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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。

细胞的膜电位最终是来自于两个因素: 电作用力和扩散。电作用力源于带相反类型电荷（正电荷和负电荷）的粒子之间的相互吸引和带有相同类型电荷（都是正电荷或都是负电荷）的粒子之间的相互排斥。扩散源于粒子从高浓度区域向低浓度区域重新分布的统计趋势。

===Voltage===

===Voltage电压===

[[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.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]]

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，电压最简单的定义由欧姆定律给出：V = IR，其中 V 是电压，I 是电流，R 是电阻。如果在电路中置入电压源（如电池），则电压源的电压越高，通过遇到的电阻的电流就越大。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，通常会指定电路中任意选定的元件作为零电位，然后得到其他元件相对于该零点测得的电压。选择哪个元件作为零点没有意义——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，依照惯例，零电平最常被定为接地的电路部分。

The same principle applies to voltage in cell biology. In electrically active tissue, the potential difference between any two points can be measured by inserting an electrode at each point, for example one inside and one outside the cell, and connecting both electrodes to the leads of what is in essence a specialized voltmeter. By convention, the zero potential value is assigned to the outside of the cell and the sign of the potential difference between the outside and the inside is determined by the potential of the inside relative to the outside zero.

The same principle applies to voltage in cell biology. In electrically active tissue, the potential difference between any two points can be measured by inserting an electrode at each point, for example one inside and one outside the cell, and connecting both electrodes to the leads of what is in essence a specialized voltmeter. By convention, the zero potential value is assigned to the outside of the cell and the sign of the potential difference between the outside and the inside is determined by the potential of the inside relative to the outside zero.

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''' {{=}} –&nabla;<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''' {{=}} –&nabla;<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''' {{=}} –&nabla;<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。

用数学术语来说，电压的定义从电场的概念开始，电场 {{math|'''E'''}} 是一个向量场，它为空间中的每一点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>}}，即 {{math|'''E''' {{=}} –&nabla;<VAR>V</VAR>}}。这个标量场 {{math|<VAR>V</VAR>}} 称为电压分布。注意，这个定义允许任意的积分常数——这就是为什么电压的绝对值没有意义。一般来说，只有在磁场对电场影响不大的情况下，电场才能被认为是保守的，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离子和驱动其运动的力===

[[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]]

[[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]]