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小第25行：
第25行： − + − 几乎所有的质膜都有一个电位通过它们，内部通常相对于外部是负电位。膜电位有两个基本功能。首先，它允许一个细胞像电池一样工作，提供动力来操作嵌入在膜中的各种“分子设备”。其次，在神经元和肌肉细胞等电激活细胞中，它用于在细胞的不同部分之间传递信号。信号是通过在膜的某一点打开或关闭离子通道而产生的，从而引起膜电位的局部变化。这种电场的变化可以被膜上相邻或更远的离子通道迅速感觉到。这些离子通道可以随着电位的变化而打开或关闭，重新产生信号。 + 第40行：
第40行： − = = = = 细胞中的膜电位最终来自于两个因素: 电力和扩散。电力产生于带有相反电荷的粒子之间的相互吸引(正电荷和负电荷)和带有相同类型电荷的粒子之间的相互斥力(正电荷和负电荷都有)。扩散源于粒子从高度集中的区域向低浓度区域重新分布的统计趋势。+ − {{Main|Voltage}}+ − − thumb|right|200px|Electric field (arrows) and contours of constant voltage created by a pair of oppositely charged objects. The electric field is at right angles to the voltage contours, and the field is strongest where the spacing between contours is the smallest. − − = = = = 电压 = = 拇指 | 右 | 200px | 电场(箭头)和由一对相反电荷的物体产生的恒定电压等值线。电场与电压等值线成直角，等值线之间的间距最小时，电场最强。 − − Voltage, which is synonymous with difference in electrical potential, is the ability to drive an electric current across a resistance. Indeed, the simplest definition of a voltage is given by Ohm's law: V=IR, where V is voltage, I is current and R is resistance. If a voltage source such as a battery is placed in an electrical circuit, the higher the voltage of the source the greater the amount of current that it will drive across the available resistance. The functional significance of voltage lies only in potential differences between two points in a circuit. The idea of a voltage at a single point is meaningless. It is conventional in electronics to assign a voltage of zero to some arbitrarily chosen element of the circuit, and then assign voltages for other elements measured relative to that zero point. There is no significance in which element is chosen as the zero point—the function of a circuit depends only on the differences not on voltages per se. However, in most cases and by convention, the zero level is most often assigned to the portion of a circuit that is in contact with ground. 第63行：
第57行： − 用数学术语来说，电压的定义从电场的概念开始，电场是一个向量场，它为空间中的每一点分配一个大小和方向。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，即，。这个标量场称为电压分布。注意，这个定义允许任意的积分常数ーー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，但这种情况通常适用于生物组织。+ 第70行：
第64行： − {{Main|Ion|Diffusion|Electrochemical gradient|Electrophoretic mobility}}+ − [[File:Diffusion.en.svg|thumb|right|250px|Ions (pink circles) will flow across a membrane from the higher concentration to the lower concentration (down a concentration gradient), causing a current. However, this creates a voltage across the membrane that opposes the ions' motion. When this voltage reaches the equilibrium value, the two balance and the flow of ions stops.<ref>Campbell Biology, 6th edition</ref>|链接=Special:FilePath/Diffusion.en.svg]]+ − thumb|right|250px|Ions (pink circles) will flow across a membrane from the higher concentration to the lower concentration (down a concentration gradient), causing a current. However, this creates a voltage across the membrane that opposes the ions' motion. When this voltage reaches the equilibrium value, the two balance and the flow of ions stops.Campbell Biology, 6th edition|alt=A schematic diagram of two beakers, each filled with water (light-blue) and a semipermeable membrane represented by a dashed vertical line inserted into the beaker dividing the liquid contents of the beaker into two equal portions. The left-hand beaker represents an initial state at time zero, where the number of ions (pink circles) is much higher on one side of the membrane than the other. The right-hand beaker represents the situation at a later time point, after which ions have flowed across the membrane from the high to low concentration compartment of the beaker so that the number of ions on each side of the membrane is now closer to equal.+ − 离子(粉红色圆圈)会从较高的浓度流向较低的浓度(沿浓度梯度下降) ，形成电流。然而，这会在膜上产生一个电压，阻止离子的运动。当这个电压达到平衡值时，两个平衡和离子流就停止了。坎贝尔生物学，第六版 | alt = 两个烧杯的原理图，每个烧杯装满水(浅蓝色)和一个半透膜，用一条虚线垂直插入烧杯，将烧杯中的液体分成相等的两部分。左手烧杯表示时间为零的初始状态，其中膜一侧的离子数(粉红色圆圈)远高于另一侧。右边的烧杯代表稍后时间点的情况，之后离子从烧杯的高浓度区间流过薄膜，使薄膜两侧的离子数目现在接近相等。+ − − Electrical signals within biological organisms are, in general, driven by [[ion]]s.<ref>Johnston and Wu, p. 9.</ref> The most important cations for the action potential are [[sodium]] (Na<sup>+</sup>) and [[potassium]] (K<sup>+</sup>).<ref name="bullock_140_141">[[Theodore Holmes Bullock|Bullock]], Orkand, and Grinnell, pp. 140–41.</ref> Both of these are ''monovalent'' cations that carry a single positive charge. Action potentials can also involve [[calcium]] (Ca<sup>2+</sup>),<ref>[[Theodore Holmes Bullock|Bullock]], Orkand, and Grinnell, pp. 153–54.</ref> which is a ''divalent'' cation that carries a double positive charge. The [[chloride]] anion (Cl<sup>−</sup>) plays a major role in the action potentials of some [[algae]],<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> but plays a negligible role in the action potentials of most animals.<ref>[[Knut Schmidt-Nielsen|Schmidt-Nielsen]], p. 483.</ref> − − 一般来说，生物有机体内的电信号是由离子驱动的。动作电位最重要的阳离子是钠(Na +)和钾(k +)。140–41.这两种阳离子都是单价阳离子，带有单个正电荷。动作电位也可以涉及钙(Ca2 +) ，布洛克，Orkand 和格林内尔，pp。153–54.它是一种带有双正电荷的二价阳离子。氯离子(Cl -)在某些藻类的动作电位中起主要作用，而在大多数动物的动作电位中起微不足道的作用。施密特-尼尔森，p. 483。 第95行：
第85行： − 每个细胞都被包裹在质膜中，质膜具有类脂双分子层的结构，其中包含许多类型的大分子。因为它是由类脂分子组成的，所以质膜本质上具有很高的电阻率，换句话说，对离子的内在渗透性很低。然而，嵌入在膜中的一些分子能够将离子从膜的一侧活跃地传送到另一侧，或者提供离子可以移动的通道。+ 第113行：
第103行： − + − − − thumb|right|350px|The sodium-potassium pump uses energy derived from ATP to exchange sodium for potassium ions across the membrane. − − = = = = 离子泵 = = 拇指 | 右 | 350px | 钠-钾泵利用 ATP 产生的能量，通过膜将钠离子与钾离子交换。+ − − [[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). − − Ion pumps are integral membrane proteins that carry out active transport, i.e., use cellular energy (ATP) to "pump" the ions against their concentration gradient. 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). − − 离子泵是完整的膜蛋白，进行主动运输，也就是说，使用细胞能量(ATP)“泵”离子对他们的浓度梯度。这种离子泵从膜的一边吸收离子(降低那边的浓度) ，然后从另一边释放离子(增加那边的浓度)。 − + 第141行：
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第128行： − {{Main|Ion channel|Passive transport}}+ − − + − thumb|Despite the small differences in their radii,CRC Handbook of Chemistry and Physics, 83rd edition, , pp. 12–14 to 12–16. ions rarely go through the "wrong" channel. For example, sodium or calcium ions rarely pass through a potassium channel.|alt=Seven spheres whose radii are proportional to the radii of mono-valent lithium, sodium, potassium, rubidium, cesium cations (0.76, 1.02, 1.38, 1.52, and 1.67 Å, respectively), divalent calcium cation (1.00 Å) and mono-valent chloride (1.81 Å). − − = = = 离子通道 = = 拇指 | 尽管它们的半径有很小的差别，化学和物理的CRC手册，第83版，pp。12-14呼叫12-16。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。 − Ion channels are integral membrane proteins 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.<br />* 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.Junge, pp. 33–37.+ − 离子通道是一种完整的膜蛋白，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的选择性比为1000:1，而钾离子和钠离子的拥有属性相同，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。虽然一些通道表现出不同的次电导水平，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，沿着该特定离子的跨膜浓度梯度向下渗透。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翻转电位值之间的差值。朱格，页。33–37.+ − [[File:Potassium channel1.png|thumb|left|200px|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.|链接=Special:FilePath/Potassium_channel1.png]]+ − thumb|left|200px|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.|alt=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.+ − − 左图 | 200px | 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。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 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. This inactivation shuts off the sodium current and plays a critical role in the action potential. 第176行：
第148行： − Ion channels can be classified by how they respond to their environment. 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 molecule, such as a neurotransmitter. Other ion channels open and close with mechanical forces. Still other ion channels—such as those of sensory neurons—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来分类。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 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 rectifiers); second, some of them are capable of being shut off by chemical ligands even though they do not require ligands in order to operate. − + − − thumb|right|300px|Ligand-gated calcium channel in closed and open states − − = = = = = 拇指 | 右 | 300px | 配体门控钙离子通道闭合态和开放态 − − Ligand-gated ion channels 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 receptors—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 glutamate that when activated allows passage of sodium and potassium ions. Another example is the GABA<sub>A</sub> receptor, a receptor for the neurotransmitter GABA that when activated allows passage of chloride ions. − − 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. 第208行：
第168行： − − Voltage-gated ion channels, 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. − − 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. 第222行：
第178行： − 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.+ − − = = = = = 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。 − The equilibrium potential of a particular ion is usually designated by the notation Eion.The equilibrium potential for any ion can be calculated using the Nernst equation.Purves et al., pp. 28–32; Bullock, Orkand, and Grinnell, pp. 133–134; Schmidt-Nielsen, pp. 478–480, 596–597; Junge, pp. 33–35 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。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: 第246行：
第198行： − − where − *Eeq,K+ is the equilibrium potential for potassium, measured in volts − *R is the universal gas constant, equal to 8.314 joules·K−1·mol−1 − *T is the absolute temperature, measured in kelvins (= K = degrees Celsius + 273.15) − *z is the number of elementary charges of the ion in question involved in the reaction − * F is the Faraday constant, equal to 96,485 coulombs·mol−1 or J·V−1·mol−1 − *[K+]o is the extracellular concentration of potassium, measured in mol·m−3 or mmol·l−1 − *[K+]i is the intracellular concentration of potassium 第263行：
第206行： − + − − Even if two different ions have the same charge (i.e., K+ and Na+), they can still have very different equilibrium potentials, provided their outside and/or inside concentrations differ. Take, for example, the equilibrium potentials of potassium and sodium in neurons. The potassium equilibrium potential EK is −84 mV with 5 mM potassium outside and 140 mM inside. On the other hand, the sodium equilibrium potential, ENa, is approximately +66 mV with approximately 12 mM sodium inside and 140 mM outside.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. − + − + − − A neuron's resting membrane potential actually changes during the 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. Glial cells are also differentiating and proliferating as development progresses in the brain. 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. − + − + + − Cell excitability is the change in membrane potential that is necessary for cellular responses in various tissues. Cell excitability is a property that is induced during early embriogenesis. Excitability of a cell has also been defined as the ease with which a response may be triggered. The resting and threshold potentials forms the basis of cell excitability and these processes are fundamental for the generation of graded and action potentials.+ − 细胞的兴奋性是细胞膜电位的变化，这是细胞在各种组织中产生反应所必需的。细胞兴奋性是早期发生过程中诱导的一种特性。细胞的兴奋性也被定义为一个反应很容易被触发。静息电位和阈值电位是细胞兴奋性的基础，这些过程是细胞分级和动作电位产生的基础。+ − The most important [[Homeostasis|regulators]] of cell excitability are the extracellular [[electrolyte]] concentrations (i.e. Na<sup>+</sup>, K<sup>+</sup>, [[Calcium metabolism|Ca<sup>2+</sup>]], Cl<sup>−</sup>, [[Magnesium in biology|Mg<sup>2+</sup>]]) and associated proteins. Important proteins that regulate cell excitability are [[voltage-gated ion channel]]s, [[ion transporter]]s (e.g. [[Na+/K+-ATPase]], [[magnesium transporter]]s, [[Acid–base homeostasis|acid–base transporters]]), [[Receptor (biochemistry)|membrane receptors]] and [[HCN channel|hyperpolarization-activated cyclic-nucleotide-gated channels]].<ref>{{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> For example, [[potassium channels]] and [[calcium-sensing receptor]]s are important regulators of excitability in [[neurons]], [[cardiac myocytes]] and many other excitable cells like [[astrocytes]].<ref>{{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> Calcium ion is also the most important [[Second messenger system|second messenger]] in excitable [[cell signaling]]. Activation of synaptic receptors initiates [[Neuroplasticity|long-lasting changes]] in neuronal excitability.<ref>{{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> [[thyroid hormones|Thyroid]], [[Adrenal gland|adrenal]] and other hormones also regulate cell excitability, for example, [[progesterone]] and [[estrogen]] modulate [[myometrial smooth muscle cell]] excitability.+ − The most important regulators of cell excitability are the extracellular electrolyte concentrations (i.e. Na+, K+, Ca<sup>2+</sup>, Cl−, Mg<sup>2+</sup>) and associated proteins. Important proteins that regulate cell excitability are voltage-gated ion channels, ion transporters (e.g. Na+/K+-ATPase, magnesium transporters, acid–base transporters), membrane receptors and hyperpolarization-activated cyclic-nucleotide-gated channels. For example, potassium channels and calcium-sensing receptors are important regulators of excitability in neurons, cardiac myocytes and many other excitable cells like astrocytes. Calcium ion is also the most important second messenger in excitable cell signaling. Activation of synaptic receptors initiates long-lasting changes in neuronal excitability. Thyroid, adrenal and other hormones also regulate cell excitability, for example, progesterone and estrogen modulate myometrial smooth muscle cell excitability.+ − 细胞兴奋性最重要的调节因子是细胞外电解质浓度(即电解质浓度)。Na + ，k + ，Ca < sup > 2 + ，Cl-，Mg < sup > 2 + )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:。Na +/k +-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。例如，钾离子通道和钙感受器是神经元、心肌细胞和许多其他可兴奋细胞如星形胶质细胞兴奋性的重要调节因子。钙离子也是可兴奋细胞信号转导中最重要的第二信使。突触受体的激活引发了神经元兴奋性的长期改变。甲状腺、肾上腺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。+ − − 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>{{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>{{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> − − Many cell types are considered to have an excitable membrane. Excitable cells are neurons, myocytes (cardiac, skeletal, smooth), vascular endothelial cells, pericytes, juxtaglomerular cells, interstitial cells of Cajal, many types of epithelial cells (e.g. beta cells, alpha cells, delta cells, enteroendocrine cells, pulmonary neuroendocrine cells, pinealocytes), glial cells (e.g. astrocytes), mechanoreceptor cells (e.g. hair cells and Merkel cells), chemoreceptor cells (e.g. glomus cells, taste receptors), some plant cells and possibly immune cells. 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. − − − + − 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+ − 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 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. − − 等效电路 = = = 拇指 | 右 | 350px | 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。电生理学家用等效电路模拟离子浓度差、离子通道和膜电容的影响，用以表示一小块膜片的电性能。该等效电路由一个并联电容器和四条通路组成，每条通路由一个可变电导的串联电池组成。电容是由类脂双分子层的性质决定的，并被认为是固定的。四条平行通路中的每一条都来自于一种主要离子，钠、钾、氯和钙。每个离子通路的电压由膜两侧的离子浓度决定; 见上面的翻转电位。每个离子通道在任何时间点的电导都是由所有离子通道的状态决定的，这些离子通道对该离子具有潜在的渗透性，包括泄漏通道、配体门控通道和电压门控离子通道。 − − For fixed ion concentrations and fixed values of ion channel conductance, the equivalent circuit can be further reduced, using the Goldman equation as described below, to a circuit containing a capacitance in parallel with a battery and conductance. In electrical terms, this is a type of RC circuit (resistance-capacitance circuit), and its electrical properties are very simple. Starting from any initial state, the current flowing across either the conductance or the capacitance decays with an exponential time course, with a time constant of , where is the capacitance of the membrane patch, and is the net resistance. For realistic situations, the time constant usually lies in the 1—100 millisecond range. In most cases, changes in the conductance of ion channels occur on a faster time scale, so an RC circuit is not a good approximation; however, the differential equation used to model a membrane patch is commonly a modified version of the RC circuit equation. − + − − 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 neurons, muscle cells, and some secretory cells in glands. 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 programmed cell death. − + − The interactions that generate the resting potential are modeled by the Goldman equation.Purves et al., pp. 32–33; Bullock, Orkand, and Grinnell, pp. 138–140; Schmidt-Nielsen, pp. 480; Junge, pp. 35–37 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.+ − − 产生静息电位的相互作用是由戈德曼方程研究所模拟的。32-33; 布洛克，Orkand，格林内尔，pp。138–140; Schmidt-Nielsen, pp.480; Junge，pp.35-37这在形式上类似于上面所示的能斯特方程，因为它是根据有关离子的电荷以及它们内外浓度之间的差别而建立的。然而，它也考虑到质膜对每个离子的相对渗透性。 第331行：
第256行： − :+ + 第339行：
第265行： − The three ions that appear in this equation are potassium (K+), sodium (Na+), and chloride (Cl−). Calcium is omitted, but can be added to deal with situations in which it plays a significant role. 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. Pi 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 +)、钠(Na +)和氯(Cl -)。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。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，这是反向阳离子项。Pi 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>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.Purves et al., p. 34; Bullock, Orkand, and Grinnell, p. 134; Schmidt-Nielsen, pp. 478–480.Purves et al., pp. 33–36; Bullock, Orkand, and Grinnell, p. 131. 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. − − − 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. 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.+ − − − 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 blowfly (Calliphora vicina) photoreceptors can be as high as -30 mV. 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 ATP.+ − − − 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, 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，未分化细胞中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。小分化细胞具有极高的拥有属性输入电阻，这意味着在细胞生命的这个阶段很少有泄漏通道存在。作为一个明显的结果，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，钠离子和钾离子的反转电位之间有静息电位。泄漏电流的减少也意味着不需要主动抽水来补偿，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 Ca2+, 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. − − 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+ channels shifts the membrane potential toward the Na+ reversal potential, which is usually around +100 mV. Likewise, opening K+ channels shifts the membrane potential toward about –90 mV, and opening Cl− channels shifts it toward about –70 mV (resting potential of most membranes). Thus, Na+ channels shift the membrane potential in a positive direction, K+ channels shift it in a negative direction (except when the membrane is hyperpolarized to a value more negative than the K+ reversal potential), and Cl− channels tend to shift it towards the resting potential. − + − thumb|center|500px|Graph displaying an EPSP, an IPSP, and the summation of an EPSP and an IPSP+ − Graded membrane potentials are particularly important in neurons, where they are produced by synapses—a temporary change in membrane potential produced by activation of a synapse by a single graded or action potential is called a postsynaptic potential. Neurotransmitters that act to open Na+ channels typically cause the membrane potential to become more positive, while neurotransmitters that activate K+ channels typically cause it to become more negative; those that inhibit these channels tend to have the opposite effect. − − 显示 EPSP、 IPSP、 EPSP 和 IPSP 分级膜电位的总和在神经元中尤其重要，因为它们是由突触产生的---- 由单个分级或动作电位激活突触而产生的突触膜电位的暂时变化称为突触后电位。神经递质的作用是打开 Na + 通道，典型地导致膜电位变得更加积极，而神经递质的作用是激活 k + 通道，典型地导致它变得更加消极; 抑制这些通道的神经递质往往有相反的效果。 − − Whether a postsynaptic potential is considered excitatory or inhibitory depends on the reversal potential for the ions of that current, and the threshold for the cell to fire an action potential (around –50mV). A postsynaptic current with a reversal potential above threshold, such as a typical Na+ current, is considered excitatory. A current with a reversal potential below threshold, such as a typical K+ current, is considered inhibitory. A current with a reversal potential above the resting potential, but below threshold, will not by itself elicit action potentials, but will produce subthreshold membrane potential oscillations. Thus, neurotransmitters that act to open Na+ channels produce excitatory postsynaptic potentials, or EPSPs, whereas neurotransmitters that act to open K+ or Cl− channels typically produce inhibitory postsynaptic potentials, or IPSPs. When multiple types of channels are open within the same time period, their postsynaptic potentials summate (are added together). 第400行：
第307行： − From the viewpoint of biophysics, the resting membrane potential is merely the membrane potential that results from the membrane permeabilities that predominate when the cell is resting. The above equation of weighted averages always applies, but the following approach may be more easily visualized.+ − At any given moment, there are two factors for an ion that determine how much influence that ion will have over the membrane potential of a cell:+ − + − − − 从生物物理学的观点来看，休眠膜电位仅仅是细胞休眠时主要的细胞膜通透性所产生的膜电位。上面的加权平均数等式总是适用的，但是下面的方法可能更容易可视化。在任何给定的时刻，有两个因素决定了离子对细胞膜电位的影响: # 离子的驱动力 # 离子的渗透率 − − If the driving force is high, then the ion is being "pushed" across the membrane. If the permeability is high, it will be easier for the ion to diffuse across the membrane. 第416行：
第318行： − − *Driving force is the net electrical force available to move that ion across the membrane. It is calculated as the difference between the voltage that the ion "wants" to be at (its equilibrium potential) and the actual membrane potential (Em). So, in formal terms, the driving force for an ion = Em - Eion − *For example, at our earlier calculated resting potential of −73 mV, the driving force on potassium is 7 mV : (−73 mV) − (−80 mV) = 7 mV. The driving force on sodium would be (−73 mV) − (60 mV) = −133 mV. − *Permeability is a measure of how easily an ion can cross the membrane. It is normally measured as the (electrical) conductance and the unit, siemens, corresponds to 1 C·s−1·V−1, that is one coulomb per second per volt of potential. − − − − 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 Em than does sodium. − − 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 ENa and far from EK. − − The more ions are permeant the more complicated it becomes to predict the membrane potential. However, this can be done using the 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. 第446行：
第336行： − − 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 mitochondria drives the production of ATP, which is the common currency of biological energy. − − 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 egg when it is fertilized by a sperm. − − 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 diffusion. 第472行：
第356行： − + − − *Bioelectrochemistry − *Electrochemical potential − *Goldman equation − *Membrane biophysics − *Microelectrode array − *Saltatory conduction − *Surface potential − *Gibbs–Donnan effect − *Synaptic potential − 第579行：
第452行： − + + + 第585行：
第460行： − + − + − + − + − + − + − − *Alberts et al. Molecular Biology of the Cell. Garland Publishing; 4th Bk&Cdr edition (March, 2002). . Undergraduate level. − *Guyton, Arthur C., John E. Hall. Textbook of medical physiology. W.B. Saunders Company; 10th edition (August 15, 2000). . Undergraduate level. − *Hille, B. Ionic Channel of Excitable Membranes Sinauer Associates, Sunderland, MA, USA; 1st Edition, 1984. − *Nicholls, J.G., Martin, A.R. and Wallace, B.G. From Neuron to Brain Sinauer Associates, Inc. Sunderland, MA, USA 3rd Edition, 1992. − *Ove-Sten Knudsen. Biological Membranes: Theory of Transport, Potentials and Electric Impulses. Cambridge University Press (September 26, 2002). . Graduate level. − *National Medical Series for Independent Study. Physiology. Lippincott Williams & Wilkins. Philadelphia, PA, USA 4th Edition, 2001. 第621行：
第489行： − − =<nowiki>= = 外部链接 = =</nowiki>= − *细胞膜的功能 − *Nernst/戈德曼方程模拟器 − *Nernst 方程计算器 − *Goldman-Hodgkin-Katz 方程计算器 − *电化学驱动力计算器 − *静息膜电位的起源-在线互动教程(Flash) − − {{Authority control}} 第640行：
第498行： − + − − Category:Cell communication − Category:Cell signaling − Category:Cellular processes − Category:Cellular neuroscience − Category:Electrochemistry − Category:Electrophysiology − Category:Membrane biology − − 类别: 细胞通讯类别: 细胞信号类别: 细胞过程类别: 细胞神经科学类别: 电化学类别: 电生理学类别: 细胞膜生物学 − − <noinclude> − −
无编辑摘要
所有的动物细胞都被一层由内嵌蛋白质的脂质双分子层组成的膜所包围。这种膜既作为绝缘层，又是离子运动的扩散阻挡层。跨膜蛋白，也被称为离子转运蛋白或离子泵蛋白，积极推动离子跨过膜并建立跨膜浓度梯度，而离子通道允许离子通过膜沿着浓度梯度移动。离子泵和离子通道在电学上相当于一组插入膜中的电池和电阻，因此在膜的两侧产生电压。
所有的动物细胞都被一层由内嵌蛋白质的脂质双分子层组成的膜所包围。这种膜既作为绝缘层，又是离子运动的扩散阻挡层。跨膜蛋白，也被称为离子转运蛋白或离子泵蛋白，积极推动离子跨过膜并建立跨膜浓度梯度，而离子通道允许离子通过膜沿着浓度梯度移动。离子泵和离子通道在电学上相当于一组插入膜中的电池和电阻，因此在膜的两侧产生电压。
Almost all plasma membranes have an electrical potential across them, with the inside usually negative with respect to the outside.<ref>{{Cite book|title=Molecular biology of the cell|last=Bruce|first=Alberts|isbn=9780815344322|edition=Sixth|location=New York, NY|oclc=887605755|date = 2014-11-18}}</ref> The membrane potential has two basic functions. First, it allows a cell to function as a battery, providing power to operate a variety of "molecular devices" embedded in the membrane.<ref>{{Cite journal|last1=Abdul Kadir|first1=Lina|last2=Stacey|first2=Michael|last3=Barrett-Jolley|first3=Richard|date=2018|title=Emerging Roles of the Membrane Potential: Action Beyond the Action Potential|journal=Frontiers in Physiology|language=English|volume=9|doi=10.3389/fphys.2018.01661|pmid=30519193|issn=1664-042X|doi-access=free}}</ref> Second, in electrically '''excitable cells''' such as [[neuron]]s and [[myocyte|muscle cells]], it is used for transmitting signals between different parts of a cell. Signals are generated by opening or closing of ion channels at one point in the membrane, producing a local change in the membrane potential. This change in the electric field can be quickly sensed by either adjacent or more distant ion channels in the membrane. Those ion channels can then open or close as a result of the potential change, reproducing the signal.
Almost all plasma membranes have an electrical potential across them, with the inside usually negative with respect to the outside.<ref name=":0">{{Cite book|title=Molecular biology of the cell|last=Bruce|first=Alberts|isbn=9780815344322|edition=Sixth|location=New York, NY|oclc=887605755|date = 2014-11-18}}</ref> The membrane potential has two basic functions. First, it allows a cell to function as a battery, providing power to operate a variety of "molecular devices" embedded in the membrane.<ref name=":1">{{Cite journal|last1=Abdul Kadir|first1=Lina|last2=Stacey|first2=Michael|last3=Barrett-Jolley|first3=Richard|date=2018|title=Emerging Roles of the Membrane Potential: Action Beyond the Action Potential|journal=Frontiers in Physiology|language=English|volume=9|doi=10.3389/fphys.2018.01661|pmid=30519193|issn=1664-042X|doi-access=free}}</ref> Second, in electrically '''excitable cells''' such as [[neuron]]s and [[myocyte|muscle cells]], it is used for transmitting signals between different parts of a cell. Signals are generated by opening or closing of ion channels at one point in the membrane, producing a local change in the membrane potential. This change in the electric field can be quickly sensed by either adjacent or more distant ion channels in the membrane. Those ion channels can then open or close as a result of the potential change, reproducing the signal.
几乎所有的质膜都有一个电位通过它们，内部通常相对于外部是负电位.<ref name=":0" /> 。膜电位有两个基本功能。首先，它允许一个细胞像电池一样工作，提供动力来操作嵌入在膜中的各种“分子设备”.<ref name=":1" /> 。其次，在神经元和肌肉细胞等电激活细胞中，它用于在细胞的不同部分之间传递信号。信号是通过在膜的某一点打开或关闭离子通道而产生的，从而引起膜电位的局部变化。这种电场的变化可以被膜上相邻或更远的离子通道迅速感觉到。这些离子通道可以随着电位的变化而打开或关闭，重新产生信号。
In non-excitable cells, and in excitable cells in their baseline states, the membrane potential is held at a relatively stable value, called the [[resting potential]]. For neurons, resting potential is defined as ranging from –80 to –70 millivolts; that is, the interior of a cell has a negative baseline voltage of a bit less than one-tenth of a volt. The opening and closing of ion channels can induce a departure from the resting potential. This is called a [[depolarization]] if the interior voltage becomes less negative (say from –70 mV to –60 mV), or a [[hyperpolarization (biology)|hyperpolarization]] if the interior voltage becomes more negative (say from –70 mV to –80 mV). In excitable cells, a sufficiently large depolarization can evoke an [[action potential]], in which the membrane potential changes rapidly and significantly for a short time (on the order of 1 to 100 milliseconds), often reversing its polarity. Action potentials are generated by the activation of certain [[voltage-gated ion channel]]s.
In non-excitable cells, and in excitable cells in their baseline states, the membrane potential is held at a relatively stable value, called the [[resting potential]]. For neurons, resting potential is defined as ranging from –80 to –70 millivolts; that is, the interior of a cell has a negative baseline voltage of a bit less than one-tenth of a volt. The opening and closing of ion channels can induce a departure from the resting potential. This is called a [[depolarization]] if the interior voltage becomes less negative (say from –70 mV to –60 mV), or a [[hyperpolarization (biology)|hyperpolarization]] if the interior voltage becomes more negative (say from –70 mV to –80 mV). In excitable cells, a sufficiently large depolarization can evoke an [[action potential]], in which the membrane potential changes rapidly and significantly for a short time (on the order of 1 to 100 milliseconds), often reversing its polarity. Action potentials are generated by the activation of certain [[voltage-gated ion channel]]s.
The membrane potential in a cell derives ultimately from two factors: electrical force and diffusion. Electrical force arises from the mutual attraction between particles with opposite electrical charges (positive and negative) and the mutual repulsion between particles with the same type of charge (both positive or both negative). Diffusion arises from the statistical tendency of particles to redistribute from regions where they are highly concentrated to regions where the concentration is low.
The membrane potential in a cell derives ultimately from two factors: electrical force and diffusion. Electrical force arises from the mutual attraction between particles with opposite electrical charges (positive and negative) and the mutual repulsion between particles with the same type of charge (both positive or both negative). Diffusion arises from the statistical tendency of particles to redistribute from regions where they are highly concentrated to regions where the concentration is low.
细胞中的膜电位最终来自于两个因素: 电力和扩散。电力产生于带有相反电荷的粒子之间的相互吸引(正电荷和负电荷)和带有相同类型电荷的粒子之间的相互斥力(正电荷和负电荷都有)。扩散源于粒子从高度集中的区域向低浓度区域重新分布的统计趋势。
===Voltage===
===Voltage===
[[File:Electric dipole.PNG|thumb|right|200px|Electric field (arrows) and contours of constant voltage created by a pair of oppositely charged objects. The electric field is at right angles to the voltage contours, and the field is strongest where the spacing between contours is the smallest.电场(箭头)和由一对相反电荷的物体产生的恒定电压等值线。电场与电压等值线成直角，等值线之间的间距最小时，电场最强。|链接=Special:FilePath/Electric_dipole.PNG]]
[[File:Electric dipole.PNG|thumb|right|200px|Electric field (arrows) and contours of constant voltage created by a pair of oppositely charged objects. The electric field is at right angles to the voltage contours, and the field is strongest where the spacing between contours is the smallest.|链接=Special:FilePath/Electric_dipole.PNG]]
Voltage, which is synonymous with ''difference in electrical potential'', is the ability to drive an electric current across a resistance. Indeed, the simplest definition of a voltage is given by [[Ohm's law]]: V=IR, where V is voltage, I is current and R is resistance. If a voltage source such as a battery is placed in an electrical circuit, the higher the voltage of the source the greater the amount of current that it will drive across the available resistance. The functional significance of voltage lies only in potential ''differences'' between two points in a circuit. The idea of a voltage at a single point is meaningless. It is conventional in electronics to assign a voltage of zero to some arbitrarily chosen element of the circuit, and then assign voltages for other elements measured relative to that zero point. There is no significance in which element is chosen as the zero point—the function of a circuit depends only on the differences not on voltages ''per se''. However, in most cases and by convention, the zero level is most often assigned to the portion of a circuit that is in contact with [[Ground (electricity)|ground.]]
Voltage, which is synonymous with ''difference in electrical potential'', is the ability to drive an electric current across a resistance. Indeed, the simplest definition of a voltage is given by [[Ohm's law]]: V=IR, where V is voltage, I is current and R is resistance. If a voltage source such as a battery is placed in an electrical circuit, the higher the voltage of the source the greater the amount of current that it will drive across the available resistance. The functional significance of voltage lies only in potential ''differences'' between two points in a circuit. The idea of a voltage at a single point is meaningless. It is conventional in electronics to assign a voltage of zero to some arbitrarily chosen element of the circuit, and then assign voltages for other elements measured relative to that zero point. There is no significance in which element is chosen as the zero point—the function of a circuit depends only on the differences not on voltages ''per se''. However, in most cases and by convention, the zero level is most often assigned to the portion of a circuit that is in contact with [[Ground (electricity)|ground.]]
电压是电势差的同义词，是驱动电流通过电阻的能力。事实上，电压最简单的定义是由欧姆定律给出的: v = IR，其中 v 是电压，i 是电流，r 是电阻。如果在电路中放置电压源(如电池) ，则电压源的电压越高，通过可用电阻的电流就越大。电压的功能意义仅在于电路中两点之间的电位差。单点电压的概念是没有意义的。在电子学中，通常的做法是给电路中任意选择的元件赋予零电压，然后给相对于该零点测量的其他元件赋予电压。选择哪个元件作为零点没有意义ーー电路的功能只取决于差值，而不取决于电压本身。然而，在大多数情况下，按照惯例，零电平最常被分配到与地接触的电路部分。
电压是电势差的同义词，是驱动电流通过电阻的能力。事实上，电压最简单的定义是由欧姆定律给出的: v = IR，其中 v 是电压，i 是电流，r 是电阻。如果在电路中放置电压源(如电池) ，则电压源的电压越高，通过可用电阻的电流就越大。电压的功能意义仅在于电路中两点之间的电位差。单点电压的概念是没有意义的。在电子学中，通常的做法是给电路中任意选择的元件赋予零电压，然后给相对于该零点测量的其他元件赋予电压。选择哪个元件作为零点没有意义ーー电路的功能只取决于差值，而不取决于电压本身。然而，在大多数情况下，按照惯例，零电平最常被分配到与地接触的电路部分。
In mathematical terms, the definition of voltage begins with the concept of an [[electric field]] {{math|'''E'''}}, a vector field assigning a magnitude and direction to each point in space. In many situations, the electric field is a [[conservative field]], which means that it can be expressed as the [[gradient]] of a scalar function {{math|<VAR>V</VAR>}}, that is, {{math|'''E''' {{=}} –∇<VAR>V</VAR>}}. This scalar field {{math|<VAR>V</VAR>}} is referred to as the voltage distribution. Note that the definition allows for an arbitrary constant of integration—this is why absolute values of voltage are not meaningful. In general, electric fields can be treated as conservative only if magnetic fields do not significantly influence them, but this condition usually applies well to biological tissue.
In mathematical terms, the definition of voltage begins with the concept of an [[electric field]] {{math|'''E'''}}, a vector field assigning a magnitude and direction to each point in space. In many situations, the electric field is a [[conservative field]], which means that it can be expressed as the [[gradient]] of a scalar function {{math|<VAR>V</VAR>}}, that is, {{math|'''E''' {{=}} –∇<VAR>V</VAR>}}. This scalar field {{math|<VAR>V</VAR>}} is referred to as the voltage distribution. Note that the definition allows for an arbitrary constant of integration—this is why absolute values of voltage are not meaningful. In general, electric fields can be treated as conservative only if magnetic fields do not significantly influence them, but this condition usually applies well to biological tissue.
用数学术语来说，电压的定义从电场的概念开始，电场 {{math|'''E'''}}, a是一个向量场，它为空间中的每一点分配一个大小和方向。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>}}, that is, {{math|'''E''' {{=}} –∇<VAR>V</VAR>}}. 即，。这个标量场称为电压分布。注意，这个定义允许任意的积分常数ーー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，但这种情况通常适用于生物组织。
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.
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.
===Ions and the forces driving their motion===
===Ions and the forces driving their motion===
[[File:Diffusion.en.svg|thumb|right|250px|Ions (pink circles) will flow across a membrane from the higher concentration to the lower concentration (down a concentration gradient), causing a current. However, this creates a voltage across the membrane that opposes the ions' motion. When this voltage reaches the equilibrium value, the two balance and the flow of ions stops.<ref name=":2">Campbell Biology, 6th edition</ref>离子(粉红色圆圈)会从较高的浓度流向较低的浓度(沿浓度梯度下降) ，形成电流。然而，这会在膜上产生一个电压，阻止离子的运动。当这个电压达到平衡值时，两个平衡和离子流就停止了。.<ref name=":2" />|链接=Special:FilePath/Diffusion.en.svg]]
两个烧杯的原理图，每个烧杯装满水(浅蓝色)和一个半透膜，用一条虚线垂直插入烧杯，将烧杯中的液体分成相等的两部分。左手烧杯表示时间为零的初始状态，其中膜一侧的离子数(粉红色圆圈)远高于另一侧。右边的烧杯代表稍后时间点的情况，之后离子从烧杯的高浓度区间流过薄膜，使薄膜两侧的离子数目现在接近相等。
Electrical signals within biological organisms are, in general, driven by [[ion]]s.<ref name=":3">Johnston and Wu, p. 9.</ref> The most important cations for the action potential are [[sodium]] (Na<sup>+</sup>) and [[potassium]] (K<sup>+</sup>).<ref name="bullock_140_141">[[Theodore Holmes Bullock|Bullock]], Orkand, and Grinnell, pp. 140–41.</ref> Both of these are ''monovalent'' cations that carry a single positive charge. Action potentials can also involve [[calcium]] (Ca<sup>2+</sup>),<ref name=":4">[[Theodore Holmes Bullock|Bullock]], Orkand, and Grinnell, pp. 153–54.</ref> which is a ''divalent'' cation that carries a double positive charge. The [[chloride]] anion (Cl<sup>−</sup>) plays a major role in the action potentials of some [[algae]],<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> but plays a negligible role in the action potentials of most animals.<ref name=":5">[[Knut Schmidt-Nielsen|Schmidt-Nielsen]], p. 483.</ref>
一般来说，生物有机体内的电信号是由离子驱动的.<ref name=":3" /> 。动作电位最重要的阳离子是钠(Na +)和钾(k +).<ref name="bullock_140_141" /> 。140–41.这两种阳离子都是单价阳离子，带有单个正电荷。动作电位也可以涉及钙(Ca2 +) ,<ref name=":4" /> ，布洛克，Orkand 和格林内尔，pp。153–54.它是一种带有双正电荷的二价阳离子。氯离子(Cl -)在某些藻类的动作电位中起主要作用,<ref name="mummert_1991" />，而在大多数动物的动作电位中起微不足道的作用.<ref name=":5" />。
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.
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.
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>
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，质膜具有类脂双分子层的结构，其中包含许多类型的大分子。因为它是由类脂分子组成的，所以质膜本质上具有很高的电阻率，换句话说，对离子的内在渗透性很低。然而，嵌入在膜中的一些分子能够将离子从膜的一侧活跃地传送到另一侧，或者提供离子可以移动的通道.<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.
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.
===Ion pumps===
===Ion pumps===
[[File:Scheme sodium-potassium pump-en.svg|thumb|right|350px|The sodium-potassium pump uses energy derived from ATP to exchange sodium for potassium ions across the membrane.|链接=Special:FilePath/Scheme_sodium-potassium_pump-en.svg]]
[[File:Scheme sodium-potassium pump-en.svg|thumb|right|350px|The sodium-potassium pump uses energy derived from ATP to exchange sodium for potassium ions across the membrane.钠-钾泵利用 ATP 产生的能量，通过膜将钠离子与钾离子交换。|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).
{{Main|Ion transporter|Active transport}}
离子泵是完整的膜蛋白，进行主动运输，也就是说，使用细胞能量(ATP)“泵”离子对他们的浓度梯度.<ref name="hodgkin_1955" />。这种离子泵从膜的一边吸收离子(降低那边的浓度) ，然后从另一边释放离子(增加那边的浓度)。
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" />
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" />
与动作电位最相关的离子泵是钠-钾离子泵，它将三个钠离子输出细胞，两个钾离子输入细胞。因此，钾离子在神经元内的浓度大约是外部浓度的20倍，而钠离子在神经元外的浓度大约是内部浓度的9倍。类似地，其他离子在神经元内外有不同的浓度，如钙、氯和镁。
与动作电位最相关的离子泵是钠-钾离子泵，它将三个钠离子输出细胞，两个钾离子输入细胞.<ref name="caldwell_1960" />。因此，钾离子在神经元内的浓度大约是外部浓度的20倍，而钠离子在神经元外的浓度大约是内部浓度的9倍.<ref name="steinbach_1943" /><ref name="hodgkin_1951" />。类似地，其他离子在神经元内外有不同的浓度，如钙、氯和镁.<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.
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.
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" />
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和细胞外离子浓度的相对比例来影响动作电位。动作电位主要涉及离子通道的开闭，而非离子泵。如果通过移除离子泵的能量源或者加入 ouabain 这样的抑制剂来关闭离子泵，轴突仍然可以在其振幅开始明显衰减之前激发数十万个动作电位。特别是，离子泵在动作电位后细胞膜的复极化过程中没有发挥重要作用。
离子泵仅通过建立细胞内和细胞外离子浓度的相对比例来影响动作电位。动作电位主要涉及离子通道的开闭，而非离子泵。如果通过移除离子泵的能量源或者加入 ouabain 这样的抑制剂来关闭离子泵，轴突仍然可以在其振幅开始明显衰减之前激发数十万个动作电位.<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没有发挥重要作用.<ref name="bullock_140_141" />。
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.
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.
===Ion channels===
===Ion channels===
[[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>''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.|链接=Special:FilePath/Action_potential_ion_sizes.svg.png]]
尽管它们的半径有很小的差别,<ref name=":6" /><nowiki>，化学和物理的CRC手册，第83版，pp。12-14呼叫12-16。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>
[[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>
离子通道是一种完整的膜蛋白，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的选择性比为1000:1，而钾离子和钠离子的拥有属性相同，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次电导水平，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，沿着该特定离子的跨膜浓度梯度向下渗透。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翻转电位值之间的差值.<ref name="junge_33_37" />。朱格，页。33–37.
[[File:Potassium channel1.png|thumb|left|200px|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.<nowiki>左图 | 200px | 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。</nowiki>|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.
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.
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。
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====
====Leakage channels====
[[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。
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。
====Ligand-gated channels====
====Ligand-gated channels====
[[File:LGIC.png|thumb|right|300px|Ligand-gated calcium channel in closed and open states|链接=Special:FilePath/LGIC.png]]
[[File:LGIC.png|thumb|right|300px|Ligand-gated calcium channel in closed and open states配体门控钙离子通道闭合态和开放态|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.
配体门控离子通道是当某种类型的化学配体与蛋白质结构结合时，其通透性大大增加的通道。动物细胞包含成百上千种这样的细胞。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。
配体门控离子通道是当某种类型的化学配体与蛋白质结构结合时，其通透性大大增加的通道。动物细胞包含成百上千种这样的细胞。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。
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.
====Voltage-dependent channels====
====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。
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。
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 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。
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。
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。
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:
:<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>
*[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>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
*[K<sup>+</sup>]<sub>i</sub> is the intracellular concentration of potassium
其中
其中
*f 是法拉第常数，等于96,485coulombsmol-1或 jv-1mol-1[ k + ] o 为细胞外钾离子浓度，在 mol-3或 mmol l-1[ k + ] i 为细胞内钾离子浓度
*f 是法拉第常数，等于96,485coulombsmol-1或 jv-1mol-1[ k + ] o 为细胞外钾离子浓度，在 mol-3或 mmol l-1[ k + ] i 为细胞内钾离子浓度
Even if two different ions have the same charge (i.e., K<sup>+</sup> and Na<sup>+</sup>), they can still have very different equilibrium potentials, provided their outside and/or inside concentrations differ. Take, for example, the equilibrium potentials of potassium and sodium in neurons. The potassium equilibrium potential ''E''<sub>K</sub> is −84 mV with 5 mM potassium outside and 140 mM inside. On the other hand, the sodium equilibrium potential, ''E''<sub>Na</sub>, is approximately +66 mV with approximately 12 mM sodium inside and 140 mM outside.<ref 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>
Even if two different ions have the same charge (i.e., K<sup>+</sup> and Na<sup>+</sup>), they can still have very different equilibrium potentials, provided their outside and/or inside concentrations differ. Take, for example, the equilibrium potentials of potassium and sodium in neurons. The potassium equilibrium potential ''E''<sub>K</sub> is −84 mV with 5 mM potassium outside and 140 mM inside. On the other hand, the sodium equilibrium potential, ''E''<sub>Na</sub>, is approximately +66 mV with approximately 12 mM sodium inside and 140 mM outside.<ref group="note" name=":0">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>
即使两种不同的离子具有相同的电荷(即 k + 和 Na +) ，只要它们的外部和/或内部浓度不同，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。钾平衡电位为 -84mv，内含140mm 的钾，外含5mm 的钾。另一方面，钠平衡电位，ENa，约为 + 66mv，内部约为12mm 钠，外部约为140mm。注意，e < sub > Na 和 e < sub > k 的符号相反。这是因为钾的浓度梯度指向细胞外，而钠的浓度梯度指向细胞内。膜电位是相对于细胞外部定义的，因此，电位 -70 mV 意味着细胞内部相对于外部是负的。
即使两种不同的离子具有相同的电荷(即 k + 和 Na +) ，只要它们的外部和/或内部浓度不同，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。钾平衡电位为 -84mv，内含140mm 的钾，外含5mm 的钾。另一方面，钠平衡电位，ENa，约为 + 66mv，内部约为12mm 钠，外部约为140mm.<ref name=":0" group="note" />。
===Changes to membrane potential during development===
===Changes to membrane potential during development===
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>{{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>{{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>{{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>
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>
= = = 发育过程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实际上发生了变化。为了让一个神经元最终发挥其完整的成年功能，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，静息膜电位变得更加消极。随着脑的发育，神经胶质细胞也在分化和增殖。这些神经胶质细胞的加入增加了机体调节细胞外钾的能力。细胞外液中的钾下降可以导致膜电位下降35mv。
= = = 发育过程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实际上发生了变化。为了让一个神经元最终发挥其完整的成年功能，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，静息膜电位变得更加消极.<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" />。这些神经胶质细胞的加入增加了机体调节细胞外钾的能力。细胞外液中的钾下降可以导致膜电位下降35mv.<ref name=":9" />。
=== Cell excitability===
=== Cell excitability===
{{Further|Excitable medium}}
{{Further|Excitable medium}}
Cell excitability is the change in membrane potential that is necessary for cellular responses in various tissues. Cell excitability is a property that is induced during early embriogenesis.<ref>{{Cite journal|last=Tosti|first=Elisabetta|date=2010-06-28|title=Dynamic roles of ion currents in early development|journal=Molecular Reproduction and Development|volume=77|issue=10|pages=856–867|doi=10.1002/mrd.21215|pmid=20586098|s2cid=38314187|issn=1040-452X|doi-access=free}}</ref> Excitability of a cell has also been defined as the ease with which a response may be triggered.<ref>{{Cite journal|last1=Boyet|first1=M.R.|last2=Jewell|first2=B.R.|date=1981|title=Analysis of the effects of changes in rate and rhythm upon electrical activity in the heart|journal=Progress in Biophysics and Molecular Biology|volume=36|issue=1|pages=1–52|doi=10.1016/0079-6107(81)90003-1|pmid=7001542|issn=0079-6107|doi-access=free}}</ref> The resting and [[threshold potential]]s forms the basis of cell excitability and these processes are fundamental for the generation of graded and action potentials.
Cell excitability is the change in membrane potential that is necessary for cellular responses in various tissues. Cell excitability is a property that is induced during early embriogenesis.<ref name=":10">{{Cite journal|last=Tosti|first=Elisabetta|date=2010-06-28|title=Dynamic roles of ion currents in early development|journal=Molecular Reproduction and Development|volume=77|issue=10|pages=856–867|doi=10.1002/mrd.21215|pmid=20586098|s2cid=38314187|issn=1040-452X|doi-access=free}}</ref> Excitability of a cell has also been defined as the ease with which a response may be triggered.<ref name=":11">{{Cite journal|last1=Boyet|first1=M.R.|last2=Jewell|first2=B.R.|date=1981|title=Analysis of the effects of changes in rate and rhythm upon electrical activity in the heart|journal=Progress in Biophysics and Molecular Biology|volume=36|issue=1|pages=1–52|doi=10.1016/0079-6107(81)90003-1|pmid=7001542|issn=0079-6107|doi-access=free}}</ref> The resting and [[threshold potential]]s forms the basis of cell excitability and these processes are fundamental for the generation of graded and action potentials.
细胞的兴奋性是细胞膜电位的变化，这是细胞在各种组织中产生反应所必需的。细胞兴奋性是早期发生过程中诱导的一种特性.<ref name=":10" />。细胞的兴奋性也被定义为一个反应很容易被触发.<ref name=":11" /> 。静息电位和阈值电位是细胞兴奋性的基础，这些过程是细胞分级和动作电位产生的基础。
The most important [[Homeostasis|regulators]] of cell excitability are the extracellular [[electrolyte]] concentrations (i.e. Na<sup>+</sup>, K<sup>+</sup>, [[Calcium metabolism|Ca<sup>2+</sup>]], Cl<sup>−</sup>, [[Magnesium in biology|Mg<sup>2+</sup>]]) and associated proteins. Important proteins that regulate cell excitability are [[voltage-gated ion channel]]s, [[ion transporter]]s (e.g. [[Na+/K+-ATPase]], [[magnesium transporter]]s, [[Acid–base homeostasis|acid–base transporters]]), [[Receptor (biochemistry)|membrane receptors]] and [[HCN channel|hyperpolarization-activated cyclic-nucleotide-gated channels]].<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> For example, [[potassium channels]] and [[calcium-sensing receptor]]s are important regulators of excitability in [[neurons]], [[cardiac myocytes]] and many other excitable cells like [[astrocytes]].<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> Calcium ion is also the most important [[Second messenger system|second messenger]] in excitable [[cell signaling]]. Activation of synaptic receptors initiates [[Neuroplasticity|long-lasting changes]] in neuronal excitability.<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> [[thyroid hormones|Thyroid]], [[Adrenal gland|adrenal]] and other hormones also regulate cell excitability, for example, [[progesterone]] and [[estrogen]] modulate [[myometrial smooth muscle cell]] excitability.
细胞兴奋性最重要的调节因子是细胞外电解质浓度(即电解质浓度)。Na + ，k + ，Ca < sup > 2 + ，Cl-，Mg < sup > 2 + )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:。Na +/k +-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" />。例如，钾离子通道和钙感受器是神经元、心肌细胞和许多其他可兴奋细胞如星形胶质细胞兴奋性的重要调节因子.<ref name=":13" /> 。钙离子也是可兴奋细胞信号转导中最重要的第二信使。突触受体的激活引发了神经元兴奋性的长期改变.<ref name=":14" />。甲状腺、肾上腺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。
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可兴奋的膜。可兴奋细胞包括神经元、心肌细胞(心肌细胞、骨骼肌细胞、光滑细胞)、血管内皮细胞、周细胞、肾小球旁细胞、 Cajal 间质细胞、许多类型的上皮细胞(如:。Β 细胞、 α 细胞、 delta 细胞、肠内分泌细胞、肺神经内分泌细胞、松果体细胞等。星形胶质细胞)、机械力受体细胞(例如:。毛细胞和默克尔细胞) ，化学感受器细胞(例如:。血管球细胞，味觉受体) ，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分离的输入信号进行符合检测的能力s.<ref name=":16" />。
许多细胞类型被认为具有可兴奋的膜。可兴奋细胞包括神经元、心肌细胞(心肌细胞、骨骼肌细胞、光滑细胞)、血管内皮细胞、周细胞、肾小球旁细胞、 Cajal 间质细胞、许多类型的上皮细胞(如:。Β 细胞、 α 细胞、 delta 细胞、肠内分泌细胞、肺神经内分泌细胞、松果体细胞等。星形胶质细胞)、机械力受体细胞(例如:。毛细胞和默克尔细胞) ，化学感受器细胞(例如:。血管球细胞，味觉受体) ，一些植物细胞，可能还有免疫细胞。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分离的输入信号进行符合检测的能力。
===Equivalent circuit===
===Equivalent circuit===
[[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|链接=Special:FilePath/Cell_membrane_equivalent_circuit.svg]]
[[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.
电生理学家用等效电路模拟离子浓度差、离子通道和膜电容的影响，用以表示一小块膜片的电性能。该等效电路由一个并联电容器和四条通路组成，每条通路由一个可变电导的串联电池组成。电容是由类脂双分子层的性质决定的，并被认为是固定的。四条平行通路中的每一条都来自于一种主要离子，钠、钾、氯和钙。每个离子通路的电压由膜两侧的离子浓度决定; 见上面的翻转电位。每个离子通道在任何时间点的电导都是由所有离子通道的状态决定的，这些离子通道对该离子具有潜在的渗透性，包括泄漏通道、配体门控通道和电压门控离子通道。
[[File:Cell membrane reduced circuit.svg|thumb|left|Reduced circuit obtained by combining the ion-specific pathways using the [[Goldman equation]]|链接=Special:FilePath/Cell_membrane_reduced_circuit.svg]]
[[File:Cell membrane reduced circuit.svg|thumb|left|Reduced circuit obtained by combining the ion-specific pathways using the [[Goldman equation]]|链接=Special:FilePath/Cell_membrane_reduced_circuit.svg]]
For fixed ion concentrations and fixed values of ion channel conductance, the equivalent circuit can be further reduced, using the [[Goldman equation]] as described below, to a circuit containing a capacitance in parallel with a battery and conductance. In electrical terms, this is a type of [[RC circuit]] (resistance-capacitance circuit), and its electrical properties are very simple. Starting from any initial state, the current flowing across either the conductance or the capacitance decays with an exponential time course, with a time constant of {{math|τ {{=}} RC}}, where {{math|C}} is the capacitance of the membrane patch, and {{math|R {{=}} 1/g<sub>net</sub>}} is the net resistance. For realistic situations, the time constant usually lies in the 1—100 millisecond range. In most cases, changes in the conductance of ion channels occur on a faster time scale, so an RC circuit is not a good approximation; however, the differential equation used to model a membrane patch is commonly a modified version of the RC circuit equation.
For fixed ion concentrations and fixed values of ion channel conductance, the equivalent circuit can be further reduced, using the [[Goldman equation]] as described below, to a circuit containing a capacitance in parallel with a battery and conductance. In electrical terms, this is a type of [[RC circuit]] (resistance-capacitance circuit), and its electrical properties are very simple. Starting from any initial state, the current flowing across either the conductance or the capacitance decays with an exponential time course, with a time constant of {{math|τ {{=}} RC}}, where {{math|C}} is the capacitance of the membrane patch, and {{math|R {{=}} 1/g<sub>net</sub>}} is the net resistance. For realistic situations, the time constant usually lies in the 1—100 millisecond range. In most cases, changes in the conductance of ion channels occur on a faster time scale, so an RC circuit is not a good approximation; however, the differential equation used to model a membrane patch is commonly a modified version of the RC circuit equation.
对于固定的离子浓度和固定的离子通道电导值，等效电路可以进一步缩小，使用下面描述的戈德曼方程电路，变成一个包含电容和电池电导并联的电路。在电学术语中，这是一种 RC 电路(阻容电路) ，其电学特性非常简单。从任何初始状态开始，流过电导或电容的电流以 EXPTIME 衰变，其时间常数为，这里是膜片的电容，这里是网电阻。在现实情况下，时间常数一般在1ー100毫秒的范围内。在大多数情况下，离子通道电导的变化发生在一个更快的时间尺度上，所以 RC 电路不是一个好的近似值; 然而，用于模拟膜片的微分方程通常是 RC 电路方程的修正版。
对于固定的离子浓度和固定的离子通道电导值，等效电路可以进一步缩小，使用下面描述的戈德曼方程电路，变成一个包含电容和电池电导并联的电路。在电学术语中，这是一种 RC 电路(阻容电路) ，其电学特性非常简单。从任何初始状态开始，流过电导或电容的电流以 EXPTIME 衰变，其时间常数为，这里是膜片的电容，这里是网电阻。在现实情况下，时间常数一般在1ー100毫秒的范围内。在大多数情况下，离子通道电导的变化发生在一个更快的时间尺度上，所以 RC 电路不是一个好的近似值; 然而，用于模拟膜片的微分方程通常是 RC 电路方程的修正版。
==Resting potential==
==Resting potential==
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>{{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>
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>
= = 静息电位 = = 当一个细胞的膜电位长时间不发生明显变化时，它被称为静息电位电压或静息电压。这个术语用于描述不可兴奋细胞的膜电位，也用于描述缺乏兴奋时可兴奋细胞的膜电位。在可兴奋细胞中，其他可能的状态是分级膜电位(可变振幅)和动作电位，这些电位通常在一个固定的时间过程中，在膜电位一分钟内上升很大，要么全有要么全无。可兴奋细胞包括神经元、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，去极化的质膜似乎是一个重要的步骤，在细胞程序性死亡。
= = 静息电位 = = 当一个细胞的膜电位长时间不发生明显变化时，它被称为静息电位电压或静息电压。这个术语用于描述不可兴奋细胞的膜电位，也用于描述缺乏兴奋时可兴奋细胞的膜电位。在可兴奋细胞中，其他可能的状态是分级膜电位(可变振幅)和动作电位，这些电位通常在一个固定的时间过程中，在膜电位一分钟内上升很大，要么全有要么全无。可兴奋细胞包括神经元、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，去极化的质膜似乎是一个重要的步骤，在细胞程序性死亡.<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.
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.
产生静息电位的相互作用是由戈德曼方程研究所模拟的.<ref name="Goldman" /> 。32-33; 布洛克，Orkand，格林内尔，pp。138–140; Schmidt-Nielsen, pp.480; Junge，pp.35-37这在形式上类似于上面所示的能斯特方程，因为它是根据有关离子的电荷以及它们内外浓度之间的差别而建立的。然而，它也考虑到质膜对每个离子的相对渗透性。
:<math>
:<math>
</math>
</math>
<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>
<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.
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 +)、钠(Na +)和氯(Cl -)。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le.<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，这是反向阳离子项。Pi 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.
从本质上讲，高盛公式将膜电位表示为单个离子类型的逆转势的加权平均数，通过渗透率加权。(虽然膜电位在动作电位期间会发生100mv 左右的变化，但细胞内外的离子浓度不会发生显著变化。当膜处于静息电位时，它们仍然接近各自的浓度。)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。As a consequence, the resting potential is usually close to the potassium reversal potential.Purves et al., p. 34; Bullock, Orkand, and Grinnell, p. 134; Schmidt-Nielsen, pp.478-480. Purves et al. ，pp.33-36; 布洛克，Orkand 和格林内尔，p. 131。但是，与其他离子不同的是，氯离子没有被主动泵入，因此平衡的翻转电位非常接近由其他离子决定的静息电位。l.<ref name="resting_potential" /><ref name=":18" />
从本质上讲，高盛公式将膜电位表示为单个离子类型的逆转势的加权平均数，通过渗透率加权。(虽然膜电位在动作电位期间会发生100mv 左右的变化，但细胞内外的离子浓度不会发生显著变化。当膜处于静息电位时，它们仍然接近各自的浓度。)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。As a consequence, the resting potential is usually close to the potassium reversal potential.Purves et al., p. 34; Bullock, Orkand, and Grinnell, p. 134; Schmidt-Nielsen, pp.478-480. Purves et al. ，pp.33-36; 布洛克，Orkand 和格林内尔，p. 131。但是，与其他离子不同的是，氯离子没有被主动泵入，因此平衡的翻转电位非常接近由其他离子决定的静息电位。
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.
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翻转电位(通常在 -80 mV)和 -40 mV 之间变化。可兴奋细胞(能够产生动作电位)的静息电位通常接近60mv ー更多的去极化电压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压变化很大，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压差。
在大多数动物细胞中，静息膜电位的数值通常在翻转电位(通常在 -80 mV)和 -40 mV 之间变化。可兴奋细胞(能够产生动作电位)的静息电位通常接近60mv ー更多的去极化电压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压变化很大，通常明显高于已分化的细胞。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压差。
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>
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>
对于电池来说，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; 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" />。
对于电池来说，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。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; 维持静息电位可能消耗超过20% 的细胞总 ATP。
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.
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，未分化细胞中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。小分化细胞具有极高的拥有属性输入电阻,<ref name="Magnuson DS et al., 1995" /> ，这意味着在细胞生命的这个阶段很少有泄漏通道存在。作为一个明显的结果，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，钠离子和钾离子的反转电位之间有静息电位。泄漏电流的减少也意味着不需要主动抽水来补偿，因此代谢成本低。
==Graded potentials==
==Graded potentials==
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.
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.
= = 分级电位 = = 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 Ca2 + ，其细胞内基线浓度非常低，即使是很小的内流量也可能增加1毫秒数量级) ，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分级电位，与动作电位相反，动作电位有固定的振幅和时间进程。
= = 分级电位 = = 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 Ca2 + ，其细胞内基线浓度非常低，即使是很小的内流量也可能增加1毫秒数量级) ，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分级电位，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.
正如我们从上面的戈德曼方程中得出的结论，增加膜的渗透性对于特定类型离子的影响会使膜电位向翻转电位的方向移动。因此，开放的钠离子通道将膜电位向钠离子翻转电位转移，通常在 + 100 mV 左右。同样，开放 k + 通道使膜电位向大约 -90 mV 的方向移动，开放 Cl 通道使其向大约 -70 mV 的方向移动(大多数膜的静息电位)。因此，Na + 通道使膜电位向正方向移动，k + 通道使其向负方向移动(除非膜超极化到比 k + 翻转电位更负的程度) ，而 Cl-通道则倾向于使其向静息电位方向移动。
正如我们从上面的戈德曼方程中得出的结论，增加膜的渗透性对于特定类型离子的影响会使膜电位向翻转电位的方向移动。因此，开放的钠离子通道将膜电位向钠离子翻转电位转移，通常在 + 100 mV 左右。同样，开放 k + 通道使膜电位向大约 -90 mV 的方向移动，开放 Cl 通道使其向大约 -70 mV 的方向移动(大多数膜的静息电位)。因此，Na + 通道使膜电位向正方向移动，k + 通道使其向负方向移动(除非膜超极化到比 k + 翻转电位更负的程度) ，而 Cl-通道则倾向于使其向静息电位方向移动。
[[File:IPSPsummation.JPG|thumb|center|500px|Graph displaying an EPSP, an IPSP, and the summation of an EPSP and an IPSP|链接=Special:FilePath/IPSPsummation.JPG]]
[[File:IPSPsummation.JPG|thumb|center|500px|Graph displaying an EPSP, an IPSP, and the summation of an EPSP and an IPSP显示 EPSP、 IPSP、 EPSP 和 IPSP |链接=Special:FilePath/IPSPsummation.JPG]]
Graded membrane potentials are particularly important in [[neuron]]s, where they are produced by [[synapse]]s—a temporary change in membrane potential produced by activation of a synapse by a single graded or action potential is called a [[postsynaptic potential]]. [[Neurotransmitter]]s that act to open Na<sup>+</sup> channels typically cause the membrane potential to become more positive, while neurotransmitters that activate K<sup>+</sup> channels typically cause it to become more negative; those that inhibit these channels tend to have the opposite effect.
Graded membrane potentials are particularly important in [[neuron]]s, where they are produced by [[synapse]]s—a temporary change in membrane potential produced by activation of a synapse by a single graded or action potential is called a [[postsynaptic potential]]. [[Neurotransmitter]]s that act to open Na<sup>+</sup> channels typically cause the membrane potential to become more positive, while neurotransmitters that activate K<sup>+</sup> channels typically cause it to become more negative; those that inhibit these channels tend to have the opposite effect.
分级膜电位的总和在神经元中尤其重要，因为它们是由突触产生的---- 由单个分级或动作电位激活突触而产生的突触膜电位的暂时变化称为突触后电位。神经递质的作用是打开 Na + 通道，典型地导致膜电位变得更加积极，而神经递质的作用是激活 k + 通道，典型地导致它变得更加消极; 抑制这些通道的神经递质往往有相反的效果。
Whether a postsynaptic potential is considered excitatory or inhibitory depends on the reversal potential for the ions of that current, and the threshold for the cell to fire an action potential (around –50mV). A postsynaptic current with a reversal potential above threshold, such as a typical Na<sup>+</sup> current, is considered excitatory. A current with a reversal potential below threshold, such as a typical K<sup>+</sup> current, is considered inhibitory. A current with a reversal potential above the resting potential, but below threshold, will not by itself elicit action potentials, but will produce [[subthreshold membrane potential oscillations]]. Thus, neurotransmitters that act to open Na<sup>+</sup> channels produce [[excitatory postsynaptic potential]]s, or EPSPs, whereas neurotransmitters that act to open K<sup>+</sup> or Cl<sup>−</sup> channels typically produce [[inhibitory postsynaptic potential]]s, or IPSPs. When multiple types of channels are open within the same time period, their postsynaptic potentials summate (are added together).
Whether a postsynaptic potential is considered excitatory or inhibitory depends on the reversal potential for the ions of that current, and the threshold for the cell to fire an action potential (around –50mV). A postsynaptic current with a reversal potential above threshold, such as a typical Na<sup>+</sup> current, is considered excitatory. A current with a reversal potential below threshold, such as a typical K<sup>+</sup> current, is considered inhibitory. A current with a reversal potential above the resting potential, but below threshold, will not by itself elicit action potentials, but will produce [[subthreshold membrane potential oscillations]]. Thus, neurotransmitters that act to open Na<sup>+</sup> channels produce [[excitatory postsynaptic potential]]s, or EPSPs, whereas neurotransmitters that act to open K<sup>+</sup> or Cl<sup>−</sup> channels typically produce [[inhibitory postsynaptic potential]]s, or IPSPs. When multiple types of channels are open within the same time period, their postsynaptic potentials summate (are added together).
突触后电位是兴奋性电位还是抑制性电位取决于该电流离子的翻转电位，以及细胞激发动作电位的阈值(大约-50mV)。如果突触后电流超过阈值，如典型的钠离子电流，则被认为是兴奋性的。翻转电位。低于阈值的翻转电位，如典型的 k + 电流，被认为是抑制电流。一个翻转电位高于静息电位阈值但低于阈值的电流本身不会引起动作电位，但是会产生阈值以下的膜电位振荡。因此，作用于开放 Na + 通道的神经递质产生兴奋性突触后电位(epsp) ，而作用于开放 k + 或 Cl-通道的神经递质通常产生抑制性突触后电位(ipsp)。当多种类型的通道在同一时间段内开放时，它们的突触后电位相加。
突触后电位是兴奋性电位还是抑制性电位取决于该电流离子的翻转电位，以及细胞激发动作电位的阈值(大约-50mV)。如果突触后电流超过阈值，如典型的钠离子电流，则被认为是兴奋性的。翻转电位。低于阈值的翻转电位，如典型的 k + 电流，被认为是抑制电流。一个翻转电位高于静息电位阈值但低于阈值的电流本身不会引起动作电位，但是会产生阈值以下的膜电位振荡。因此，作用于开放 Na + 通道的神经递质产生兴奋性突触后电位(epsp) ，而作用于开放 k + 或 Cl-通道的神经递质通常产生抑制性突触后电位(ipsp)。当多种类型的通道在同一时间段内开放时，它们的突触后电位相加。
# That ion's permeability
# That ion's permeability
从生物物理学的观点来看，休眠膜电位仅仅是细胞休眠时主要的细胞膜通透性所产生的膜电位。上面的加权平均数等式总是适用的，但是下面的方法可能更容易可视化。在任何给定的时刻，有两个因素决定了离子对细胞膜电位的影响: # #
#That ion's driving force离子的驱动力
#That ion's driving force
#That ion's permeability离子的渗透率
#That ion's permeability
If the driving force is high, then the ion is being "pushed" across the membrane. If the permeability is high, it will be easier for the ion to diffuse across the membrane.
If the driving force is high, then the ion is being "pushed" across the membrane. If the permeability is high, it will be easier for the ion to diffuse across the membrane.
*For example, at our earlier calculated resting potential of −73 mV, the driving force on potassium is 7 mV : (−73 mV) − (−80 mV) = 7 mV. The driving force on sodium would be (−73 mV) − (60 mV) = −133 mV.
*For example, at our earlier calculated resting potential of −73 mV, the driving force on potassium is 7 mV : (−73 mV) − (−80 mV) = 7 mV. The driving force on sodium would be (−73 mV) − (60 mV) = −133 mV.
*'''Permeability''' is a measure of how easily an ion can cross the membrane. It is normally measured as the (electrical) conductance and the unit, [[Siemens (unit)|siemens]], corresponds to 1 C·s<sup>−1</sup>·V<sup>−1</sup>, that is one [[coulomb]] per second per volt of potential.
*'''Permeability''' is a measure of how easily an ion can cross the membrane. It is normally measured as the (electrical) conductance and the unit, [[Siemens (unit)|siemens]], corresponds to 1 C·s<sup>−1</sup>·V<sup>−1</sup>, that is one [[coulomb]] per second per volt of potential.
*驱动力是使离子在膜上移动的净电力。它被计算为离子“希望”处于的电压(其平衡电位)和实际膜电位(Em)之间的差值。因此，在正式术语中，离子的驱动力 = Em-Eion
*驱动力是使离子在膜上移动的净电力。它被计算为离子“希望”处于的电压(其平衡电位)和实际膜电位(Em)之间的差值。因此，在正式术语中，离子的驱动力 = Em-Eion
*例如，在我们早先计算的静息电位为-73 mV，钾的驱动力为7 mV: (- 73 mV)-(- 80 mV) = 7 mV。钠离子的驱动力为(- 73 mV)-(60 mV) =-133 mV。
*例如，在我们早先计算的静息电位为-73 mV，钾的驱动力为7 mV: (- 73 mV)-(- 80 mV) = 7 mV。钠离子的驱动力为(- 73 mV)-(60 mV) =-133 mV。
*渗透性是衡量离子通过细胞膜的容易程度。它通常被测量为(电)导和单位，西门子，相当于1 c s-1 v-1，即一库仑每秒每伏特的电位。
*渗透性是衡量离子通过细胞膜的容易程度。它通常被测量为(电)导和单位，西门子，相当于1 c s-1 v-1，即一库仑每秒每伏特的电位。
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.
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 Em 的影响是钠的20倍。
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 Em 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>.
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，考虑另一种情况ーー动作电位的峰值。在这里，钠的渗透率较高，钾的渗透率相对较低。因此，膜移动到近 ENa 和远离 EK。
然而，考虑另一种情况ーー动作电位的峰值。在这里，钠的渗透率较高，钾的渗透率相对较低。因此，膜移动到近 ENa 和远离 EK。
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.
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.
离子越多，预测膜电位就越复杂。然而，这可以用 Goldman-Hodgkin-Katz 方程或加权平均数方程来实现。通过在任意时刻输入离子的浓度梯度和渗透率，就可以在那个时刻测定膜电位。方程的意思是，在任何时候，膜电位的值都是所有离子平衡势的加权平均数。“权重”是离子在膜上的相对渗透性。
离子越多，预测膜电位就越复杂。然而，这可以用 Goldman-Hodgkin-Katz 方程或加权平均数方程来实现。通过在任意时刻输入离子的浓度梯度和渗透率，就可以在那个时刻测定膜电位。方程的意思是，在任何时候，膜电位的值都是所有离子平衡势的加权平均数。“权重”是离子在膜上的相对渗透性。
==Effects and implications==
==Effects and implications==
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.
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.
当细胞消耗能量来运输离子并建立膜电位时，它们反过来利用这种潜能来运输其他离子和代谢物，如糖。线粒体的膜电位驱动 ATP 的产生，ATP 是生物能量的通用货币。
当细胞消耗能量来运输离子并建立膜电位时，它们反过来利用这种潜能来运输其他离子和代谢物，如糖。线粒体的膜电位驱动 ATP 的产生，ATP 是生物能量的通用货币。
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]].
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。膜电位的这些变化可以与其他细胞交流(如动作电位) ，或者在细胞内发生变化，这些变化发生在卵子和精子受精时。
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。膜电位的这些变化可以与其他细胞交流(如动作电位) ，或者在细胞内发生变化，这些变化发生在卵子和精子受精时。
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]].
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]].
在神经细胞中，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。这两种通量都是通过被动扩散产生的。
在神经细胞中，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。这两种通量都是通过被动扩散产生的。
*[[Surface potential]]
*[[Surface potential]]
*[[Gibbs–Donnan effect]]
*[[Gibbs–Donnan effect]]
* [[Synaptic potential]]
* [[Synaptic potential]]<br />
*
*
==Notes==
==Notes==
<references group="note" />
<references 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.
注意，e < sub > Na 和 e < sub > k 的符号相反。这是因为钾的浓度梯度指向细胞外，而钠的浓度梯度指向细胞内。膜电位是相对于细胞外部定义的，因此，电位 -70 mV 意味着细胞内部相对于外部是负的。
==References==
==References==
==Further reading==
==Further reading==
*Alberts et al. ''Molecular Biology of the Cell''. Garland Publishing; 4th Bk&Cdr edition (March, 2002). {{ISBN|0-8153-3218-1}}. Undergraduate level.
*Alberts et al. ''Molecular Biology of the Cell''. Garland Publishing; 4th Bk&Cdr edition (March, 2002). Undergraduate level.
*Guyton, Arthur C., John E. Hall. ''Textbook of medical physiology''. W.B. Saunders Company; 10th edition (August 15, 2000). {{ISBN|0-7216-8677-X}}. Undergraduate level.
*Guyton, Arthur C., John E. Hall. ''Textbook of medical physiology''. W.B. Saunders Company; 10th edition (August 15, 2000). Undergraduate level.
*Hille, B. ''Ionic Channel of Excitable Membranes'' Sinauer Associates, Sunderland, MA, USA; 1st Edition, 1984. {{ISBN|0-87893-322-0}}
*Hille, B. ''Ionic Channel of Excitable Membranes'' Sinauer Associates, Sunderland, MA, USA; 1st Edition, 1984.
*Nicholls, J.G., Martin, A.R. and Wallace, B.G. ''From Neuron to Brain'' Sinauer Associates, Inc. Sunderland, MA, USA 3rd Edition, 1992. {{ISBN|0-87893-580-0}}
*Nicholls, J.G., Martin, A.R. and Wallace, B.G. ''From Neuron to Brain'' Sinauer Associates, Inc. Sunderland, MA, USA 3rd Edition, 1992.
*Ove-Sten Knudsen. ''Biological Membranes: Theory of Transport, Potentials and Electric Impulses''. Cambridge University Press (September 26, 2002). {{ISBN|0-521-81018-3}}. Graduate level.
*Ove-Sten Knudsen. ''Biological Membranes: Theory of Transport, Potentials and Electric Impulses''. Cambridge University Press (September 26, 2002). Graduate level.
*National Medical Series for Independent Study. ''Physiology''. Lippincott Williams & Wilkins. Philadelphia, PA, USA 4th Edition, 2001. {{ISBN|0-683-30603-0}}
*National Medical Series for Independent Study. ''Physiology''. Lippincott Williams & Wilkins. Philadelphia, PA, USA 4th Edition, 2001.
=<nowiki>= 深入阅读 =</nowiki> =
=<nowiki>= 深入阅读 =</nowiki> =
*Electrochemical Driving Force Calculator
*Electrochemical Driving Force Calculator
*The Origin of the Resting Membrane Potential - Online interactive tutorial (Flash)
*The Origin of the Resting Membrane Potential - Online interactive tutorial (Flash)
{{DEFAULTSORT:Membrane Potential}}
{{DEFAULTSORT:Membrane Potential}}
[[Category:Electrophysiology]]
[[Category:Electrophysiology]]
[[Category:Membrane biology]]
[[Category:Membrane biology]]
<small>This page was moved from [[wikipedia:en:Membrane potential]]. Its edit history can be viewed at [[膜电位/edithistory]]</small>
<small>This page was moved from [[wikipedia:en:Membrane potential]]. Its edit history can be viewed at [[膜电位/edithistory]]</small></noinclude>
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