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Hi everyone~~
从今天起，我准备每周一推出一个大家感兴趣的Topic，围绕这个topic提供速度、越障、听力(video/audio)素材。如果你对科学技术、医药健康领域的某个话题感兴趣，或者有好的题材、资料推荐，欢迎联系我。
基于lovecloris,神猴,饭饭等童鞋的意见（在此表示谢意），本期隆重推出——生物钟(circadian clock)。让我们一起来学习这背后的生物学知识，合理作息，健康生活，高效学习
大家做完阅读训练后，来练下听力吧（暴力推荐！）：
Christmas Lectures 1998: Nancy Rothwell - Times of our lives
http://richannel.org/christmas-lectures-1998-nancy-rothwell--times-of-our-lives,
The Royal Institute每年圣诞会举行面向青少年的科普讲座，这是1998年的其中一期，就是这个话题…这个演讲超赞，有好多现场演示实验….
跟这个1998系列演讲配套的publication我也上传了，见附件。同样隆重推荐！是演讲者Professor Nancy Rothwell写的，深入浅出，图文并茂。本来我是想将它作为阅读材料的，但可惜这个pdf里不支持文本操作….感兴趣的同学当further reading吧~
Enjoy!
速度
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Your Internal Sleep Clock
Circadian rhythm isn't a new type of dance step; it has to do with our internal sleep clock. Learn about how your sleep clock works.
Your pattern of sleep and waking is run by the body’s internal sleep clock. Governed by light, your internal sleep clock tells you when it’s time to fall asleep and wake up. Your internal sleep clock, otherwise known as the circadian rhythm, runs on a 24-hour cycle. Disruptions to the circadian rhythm and your internal sleep clock can deprive you of sleep. This, in turn, can cause health problems by disrupting all the physiological, biological, and chemical functions that are affected by sleep.
Your sleep clock is influenced by light signals to the retina (the back of the eye), neural (nerve) pathways to a specific part of the brain that govern wakefulness and sleep, exhaustion and the length of time you've been awake, your natural circadian rhythm, and daylight-saving time and seasons.
Your Internal Sleep Clock: How It Works
Light comes into the eye through the retina, travels down a neural pathway into a part of the brain called the suprachiasmatic nucleus, and signals that it’s time to be awake, says Lisa Shives, MD, a sleep specialist at Northshore Sleep Medicine in Evanston, Ill., and spokesperson for the American Academy of Sleep Medicine. “That starts a whole cascade of neurotransmitters that wake you up and are involved in wakefulness.”
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Sleep is also governed by conflicting forces. Dr. Shives says that light is one of the most powerful signals that tell your body to remain awake — however, a signal saying "stay asleep" (especially if you're sleep-deprived) can override the fact that sunlight is shining all around you.
“One of the most powerful cues that you should sleep is what we call the homeostatic force that builds up," says Shives. The longer you are awake, the more likely you are to get tired, so the urge to sleep builds over a 16-hour period. This need for sleep waxes or wanes throughout the day.
Your Internal Sleep Clock: Circadian Rhythm
The study of sleep is a relatively young field; research began in the United States during the 1960s and 1970s. The first biological clock was identified in fruit flies during the early '70s. Clinically, sleep only became a relevant subspecialty in the 1980s but "didn’t officially achieve subspecialty status in the academic hierarchies of American medicine until 2006,” Shives says.
A circadian rhythm refers to the body’s internal sleep clock and all the physiological functions that revolve around it. Circadian rhythm "derives its name from Latin; it means ‘around the day.’ It’s a fancy term for the fact that human beings have an internal 24-hour clock,” says Shives.
Back in the 1930s, researchers conducted “cave studies” — volunteers were sequestered in caves and deprived of natural light — and speculated that the body’s internal clock revolved around a 25-hour cycle, says Shives. “But more recent studies show that it’s closer to 24 hours.”
If you listen to your body, you will be in tune with your circadian rhythm. Don't hit the metaphorical snooze button and ignore your internal clock — it will keep you awake and productive or relaxed and ready for bed when you need to be.
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10 Tips to Reset Your Internal Clock
People with delayed sleep phase syndrome have trouble getting up in the morning and going to bed at the right time. The body's internal clock can be reset, however, with the help of a few sleep strategies.
Who doesn’t know at least one night owl who stays up until 1 or 2 a.m. every night, only to struggle to get out of bed the next morning to make it to school or work on time? To those on the outside, these people may seem undisciplined or even lazy, but in reality they may simply be at the mercy of their genes.
Each of us has an individual sleep schedule kept on track by our circadian rhythms, which is biological activity regulated by body temperature, sleep cycle, hormone secretion, and external factors like light and darkness. Our internal clock is located in a part of the brain called the suprachiasmatic nuclei (SCN) of the hypothalamus.
“The ‘master’ circadian clock in the SCN receives light information from the retina in the eye, which sends the information to several parts of the brain, including the pineal gland, responsible for the release of melatonin,” says Rochelle Zozula, PhD, coordinator at Capital Health’s Center for Sleep Medicine in Hamilton, N.J. “Light will suppress the production of melatonin, which is directly involved in the process of sleep initiation.”
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Sleep Schedule Variations
For some people, however, despite these physical and environmental cues, their internal clocks do not sync up with the world’s expectations. About 1 percent of adults have advanced sleep phase disorder — they go to bed early, from 6 p.m. to 9 p.m. and wake up early, between 1 a.m. and 5 a.m. While inconvenient, many can still function well within society.
Other people, however, are not so lucky. Estimates are that as many as 15 percent of teenagers and adults may experience the flip side of advanced sleep phase disorder — delayed sleep phase syndrome (DSPS).
“DSPS is a circadian rhythm disorder associated with an inability to fall asleep at the individual’s desired time [typically they fall asleep several hours later] and an inability to wake up at the desired time,” says Zozula. “Due to the individual’s daytime obligations, a person with DSPS may be forced to wake up earlier and go against their natural circadian tendency.” This can lead to chronic sleep deprivation, increased psychological stress (almost 50 percent of people with DSPS also experience depression), and even obesity. Some recent research indicates that your body clock may also affect your risk for Alzheimer’s and schizophrenia — not to mention the fact that it can cause daytime sleepiness, which increases the risk of motor vehicle and workplace accidents.
10 Tips for Resetting Your Internal Clock
Fortunately, there are some things people with delayed sleep phase syndrome can do to help reset their biological clocks:
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1. Schedule a doctor visit. See a doctor if your sleep schedule is interfering with job and other responsibilities.
2. Adjust your bedtime. Try slowly scaling back your bedtime until you are at the desired hour (often you may need help from a physician with this).
3. Do not nap. Even if you feel tired, napping can interfere with going to sleep at night.
4. Do not sleep in. Getting up at the same time every day is important in maintaining a functioning sleep schedule.
5. Be strict about your sleep schedule. Once you have reached a workable bedtime, don’t allow yourself to stray from it. Even one late night can ruin the progress you’ve made.
6. Try light therapy. Consider “bright-light therapy,” a timed exposure to bright light in the morning. This should be done under a doctor’s care, as light intensity, timing, duration, and distance from the light source all need to be specific.
7. Avoid night light. According to research from Rush University Medical Centre in Chicago, exposure to evening light shifts your body clock to a later schedule. When possible, avoid bright and outdoor light close to bedtime and keep your surroundings dim at night.
8. Try melatonin with monitoring by a health professional. This therapy might help, but there could be side effects in some people as well as contraindications with other medications, both prescribed and over-the-counter, so work with your doctor on this strategy.
9. Avoid eating or exercising too close to bedtime. Also watch out for caffeine and nicotine, both of which are stimulants.
10. Set the mood. Finally, create a relaxing bedtime routine with a warm bath and relaxing music, for instance. Make sure your bed is comfortable, the room is dark, and the temperature is not too warm.
Changing your sleep schedule is not easy when you have delayed sleep phase syndrome, but with the proper discipline it can be done.
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速度阅读文来自：
http://www.everydayhealth.com/sleep/101/circadian-rhythms.aspx
http://www.everydayhealth.com/sleep/insomnia/resetting-your-clock.aspx
越障
THE TIME OF OUR LIVES
Take the red-eye from California to New York, and you'll experience firsthand the effects of your body's internal clock. If you feel drowsy or 'jet lagged' after the flight, it's because there's been a disruption to your natural circadian rhythms. Your internal clock is saying it's 3 a.m., but outside, it's time for breakfast.
Living organisms evolved an internal biological clock, called the Circadian rhythm, to help their bodies adapt to the daily cycle of day and night (light and dark) as the Earth rotates every 24 hours. The term 'circadian' comes from the Latin words for about (circa) a day (diem).
Circadian rhythms are controlled by "clock genes" that carry the genetic instructions to produce proteins. The levels of these proteins rise and fall in rhythmic patterns. These oscillating biochemical signals control various functions, including when we sleep and rest, and when we are awake and active. Circadian rhythms also control body temperature, heart activity, hormone secretion, blood pressure, oxygen consumption, metabolism and many other functions.
Daily cycles also regulate the levels of substances in our blood, including red blood cells, blood sugar, gases and ions such as potassium and sodium. Our internal clocks may even influence our mood, particularly in the form of wintertime depression known as seasonal affective disorder (SAD).
A biological clock has three parts: a way to receive light, temperature or other input from the environment to set the clock; the clock itself, which is a chemical timekeeping mechanism; and genes that help the clock control the activity of other genes.
In the last few decades, scientists have discovered the genes responsible for running the internal clocks: period (per), clock (clk), cycle (cyc), timeless (tim), frequency (frq), doubletime (dbt) and others.
Genes that control circadian rhythms have been found in organisms ranging from people to mice, fish, fruit flies, plants, molds and even single-celled, blue-green algae known as cyanobacteria.
Where is the body's master clock?
The master circadian clock that regulates 24-hour cycles throughout our bodies is found in a region called the suprachiasmatic nuclei (SCN) in the hypothalamus of the brain. The SCN is made up of two tiny clusters of several thousand nerve cells that "tell time" based on external cues, such as light and darkness. The SCN regulates sleep, metabolism, and hormone production.
How important is the SCN? When a rat's SCN is removed, its daily cycle of activity and sleep is disrupted. The SCN still produces rhythmic chemical signals, even after it has been removed from an animal's brain.
The SCN is believed to synchronize "local" clocks in organs and tissues throughout the body, either through hormones or changes in body temperature. Gene-operated clocks independent of the brain's master pacemaker have been found in the liver, lung, testis, connective tissue and muscle.
One example of how a local clock works comes from fruit flies. Cells in their antennae display a circadian rhythm independent of the brain's master clock. The antennae oscillations correlate with sense of smell, which is more sensitive at night than during the day.
How many hours are in a biological clock?
The human circadian rhythm is not exactly 24 hours - it's actually 10 to 20 minutes longer. Other species have circadian rhythms ranging from 22 to 28 hours. The biological clock in living organisms keeps working even when the organism is removed from natural light. Without daylight, the biological clock will eventually start running on its own natural cycle. But as soon as morning light hits the eyes, the clock will reset to match the earth's 24-hour day.
Why aren't organisms' internal clocks exactly 24 hours long? A computer simulation suggests competition for food and other resources is most intense among species with 24-hour cycles. If you eat at the same time as everyone else, you're less likely to get your share. Our slightly out of sync internal clock may have evolved to help us survive the competition.
Biological clocks also play a role in longer cycles such as hibernation, bird migrations and even annual changes in the color of a hamster's coat. When the animal brain records longer days in the spring and shorter days in the fall, it triggers hormone secretion that influences these events.
How do clock genes work?
Clock genes send out instructions that dictate protein production. The genes interact with each other to produce daily fluctuations in the amount of proteins produced.
The central player is the per gene, which produces the PER protein. PER levels are highest during early evening and lowest early in the day.
In fruit flies, the clk and cyc genes work together to activate the per and tim genes so they produce proteins. Those proteins, PER and TIM, then combine and slowly accumulate in the cell nucleus, where they slow down the clk and cyc genes, which in turn deactivates per and tim and stops further production of the PER and TIM proteins. As PER and TIM diminish, clk and cyc kick into action again, starting a new daily cycle.
The cycle is a bit more complicated in mammals, in which clk works with a gene named Bmal1 instead of with cyc. Also, mammals have three versions of the Per gene.
Other clock genes also play a role. In the fruit fly, the dbt gene produces a protein that helps break down the per protein to keep it at just the right levels for the particular time of day. A gene named pdf for pigment-dispersing protein produces a protein that appears to tell the rest of the fly's body what time it is according to the master clock in its brain.
How do clock genes influence sleep?
Clock genes normally keep us awake during the day and asleep at night. But when a clock gene mutates, it can disrupt the normal sleep cycle.
A mutant hPer2 gene is responsible for an inherited sleep pattern known as "familial advanced sleep phase syndrome" (FASPS). People with FASPs are "morning larks" who usually get sleepy by 7 p.m. and wake up around 2 a.m. Another sleep condition, called "delayed sleep phase syndrome," has the opposite effect, turning people who have it into extreme night owls. They fall asleep very late and have trouble waking up in the morning. Delayed sleep phase syndrome has been linked to the hPer3 gene.
Any student who has studied during an "all-nighter" knows the circadian clock isn't the only sleep influencer. Our need for sleep also plays a role. When rats are awake and vigilant, their brain's master clock is more active. When rats are deprived of sleep, their master-clock doesn't respond normally during different times of day.
Sunlight resets the internal biological clock every day so it is synchronized with a 24-hour day. If you lived in an underground bunker under constant artificial light, you would continue to follow an approximately 24-hour sleep-wake pattern, but your cycles would slowly get out of phase with actual daytime and nighttime.
Air travel to a distant time zone can also disrupt normal cycles. The resulting jet lag is both a disconnect between local time and your body's time, and a disconnect between your brain's master clock and local clocks in tissues throughout your body. Once you arrive at your destination, the change in daylight hours will "entrain" or reset your internal clock, but it will take a few days to get rid of the jet lag.
What are the health implications of clock genes?
Understanding exactly how clock genes work may help scientists develop new medicines that adjust or reset the human biological clock to treat the ill effects of jet lag, night shift work or wintertime depression. Clock genes may also offer clues to sleep disorders such as narcolepsy, which makes people feel sleepy during the day.
Our internal clock controls hormone levels, which can affect the way our bodies respond to certain medications. Better knowledge of circadian rhythms may improve the effectiveness of medications by revealing the best times to take them.
Light is used to treat people with seasonal affective disorder, the form of depression that surfaces during the shorter days of winter. Some research indicates light therapy is more effective if it is synchronized with a patient's internal clock, which is why some patients are treated with exposure to bright light early in the morning. Bright light also has been used to help people adjust to jet lag and to changes in work shifts.
Clock genes may some day help scientists treat cancer. At least eight clock genes are known to coordinate normal functions such as cell proliferation (which is uncontrolled in cancer) and cell suicide (which fails to occur in tumor cells). One study found that without the mPer2 gene, mouse cells with damaged DNA become cancerous instead of committing cell suicide. If clock genes actually play a role in cancer, they could be a target for new drugs that might disrupt the "clock" to halt the cancer.
Aging may disrupt the synchronization of local clocks throughout the body and their synchronization with the brain's master timekeeper. One study found that electrical activity in the internal clocks of aging rats was not as regular as in younger rats, so the aging rats did what elderly people often do: they napped during the day.
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摘自：http://learn.genetics.utah.edu/content/begin/dna/clockgenes/ |
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发表于 2012-3-5 09:53:30
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楼主
发表于 2012-3-5 11:13:14
baby你太好啦~~
