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  • How do nerves work?

    神經是如何運作呢?

  • Are nerves simply the wires in the body

    難道神經就只像是

  • that conduct electricity, like the wires in the walls of your home

    牆壁裡的線路或 連接你電腦的電線一樣

  • or in your computer?

    傳導電流嗎?

  • This is an analogy often made,

    這是以個常用的比喻,

  • but the reality is that nerves have a much more complex job in the body.

    但事實上人體內 神經的功能卻是複雜許多。

  • They are not just the wires, but the cells that are the sensors,

    它們不只是傳遞線路, 有些細胞是感受器,

  • detectors of the external and internal world,

    負責偵測身體內外的變化;

  • the transducers that convert information to electrical impulses,

    有些像是轉換器, 接著將訊息轉化為電能脈衝;

  • the wires that transmit these impulses,

    有些像電線, 傳遞這些脈衝;

  • the transistors that gate the information

    有些像是電晶體般是訊號的閘道,

  • and turn up or down the volume-

    並能調整其強度;

  • and finally, the activators that take that information

    最後,動器接受到訊號

  • and cause it to have an effect on other organs.

    並對其他器官產生影響。

  • Consider this. Your mother gently strokes your forearm

    想想這個吧: 你媽媽輕拍你的手臂,

  • and you react with pleasure.

    而你感到快樂。

  • Or a spider crawls on your forearm and you startle and slap it off.

    或蜘蛛爬到你手臂上, 你嚇了一跳後把牠拍開。

  • Or you brush your forearm against a hot rack while removing a cake from the oven

    或當你把蛋糕拿出烤爐時, 你的前臂擦過上面高溫的鐵架,

  • and you immediately recoil.

    讓你立刻往後縮了一下。

  • Light touch produced pleasure, fear, or pain.

    輕觸產生了愉快、害怕或是疼痛。

  • How can one kind of cell have so many functions?

    一種細胞怎麼包含這麼多功能呢?

  • Nerves are in fact bundles of cells called neurons

    事實上神經是由一大叢 被稱為神經元的細胞組成

  • and each of these neurons is highly specialized to carry nerve impulses,

    而每一個神經元都會 對應到專一的神經脈衝。

  • their form of electricity,

    這種脈衝是以電的形式進行。

  • in response to only one kind of stimulus, and in only one direction.

    只針對一種刺激反應, 並只能將訊號傳往單一方向。

  • The nerve impulse starts with a receptor,

    神經脈衝始於受器。

  • a specialized part of each nerve,

    受器是神經細胞上特殊的部位,

  • where the electrical impulse begins.

    也是電能脈衝起始的地方。

  • One nerve's receptor might be a thermal receptor,

    神經細胞的受器可能是一個溫度感受器,

  • designed only to respond to a rapid increase in temperature.

    專門負責感應快速升高的溫度。

  • Another receptor type is attached to the hairs of the forearm,

    另外一種受器依附在前臂的毛髮上,

  • detecting movement of those hairs, such as when a spider crawls on your skin.

    偵測毛髮的震動, 例如:蜘蛛在皮膚上的爬行。

  • Yet another kind of neuron is low-threshold mechanoreceptor,

    有另外一種閾值較低的機械性受器, (譯注:閾值指是刺激受器、產生脈衝訊號的基準)

  • activated by light touch.

    它們會被輕觸啓動。

  • Each of these neurons then carry their specific information:

    每一種神經元傳遞特殊的訊息:

  • pain, warning, pleasure.

    疼痛、警覺、愉悅。

  • And that information is projected to specific areas of the brain

    而這些訊號藉由電能脈衝,

  • and that is the electrical impulse.

    投射到腦部特殊的區域。

  • The inside of a nerve is a fluid that is very rich in the ion potassium.

    在神經細胞中的液體含有高濃度的鉀離子。

  • It is 20 times higher than in the fluid outside the nerve

    在神經細胞內 鉀離子濃度是胞外的 20 倍。

  • while that outside fluid has 10 times more sodium than the inside of a nerve.

    而神經細胞外 鈉離子濃度是胞內的 10 倍

  • This imbalance between sodium outside and potassium inside the cell

    神經細胞內外鈉、鉀離子的不平衡

  • results in the inside of the nerve having a negative electrical charge

    導致神經細胞內相較於

  • relative to the outside of the nerve,

    胞外帶有約

  • about equal to -70 or -80 millivolts.

    -70 或 -80 毫伏特的電位能。

  • This is called the nerve's resting potential.

    這稱為神經的靜止電位。

  • But in response to that stimulus the nerve is designed to detect,

    在神經細胞接受到特定的刺激時,

  • pores in the cell wall near the receptor of the cell open.

    受器附近細胞的 細胞膜上通道會開啓。

  • These pores are specialized protein channels

    這些孔洞是特殊的蛋白質通道,

  • that are designed to let sodium rush into the nerve.

    它們可以讓鈉離子進入神經細胞。

  • The sodium ions rush down their concentration gradient,

    因為濃度差異,鈉離子會快速地湧入細胞,

  • and when they do, the inside of the nerve becomes more positively charged-

    這會讓細胞內的電位能偏向正電 ——

  • about +40 millivolts.

    大約 +40 毫伏特。

  • While this happens, initially in the nerve right around the receptor,

    這會先發生在受器附近的神經細胞,

  • if the change in the nerve's electrical charge is great enough,

    一但改變發生時, 如果神經細胞中電位能變化

  • if it reaches what is called threshold,

    達到閾值,

  • the nearby sodium ion channels open, and then the ones nearby those,

    鄰近的鈉離子通到就會開啓, 並促成下一組通道的開啓,

  • and so on, and so forth,

    並依此類推。

  • so that the positivity spreads along the nerve's membrane

    所以正電訊號就可以 在神經細胞膜上傳遞

  • to the nerve's cell body

    到細胞本體,

  • and then along the nerve's long, thread-like extension, the axon.

    然後傳向一個 長線狀的突出,這叫軸突。

  • Meanwhile, potassium ion channels open,

    在此同時,鉀離子通到會開啓,

  • potassium rushes out of the nerve,

    換鉀離子衝出神經細胞,

  • and the membrane voltage returns to normal.

    並讓膜電位回覆正常。

  • Actually, overshooting it a bit.

    事實上,會超過正常一點點。

  • And during this overshoot,

    在電位能低於正常值時

  • the nerve is resistant to further depolarization- it is refractory,

    神經較不容易被活化, 這被稱為「不反應期」

  • which prevents the nerve electrical impulse from traveling backwards.

    這防止神經脈衝往回傳遞。

  • Then, ion pumps pump the sodium back back out of the nerve,

    再來,離子幫浦將 鈉離子汲出神經細胞外

  • and the potassium back into the nerve,

    再將鉀離子運回細胞,

  • restoring the nerve to its normal resting state.

    使細胞回覆到正常的靜止電位。

  • The end of the nerve, the end of the axon,

    在神經細胞的末梢, 也就是軸突的尾端,

  • communicates with the nerve's target.

    會負責傳遞訊號給下一個標的。

  • This target will be other nerves in a specialized area of the spinal cord,

    它的標的可能是 一個位於脊椎的神經細胞,

  • to be processed and then transmitted up to the brain.

    那裡的神經細胞可以 處理並傳遞訊號給腦部。

  • Or the nerve's target may be another organ, such as a muscle.

    神經的標的也有可能是某個組織, 例如:肌肉組織。

  • When the electrical impulse reaches the end of the nerve,

    當神經脈衝到達細胞末端時,

  • small vesicles, or packets, containing chemical neurotransmitters,

    一些的囊泡,也可說是 包含化學傳導物質小包裹,

  • are released by the nerve and rapidly interact with the nerve's target.

    會被神經細胞釋放, 並快速的和其標的作用,

  • This process is called synaptic transmission,

    這過程就稱為突觸傳導。

  • because the connection between the nerve and the next object in the chain

    這是因為連接神經和標的

  • is called a synapse. And it is here, in this synapse,

    被稱為突觸。而也是在突觸這裡,

  • that the neuron's electrical information can be modulated,

    神經脈衝可以被調整、

  • amplified,

    放大、

  • blocked altogether

    阻斷

  • or translated to another informational process.

    或者轉換成另一種訊號處理。

How do nerves work?

神經是如何運作呢?

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B2 中高級 中文 TED-Ed 神經 細胞 離子 脈衝 訊號

【TED-Ed】神經是如何工作的?- 艾略特-克雷恩 (【TED-Ed】How do nerves work? - Elliot Krane)

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    稲葉白兎 發佈於 2021 年 01 月 14 日
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