تدريب Shadowing: How does caffeine keep us awake? - Hanan Qasim - تعلم التحدث بالإنجليزية مع YouTube

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Over 100,000 metric tons of caffeine are consumed around the world every year.
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Over 100,000 metric tons of caffeine are consumed around the world every year.
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That's equivalent to the weight of 14 Eiffel Towers.
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Most of this caffeine is consumed in coffee and tea, but it's also ingested in some sodas, chocolate, caffeine pills, and even beverages labeled decaf.
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Caffeine helps us feel alert, focused, happy, and energetic, even if we haven't had enough sleep.
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But it can also raise our blood pressure, and make us feel anxious.
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It's the world most widely used drug.
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So how does it keep us awake?
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Caffeine evolved in plants where it serves a few purposes.
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In high doses, as it's found in the leaves and seeds of certain species, it's toxic to insects.
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But when they consume it in lower doses, as it's found in nectar, it can actually help them remember and revisit flowers.
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In the human body, caffeine acts as a stimulant for the central nervous system.
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It keeps us awake by blocking one of the body's key sleep-inducing molecules, a substance called adenosine.
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Your body needs a constant supply of energy, which it gets by breaking down a high-energy molecule called ATP.
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In the process, it liberates adenosine, ATP's chemical backbone.
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Neurons in your brain have receptors perfectly tailored to this molecule.
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When adenosine docks to these receptors, it activates a cascade of biochemical reactions that cause neurons to fire more sluggishly and slow the release of important brain-signaling molecules.
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In other words, you get sleepy.
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Caffeine is what's called an adenosine receptor antagonist.
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That means it derails this process of slowing your neurons down by blocking adenosine receptors.
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Caffeine and adenosine have a similar molecular structure, close enough that caffeine can wedge into the adenosine receptors, but not close enough to activate them.
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To summarize, adenosine inhibits your neurons.
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Caffeine inhibits the inhibitor, so it stimulates you.
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Caffeine can also boost positive feelings.
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In some neurons, the adenosine receptors are linked to receptors for another molecule called dopamine.
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One of dopamine's roles in the brain is to promote feelings of pleasure.
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When adenosine docks in one of these paired receptors, that can make it harder for dopamine to fit in its own spot, interrupting its mood-lifting work.
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But when caffeine takes adenosine's place, it doesn't have the same effect, and dopamine can slide in.
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There's evidence that caffeine's effects on adenosine and dopamine receptors can have long-term benefits, too, reducing the risk of diseases like Parkinson's, Alzheimer's, and some types of cancer.
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Caffeine can also ramp up the body's ability to burn fat.
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In fact, some sports organizations think that caffeine gives athletes an unfair advantage and have placed limits on its consumption.
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From 1972 until 2004, Olympic athletes had to stay below a certain blood-caffeine concentration to compete.
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Of course, not all of caffeine's effects are so helpful.
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It might make you feel better and more alert, but it can also raise your heart rate and blood pressure, cause increased urination or diarrhea, and contribute to insomnia and anxiety.
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Plus, the foods and beverages caffeine is found in have their own impacts on your body that have to be taken into account.
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Your brain can adapt to regular consumption of caffeine.
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If your adenosine receptors are perpetually clogged, your body will manufacture extra ones.
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That way, even with caffeine around, adenosine can still do its job of signaling the brain to power down.
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That's why you may find you need to consume more and more caffeine to feel as alert.
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There are more and more adenosine receptors to block.
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It's also why if you suddenly quit caffeine, you may experience an unpleasant withdrawal.
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With plenty of receptors and no competition, adenosine can work overtime, causing symptoms like headaches, tiredness, and depressed moods.
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But in a few days, the extra adenosine receptors will disappear, your body will readjust, and you'll feel just as alert as ever, even without an infusion of the world's most popular stimulant.
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المفردات والعبارات الأساسية

  • كافيين - Caffeine
  • الينوزين - Adenosine
  • مستقبلات - Receptors
  • الجهاز العصبي المركزي - Central Nervous System
  • التحفيز - Stimulation
  • مشاعر السعادة - Feelings of pleasure
  • الاعتماد على الكافيين - Caffeine dependence
  • الأعراض الانسحابية - Withdrawal symptoms

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