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{{Short description|Process by which neurons communicate with each other by changes in their membrane potentials}}

{{Short description|Process by which neurons communicate with each other by changes in their membrane potentials}}

[[File:Action Potential.gif|thumb|upright=1.5|As an action potential （nerve impulse） travels down an [[axon]] there is a change in polarity across the [[cell membrane|membrane]] of the axon. In response to a signal from another [[neuron]], sodium- （Na⁺） and potassium- （K⁺） gated [[Voltage-gated ion channel|ion channels]] open and close as the membrane reaches its [[threshold potential]]. Na⁺ channels open at the beginning of the action potential, and Na⁺ moves into the axon, causing [[depolarization]]. [[Repolarization]] occurs when the K⁺ channels open and K⁺ moves out of the axon, creating a change in polarity between the outside of the cell and the inside. The impulse travels down the axon in one direction only, to the [[axon terminal]] where it signals other neurons.

[[File:Action Potential.gif|thumb|upright=1.5|当动作电位（神经冲动）沿着轴突传导时，轴突的跨膜的极性发生变化。响应来自其他神经元的信号，Na⁺ 和 K⁺ 门控的离子通道随着膜电位达到其阈值电位而打开和关闭。动作电位开始时 Na⁺ 通道打开，Na⁺ 进入轴突，导致去极化。当 K⁺ 通道打开而 K⁺ 移出轴突时，就会发生复极化，从而在细胞的外部和内部之间产生极性变化。神经脉冲仅在一个方向上沿着轴突行进，到达轴突末端，在那里它向其他神经元发出信号。|链接=Special:FilePath/Action_Potential.gif]]

 

当动作电位（神经冲动）沿着轴突传导时，轴突的跨膜的极性发生变化。响应来自另一个神经元的信号，Na⁺ 和 K⁺ 门控的离子通道随着膜电位达到其阈值电位而打开和关闭。动作电位开始时 Na⁺ 通道打开，Na⁺ 进入轴突，导致去极化。当 K⁺ 通道打开而 K⁺ 移出轴突时，就会发生复极化，从而在细胞的外部和内部之间产生极性变化。神经脉冲仅在一个方向上沿着轴突行进，到达轴突末端，在那里它向其他神经元发出信号。|链接=Special:FilePath/Action_Potential.gif]]

生理学上，动作电位（action potential, AP）就是特定细胞位置的膜电位迅速上升又迅速下降的过程<ref name=":3">{{cite journal | vauthors = Hodgkin AL, Huxley AF | title = A quantitative description of membrane current and its application to conduction and excitation in nerve | journal = The Journal of Physiology | volume = 117 | issue = 4 | pages = 500–44 | date = August 1952 | pmid = 12991237 | pmc = 1392413 | doi = 10.1113/jphysiol.1952.sp004764 }}</ref> ：这种去极化会导致相邻位置同样地去极化。动作电位可在神经元、肌肉细胞、内分泌细胞等类型的称为可兴奋细胞（excitable cells）的动物细胞以及某些植物细胞中发生。

生理学上，动作电位（action potential, AP）就是特定细胞位置的膜电位迅速上升又迅速下降的过程<ref name=":3">{{cite journal | vauthors = Hodgkin AL, Huxley AF | title = A quantitative description of membrane current and its application to conduction and excitation in nerve | journal = The Journal of Physiology | volume = 117 | issue = 4 | pages = 500–44 | date = August 1952 | pmid = 12991237 | pmc = 1392413 | doi = 10.1113/jphysiol.1952.sp004764 }}</ref> ：这种去极化会导致相邻位置同样地去极化。动作电位可在神经元、肌肉细胞、内分泌细胞等类型的称为可兴奋细胞（excitable cells）的动物细胞以及某些植物细胞中发生。

==概述==

==概述==

[[File:Action potential basic shape.svg|thumb|right|Shape of a typical action potential. The membrane potential remains near a baseline level until at some point in time, it abruptly spikes upward and then rapidly falls.典型的动作电位波形。膜电位一直保持在接近基线水平，直到某个时间点突然上升，然后迅速下降。|链接=Special:FilePath/Action_potential_basic_shape.svg]]

[[File:Action potential basic shape.svg|thumb|right|典型的动作电位波形。膜电位一直保持在接近基线水平，直到某个时间点突然上升，然后迅速下降。|链接=Special:FilePath/Action_potential_basic_shape.svg]]

动物、植物和真菌的细胞膜几乎都在细胞外部和内部维持一个电压差，称为膜电位（membrane potential）。动物细胞的跨膜电压一般是 -70 mV。这意味着细胞内部相对于外部存在一个负电压。在大多数类型的细胞中，膜电位通常相当稳定。而某些类型的细胞具有电活性，即它们的电压随着时间而波动。在某些类型的有电活性的细胞，包括神经元和肌肉细胞中，电压波动的通常形式为迅速上升而后迅速下降。这些升降的循环即为动作电位。在某些类型的神经元中，整个升降循环在千分之几秒内发生。在肌肉细胞中，典型的动作电位持续时间约为五分之一秒。在其他类型的细胞和植物中，动作电位可能持续三秒或更长时间<ref name=":5">{{Cite journal|last=Pickard|first=Barbara | name-list-style = vanc |date=June 1973|title=Action Potentials in Higher Plants|url=http://www.esalq.usp.br/lepse/imgs/conteudo_thumb/Action-Potentials-in-Higher-Plants-1.pdf|journal=The Botanical Review|volume=39|issue=2|pages=188|doi=10.1007/BF02859299|s2cid=5026557 }}</ref>。

动物、植物和真菌的细胞膜几乎都在细胞外部和内部维持一个电压差，称为膜电位（membrane potential）。动物细胞的跨膜电压一般是 -70 mV。这意味着细胞内部相对于外部存在一个负电压。在大多数类型的细胞中，膜电位通常相当稳定。而某些类型的细胞具有电活性，即它们的电压随着时间而波动。在某些类型的有电活性的细胞，包括神经元和肌肉细胞中，电压波动的通常形式为迅速上升而后迅速下降。这些升降的循环即为动作电位。在某些类型的神经元中，整个升降循环在千分之几秒内发生。在肌肉细胞中，典型的动作电位持续时间约为五分之一秒。在其他类型的细胞和植物中，动作电位可能持续三秒或更长时间<ref name=":5">{{Cite journal|last=Pickard|first=Barbara | name-list-style = vanc |date=June 1973|title=Action Potentials in Higher Plants|url=http://www.esalq.usp.br/lepse/imgs/conteudo_thumb/Action-Potentials-in-Higher-Plants-1.pdf|journal=The Botanical Review|volume=39|issue=2|pages=188|doi=10.1007/BF02859299|s2cid=5026557 }}</ref>。

===典型的神经元过程===

===典型的神经元过程===

[[File:Action potential.svg|thumb|300px|Approximate plot of a typical action potential shows its various phases as the action potential passes a point on a [[cell membrane]]. The membrane potential starts out at approximately −70 mV at time zero. A stimulus is applied at time = 1 ms, which raises the membrane potential above −55 mV （the threshold potential）. After the stimulus is applied, the membrane potential rapidly rises to a peak potential of +40 mV at time = 2 ms. Just as quickly, the potential then drops and overshoots to −90 mV at time = 3 ms, and finally the resting potential of −70 mV is reestablished at time = 5 ms.

[[File:Action potential.svg|thumb|300px|典型动作电位的近似图显示了动作电位经过细胞膜上一点时的各个阶段。膜电位开始时（时间零点）约为−70 mV。在时间 = 1 ms 时施加刺激，这会将膜电位提高到 −55 mV（阈值电位）以上。施加刺激后，膜电位在时间= 2 ms 时迅速上升到 +40 mV 的峰值电位。在时间 = 3 ms 时膜电位又快速下降并过冲至 −90 mV，最后在时间 = 5 ms 时重新建立 −70 mV 的静息电位。|链接=Special:FilePath/Action_potential.svg]]

 

典型动作电位的近似图显示了动作电位经过细胞膜上一点时的各个阶段。膜电位在时间零点开始时约为−70 mV。在时间 = 1 ms 处施加刺激，这会将膜电位提高到 −55 mV（阈值电位）以上。施加刺激后，膜电位在时间= 2 ms时迅速上升到+40 mV的峰值电位。同样快速，电位在时间 = 3 ms 时下降并过冲至 −90 mV，最后在时间 = 5 ms 时重新建立 −70 mV 的静息电位。|链接=Special:FilePath/Action_potential.svg]]

动物身体组织中的细胞都是电极化的——换句话说，它们维持一个跨细胞质膜的电压差，即所谓的膜电位。这种电极化是嵌入在质膜的蛋白质结构（称为离子泵和离子通道）之间复杂的相互作用中产生的。神经元细胞膜上的离子通道在不同的细胞部位而类型不同，因而树突、轴突和胞体具有不同的电特性。因此，神经元质膜仅在某些部位是可兴奋的（能够产生动作电位）。近年的研究表明，神经元最易兴奋的部位是轴丘（轴突出离胞体的部位）后的部位，称为轴突始段（axonal initial segment），但在大多数情况下轴突和胞体也是可兴奋的<ref name=":6">{{cite journal | vauthors = Leterrier C | title = The Axon Initial Segment: An Updated Viewpoint | journal = The Journal of Neuroscience | volume = 38 | issue = 9 | pages = 2135–2145 | date = February 2018 | pmid = 29378864 | pmc = 6596274 | doi = 10.1523/JNEUROSCI.1922-17.2018 }}</ref>。

动物身体组织中的细胞都是电极化的——换句话说，它们维持一个跨细胞质膜的电压差，即所谓的膜电位。这种电极化是嵌入在质膜的蛋白质结构（称为离子泵和离子通道）之间复杂的相互作用中产生的。神经元细胞膜上的离子通道在不同的细胞部位而类型不同，因而树突、轴突和胞体具有不同的电特性。因此，神经元质膜仅在某些部位是可兴奋的（能够产生动作电位）。近年的研究表明，神经元最易兴奋的部位是轴丘（轴突出离胞体的部位）后的部位，称为轴突始段（axonal initial segment），但在大多数情况下轴突和胞体也是可兴奋的<ref name=":6">{{cite journal | vauthors = Leterrier C | title = The Axon Initial Segment: An Updated Viewpoint | journal = The Journal of Neuroscience | volume = 38 | issue = 9 | pages = 2135–2145 | date = February 2018 | pmid = 29378864 | pmc = 6596274 | doi = 10.1523/JNEUROSCI.1922-17.2018 }}</ref>。

因此，电压门控离子通道在膜电位处于某些水平时倾向于打开，在其他水平时倾向于关闭。然而，膜电位和离子通道的状态之间在大多数情况下是一种概率关系，并且存在时间延迟。离子通道在不可预测的时间在不同构象之间切换：膜电位决定状态切换速率和单位时间每种切换类型的概率。

因此，电压门控离子通道在膜电位处于某些水平时倾向于打开，在其他水平时倾向于关闭。然而，膜电位和离子通道的状态之间在大多数情况下是一种概率关系，并且存在时间延迟。离子通道在不可预测的时间在不同构象之间切换：膜电位决定状态切换速率和单位时间每种切换类型的概率。

[[File:Blausen 0011 ActionPotential Nerve.png|thumb|300px|left|Action potential propagation along an axon|链接=Special:FilePath/Blausen_0011_ActionPotential_Nerve.png]]

[[File:Blausen 0011 ActionPotential Nerve.png|thumb|300px|left|Action potential propagation along an axon沿着轴突的动作电位传导|链接=Special:FilePath/Blausen_0011_ActionPotential_Nerve.png]]

电压门控离子通道能够产生动作电位，是因为它们能够产生正反馈回路：膜电位控制离子通道的状态，而离子通道的状态控制膜电位。因此，在某些情况下，膜电位的上升会导致离子通道打开，又导致膜电位的进一步上升。当这种正反馈循环（Hodgkin 循环）爆发性地进行时，就会产生动作电位。电压门控离子通道的生物物理特性决定了动作电位的时间和幅度轨迹。存在几种能产生动作电位所必需的正反馈回路的离子通道。电压门控性钠通道负责神经传导的快速动作电位。肌细胞和某些类型的神经元的稍慢的动作电位是由电压门控钙通道产生的。每种类型都有多种变体，具有不同的电压灵敏度和不同的时间动力学。

电压门控离子通道能够产生动作电位，是因为它们能够产生正反馈回路：膜电位控制离子通道的状态，而离子通道的状态控制膜电位。因此，在某些情况下，膜电位的上升会导致离子通道打开，又导致膜电位的进一步上升。当这种正反馈循环（Hodgkin 循环）爆发性地进行时，就会产生动作电位。电压门控离子通道的生物物理特性决定了动作电位的时间和幅度轨迹。存在几种能产生动作电位所必需的正反馈回路的离子通道。电压门控性钠通道负责神经传导的快速动作电位。肌细胞和某些类型的神经元的稍慢的动作电位是由电压门控钙通道产生的。每种类型都有多种变体，具有不同的电压灵敏度和不同的时间动力学。

==Neurotransmission神经传递==

==Neurotransmission神经传递==

===Anatomy of a neuron 神经元的解剖学===

===Anatomy of a neuron 神经元的解剖学===

 

Neurons are electrically excitable cells composed, in general, of one or more dendrites, a single [[soma (biology)|soma]], a single axon and one or more [[axon terminal]]s. Dendrites are cellular projections whose primary function is to receive synaptic signals. Their protrusions, known as [[dendritic spine]]s, are designed to capture the neurotransmitters released by the presynaptic neuron. They have a high concentration of [[ligand-gated ion channel]]s. These spines have a thin neck connecting a bulbous protrusion to the dendrite. This ensures that changes occurring inside the spine are less likely to affect the neighboring spines. The dendritic spine can, with rare exception （see [[Long-term potentiation#Properties|LTP]]）, act as an independent unit. The dendrites extend from the soma, which houses the [[Cell nucleus|nucleus]], and many of the "normal" [[eukaryote|eukaryotic]] organelles. Unlike the spines, the surface of the soma is populated by voltage activated ion channels. These channels help transmit the signals generated by the dendrites. Emerging out from the soma is the [[axon hillock]]. This region is characterized by having a very high concentration of voltage-activated sodium channels. In general, it is considered to be the spike initiation zone for action potentials, i.e. the [[trigger zone]]. Multiple signals generated at the spines, and transmitted by the soma all converge here. Immediately after the axon hillock is the axon. This is a thin tubular protrusion traveling away from the soma. The axon is insulated by a [[myelin]] sheath. Myelin is composed of either [[Schwann cells]] （in the peripheral nervous system） or [[oligodendrocytes]] （in the central nervous system）, both of which are types of [[glial cells]]. Although glial cells are not involved with the transmission of electrical signals, they communicate and provide important biochemical support to neurons. To be specific, myelin wraps multiple times around the axonal segment, forming a thick fatty layer that prevents ions from entering or escaping the axon. This insulation prevents significant signal decay as well as ensuring faster signal speed. This insulation, however, has the restriction that no channels can be present on the surface of the axon. There are, therefore, regularly spaced patches of membrane, which have no insulation. These [[nodes of Ranvier]] can be considered to be "mini axon hillocks", as their purpose is to boost the signal in order to prevent significant signal decay. At the furthest end, the axon loses its insulation and begins to branch into several [[axon terminal]]s. These presynaptic terminals, or synaptic boutons, are a specialized area within the axon of the presynaptic cell that contains [[neurotransmitters]] enclosed in small membrane-bound spheres called [[synaptic vesicle]]s.

Neurons are electrically excitable cells composed, in general, of one or more dendrites, a single [[soma (biology)|soma]], a single axon and one or more [[axon terminal]]s. Dendrites are cellular projections whose primary function is to receive synaptic signals. Their protrusions, known as [[dendritic spine]]s, are designed to capture the neurotransmitters released by the presynaptic neuron. They have a high concentration of [[ligand-gated ion channel]]s. These spines have a thin neck connecting a bulbous protrusion to the dendrite. This ensures that changes occurring inside the spine are less likely to affect the neighboring spines. The dendritic spine can, with rare exception （see [[Long-term potentiation#Properties|LTP]]）, act as an independent unit. The dendrites extend from the soma, which houses the [[Cell nucleus|nucleus]], and many of the "normal" [[eukaryote|eukaryotic]] organelles. Unlike the spines, the surface of the soma is populated by voltage activated ion channels. These channels help transmit the signals generated by the dendrites. Emerging out from the soma is the [[axon hillock]]. This region is characterized by having a very high concentration of voltage-activated sodium channels. In general, it is considered to be the spike initiation zone for action potentials, i.e. the [[trigger zone]]. Multiple signals generated at the spines, and transmitted by the soma all converge here. Immediately after the axon hillock is the axon. This is a thin tubular protrusion traveling away from the soma. The axon is insulated by a [[myelin]] sheath. Myelin is composed of either [[Schwann cells]] （in the peripheral nervous system） or [[oligodendrocytes]] （in the central nervous system）, both of which are types of [[glial cells]]. Although glial cells are not involved with the transmission of electrical signals, they communicate and provide important biochemical support to neurons. To be specific, myelin wraps multiple times around the axonal segment, forming a thick fatty layer that prevents ions from entering or escaping the axon. This insulation prevents significant signal decay as well as ensuring faster signal speed. This insulation, however, has the restriction that no channels can be present on the surface of the axon. There are, therefore, regularly spaced patches of membrane, which have no insulation. These [[nodes of Ranvier]] can be considered to be "mini axon hillocks", as their purpose is to boost the signal in order to prevent significant signal decay. At the furthest end, the axon loses its insulation and begins to branch into several [[axon terminal]]s. These presynaptic terminals, or synaptic boutons, are a specialized area within the axon of the presynaptic cell that contains [[neurotransmitters]] enclosed in small membrane-bound spheres called [[synaptic vesicle]]s.

神经元是可电兴奋的细胞，一般由一个或多个树突、一个胞体、一个轴突和一个或多个轴突终末组成的。树突是细胞的突起，其主要功能是接收突触信号。它们的突起被称为树突棘，用来捕获突触前神经元释放的神经递质。它们具有高浓度的配体门控离子通道。这些棘有一个细细的颈部，连接球状突起和树突。这确保树突棘内部发生的变化不太可能影响邻近的树突棘。树突棘除了极少数例外（见 LTP），可以作为一个独立的单位。树突从胞体延伸出来，胞体是细胞核和许多“正常”的真核细胞器的所在地。与树突棘不同，胞体的表面布满了电压激活的离子通道。这些通道帮助传输由树突产生的信号。从躯体出来的是轴丘。这个区域的特征是有非常高浓度的电压激活钠离子通道。一般认为它是动作电位的尖峰起始区，或触发区。在树突棘处产生的多个信号，由胞体传输的信号都在这里汇聚。紧跟在轴丘之后的是轴突。这是一个细管状突起，从胞体中游离出来。轴突由髓鞘绝缘。髓鞘由施万细胞（周围神经系统）或少突胶质细胞（中枢神经系统）组成，这两种细胞都是神经胶质细胞。虽然神经胶质细胞不参与电信号的传递，但它们可以相互沟通，为神经元提供重要的生化支持。具体来说，髓磷脂在轴突周围多次包裹，形成一层厚厚的脂肪层，阻止离子进入或逃离轴突。这种绝缘防止显着的信号衰减，以及确保更快的信号速度。然而，这种绝缘有一个限制，即轴突表面不能有通道。因此，有规则间隔的膜片，没有绝缘层。这些郎飞结可以被认为是“迷你轴突小丘”，因为他们的目的是增强信号，以防止重大信号衰减。在最远端，轴突失去了它的绝缘性，并开始分支成几个轴突终端。这些突触前终末，或称突触终结，是突触前细胞轴突内的一个特殊区域，其中包含神经递质，这些神经递质被包裹在被称为突触小泡的小膜内。

神经元是电兴奋型细胞，一般由一个或多个树突、一个胞体、一个轴突和一个或多个轴突末梢组成的。树突是细胞的突起，其主要功能是接收突触信号。它们的突起被称为树突棘，用来捕获突触前神经元释放的神经递质。它们具有高浓度的配体门控离子通道。这些棘有一个细细的颈部，连接球状突起和树突。这确保树突棘内部发生的变化不太可能影响邻近的树突棘。树突棘除了极少数例外（见 LTP），可以作为一个独立的单位。树突从胞体延伸出来，胞体是细胞核和许多“正常”的真核细胞器的所在地。与树突棘不同，胞体的表面布满了电压激活的离子通道。这些通道帮助传输由树突产生的信号。从躯体出来的是轴丘。这个区域的特征是有非常高浓度的电压激活钠离子通道。一般认为它是动作电位的尖峰起始区，或触发区。在树突棘处产生的多个信号，由胞体传输的信号都在这里汇聚。紧跟在轴丘之后的是轴突。这是一个细管状突起，从胞体中游离出来。轴突由髓鞘绝缘。髓鞘由施万细胞（周围神经系统）或少突胶质细胞（中枢神经系统）组成，这两种细胞都是神经胶质细胞。虽然神经胶质细胞不参与电信号的传递，但它们可以相互沟通，为神经元提供重要的生化支持。具体来说，髓磷脂在轴突周围多次包裹，形成一层厚厚的脂肪层，阻止离子进入或逃离轴突。这种绝缘防止显着的信号衰减，以及确保更快的信号速度。然而，这种绝缘有一个限制，即轴突表面不能有通道。因此，有规则间隔的膜片，没有绝缘层。这些郎飞结可以被认为是“迷你轴突小丘”，因为他们的目的是增强信号，以防止重大信号衰减。在最远端，轴突失去了它的绝缘性，并开始分支成几个轴突终端。这些突触前终末，或称突触终结，是突触前细胞轴突内的一个特殊区域，其中包含神经递质，这些神经递质被包裹在被称为突触小泡的小膜内。

===Initiation===

===Initiation===