Wellness, Home & Lifestyle, Science & Tech

How Sleep Works

Matthew Walker

Lesson time 11:08 min

Matthew helps you identify your 24-hour “master clock” and how to understand it.

Students give MasterClass an average rating of 4.7 out of 5 stars

Topics include: Melatonin Misconceptions • Sleep’s Ebb and Flow


[MUSIC PLAYING] - There are ultimately two factors that will determine your alertness during the day and then also the transition to being sleep at night. The first of these two factors is called sleep pressure. From the moment that you woke up this morning, a chemical has been building up in your brain. That chemical is called adenosine. It's a chemical pressure. And the more of that adenosine that builds up, the sleepier that you feel. And then when we sleep, the brain actually removes and takes away all of that adenosine. And so after eight hours of good, healthy quality sleep we'll wake up feeling refreshed, and we feel alert and we can sustain that alertness throughout the following day. The second of those two factors is called the circadian rhythm. We all have a circadian rhythm, a 24 hour cycling rhythm. It almost looks like this sinusoidal wave that goes up and down, and your circadian rhythm is controlled by a center within your brain called the suprachiasmatic nucleus. And the suprachiasmatic nucleus or the 24 hour clock within our brain drums out a rise in activity throughout the morning, and it starts to peak just, sort of, before midday. And then it will sustain our activity throughout the afternoon, and then gradually as we're getting into the evening the circadian drive to be active will actually shift, and it will start to come down again. And then it will hit its lowest point some hours into our sleep cycle usually three to four hours after we've gone to bed. And then at that point, your circadian rhythm starts to swing back up again. And it will start to rise and peak just before we start to wake up. So we have these two factors then that help regulate when we're awake and when we're asleep, and we can plot those two things and it can help us understand how they interact. As we move towards the evening, now sleep pressure has continued to rise. It's starting to get to its peak. But your circadian rhythm is now starting to drop off. It's going on it's awesome downstroke, and so it's driving our rhythmic activity and the signal of alertness downwards. And we're getting this beautiful weight, this high level of sleepiness from sleep pressure. And we think, gosh, I'm tired. It's really time to go to bed. I'm ready to sleep. But how does the suprachiasmatic nucleus communicate its signal of activity and then darkness for sleep at night to the rest of the brain and the body? Well, the suprachiasmatic nucleus uses a hormone, a chemical called melatonin to circulate through the brain and the body to tell the brain and the body it's now night time. It's darkness. It's time to be asleep. And so your suprachiasmatic nucleus uses a variety of signals in addition to its own 24 hour rhythm to precisely get you to your 24 hour clock. One of the signals that it uses is daylight. And when you're suprachiasmatic nucleus is receiving daylight during the day through the retina in the eye and it streams back and directly...

About the Instructor

As a professor of neuroscience and psychology at UC Berkeley and the director of the Center for Human Sleep Science, Matthew Walker is an expert on sleep. In this class, he will illuminate the science behind sleep and teach you how to increase the quality and quantity of your sleep. Learn how to prevent sleep debt, navigate the effects of alcohol and caffeine, and improve your health. Your best sleep starts tonight.

Featured Masterclass Instructor

Matthew Walker

Neuroscience professor Matthew Walker teaches you the science of sleep and how to optimize it to better your overall health.

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