我们为什么需要睡觉?

未能成功加载,请稍后再试
0/0

[ MUSIC] For many of us, the worst moment of every day goes something like this

[ ALARM CLOCK NOISE] That noise marks our daily return from the mysterious world that we call sleep.

We spend a third of our lives asleep, yet, other than the odd snapshot of a dream here and there, most of us have no idea what happens after we close our eyes. Luckily we're in good company, because there's also a lot scientists don't know about sleep too.

For a long time, it was just something that happened, everyone assumed that our brains were hitting the reset button and just turning off for a while. But in the past few decades it's become clear that sleep might be the single most important behavior that humans and other animals experience.

It might seem like we don't do much while we're sleep, but neuroscience tells a different story. Human sleep patterns are controlled by two competing networks of chemical and electrical signals in the brain.

During our waking hours, neurotransmitters released deep within our brain keep our cerebral cortex alert and primed for consciousness. But throughout the day, as our neurons break down ATP for energy, the byproduct adenosine builds up and activates sleep control neurons near the hypothalamus.

A special region in the center of our brain acts as our master biological clock. Light sensitive cells in our retinas feed signals deep into that brain region, training neurons to sync up with Earth's 24 hour cycle of day and night.

These circadian rhythms are the control switch that tells us when to feel sleepy or awake. As the world goes dark, this master switch tells our pineal gland to increase levels of the hormone melatonin in the bloodstream, sort of like a chemical lullaby.

Feelings of fatigue set in, body temperature lowers slightly, that heat loss is actually why many of us like to fall asleep with our feet sticking out of the covers, true story! Together all this neurochemistry sends one clear message to our bodies: when it's dark, it's time to go to bed.

Unfortunately, in modern times, darkness is increasingly rare. In the United States, 99 percent of people live in areas that meet standards for light pollution, and we've got one person to thank for that: Thomas Alva Edison.

下载全新《每日英语听力》客户端,查看完整内容