that generate the resting potential are modeled by the [[Goldman equation]].<ref name="Goldman">Purves ''et al.'', pp. 32–33; [[Theodore Holmes Bullock|Bullock]], Orkand, and Grinnell, pp. 138–140; Schmidt-Nielsen, pp. 480; Junge, pp. 35–37</ref> This is similar in form to the Nernst equation shown above, in that it is based on the charges of the ions in question, as well as the difference between their inside and outside concentrations. However, it also takes into consideration the relative permeability of the plasma membrane to each ion in question. − − 戈德曼方程可以模拟产生静息电位的相互作用。<ref name="Goldman" /> 形式上类似于上述的能斯特方程，也是基于有关离子的电荷及其细胞内外浓度差而建立的。当然，它也考虑了质膜对每种离子的相对渗透性。 第197行：
第159行： − + − − <nowiki>E_{m} = \frac{RT}{F} \ln{ \left（ \frac{ P_{\mathrm{K}}[\mathrm{K}^{+}]_\mathrm{out} + P_{\mathrm{Na}}[\mathrm{Na}^{+}]_\mathrm{out} + P_{\mathrm{Cl}}[\mathrm{Cl}^{-}]_\mathrm{in}}{ P_{\mathrm{K}}[\mathrm{K}^{+}]_\mathrm{in} + P_{\mathrm{Na}}[\mathrm{Na}^{+}]_\mathrm{in} + P_{\mathrm{Cl}}[\mathrm{Cl}^{-}]_\mathrm{out}} \right） }</nowiki> − − The three ions that appear in this equation are potassium （K<sup>+</sup>）, sodium （Na<sup>+</sup>）, and chloride （Cl<sup>−</sup>）. Calcium is omitted, but can be added to deal with situations in which it plays a significant role.<ref name="goldman_calcium">{{cite journal | author = Spangler SG | year = 1972 | title = Expansion of the constant field equation to include both divalent and monovalent ions | journal = Alabama Journal of Medical Sciences | volume = 9 | pages = 218–23|pmid=5045041 | issue = 2 }}</ref> Being an anion, the chloride terms are treated differently from the cation terms; the intracellular concentration is in the numerator, and the extracellular concentration in the denominator, which is reversed from the cation terms. ''P''<sub>i</sub> stands for the relative permeability of the ion type i. − − 在这个方程式中出现的三个离子是钾（K<sup>+</sup>）、（Na<sup>+</sup>）和（Cl<sup>−</sup>）。钙是省略的，但可以添加到处理的情况下，它发挥了重要的作用。<ref name="goldman_calcium" /> 作为一个阴离子，氯离子项处理不同于阳离子项；细胞内浓度是在分子，胞外浓度在分母，这与阳离子项是反过来的。''P''<sub>i</sub> 代表离子类型 i 的相对渗透率。 − 从本质上讲，戈德曼公式将膜电位表示为单个离子类型的逆转电位的渗透率加权平均。（虽然膜电位在动作电位期间会发生100 mV 左右的变化，但细胞内外的离子浓度不会发生显著变化，仍然接近膜处于静息电位时各自的浓度。）在大多数动物细胞中，静息状态下钾的通透性比钠的通透性高得多。但是，与其他离子不同的是，氯离子没有被主动泵入，因此平衡的逆转电位非常接近由其他离子决定的静息电位。<ref name="resting_potential" /><ref name=":18" /> + − − Values of resting membrane potential in most animal cells usually vary between the potassium reversal potential （usually around -80 mV） and around -40 mV. The resting potential in excitable cells （capable of producing action potentials） is usually near -60 mV—more depolarized voltages would lead to spontaneous generation of action potentials. Immature or undifferentiated cells show highly variable values of resting voltage, usually significantly more positive than in differentiated cells.<ref name="Magnuson DS et al., 1995">{{cite journal | doi = 10.1016/0165-3806(94)00166-W |vauthors=Magnuson DS, Morassutti DJ, Staines WA, McBurney MW, Marshall KC | date = Jan 14, 1995| title = In vivo electrophysiological maturation of neurons derived from a multipotent precursor (embryonal carcinoma) cell line | journal = Developmental Brain Research| volume = 84|issue = 1| pages = 130–41 | pmid = 7720212}}</ref> In such cells, the resting potential value correlates with the degree of differentiation: undifferentiated cells in some cases may not show any transmembrane voltage difference at all. − − 在大多数动物细胞中，静息膜电位的数值通常在逆转电位（通常在 -80 mV）和 -40 mV 之间变化。（能够产生动作电位的）兴奋性细胞的静息电位通常接近 -60 mV ——更多的去极化电位会导致动作电位的自然发生。未成熟或未分化细胞的静息电位变化很大，通常明显高于已分化的细胞.<ref name="Magnuson DS et al., 1995" /> 。在这些细胞中，静息电位值与分化程度相关: 在某些情况下未分化的细胞可能根本没有任何跨膜电位差。 − − Maintenance of the resting potential can be metabolically costly for a cell because of its requirement for active pumping of ions to counteract losses due to leakage channels. The cost is highest when the cell function requires an especially depolarized value of membrane voltage. For example, the resting potential in daylight-adapted [[Calliphoridae|blowfly]] （''Calliphora vicina''） [[Simple eyes in invertebrates|photoreceptor]]s can be as high as -30 mV.<ref name="Juusola M et al., 1994">{{cite journal | doi = 10.1085/jgp.104.3.593 |vauthors=Juusola M, Kouvalainen E, Järvilehto M, Weckström M | date = Sep 1994| title = Contrast gain, signal-to-noise ratio, and linearity in light-adapted blowfly photoreceptors| journal = J Gen Physiol| volume = 104| issue = 3| pages = 593–621|pmid = 7807062 | pmc = 2229225}}</ref> This elevated membrane potential allows the cells to respond very rapidly to visual inputs; the cost is that maintenance of the resting potential may consume more than 20% of overall cellular [[Adenosine triphosphate|ATP]].<ref name="Laughlin SB et al., 2008">{{cite journal |vauthors=Laughlin SB, de Ruyter van Steveninck RR, Anderson JC | date = May 1998| title = The metabolic cost of neural information| journal = Nat. Neurosci.| volume = 1| issue = 1| pages = 36–41|pmid = 10195106 | doi = 10.1038/236| s2cid = 204995437}}</ref> − 对于细胞来说，维护静息电位的代谢成本可能很高，因为它需要主动泵入离子来抵消泄漏通道造成的损失。当细胞功能需要特别去极化值膜电位时，成本最高。例如，静息电位在日光适应的绿头丽蝇（红头丽蝇）光感受器可高达 -30mv.<ref name="Juusola M et al., 1994" /> 。这种升高的膜电位可以使细胞对视觉输入作出非常迅速的反应；代价就是维持静息电位可能消耗超过 20% 的细胞总 ATP。<ref name="Laughlin SB et al., 2008" />+ − On the other hand, the high resting potential in undifferentiated cells does not necessarily incur a high metabolic cost. This apparent paradox is resolved by examination of the origin of that resting potential. Little-differentiated cells are characterized by extremely high input resistance,<ref name="Magnuson DS et al., 1995" /> which implies that few leakage channels are present at this stage of cell life. As an apparent result, potassium permeability becomes similar to that for sodium ions, which places resting potential in-between the reversal potentials for sodium and potassium as discussed above. The reduced leakage currents also mean there is little need for active pumping in order to compensate, therefore low metabolic cost.+ − 另一方面，未分化的细胞的高静息电位并不一定导致高代谢成本。这个明显的悖论通过研究静息电位的起源得到了解决。较少分化的细胞具有极高的的输入电阻,<ref name="Magnuson DS et al., 1995" /> ，这意味着在细胞生命的这个阶段很少存在泄漏通道。明显的结果就是，钾离子的渗透性变得类似于钠离子的渗透性，正如上面讨论的，使静息电位位于钠离子和钾离子的反转电位之间。泄漏电流的减少也意味着不需要活跃的钠钾泵活动来补偿，因此代谢成本低。+ − As explained above, the potential at any point in a cell's membrane is determined by the ion concentration differences between the intracellular and extracellular areas, and by the permeability of the membrane to each type of ion. The ion concentrations do not normally change very quickly （with the exception of Ca<sup>2+</sup>, where the baseline intracellular concentration is so low that even a small influx may increase it by orders of magnitude）, but the permeabilities of the ions can change in a fraction of a millisecond, as a result of activation of ligand-gated ion channels. The change in membrane potential can be either large or small, depending on how many ion channels are activated and what type they are, and can be either long or short, depending on the lengths of time that the channels remain open. Changes of this type are referred to as '''graded potentials''', in contrast to action potentials, which have a fixed amplitude and time course.+ − − 第252行：
第200行： − So, in a resting membrane, while the driving force for potassium is low, its permeability is very high. Sodium has a huge driving force but almost no resting permeability. In this case, potassium carries about 20 times more current than sodium, and thus has 20 times more influence over ''E''<sub>m</sub> than does sodium.+ − − 因此，在静息膜中，钾离子的驱动力较低，而钾离子的通透性却很高。钠具有巨大的驱动力，但几乎没有静息通透性。在这种情况下，钾的电流是钠的 20 倍，因此对 ''E''<sub>m</sub> 的影响是钠的 20 倍。 − − However, consider another case—the peak of the action potential. Here, permeability to Na is high and K permeability is relatively low. Thus, the membrane moves to near ''E''<sub>Na</sub> and far from ''E''<sub>K</sub>. − − 然而，考虑另一种情况——动作电位的峰值。在这里，钠的渗透率较高，钾的渗透率相对较低。因此，膜电位接近 ''E''<sub>Na</sub> 而远离 ''E''<sub>K</sub>。 − − The more ions are permeant the more complicated it becomes to predict the membrane potential. However, this can be done using the [[Goldman equation|Goldman-Hodgkin-Katz equation]] or the weighted means equation. By plugging in the concentration gradients and the permeabilities of the ions at any instant in time, one can determine the membrane potential at that moment. What the GHK equations means is that, at any time, the value of the membrane potential will be a weighted average of the equilibrium potentials of all permeant ions. The "weighting" is the ions relative permeability across the membrane. − − 可通透的离子越多，预测膜电位就越发复杂。不过，这可以用 GHK 方程（Goldman-Hodgkin-Katz equation）或加权平均方程来实现。通过在任意时刻输入离子的浓度梯度和渗透率，就可确定那个时刻的膜电位。GHK 方程表明，任一时刻的膜电位值是所有通透的离子的平衡电位的加权平均。这里的“权重”是离子的跨膜相对渗透性。 − − ==Effects and implications 效应与意义== − While cells expend energy to transport ions and establish a transmembrane potential, they use this potential in turn to transport other ions and metabolites such as sugar. The transmembrane potential of the [[mitochondrial membrane|mitochondria]] drives the production of [[Adenosine triphosphate|ATP]], which is the common currency of biological energy. − 当细胞消耗能量来转运离子并建立膜电位时，它们反过来利用这种势能来转运其他离子和糖等代谢物。线粒体的膜电位驱动 ATP 的产生，ATP 是生物能量的通货。+ − Cells may draw on the energy they store in the resting potential to drive action potentials or other forms of excitation. These changes in the membrane potential enable communication with other cells （as with action potentials） or initiate changes inside the cell, which happens in an [[Ovum|egg]] when it is [[fertilization|fertilized]] by a [[sperm]].+ − 细胞可以利用它们在静息电位中储存的能量来驱动动作电位或其他形式的兴奋。这些膜电位变化可以与其他细胞交流（如动作电位），或产生在细胞内反应，比如卵细胞和精子受精时发生的。+ + − In neuronal cells, an action potential begins with a rush of sodium ions into the cell through sodium channels, resulting in depolarization, while recovery involves an outward rush of potassium through potassium channels. Both of these fluxes occur by [[passive transport|passive diffusion]].+ − 在神经细胞，一个动作电位开始于钠离子通过钠离子通道涌入细胞，导致去极化，而恢复过程中钾离子通过钾离子通道向外涌入。这两种流向都是通过被动扩散产生的。+
无编辑摘要
===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.
[[File:Cell membrane detailed diagram en.svg|thumb|right|500px|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。细胞膜上有各种生物分子，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]]
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>
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>
===易化扩散和易化转运 ===
===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。|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。
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（carrier protein），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===
===离子泵===
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。
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。
钠钾泵的转运速度相对较慢。如果开始时细胞内外是等浓度的钠离子和钾离子，那么需要钠钾泵工作几个小时才能建立平衡。钠钾泵始终在运转，但其泵送效率会随着可用的钠离子和钾离子的浓度下降而逐渐降低。
离子泵建立离子浓度在细胞内外的相对比例，从而影响动作电位。但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。
===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|尽管半径的差异很小,<ref name=":6">''CRC Handbook of Chemistry and Physics'', 83rd edition, {{ISBN|0-8493-0483-0}}, pp. 12–14 to 12–16.</ref> 离子很少通过“错的”的通道。例如，钠离子或钙离子很少通过钾离子通道。|链接=Special:FilePath/Action_potential_ion_sizes.svg.png]]
离子通道是一种内在膜蛋白，其形成通道孔，从而让离子在细胞外液和细胞内部穿梭。大多数钾离子通道对单个离子具有特异性（选择性） ; 例如，大多数钾离子通道对钾与钠的典型的选择率为 1000:1，尽管钾离子和钠离子带同样的电荷，只是半径略有不同。通道孔通常非常小，以至于离子必须以单列顺序通过。<ref name="eisenman_theory">{{cite book | author = Eisenman G | year = 1961 | chapter = On the elementary atomic origin of equilibrium ionic specificity | title = Symposium on Membrane Transport and Metabolism | editor = A Kleinzeller |editor2=A Kotyk | publisher = Academic Press | location = New York | pages = 163–79}}{{cite book | author = Eisenman G | year = 1965 | chapter = Some elementary factors involved in specific ion permeation | title = Proc. 23rd Int. Congr. Physiol. Sci., Tokyo | publisher = Excerta Med. Found. | location = Amsterdam | pages = 489–506}}<br />* {{cite journal |vauthors=Diamond JM, Wright EM | year = 1969 | title = Biological membranes: the physical basis of ion and nonekectrolyte selectivity | journal = Annual Review of Physiology | volume = 31 | pages = 581–646 | doi = 10.1146/annurev.ph.31.030169.003053 | pmid = 4885777}}</ref> 通道孔或开或关，但某些通道也存在亚电导水平。当通道打开时，离子通过通道孔，顺着该离子种类的跨膜浓度梯度渗透。离子通过通道的速率，即单通道电流大小，是由该离子的最大通道电导和电化学驱动力决定的，即瞬时膜电位与逆转电位（reversal potential）的差值。<ref name="junge_33_37">Junge, pp. 33–37.</ref>
[[File:Potassium channel1.png|thumb|left|200px|描绘了开放的钾离子通道，中央以紫色显示的钾离子，省略了氢原子。当通道关闭时，离子就不能通过了。|链接=Special:FilePath/Potassium_channel1.png]]
四聚体钾离子通道的示意棍棒图，其中每个单体亚基都对称地排列在中央的离子导孔周围。显示的孔轴与屏幕垂直。灰色、红色和蓝色球体分别表示碳原子、氧原子和氮原子。通道中央的紫色球体表示单个钾离子。
一个通道可能有几种不同的状态（对应于蛋白质的不同构象） ，但每种状态要么是开放的，要么是关闭的。一般来说，闭合状态要么对应于孔的收缩ーー使其不能通过离子ーー要么对应于蛋白质的一个单独部分，堵塞孔。例如，依赖电压的钠通道失活，其中一部分蛋白质摆动进入孔隙，封闭它。这种失活切断了钠电流，在动作电位中起着关键作用。
一个通道可能有几种不同的状态（对应于蛋白质的不同构象） ，但每种状态要么打开要么关闭。一般而言，关闭的状态要么是孔收缩使得离子不能通过，要么是蛋白的单独部分堵塞了孔。例如，电压依赖的钠通道失活时，蛋白的一段摆入并封闭了孔隙。<ref>{{cite journal |vauthors=Cai SQ, Li W, Sesti F |title=Multiple modes of a-type potassium current regulation |journal=Curr. Pharm. Des. |volume=13 |issue=31 |pages=3178–84 |year=2007 |pmid=18045167 |doi=10.2174/138161207782341286}}</ref> 这种失活切断了钠电流，在动作电位中起着关键作用。
Ion channels can be classified by how they respond to their environment.<ref name="goldin_2007">{{cite book | author = Goldin AL | year = 2007 | chapter = Neuronal Channels and Receptors | title = Molecular Neurology | editor = Waxman SG | publisher = Elsevier Academic Press | location = Burlington, MA | isbn = 978-0-12-369509-3 | pages = 43–58}}</ref> For example, the ion channels involved in the action potential are ''voltage-sensitive channels''; they open and close in response to the voltage across the membrane. ''Ligand-gated channels'' form another important class; these ion channels open and close in response to the binding of a [[ligand (biochemistry)|ligand molecule]], such as a [[neurotransmitter]]. Other ion channels open and close with mechanical forces. Still other ion channels—such as those of [[sensory neuron]]s—open and close in response to other stimuli, such as light, temperature or pressure.
Ion channels can be classified by how they respond to their environment.<ref name="goldin_2007">{{cite book | author = Goldin AL | year = 2007 | chapter = Neuronal Channels and Receptors | title = Molecular Neurology | editor = Waxman SG | publisher = Elsevier Academic Press | location = Burlington, MA | isbn = 978-0-12-369509-3 | pages = 43–58}}</ref> For example, the ion channels involved in the action potential are ''voltage-sensitive channels''; they open and close in response to the voltage across the membrane. ''Ligand-gated channels'' form another important class; these ion channels open and close in response to the binding of a [[ligand (biochemistry)|ligand molecule]], such as a [[neurotransmitter]]. Other ion channels open and close with mechanical forces. Still other ion channels—such as those of [[sensory neuron]]s—open and close in response to other stimuli, such as light, temperature or pressure.
离子通道可以根据它们对环境的反应方式来分类。<ref name="goldin_2007" /> 例如，动作电位用到的电压敏感通道（''voltage-sensitive channels''），随着跨膜电压的变化而开关。配体门控通道（''Ligand-gated channels''）则因配体分子，如神经递质，的结合而打开或关闭。其他离子通道随机械力的作用而打开和关闭。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。
====泄露通道====
====泄露通道====
泄漏通道（leakage channels）可谓最简单的离子通道类型，因其渗透率几乎是恒定的。神经元中最重要的泄露通道是钾离子通道和氯离子通道，但其性质并非完全恒定的：首先，其中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。
====配体门控离子通道====
====Ligand-gated channels 配体门控离子通道====
[[File:LGIC.png|thumb|right|300px|闭合态和开放态的配体门控钙离子通道|链接=Special:FilePath/LGIC.png]]
[[File:LGIC.png|thumb|right|300px|闭合态和开放态的配体门控钙离子通道|链接=Special:FilePath/LGIC.png]]
[[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。
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。动物细胞没有上千也有几百种这类通道。其中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，受到而门控这些通道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.
:<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
===发育中膜电位的变化===
===发育中膜电位的变化===
神经元的静息膜电位在生物体发育过程中会发生变化。为了让神经元最终执行其完整的成年期功能，它的潜能必须在发育过程中受到严格的调控。随着生物体的发育，静息膜电位变得更负。<ref name=":7">{{Cite journal|last1=Sanes|first1=Dan H.|last2=Takács|first2=Catherine|date=1993-06-01|title=Activity-dependent Refinement of Inhibitory Connections|journal=European Journal of Neuroscience|language=en|volume=5|issue=6|pages=570–574|doi=10.1111/j.1460-9568.1993.tb00522.x|pmid=8261131|s2cid=30714579|issn=1460-9568}}</ref> 随着脑的发育，神经胶质细胞也在分化和增殖。<ref name=":8">{{Cite journal|last1=KOFUJI|first1=P.|last2=NEWMAN|first2=E. A.|date=2004-01-01|journal=Neuroscience|volume=129|issue=4|pages=1045–1056|doi=10.1016/j.neuroscience.2004.06.008|issn=0306-4522| pmc=2322935 |pmid=15561419|title=Potassium buffering in the central nervous system}}</ref> 增加的神经胶质细胞增加了机体调节细胞外钾的能力。细胞外液中的钾的下降可导致膜电位下降 35 mV。<ref name=":9">{{Cite book|title=Development of the nervous system|last1=Sanes|first1=Dan H.|last2=Reh|first2=Thomas A|date=2012-01-01|publisher=Elsevier Academic Press|isbn=9780080923208|pages=211–214|oclc=762720374|edition=Third}}</ref>
=== 细胞兴奋性===
=== 细胞兴奋性===
细胞兴奋性最重要的调节因子是细胞外电解质浓度（即 Na<sup>+</sup>, K<sup>+</sup>, [[Calcium metabolism|Ca<sup>2+</sup>]], Cl<sup>−</sup>, [[Magnesium in biology|Mg<sup>2+</sup>]]）及其相关蛋白。调节细胞兴奋性的重要蛋白质是电压门控离子通道、离子转运蛋白（如钠钾 ATP 酶、镁转运蛋白、酸碱转运蛋白）、膜受体和超极化激活的环核苷酸门控通道 <ref name=":12">{{Cite journal|last1=Spinelli|first1=Valentina|last2=Sartiani|first2=Laura|last3=Mugelli|first3=Alessandro|last4=Romanelli|first4=Maria Novella|last5=Cerbai|first5=Elisabetta|date=2018|title=Hyperpolarization-activated cyclic-nucleotide-gated channels: pathophysiological, developmental, and pharmacological insights into their function in cellular excitability|journal=Canadian Journal of Physiology and Pharmacology|volume=96|issue=10|pages=977–984|doi=10.1139/cjpp-2018-0115|pmid=29969572|issn=0008-4212|hdl=1807/90084|hdl-access=free}}</ref>。例如，钾离子通道和钙敏感受体是神经元、心肌细胞和星形胶质细胞等其他兴奋性细胞的兴奋性的重要调节因子<ref name=":13">{{Cite journal|last1=Jones|first1=Brian L.|last2=Smith|first2=Stephen M.|date=2016-03-30|title=Calcium-Sensing Receptor: A Key Target for Extracellular Calcium Signaling in Neurons|journal=Frontiers in Physiology|volume=7|page=116|doi=10.3389/fphys.2016.00116|pmid=27065884|pmc=4811949|issn=1664-042X|doi-access=free}}</ref> 。钙离子也是兴奋性细胞信号转导中最重要的第二信使。突触受体的激活产生神经元兴奋性的长期改变 <ref name=":14">{{Cite journal|last1=Debanne|first1=Dominique|last2=Inglebert|first2=Yanis|last3=Russier|first3=Michaël|date=2019|title=Plasticity of intrinsic neuronal excitability|journal=Current Opinion in Neurobiology|language=en|volume=54|pages=73–82|doi=10.1016/j.conb.2018.09.001|pmid=30243042|s2cid=52812190|url=https://hal-amu.archives-ouvertes.fr/hal-01963474/file/Debannne-Russier-2019.pdf}}</ref>。甲状腺激素、肾上腺激素和其他激素也调节细胞的兴奋性，例如，孕酮和雌激素调节子宫平滑肌细胞的兴奋性。
细胞兴奋性最重要的调节因子是细胞外电解质浓度（即 Na<sup>+</sup>, K<sup>+</sup>, [[Calcium metabolism|Ca<sup>2+</sup>]], Cl<sup>−</sup>, [[Magnesium in biology|Mg<sup>2+</sup>]]）及其相关蛋白。调节细胞兴奋性的重要蛋白质是电压门控离子通道、离子转运蛋白（如钠钾 ATP 酶、镁转运蛋白、酸碱转运蛋白）、膜受体和超极化激活的环核苷酸门控通道 <ref name=":12">{{Cite journal|last1=Spinelli|first1=Valentina|last2=Sartiani|first2=Laura|last3=Mugelli|first3=Alessandro|last4=Romanelli|first4=Maria Novella|last5=Cerbai|first5=Elisabetta|date=2018|title=Hyperpolarization-activated cyclic-nucleotide-gated channels: pathophysiological, developmental, and pharmacological insights into their function in cellular excitability|journal=Canadian Journal of Physiology and Pharmacology|volume=96|issue=10|pages=977–984|doi=10.1139/cjpp-2018-0115|pmid=29969572|issn=0008-4212|hdl=1807/90084|hdl-access=free}}</ref>。例如，钾离子通道和钙敏感受体是神经元、心肌细胞和星形胶质细胞等其他兴奋性细胞的兴奋性的重要调节因子<ref name=":13">{{Cite journal|last1=Jones|first1=Brian L.|last2=Smith|first2=Stephen M.|date=2016-03-30|title=Calcium-Sensing Receptor: A Key Target for Extracellular Calcium Signaling in Neurons|journal=Frontiers in Physiology|volume=7|page=116|doi=10.3389/fphys.2016.00116|pmid=27065884|pmc=4811949|issn=1664-042X|doi-access=free}}</ref> 。钙离子也是兴奋性细胞信号转导中最重要的第二信使。突触受体的激活产生神经元兴奋性的长期改变 <ref name=":14">{{Cite journal|last1=Debanne|first1=Dominique|last2=Inglebert|first2=Yanis|last3=Russier|first3=Michaël|date=2019|title=Plasticity of intrinsic neuronal excitability|journal=Current Opinion in Neurobiology|language=en|volume=54|pages=73–82|doi=10.1016/j.conb.2018.09.001|pmid=30243042|s2cid=52812190|url=https://hal-amu.archives-ouvertes.fr/hal-01963474/file/Debannne-Russier-2019.pdf}}</ref>。甲状腺激素、肾上腺激素和其他激素也调节细胞的兴奋性，例如，孕酮和雌激素调节子宫平滑肌细胞的兴奋性。
许多细胞类型被认为具有兴奋性膜。兴奋性细胞包括神经元、肌细胞（心肌细胞、骨骼肌细胞、平滑肌细胞）、血管内皮细胞、周细胞、肾小球旁细胞、Cajal 间质细胞、多种类型的上皮细胞（如 β 细胞、α 细胞、δ 细胞、肠内分泌细胞、肺神经内分泌细胞、松果体细胞）、胶质细胞（例如星形胶质细胞）、机械感觉受体细胞（例如毛细胞和 Merkel 细胞）、化学感觉受体细胞（例如血管球细胞、味觉受体细胞）、一些植物细胞，可能还有免疫细胞。<ref name=":15">{{Cite journal|last1=Davenport|first1=Bennett|last2=Li|first2=Yuan|last3=Heizer|first3=Justin W.|last4=Schmitz|first4=Carsten|last5=Perraud|first5=Anne-Laure|date=2015-07-23|title=Signature Channels of Excitability no More: L-Type Channels in Immune Cells|journal=Frontiers in Immunology|volume=6|page=375|doi=10.3389/fimmu.2015.00375|pmid=26257741|pmc=4512153|issn=1664-3224|doi-access=free}}</ref> 星形胶质细胞表现出一种非电兴奋性，基于检测突触信号的几种受体相关的胞内钙离子浓度变化。神经元中，某些细胞部分具有不同的膜特性，例如，树突的兴奋性赋予神经元对空间上分离的输入信号进行重合检测的能力 <ref name=":16">{{Cite journal|last=Sakmann|first=Bert|date=2017-04-21|title=From single cells and single columns to cortical networks: dendritic excitability, coincidence detection and synaptic transmission in brain slices and brains|journal=Experimental Physiology|volume=102|issue=5|pages=489–521|doi=10.1113/ep085776|pmid=28139019|pmc=5435930|issn=0958-0670|doi-access=free}}</ref>。
===等效电路===
[[File:Cell membrane equivalent circuit.svg|thumb|right|350px|Equivalent circuit for a patch of membrane, consisting of a fixed capacitance in parallel with four pathways each containing a battery in series with a variable conductance膜片的等效电路，由一个固定电容和四条并联通路组成。每条并联通路串联一个电池和可变电导。|链接=Special:FilePath/Cell_membrane_equivalent_circuit.svg]]
===Equivalent circuit等效电路===
[[File:Cell membrane equivalent circuit.svg|thumb|right|350px|Equivalent circuit for a patch of membrane, consisting of a fixed capacitance in parallel with four pathways each containing a battery in series with a variable conductance膜片的等效电路，由固定电容组成，并联四条通路，每条通路串联一个电池，电导率可变。|链接=Special:FilePath/Cell_membrane_equivalent_circuit.svg]]
Electrophysiologists model the effects of ionic concentration differences, ion channels, and membrane capacitance in terms of an [[equivalent circuit]], which is intended to represent the electrical properties of a small patch of membrane. The equivalent circuit consists of a capacitor in parallel with four pathways each consisting of a battery in series with a variable conductance. The capacitance is determined by the properties of the lipid bilayer, and is taken to be fixed. Each of the four parallel pathways comes from one of the principal ions, sodium, potassium, chloride, and calcium. The voltage of each ionic pathway is determined by the concentrations of the ion on each side of the membrane; see the [[Membrane potential#Reversal potential|Reversal potential]] section above. The conductance of each ionic pathway at any point in time is determined by the states of all the ion channels that are potentially permeable to that ion, including leakage channels, ligand-gated channels, and voltage-gated ion channels.
Electrophysiologists model the effects of ionic concentration differences, ion channels, and membrane capacitance in terms of an [[equivalent circuit]], which is intended to represent the electrical properties of a small patch of membrane. The equivalent circuit consists of a capacitor in parallel with four pathways each consisting of a battery in series with a variable conductance. The capacitance is determined by the properties of the lipid bilayer, and is taken to be fixed. Each of the four parallel pathways comes from one of the principal ions, sodium, potassium, chloride, and calcium. The voltage of each ionic pathway is determined by the concentrations of the ion on each side of the membrane; see the [[Membrane potential#Reversal potential|Reversal potential]] section above. The conductance of each ionic pathway at any point in time is determined by the states of all the ion channels that are potentially permeable to that ion, including leakage channels, ligand-gated channels, and voltage-gated ion channels.
==静息电位==
==静息电位==
当一个细胞的膜电位长时间不发生明显变化时，被称为静息电位（resting potential）或静息电压（resting voltage）。这个概念可用于非兴奋性细胞的膜电位，也可用于兴奋性细胞在未受刺激时的膜电位。兴奋性细胞在静息电位的状态之外，还有幅值可变的级量膜电位，以及动作电位这种幅值较大、全或无出现、有固定时间过程的膜电位上升。兴奋性细胞包括神经元、肌细胞和腺体中的一些分泌细胞。然而，即使在其他类型的细胞中，膜电位也会因为环境或细胞内的刺激而发生变化。例如，质膜去极化似乎是细胞程序性死亡的一个重要步骤。<ref name=":17">{{cite journal |vauthors=Franco R, Bortner CD, Cidlowski JA |title=Potential roles of electrogenic ion transport and plasma membrane depolarization in apoptosis |journal=J. Membr. Biol. |volume=209 |issue=1 |pages=43–58 |date=January 2006 |pmid=16685600 |doi=10.1007/s00232-005-0837-5|s2cid=849895 |url=https://zenodo.org/record/1232645 }}</ref>
戈德曼方程可以模拟产生静息电位的相互作用。<ref name="Goldman">Purves ''et al.'', pp. 32–33; [[Theodore Holmes Bullock|Bullock]], Orkand, and Grinnell, pp. 138–140; Schmidt-Nielsen, pp. 480; Junge, pp. 35–37</ref> 形式上类似于上述的能斯特方程，也是基于有关离子的电荷及其细胞内外浓度差而建立的。当然，它也考虑了质膜对每种离子的相对渗透性。
:<math>
:<math>
</math>
</math>
在这个方程式中出现的三个离子是钾（K<sup>+</sup>）、（Na<sup>+</sup>）和（Cl<sup>−</sup>）。钙不在方程里，但在其发挥重要作用的时候可以加进去。<ref name="goldman_calcium">{{cite journal | author = Spangler SG | year = 1972 | title = Expansion of the constant field equation to include both divalent and monovalent ions | journal = Alabama Journal of Medical Sciences | volume = 9 | pages = 218–23|pmid=5045041 | issue = 2 }}</ref> 作为一个阴离子，氯离子项的处理不同于阳离子项；细胞内浓度放在分子，胞外浓度放在分母，这与阳离子项是反过来的。''P''<sub>i</sub> 代表离子类型 i 的相对渗透率。
In essence, the Goldman formula expresses the membrane potential as a weighted average of the reversal potentials for the individual ion types, weighted by permeability. （Although the membrane potential changes about 100 mV during an action potential, the concentrations of ions inside and outside the cell do not change significantly. They remain close to their respective concentrations when then membrane is at resting potential.） In most animal cells, the permeability to potassium is much higher in the resting state than the permeability to sodium. As a consequence, the resting potential is usually close to the potassium reversal potential.<ref name="resting_potential">Purves ''et al.'', p. 34; [[Theodore Holmes Bullock|Bullock]], Orkand, and Grinnell, p. 134; [[Knut Schmidt-Nielsen|Schmidt-Nielsen]], pp. 478–480.</ref><ref name=":18">Purves ''et al.'', pp. 33–36; [[Theodore Holmes Bullock|Bullock]], Orkand, and Grinnell, p. 131.</ref> The permeability to chloride can be high enough to be significant, but, unlike the other ions, chloride is not actively pumped, and therefore equilibrates at a reversal potential very close to the resting potential determined by the other ions.
In essence, the Goldman formula expresses the membrane potential as a weighted average of the reversal potentials for the individual ion types, weighted by permeability. （Although the membrane potential changes about 100 mV during an action potential, the concentrations of ions inside and outside the cell do not change significantly. They remain close to their respective concentrations when then membrane is at resting potential.） In most animal cells, the permeability to potassium is much higher in the resting state than the permeability to sodium. As a consequence, the resting potential is usually close to the potassium reversal potential.<ref name="resting_potential">Purves ''et al.'', p. 34; [[Theodore Holmes Bullock|Bullock]], Orkand, and Grinnell, p. 134; [[Knut Schmidt-Nielsen|Schmidt-Nielsen]], pp. 478–480.</ref><ref name=":18">Purves ''et al.'', pp. 33–36; [[Theodore Holmes Bullock|Bullock]], Orkand, and Grinnell, p. 131.</ref> The permeability to chloride can be high enough to be significant, but, unlike the other ions, chloride is not actively pumped, and therefore equilibrates at a reversal potential very close to the resting potential determined by the other ions.
本质上，戈德曼公式将膜电位表示为单个离子类型的逆转电位的渗透率加权平均。（虽然膜电位在动作电位期间会发生100 mV 左右的变化，但细胞内外的离子浓度不会发生显著变化，仍然接近膜处于静息电位时各自的浓度。）在大多数动物细胞中，静息状态下钾的通透性比钠的通透性高得多。但是，与其他离子不同的是，氯离子没有被主动泵入，因此平衡的逆转电位非常接近由其他离子决定的静息电位。<ref name="resting_potential" /><ref name=":18" />
在大多数动物细胞中，静息膜电位的数值通常在钾离子的逆转电位（通常在 -80 mV）和 -40 mV 之间变化。（能够产生动作电位的）兴奋性细胞的静息电位通常接近 -60 mV ——更多的去极化电位会导致动作电位的自发发生。未成熟或未分化细胞的静息电位数值变化很大，通常明显高于已分化的细胞.<ref name="Magnuson DS et al., 1995">{{cite journal | doi = 10.1016/0165-3806(94)00166-W |vauthors=Magnuson DS, Morassutti DJ, Staines WA, McBurney MW, Marshall KC | date = Jan 14, 1995| title = In vivo electrophysiological maturation of neurons derived from a multipotent precursor (embryonal carcinoma) cell line | journal = Developmental Brain Research| volume = 84|issue = 1| pages = 130–41 | pmid = 7720212}}</ref> 。在这些细胞中，静息电位值与分化程度相关：在某些情况下未分化的细胞可能完全没有跨膜电位差。
对于细胞来说，维护静息电位的代谢成本可能很高，因为它需要主动泵入离子来抵消泄漏通道导致的流失。当细胞功能需要更加去极化的膜电位时，成本最高。例如，日光适应的绿头丽蝇（Calliphora vicina）的光感受器的静息电位可高达 -30 mV。<ref name="Juusola M et al., 1994">{{cite journal | doi = 10.1085/jgp.104.3.593 |vauthors=Juusola M, Kouvalainen E, Järvilehto M, Weckström M | date = Sep 1994| title = Contrast gain, signal-to-noise ratio, and linearity in light-adapted blowfly photoreceptors| journal = J Gen Physiol| volume = 104| issue = 3| pages = 593–621|pmid = 7807062 | pmc = 2229225}}</ref> 这种升高的膜电位可以使细胞对视觉输入做出极其迅速的反应；代价就是维持静息电位可能消耗超过 20% 的细胞总 ATP。<ref name="Laughlin SB et al., 2008">{{cite journal |vauthors=Laughlin SB, de Ruyter van Steveninck RR, Anderson JC | date = May 1998| title = The metabolic cost of neural information| journal = Nat. Neurosci.| volume = 1| issue = 1| pages = 36–41|pmid = 10195106 | doi = 10.1038/236| s2cid = 204995437}}</ref>
另一方面，未分化的细胞的高静息电位并不一定导致高代谢成本。这看似矛盾，可以通过研究静息电位的来源解决。较少分化的细胞具有极高的的输入电阻，<ref name="Magnuson DS et al., 1995" /> 这意味着在细胞生命的这个阶段很少存在泄漏通道。明显的结果就是，钾离子的渗透性变得跟钠离子的类似，正如上面讨论的，而使静息电位处于钠离子和钾离子的反转电位之间。泄漏电流的减少也意味着不需要活跃的钠钾泵活动来补偿，因此代谢成本低。
==级量电位==
==级量电位==
如上所述，细胞膜上任何一点的电位取决于细胞内和细胞外区域离子浓度的差异，以及细胞膜对每种离子的通透性。离子浓度通常不会很快改变（除了 Ca<sup>2+</sup> ，其细胞内基线浓度非常低，即使是很小的内流量也可能产生数量级的增加），但是由于配体门控离子通道的激活，离子的通透性可以在几分之一毫秒内改变。膜电位的变化可大可小，取决于激活的离子通道的数量和类型；也可长可短，取决于通道保持开放的时间长短。这种类型的变化被称为级量电位（graded potentials），不同于有固定的振幅和时间进程的动作电位。
如上所述，细胞膜上任何一点的电位取决于细胞内和细胞外区域离子浓度的差异，以及细胞膜对每种离子的通透性。离子浓度通常不会很快改变（除了 Ca<sup>2+</sup> ，其细胞内基线浓度非常低，即使是很小的内流量也可能产生数量级的增加），但是由于配体门控离子通道的激活，离子的通透性可以在几分之一毫秒内改变。膜电位的变化可大可小，取决于激活的离子通道的数量和类型；也可长可短，取决于通道保持开放的时间长短。这种类型的变化被称为级量电位（），与动作电位相反，动作电位有固定的振幅和时间进程。
As can be derived from the [[Goldman equation]] shown above, the effect of increasing the permeability of a membrane to a particular type of ion shifts the membrane potential toward the reversal potential for that ion. Thus, opening Na<sup>+</sup> channels shifts the membrane potential toward the Na<sup>+</sup> reversal potential, which is usually around +100 mV. Likewise, opening K<sup>+</sup> channels shifts the membrane potential toward about –90 mV, and opening Cl<sup>−</sup> channels shifts it toward about –70 mV （resting potential of most membranes）. Thus, Na<sup>+</sup> channels shift the membrane potential in a positive direction, K<sup>+</sup> channels shift it in a negative direction （except when the membrane is hyperpolarized to a value more negative than the K<sup>+</sup> reversal potential）, and Cl<sup>−</sup> channels tend to shift it towards the resting potential.
As can be derived from the [[Goldman equation]] shown above, the effect of increasing the permeability of a membrane to a particular type of ion shifts the membrane potential toward the reversal potential for that ion. Thus, opening Na<sup>+</sup> channels shifts the membrane potential toward the Na<sup>+</sup> reversal potential, which is usually around +100 mV. Likewise, opening K<sup>+</sup> channels shifts the membrane potential toward about –90 mV, and opening Cl<sup>−</sup> channels shifts it toward about –70 mV （resting potential of most membranes）. Thus, Na<sup>+</sup> channels shift the membrane potential in a positive direction, K<sup>+</sup> channels shift it in a negative direction （except when the membrane is hyperpolarized to a value more negative than the K<sup>+</sup> reversal potential）, and Cl<sup>−</sup> channels tend to shift it towards the resting potential.
*'''驱动力（Driving force）'''是使离子在膜上移动的净电力。计算上就是离子“希望”处于的电位（其平衡电位）和实际膜电位（''E''<sub>m</sub>）的差值。因此，形式上，离子的驱动力 = ''E''<sub>m</sub> - ''E''<sub>ion</sub>。例如，在我们前面计算钾离子的静息电位为 -73 mV，那么其驱动力为 7 mV：（- 73 mV）-（- 80 mV） = 7 mV。钠离子的驱动力为（- 73 mV）-（60 mV） =-133 mV。
*'''驱动力（Driving force）'''是使离子在膜上移动的净电力。计算上就是离子“希望”处于的电位（其平衡电位）和实际膜电位（''E''<sub>m</sub>）的差值。因此，形式上，离子的驱动力 = ''E''<sub>m</sub> - ''E''<sub>ion</sub>。例如，在我们前面计算钾离子的静息电位为 -73 mV，那么其驱动力为 7 mV：（- 73 mV）-（- 80 mV） = 7 mV。钠离子的驱动力为（- 73 mV）-（60 mV） =-133 mV。
*'''渗透性（Permeability）'''是衡量离子通过细胞膜的容易程度。它通常用（电）导度量，其单位是西门子（ [[Siemens (unit)|siemens]]），相当于 1 C·s<sup>−1</sup>·V<sup>−1</sup>，即一库仑每秒每伏特的电位。
*'''渗透性（Permeability）'''是衡量离子通过细胞膜的容易程度。它通常用（电）导度量，其单位是西门子（ [[Siemens (unit)|siemens]]），相当于 1 C·s<sup>−1</sup>·V<sup>−1</sup>，即一库仑每秒每伏特的电位。
因此，在静息膜中，钾离子的驱动力较低，但其通透性很高。钠具有巨大的驱动力，但几乎没有静息通透性。在这种情况下，钾的电流是钠的 20 倍，因此对 ''E''<sub>m</sub> 的影响是钠的 20 倍。
然而，考虑另一种情况——动作电位的峰值。此刻，钠的渗透率较高，钾的渗透率相对较低。因此，膜电位接近 ''E''<sub>Na</sub> 而远离 ''E''<sub>K</sub>。
可通透的离子越多，预测膜电位就越发复杂。不过，这可以用 GHK 方程（Goldman-Hodgkin-Katz equation）或加权平均方程来实现。通过输入任意时刻离子的浓度梯度和渗透率，就可确定那个时刻的膜电位。GHK 方程表明，任一时刻的膜电位值是所有通透的离子的平衡电位的加权平均。这里的“权重”是离子的相对跨膜渗透性。
==效应与意义==
细胞消耗能量来转运离子并建立膜电位，它们进而利用这种势能来转运其他离子和糖等代谢物。线粒体的膜电位驱动生物能量通货 ATP 的产生。
细胞可以利用它们在静息电位中储存的能量来驱动动作电位或其他形式的兴奋。这些膜电位变化让细胞能与其他细胞通讯（比如动作电位），或引起诸如卵细胞和精子受精时细胞内的变化。
在神经细胞，一个动作电位始于钠离子通过钠离子通道涌入细胞，导致去极化，而复极化过程中钾离子通过钾离子通道向外涌出。内流和外流都是被动扩散（passive diffusion）过程。
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