All living organisms experience rhythmic changes, which tend to coincide with seasonal or daily environmental changes. Most organisms (including humans) have internal biological clocks these are called endogenous pacemakers, which are influenced by external environmental factors called exogenous zeitgebers, to control these periodic changes.
所有的生物体都经历着节律性的变化，这些变化往往与季节性或日常环境变化相吻合。大多数生物体（包括人类）都有内部生物钟，这些生物钟被称为内源性起搏器，它们受到外部环境因素的影响，被称为外源性起搏器，以控制这些周期性变化。
These are rhythms lasting 'about one day'. The best example of a circadian rhythm is the sleep-wake cycle, associated with which are many cyclical changes with active and dormant periods, for example body temperature and urine production. These rhythms allow animals to prepare for predictable daily environmental changes, such as night and day.
这些是持续 "大约一天 "的节奏。昼夜节律的最好例子是睡眠-觉醒周期，与之相关的是许多活跃期和休眠期的周期性变化，例如体温和尿液分泌。这些节律使动物能够为可预测的日常环境变化做好准备，如夜晚和白天。
Research has involved participants being deprived of possible zeitgebers ('time-givers') like sunrise and sunset, temperature changes during a 24 hour period and wristwatches! Participants tend to maintain a cyclical rhythm but it extends to about 25 hours (Siffre, 1975).
研究表明，参与者被剥夺了可能的媒介（"时间提供者"），如日出和日落、24小时内的温度变化和手表！参与者倾向于保持周期性的节奏。参与者倾向于保持一个周期性的节奏，但它延伸到大约25个小时（Siffre, 1975）。
So, endogenous pacemakers can keep a rhythm but exogenous zeitgebers are needed to stick to a 24 hour rhythm.
因此，内源性起搏器可以保持一个节奏，但要坚持24小时的节奏则需要外源性的zeitgebers。
Where is the brain's internal clock? 大脑的内部时钟在哪里？
The suprachiasmatic nucleus (SCN) in the hypothalamus is a bundle of nerves with an inbuilt circadian rhythm. This is a particularly important endogenous pacemaker. Evidence for this comes from studies in which the SCN has been cut in hamsters to result in disrupted circadian rhythms (Menaker et al., 1978).
下丘脑中的上核（SCN）是一束具有内在昼夜节律的神经。这是一个特别重要的内源性起搏器。这方面的证据来自于一些研究，即切断仓鼠的SCN，导致昼夜节律紊乱（Menaker等人，1978）。
What keeps the brain to a 24 hour rhythm? 是什么使大脑保持24小时的节律？
Without light the brain's day would be 25 hours long (a free-running clock). Light is a very important zeitgeber - flashes of light are enough to 'reset' the internal clocks of animals living in the dark (Aschoff, 1979). One blind man needed to take stimulant and tranquilizing drugs to maintain a 24 hour cycle!
如果没有光，大脑的一天将是25个小时（一个自由运行的时钟）。光是一个非常重要的媒介--闪光足以 "重置 "生活在黑暗中的动物的内部时钟（Aschoff，1979）。一个盲人需要服用兴奋剂和镇静剂来维持24小时的周期！这就是光。
How does light ensure mammals maintain a 24 hour rhythm? 光线如何确保哺乳动物保持24小时的节奏？
The pineal gland in the brain converts the neurotransmitter serotonin into the hormone melatonin.
大脑中的松果体将神经递质5-羟色胺转换为激素褪黑激素。
Melatonin is released into the blood stream and causes rhythmic changes around the body. Although the need for sleep is not affected by light, melatonin plays a role in the coordination of the sleep-wake cycle.
褪黑激素被释放到血流中，引起身体周围的节律性变化。虽然睡眠的需要不受光线的影响，但褪黑激素在睡眠-觉醒周期的协调中起着作用。
These are rhythmic cycles with a period of less than one day. Examples include levels of alertness throughout the day and the cycle of brain activity during sleep.
这些是周期小于一天的节律性周期。例子包括全天的警觉性水平和睡眠期间的大脑活动周期。
The use of an electroencephalogram (EEG) can show the electrical activity of the brain. There are different patterns of activity at different times during sleep (Rechtschaffen & Kales, 1968).
使用脑电图（EEG）可以显示大脑的电活动。在睡眠期间，不同时间有不同的活动模式（Rechtschaffen & Kales, 1968）。
The table below gives some information about the different stages of sleep 下表给出了一些关于睡眠的不同阶段的信息:
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Stage of sleep 睡眠的阶段: |
Characteristics 特征: |
EEG trace 脑电图追踪: |
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Non-REM Stage 1. 非REM阶段1 |
Theta waves, slow rolling eyes, easily awoken, duration: about 10 minutes. Theta波，眼睛缓慢滚动，容易被唤醒，持续时间：约10分钟。 |
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Non-REM Stage 2. 非REM阶段2 |
Irregular trace, some theta waves, sleep spindles and K-complexes, duration: about 15 minutes. 不规则的痕迹，一些θ波、睡眠主轴和K-复合体，持续时间：约15分钟。 |
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Non-REM Stage 3. 非REM阶段3 |
Deep sleep, high amplitude delta waves (<50% of trace). 深度睡眠，高振幅delta波（<50%的痕迹）。 |
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Non-REM Stage 4. 非REM阶段4 |
Deep sleep, high amplitude delta waves (>50% of trace). 深度睡眠，高振幅delta波（>50%的痕迹）。 |
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REM. |
Beta waves, paralysis, eye movement, vivid and visual dreaming. β波、麻痹、眼球运动、生动和视觉的梦境。 |
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Here is a graph of a typical night's sleep 下面是一个典型的夜间睡眠图表 :
Here are some important points to note 这里有一些需要注意的要点:
- Each cycle lasts for about 90 minutes. 每个周期持续约90分钟。
- The amount of Stage 3 & 4 sleep decreases each cycle. 第三和第四阶段的睡眠量在每个周期都会减少。
- The amount of REM sleep increases each cycle. 快速眼动睡眠的数量在每个周期都会增加。
These are rhythms with a period of greater than a day. The menstrual cycle is an example of an infradian rhythm. Infradian rhythms that occur as a result of seasonal changes, for example, migration and hibernation are called circannual rhythms.
这些是周期大于一天的节律。月经周期就是一个次日节律的例子。由于季节性变化而发生的非昼夜节律，例如迁徙和冬眠，被称为环年节律。
The menstrual cycle has a period of about 28 days, although the timing can vary according to environmental factors. For example, menstrual cycles may become synchronised if women spend a lot of time together, possibly due to the effect of pheromones passing between them.
月经周期的周期约为28天，尽管时间可以根据环境因素而变化。例如，如果妇女经常在一起，月经周期可能会变得同步，这可能是由于她们之间传递信息素的影响。
Circannual rhythms are under the control of body clocks. But, again, light makes them run on time by influencing melatonin levels.
周期性节律是在身体时钟的控制下进行的。但是，同样，光线通过影响褪黑激素水平使它们按时运行。
It is how much light or the daylength, (known as the photoperiod) that provides the useful information about the changes in the seasons; lengthening days mean Spring and Summer are coming and shortening days predict the onset of Autumn and Winter.
是多少光照或日照时间（称为光周期）提供了关于季节变化的有用信息；日照时间延长意味着春天和夏天的到来，日照时间缩短预示着秋天和冬天的到来。
In humans, the increased levels of melatonin in autumn appears to lead to a form of depression known as SAD (seasonal affective disorder). This can be treated by exposure to a bright light for several hours per day.
在人类中，秋季褪黑激素水平的增加似乎导致了一种被称为SAD（季节性情感障碍）的抑郁症。这可以通过每天暴露在明亮的光线下几个小时来治疗。
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