章节大纲

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  • 神经脉冲

    Is it really electrical?
    ::真的有电吗?

    Yes, it is. A nerve impulse is generated by the unequal distribution of ions . The charges on all these ions result in the generation of an electrical signal.
    ::是的 离子分布不均引发神经冲动 所有这些离子的电荷导致电信号的生成

    Nerve Impulses
    ::神经因子

    In the late 18 th century, the Italian doctor and physicist Luigi Galvani first recorded the action of electricity on the muscle tissue of frogs . He noted that an electrical charge applied to a nerve in the legs of a dead frog made the legs move. Galvani attributed the movement of the frog’s to an electrical current that was carried by the nerves. Galvani coined the term " electricity" to describe this vital force for life.
    ::18世纪末,意大利医生和物理学家Luigi Galvani首次记录了对青蛙肌肉组织进行的电动。 他指出,对一只死青蛙腿神经的电荷使双腿移动。 Galvani将青蛙运动归因于神经携带的电流。 Galvani用“电”一词来描述生命的这一关键力量。

    Galvani believed that animal electricity came from the muscles and was unique to living creatures. However, his fellow Italian and physicist, Alessandro Volta, disagreed with him and reasoned that animal electricity was a physical phenomenon that occurred between metals. Volta disproved Galvani’s claim by building the first battery, which showed that a current could flow outside an organism’s body. Since then, scientists have learned much more about electrical charges in living systems.
    ::加尔瓦尼认为动物的电力来自肌肉,是生命生物独有的。 然而,他的意大利同事和物理学家Alessandro Volta(Alessandro Volta)不同意他的观点,认为动物电力是金属之间发生的物理现象。 沃尔塔(Volta)通过建造第一个电池推翻了加尔瓦尼的主张,这表明水流可以在生物体身体外流动。 自那时以来,科学家们更多地了解了生物系统中的电费。

    Ion Channels and Nerve Impulses
    ::Ion 频道和神经元音源

    Ion channels use energy to build and maintain a concentration gradient of ions between the extracellular fluid and the cell’s cytosol , as shown in Figure . This concentration gradient results in a net negative charge on the inside of the membrane and a positive charge on the outside. This difference causes a voltage difference across the membrane. Voltage is electrical potential energy that is caused by a separation of opposite charges, in this case across the membrane. The voltage across a membrane is called the membrane potential . The membrane potential is the basis for the conduction of nerve impulses along the of . Ions that are important in the formation of a nerve impulse include sodium (Na + ) and potassium (K + ).
    ::如图所示,离子信道利用能量在细胞外液体和细胞细胞索之间建造和保持一种离子浓度梯度的梯度。这种浓度梯度导致膜内的净负电荷,外部正电荷。这种差异造成膜上的电压差异。电压是电能的潜在能量,这种能量是由相对电荷分离造成的,在此情况下,横跨膜膜。膜上的电压被称为膜潜力。膜潜力是沿膜内神经脉冲传导的基础。在形成神经脉冲中重要的离子包括钠(Na+)和钾(K+)。

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    The sodium-potassium pump maintains the resting potential of a neuron. This pump keeps the concentration of sodium outside the cell greater than the concentration inside the cell while keeping the concentration of potassium inside the cell greater than the concentration of potassium outside the cell.
    ::钠-钾泵保持神经元的休息潜力。该泵使钠在细胞外的浓度大于细胞内的浓度,同时使细胞内钾的浓度大于细胞外钾的浓度。

    Ion channels and ion pumps are very specific; they allow only certain ions through the cell membrane. For example, potassium channels will allow only potassium ions through, and the acts only on sodium and potassium ions. Ion transport proteins have a special role in the nervous systems because voltage-gated ion channels and ion pumps are essential for forming a nerve impulse.
    ::离子导管和离子泵非常具体;它们只允许通过细胞膜的某些离子;例如,钾导管只允许通过钾离子,只有钠离子和钾离子才会发生作用。 离子传输蛋白在神经系统中具有特殊作用,因为电压加压离子导管和离子泵对于形成神经脉冲至关重要。

    Resting Potential
    ::恢复潜力

    When a neuron is not conducting a nerve impulse, it is said to be at rest. The resting potential is the resting state of the neuron, during which time the neuron has an overall negative charge. The resting potential in neurons is approximately -70 milliVolts (mV). The negative sign indicates the negative charge inside the relative to the outside.
    ::当神经元没有神经脉冲时,据说神经元处于休息状态。休息潜力是神经元的休息状态,在休息期间,神经元具有总体负电荷。神经元的休息潜力约为 - 70毫伏特。负信号显示相对外部的负电荷。

    The reasons for the overall negative charge of the cell include the following:
    ::对牢房总体负收费的原因包括:

    • The sodium-potassium pump removes Na + ions from the cell by . A net negative charge inside the cell is due to the higher concentration of Na + ions outside the cell than inside the cell.
      ::钠-钾泵将Na+离子从细胞中除去。 电池内的净负电荷是由于细胞外的 Na+离子浓度高于细胞内。
    • Most cells have potassium-selective ion channel that remain open all the time. The K + ions move down the concentration gradient (passively) through these potassium channels and out of the cell, which results in a build-up of excess positive charge outside of the cell.
      ::大部分细胞的钾选择性离子渠道始终是开放的。 K+离子通过这些钾渠道和细胞外的浓度梯度(被动地)向下移动,导致细胞外的超重正电荷增加。
    • There are a number of large, negatively charged molecules, such as proteins, inside the cell.
      ::细胞内有一些大的负电荷分子,如蛋白质。

    Action Potential
    ::行动潜力

    An action potential , also called a nerve impulse, is an electrical charge that travels along the membrane of a neuron. It can be generated when a neuron’s membrane potential is changed by chemical signals from a nearby cell. In an action potential, the cell membrane potential changes quickly from negative to positive as sodium ions flow into the cell through ion channels, while potassium ions flow out of the cell, as shown in  Figure .
    ::行动潜力也被称为神经脉冲,它是一种沿着神经神经元的膜穿行的电荷。 当神经神经元的膜潜力被附近细胞的化学信号改变时,它就会产生。 在行动潜力中,细胞膜可能迅速从负变化到正变化,因为钠离子通过离子通道流入细胞,而钾离子则从细胞流出,如图所示。

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    An action potential speeds along an axon in milliseconds.
    ::行动潜力在毫秒内沿着斧子加速 。

    The change in membrane potential results in the cell becoming depolarized. An action potential works on an all-or-nothing basis. That is, the membrane potential has to reach a certain level of depolarization, called the threshold, otherwise an action potential will not start. This threshold potential varies, but is generally about 15 millivolts (mV) more positive than the cell's resting membrane potential. If a membrane depolarization does not reach the threshold level, an action potential will not happen. You can see in  Figure that two depolarizations did not reach the threshold level of -55mV.
    ::薄膜的改变可能导致细胞脱冰。 一种行动潜力在完全或毫无作用的基础上发挥作用。 也就是说, 薄膜的潜力必须达到某种程度的脱冰, 称为临界值, 否则行动潜力不会开始。 这种临界值可能不同, 但一般而言比细胞保持的膜潜力更积极的大约是15毫伏。 如果膜脱极没有达到临界值, 行动潜力就不会发生。 您可以在图中看到, 两种脱极没有达到55毫伏的临界值。

    The first channels to open are the sodium ion channels, which allow sodium ions to enter the cell. The resulting increase in positive charge inside the cell (up to about +40 mV) starts the action potential. Potassium ion channels then open, allowing potassium ions to flow out of the cell, which ends the action potential. Both of the ion channels then close, and the sodium-potassium pump restores the resting potential of -70 mV. The action potential will move down the axon toward the like a wave would move along the surface of .
    ::第一个打开的渠道是钠离子通道,它允许钠离子进入细胞。因此,细胞内正电荷的增加(大约为+40mV)开始产生行动潜力。然后钾离子通道打开,允许钾离子从细胞中流出,从而结束行动潜力。离子通道关闭后,钠-钾泵恢复了-70mV的休息潜力。行动潜力会像波浪一样向轴向下移动。

    In myelinated neurons, ion flows occur only at the nodes of Ranvier. As a result, the action potential signal "jumps" along the axon membrane from node to node rather than spreading smoothly along the membrane, as they do in axons that do not have a myelin sheath . This is due to a clustering of Na + and K + ion channels at the Nodes of Ranvier. Unmyelinated axons do not have nodes of Ranvier, and ion channels in these axons are spread over the entire membrane surface.
    ::在宫颈神经中,离子流只出现在兰维尔节点上,因此,在轴膜线从节点到节点上,行动潜在的信号“跳动”,而不是像在没有髓草原的轴轴中那样,在膜线上顺利扩散。这是因为在兰维尔节点上将纳+和K+离子通道聚集在一起。未受宫颈的轴线没有兰维尔节点,这些轴线的离子通道分布在整个膜表面。

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    The changes in membrane potential during an action potential. Note the failed initiations that did not start an action potential. These depolarizations did not reach the threshold level (of about -55mV), so they did not start an action potential.
    ::行动潜力期间膜潜力的变化。 注意未启动行动潜力的失败启动。 这些脱极没有达到( 约 - 55mV) 的临界值, 因此它们没有启动行动潜力 。

     

    Types of Neurons
    ::中子类型

    Neurons are highly specialized for the processing and transmission of cellular signals and can be classified by their structure or function. Structural is based on the number of dendrites and axons that a cell has. Functional classification groups neurons according to the direction in which the nerve impulse is moving in relation to the CNS.
    ::神经高度专门处理和传输细胞信号,可按其结构或功能进行分类。结构依据细胞的 dendrite和轴数。功能分类根据神经脉冲相对于 CNS 的动向将神经元分组。

    There are three functional groups of nerves:
    ::神经有三种功能组:

    • Sensory neurons carry signals from tissues and organs to the and are sometimes also called afferent neurons. Sensory neurons typically have long dendrites and short axons. Sensory neurons are found in reflex arcs and are involved in several forms of involuntary behavior including pain avoidance.
      ::感官神经元将信号从组织和器官传到组织或器官,有时也被称为远征神经元,感官神经元通常具有长长的外衣和短轴,感官神经元在反射弧中发现,并涉及多种形式的非自愿行为,包括避免疼痛。
    • Motor neurons carry signals from the central nervous system to muscles and glands and are sometimes called efferent neurons. Motor neurons have long axons and short dendrites.
      ::机动神经元从中枢神经系统向肌肉和腺传递信号,有时被称为神经元,机动神经元有长轴和短纹。
    • Interneurons connect sensory and motor neurons in neural pathways that go through the central nervous system. Interneurons are also called association or relay neurons. Interneurons are found only in the central nervous system where they connect neurons to other neurons.
      ::内中子将中枢神经系统的神经路径中的感官和运动神经元连接起来,间中子也被称为关联或中继神经元,只有在中枢神经系统中才发现间中子,它们将神经元与其他神经元连接在一起。

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    This axon is part of a motor neuron. It transmits nerve impulses to a skeletal muscle, causing the muscle to contract.
    ::这斧子是运动神经元的一部分,它将神经脉冲传送到骨骼肌肉,导致肌肉萎缩。

    Summary
    ::摘要

    • Ion channels maintain the resting potential within a neuron.
      ::离子频道在神经元中保持休息潜力
    • After an influx of sodium causes the neuron's membrane potential to exceed its threshold, an action potential (nerve impulse) sends an electrical signal down the axon.
      ::在钠大量流入后,神经元的膜潜力超过了临界值, 行动潜力(神经冲动)向斧子发出电信号。

    Review
    ::回顾

    1. How does an ion channel function?
      ::离子频道如何运作 ?
    2. What is the difference between an action and resting potential?
      ::采取行动与发挥潜力之间有什么区别?
    3. In relation to the nerve impulse, what is the threshold?
      ::关于神经冲动,门槛是多少?

    Explore More
    ::探索更多

     

     

    Use the video above to answer the following questions:
    ::使用以上视频回答下列问题:

    1. How does the action potential propagate?
      ::行动潜力是如何传播的?
    2. What prevents the action potential from propagating backwards?
      ::是什么阻止行动潜力向后传播?