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  • 中空之间的通信

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    How does a signal move from one to the next?
    ::信号如何从一个移动到下一个?

    It literally jumps by way of a chemical transmitter. Notice the two cells are not connected, but are separated by a small gap—the synapse, which is the space between a and the next cell.
    ::它实际上通过化学发射机而跳跃。注意这两个细胞没有连接,而是被一个小缝隙——即突触——隔开。 突触是细胞与下一个细胞之间的空间。

    Communication Between Neurons
    ::中空之间的通信

    Neurons communicate with each other at specialized junctions called synapses. Synapses are also found at junctions between neurons and other cells such as muscle cells (see Figure ).
    ::神经元与肌肉细胞等其他细胞之间的交接点也发现神经元与肌肉细胞等其他细胞之间的交接点(见图 )。

    There are two types of synapses:
    ::有两种突触类型:

    • Chemical synapses use chemical signaling molecules as messengers.
      ::化学突触利用化学信号分子作为送信员。
    • Electrical synapses use ions as messengers.
      ::电突触利用离子作为信使。

    We will primarily discuss chemical synapses here. At a chemical synapse, the axon terminal of one neuron usually does not touch the other cell; the gap is called a synaptic cleft . The transmitting cell is called the presynaptic neuron, and the receiving cell is called the postsynaptic cell or, if it is another neuron, the postsynaptic neuron.
    ::我们在这里主要讨论化学突触。 在化学突触中, 一个神经元的xon终端通常不触动另一个细胞; 空隙被称为合成裂缝。 传输细胞被称为预合成神经元, 接收细胞被称为后合成神经元, 或者,如果是另一个神经元, 则称为后合成神经元。

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    Right: At a synapse, neurotransmitters are released by the axon terminal. They bind with receptors on the other cell. Left: A synapse between a neuron and a muscle cell. The connection between a neuron and a muscle cell is called a neuromuscular junction. The finger-like projections of the axon are the axon terminals. An action potential moves down to the axon terminals where it causes a chemical message called a neurotransmitter to be released into the synaptic cleft. The neurotransmitter then causes an action potential to start on the membrane of the muscle cell.
    ::右 : 在突触处, 神经传导器会通过xon终端释放出来。 它们会与其他细胞的受体捆绑在一起。 左 : 神经元和肌肉细胞之间的突触。 神经元和肌肉细胞之间的联系被称为神经肌肉交叉口。 轴的手指一样的投影是轴终端。 行动潜力会下到xon终端, 从而导致被称为神经传感器的化学信息被释放到神经左裂处。 神经感应器会引发一个行动潜力, 开始在肌肉细胞的膜上 。

    Your brain has a huge number of synapses. Each of your 10 12 (one trillion) neurons—including glial cells—has, on average, 7,000 synaptic connections to other neurons. It has been estimated that the brain of a three-year-old child has about 10 16 (10 quadrillion) synapses, though this number declines with age and levels off by . An adult has between 10 15 and 5 x 10 15 (1 to 5 quadrillion) synapses.
    ::您的大脑中有大量突触。 您的1012( 1万亿) 神经元 — — 包括滑翔细胞 — — 平均有7000个与其他神经元的合成连接。 据估计,三岁儿童的大脑中大约有1016个突触( 10 4krillion) , 尽管这个数字随着年龄和水平的下降而下降。 成年人有1015到 5 x 1015(1至 5 4krillion) 的突触( 1- 5 krillion) 。

    Neurotransmitter Release
    ::神经分质释放

    A neurotransmitter is a chemical message that is used to relay electrical signals between a neuron and another cell. Neurotransmitter molecules are made inside the presynaptic neuron and stored in vesicles at the axon terminal. Some neurons make only one type of neurotransmitter, but most neurons make two or more types of neurotransmitters. When an action potential reaches the axon terminal, it causes the neurotransmitter vesicles to fuse with the terminal membrane, and the neurotransmitters are released into the synaptic cleft. The neurotransmitters then diffuse across the synaptic cleft and bind to receptor proteins on the membrane of the postsynaptic cell, as shown in  Figure .
    ::神经传递器是一种化学信息,用于在神经神经与另一个细胞之间传递电子信号。神经传递器分子在预发性神经神经元中制造,并存储在轴终端的输卵管中。有些神经元只制造一种类型的神经传递器,但大多数神经元制造两种或两种以上类型的神经传递器。当行动潜力到达轴终端时,它导致神经传递性输卵管与终端膜结合,神经传递器释放到合成裂口中。神经传输器随后扩散到突发性裂口,然后与后发性细胞膜上的受体蛋白结合,如图所示。

    Closeup of synapse during signal transmission

    The synaptic cleft. Neurotransmitters that are released into the synaptic cleft diffuse across the synaptic membrane and bind to receptor proteins on the post synaptic cell.
    ::突触裂口。神经传导器释放到突触裂裂体的分布中, 并粘附于后突触细胞上的受体蛋白。

    Neurotransmitter Action
    ::神经保证动作

    Many types of neurotransmitters exist, a few of which are listed in  Table . Neurotransmitters can have an excitatory or inhibitory effect on the postsynaptic cell. An excitatory neurotransmitter helps initiate an action potential, and an inhibitory neurotransmitter helps prevent one from starting. Glutamate is the most common excitatory transmitter in the body, while GABA and glycine are inhibitory neurotransmitters. The release of acetylcholine, an excitatory neurotransmitter, causes an inflow of positively charged sodium ions (Na + ) into the postsynaptic neuron. This inflow of positive charge causes a depolarization of the membrane at that point. The depolarization then spreads to the rest of the postsynaptic neuron. Acetylcholine is the neurotransmitter that initiates muscle movement .
    ::存在许多种类的神经递解器,其中有一些在表1中列出。神经递解器可能对后合成细胞产生刺激或抑制效应。刺激性神经递解器有助于启动行动潜力,抑制性神经递解器有助于防止其启动。Glutamate是人体中最常见的刺激发射机,而GABA和Glycine是抑制性神经递解器。乙酰胆碱(一种刺激性神经递解器)的释放,导致对后合成神经的正电离物(Na+)流入。这种阳性电荷的流入导致该点的membrane分解。脱极化随后扩散到后合成神经的其余部分。Acetylcolline是引发肌肉运动的神经递解者。

    The effect of a neurotransmitter can also depend on the receptor to which it binds. The same neurotransmitter can be either excitatory or inhibitory by causing different changes in the membrane potential of the cell; the opening or closing of ion channels depends on the membrane potential.
    ::神经传输器的效果也取决于它所绑定的受体。 同一神经传输器既可以是刺激性的,也可以是抑制性的,因为它导致细胞膜潜力的不同变化;离子通道的开关取决于膜潜力。

    Common Neurotransmitters and Their Receptors
    Name Receptor Name and Type Ions Involved
    Glutamate (glutamic acid) Glutamate receptors (ligand-gated ion channels and G protein-coupled receptors) Ca 2+ , K + , Na +
    Acetylcholine Acetylcholine receptors (ligand-gated ion channel) Na +
    Norepinephrine (noradrenaline) Adrenoceptors (G protein-coupled receptors) Ca2 +
    Epinephrine (adrenaline) Adrenoceptors (G protein-coupled receptors) Ca 2+
    Serotonin (5-hydroxytryptamine)

    5-HT receptors 5-HT 3 is a ligand-gated ion channel
    ::5-HT 5-HT 5-HT3 受体是电离离信道

    5-HT 1 , 5-HT 2 , 5-HT 4 , 5-HT 5 A, 5-HT 7 are G protein-coupled receptors
    ::5-HT1、5-HT1、5-HT2、5-HT4、5-HT4、5-HT5A、5-HT7是G蛋白共聚受体

    		K + , Na +
    Gamma-aminobutyric acid (GABA) GABA A and GABA C (ligand-gated ion channels) GABA B (G protein-coupled receptors) Cl - K +
    Histamine Histamine receptors (H1, H2, H3, H4) (G protein-coupled receptors)

    Neurotransmitter receptors can be gated ion channels that open or close through neurotransmitter binding, or they can be protein-linked receptors. Protein-linked receptors are not ion channels; instead, they cause a signal transduction that involves and other molecules (called second messengers) in the postsynaptic cell. Refer to the : Signal Transduction concept for more information about signal transduction mechanisms.
    ::神经感应器受体可以是打开或关闭的离子信道,通过神经感应器捆绑打开或关闭,也可以是蛋白质相联受体。 蛋白质相联受体不是离子通道;相反,它们引发信号感应,涉及后合成细胞中的信号感应和其他分子(称为第二送信员)。 参考:信号感应概念,以获得更多关于信号感应机制的信息。

    Neurotransmitter Reuptake
    ::神经中质存储器回录

    Many neurotransmitters are removed from the synaptic cleft by neurotransmitter transporters in a process called reuptake. Reuptake is the removal of neurotransmitters from the synapse by the presynaptic neuron. Reuptake happens after the neurotransmitters have transmitted a . Without reuptake, the neurotransmitter molecules might continue to stimulate or inhibit an action potential in the postsynaptic neuron. The process of release and reuptake of neurotransmitters is shown in Figure .
    ::许多神经传导器从神经传导器以神经传导器的神经突触器裂开处被清除,其过程被称为重新接受。重新接受是指通过预传导神经从神经突触器移开神经传导器。重新接受发生在神经传导器传输后。不重新接受,神经传导分子可能继续刺激或抑制后传导神经的动作潜力。神经传导器的释放和重新获取过程见图。

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    A synapse before and during reuptake. Neurotransmitter transporter proteins (also called reuptake pumps) release the neurotransmitters and also reuptake them from the synaptic cleft. Reuptake is a way of controlling the effect the neurotransmitters have on the postsynaptic cell.
    ::重新接受之前和期间的突触。 神经分质传输器蛋白( 也称为重新接受泵) 释放神经传送器, 并将它们从合成裂缝中重新吸收。 重新接受是控制神经传送器对后合成细胞的影响的一种方法。

    Reuptake is carried out by transporter that bind to the released transmitters and actively transport them across the plasma membrane and back into the presynaptic neuron. Reuptake is a form of recycling - the neuron takes back the released neurotransmitter for later use. The reuptake of neurotransmitters is the target of some types of medicine. For example, serotonin is a neurotransmitter that is produced by neurons in the brain. Serotonin is believed to play an important role in the regulation of mood, emotions, and appetite. After release into the synaptic cleft, serotonin molecules either attach to the serotonin receptors (called 5-HT receptors) of the postsynaptic neuron, or they attach to receptors on the surface of the presynaptic neuron that produced the serotonin molecules for reuptake. Medicines called selective serotonin reuptake inhibitors (SSRIs) block the reuptake of the neurotransmitter serotonin. This blocking action increases the amount of serotonin in the synaptic cleft, which prolongs the effect of the serotonin on the postsynaptic neuron. Some scientists hypothesize that decreased levels of serotonin in the brain are linked to clinical depression and other mental illnesses. So SSRI medications, such as sertraline and fluoxetine, are often prescribed for depression and anxiety disorders.
    ::与释放的发报机捆绑在一起的运输者进行重新接收,并积极将它们传送到血浆间膜中,然后运回先发性神经神经。 重新获取是一种循环利用形式, 神经元将释放的神经传输器带回以后使用。 重新接收神经传递器是某些种类药物的目标。 例如, 血清素是神经神经神经元生成的神经输解器产生的神经传递器。 据认为, 赛罗通宁在调控情绪、 情绪和食欲方面起着重要作用。 释放后, 血清分子要么附在血清受体( 称为5HT 受体) 后, 要么附在后再使用。 重新接收神经传递器是某些类型的药物。 药物在调控情绪、 情绪和胃食欲中, 血清中选择性的血清反应抑制器( SSRIs) 阻塞了神经调调试器的重新接收。 这种抑制作用往往会增加神经内分泌的神经内分泌的内分泌, 的神经内分泌的神经分泌的分泌的分泌作用。

    Another way that a neurotransmitter is removed from a synapse is digestion by an enzyme. At cholinergic synapses (where acetylcholine is the neurotransmitter), the enzyme acetylcholinesterase breaks down acetylcholine.
    ::在胆碱基突触中(乙酰胆碱是神经飘移剂),酶乙酰胆碱酯酶会分解乙酰胆碱酯酶。

    Neurotransmitters and Disease
    ::神经中继器和疾病

    Diseases that affect nerve can have serious consequences. A person with Parkinson's disease has a deficiency of the neurotransmitter dopamine. Progressive death of brain cells that produce dopamine increases this deficit, which causes tremors and a stiff, unstable posture. L-dopa is a chemical related to dopamine that, when given as a medicine, eases some of the symptoms of Parkinson’s disease. L-dopa acts as a substitute neurotransmitter, but it cannot reverse the disease.
    ::影响神经的疾病可以产生严重的后果。 患有帕金森病的人缺乏神经分质多巴胺。 生产多巴胺的脑细胞的逐渐死亡会增加这种赤字,从而导致颤抖和僵硬、不稳定的姿态。 L-dopa是一种与多巴胺有关的化学物质,如果作为药物使用,可以缓解帕金森病的某些症状。 L-dopa充当替代神经分质者,但无法扭转这一疾病。

    The soil Clostridium tetani produces a neurotoxin that causes the disease tetanus. The bacteria usually get into the body through an injury caused by an object that is contaminated with C. tetani spores, such as a puncture wound caused by stepping on a nail. The C. tetani neurotoxin blocks the release of the neurotransmitter GABA, which causes to relax after contraction. When the release of GABA is blocked, the muscle tissue does not relax and remains contracted. Tetanus can be fatal when it affects the used in . Thankfully, tetanus is treatable and can be prevented by vaccination .
    ::C. C. Tetani 神经毒素阻塞神经中继器的释放,导致收缩后放松。当GABA的释放被堵住时,肌肉组织不会松动,会继续萎缩。Tetani 螺旋体在影响使用时会致命。感恩的是,破伤风是可以治疗的,并且可以通过接种预防。

    Another bacterium, called Clostridium botulinum, produces a toxin that is occasionally found in preserved foods that have been improperly sterilized. The toxin causes a disease called botulism. Botulinum toxin blocks the release of the excitatory neurotransmitter acetylcholine. Blockage of acetylcholine causes the progressive relaxation of muscles because they are unable to contract. The resultant paralysis of the muscles used for breathing can be fatal unless the patient is treated with a respirator.
    ::另一种细菌,叫做肉毒杆菌,产生一种毒素,有时在被不当消毒的保存食品中发现。毒素造成一种叫做肉毒杆菌的疾病。肉毒杆菌毒素阻止了兴奋性神经毒素乙酰胆碱酯酶释放。乙酰胆碱的阻塞导致肌肉逐渐放松,因为肌肉无法收缩。用于呼吸的肌肉因此瘫痪,除非病人得到呼吸器的治疗,否则会致命。

    Synapses and Recent Research
    ::合成和近期研究

    Recent studies have found that electrical synapses are more common in the than were previously thought. An electrical synapse is a link between two neighboring neurons that is formed at a narrow gap between the pre and postsynaptic cells called a gap junction. At gap junctions, cells are about 3.5 nm from each other, a much shorter distance than the 20 to 40 nm distance that separates cells at chemical synapses.
    ::最近的研究发现,电气突触比以前想象的更为常见。 电突触是两个相邻神经元之间的连接,两个相邻神经元的形成是前与后后合成细胞之间的狭小距离,即所谓的“隔缝交界点 ” 。 在隔缝交界点,细胞相互之间大约为3.5 nm,距离比化学突触中分离细胞的20-40 nm距离要短得多。

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    Electrical synapses. Cell signaling at electrical synapses is much faster than signaling at chemical synapses. The image at the bottom left of the figure shows the location of gap junctions between cells.
    ::电突触。 电突触时的细胞信号比化学突触时的信号快得多。 图左下方的图像显示了单元格间隔点的位置 。

    Each gap junction has many channels that cross the plasma membranes of both cells, as is shown in  Figure . Gap junction channels are wide enough to allow ions and even medium sized molecules, like signaling molecules, to flow from one cell to the next. For example, when positive ions move through the channel into the next cell, the extra positive charges depolarize the postsynaptic cell.
    ::如图所示,每个空隙连接点有许多跨过两个细胞等离子膜的通道。空隙连接点的通道宽到足以让离子甚至中等分子(如信号分子)从一个细胞流向下一个细胞。例如,当正离子穿过通道进入下一个细胞时,额外的正电荷会使后合成细胞的极化。

    Signaling at electrical synapses is faster than the chemical signaling that occurs across chemical synapses. Ions directly depolarize the postsynaptic cell without the need for receptors to recognize chemical messengers, which occurs at chemical synapses. Such fast communication between neurons may indicate that, in some parts of the brain, large groups of neurons can work as a single unit to process information. Electrical synapses are numerous in the retina and cerebral cortex.
    ::电突触的信号比化学突触之间发生的化学信号更快。 离子直接分解后合成细胞,而不需要受体识别化学信使,这在化学突触中发生。 神经元之间的这种快速沟通可能表明,在大脑的某些部分,大量神经元可以作为一个单一的单位处理信息。 视网膜和脑皮层中的电突触很多。

    In addition to neurons, glial cells are an important part of the nervous system. The word glia means "glue" in Greek. Glial cells can be thought of as partners to neurons because they aid in the maintenance of , signal transduction, formation of myelin, and provide support and nutrition. There are far more glial cells than neurons, and it has been estimated that glial cells outnumber neurons by as many as 50:1. Nonetheless, the role of glial cells has been underestimated, but their role has recently begun to be appreciated more by researchers. The importance of neurons as the sole conductive cells of the nervous system, known as the neuron doctrine, has been questioned by recent research.
    ::除了神经元之外, 滑翔细胞是神经系统的一个重要部分。 希腊语中的“ 螺旋”一词的意思是“ 凝胶 ” 。 凝胶细胞可以被视为神经元的合作伙伴,因为它们有助于神经元的维护、 信号转换、 丝琳的形成, 以及提供支持和营养。 与神经元相比, 滑翔细胞的种类远多于神经元,据估计, 滑翔细胞的数量比神经元多50:1。 尽管如此, 滑翔细胞的作用被低估了, 但它们的作用最近开始受到研究人员更多的重视。 神经元作为神经系统的唯一导体细胞的重要性, 被称为神经学说, 受到最近研究的质疑。

     

     

    Summary
    ::摘要

    • In chemical synapses, neurotransmitters are sent across the synaptic cleft to pass signals from a neuron to the next cell. Afterwards, these neurotransmitters are returned to the presynaptic neuron in a process called reuptake.
      ::在化学突触中,神经传导器被发送到神经元裂缝的交叉口,从神经元传递信号到下一个细胞。随后,这些神经传导器被返回到预合成神经元,其过程被称为重新接受。
    • Dozens of neurotransmitters exist; some are excitatory and some are inhibitory.
      ::存在数十种神经传送器;有些是兴奋剂,有些是抑制剂。
    • Electrical synapses are significantly smaller than chemical synapses, and they transmit signals significantly faster.
      ::电突触比化学突触要小得多,它们传送信号的速度要快得多。

    Review
    ::回顾

    1. What is the fundamental difference between chemical and electric synapses?
      ::化学和电突触之间的根本区别是什么?
    2. Describe the process a neurotransmitter goes through when passing messages across a chemical synapse.
      ::描述神经传输器在通过化学突触传递信息时经历的过程。
    3. What happens in situations when nerve communication is hindered?
      ::当神经通讯受到阻碍时会发生什么情况?