Introduction 簡介
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.
所有的生物體都經歷着節律性的變化，這些變化往往與季節性或日常環境變化相吻合。大多數生物體（包括人類）都有內部生物鐘，這些生物鐘被稱為內源性起搏器，它們受到外部環境因素的影響，被稱為外源性起搏器，以控制這些周期性變化。
Circadian rhythms 晝夜節律
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.
這些是持續 "大約一天 "的節奏。晝夜節律的最好例子是睡眠-覺醒周期，與之相關的是許多活躍期和休眠期的周期性變化，例如體溫和尿液分泌。這些節律使動物能夠為可預測的日常環境變化做好準備，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，參與者被剝奪了可能的媒介（"時間提供者"），如日出和日落、24小時內的溫度變化和手錶！參與者傾向於保持周期性的節奏。參與者傾向於保持一個周期性的節奏，但它延伸到大約25個小時（Siffre, 1975）。
So, endogenous pacemakers can keep a rhythm but exogenous zeitgebers are needed to stick to a 24 hour rhythm.
因此，內源性起搏器可以保持一個節奏，但要堅持24小時的節奏則需要外源性的zeitgebers。
Where is the brain's internal clock? 大腦的內部時鐘在哪裡？
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).
下丘腦中的上核（SCN）是一束具有內在晝夜節律的神經。這是一個特別重要的內源性起搏器。這方面的證據來自於一些研究，即切斷倉鼠的SCN，導致晝夜節律紊亂（Menaker等人，1978）。
What keeps the brain to a 24 hour rhythm? 是什麼使大腦保持24小時的節律？
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!
如果沒有光，大腦的一天將是25個小時（一個自由運行的時鐘）。光是一個非常重要的媒介--閃光足以 "重置 "生活在黑暗中的動物的內部時鐘（Aschoff，1979）。一個盲人需要服用興奮劑和鎮靜劑來維持24小時的周期！這就是光。
How does light ensure mammals maintain a 24 hour rhythm? 光線如何確保哺乳動物保持24小時的節奏？
The pineal gland in the brain converts the neurotransmitter serotonin into the hormone melatonin.
大腦中的松果體將神經遞質5-羥色胺轉換為激素褪黑激素。
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.
褪黑激素被釋放到血流中，引起身體周圍的節律性變化。雖然睡眠的需要不受光線的影響，但褪黑激素在睡眠-覺醒周期的協調中起着作用。
Ultradian rhythms 超晝夜節律
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.
這些是周期小於一天的節律性周期。例子包括全天的警覺性水平和睡眠期間的大腦活動周期。
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).
使用腦電圖（EEG）可以顯示大腦的電活動。在睡眠期間，不同時間有不同的活動模式（Rechtschaffen & Kales, 1968）。
The table below gives some information about the different stages of sleep 下表給出了一些關於睡眠的不同階段的信息:
Stage of sleep 睡眠的階段: | Characteristics 特徵: | EEG trace 腦電圖追蹤: |
Non-REM Stage 1. 非REM階段1 | Theta waves, slow rolling eyes, easily awoken, duration: about 10 minutes. Theta波，眼睛緩慢滾動，容易被喚醒，持續時間：約10分鐘。 |
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Non-REM Stage 2. 非REM階段2 | Irregular trace, some theta waves, sleep spindles and K-complexes, duration: about 15 minutes. 不規則的痕迹，一些θ波、睡眠主軸和K-複合體，持續時間：約15分鐘。 |
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Non-REM Stage 3. 非REM階段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階段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、眼球運動、生動和視覺的夢境。 |
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Here is a graph of a typical night's sleep 下面是一個典型的夜間睡眠圖表 :
Here are some important points to note 這裡有一些需要注意的要點:
- Each cycle lasts for about 90 minutes. 每個周期持續約90分鐘。
- The amount of Stage 3 & 4 sleep decreases each cycle. 第三和第四階段的睡眠量在每個周期都會減少。
- The amount of REM sleep increases each cycle. 快速眼動睡眠的數量在每個周期都會增加。
Infradian rhythms 下行節律
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.
這些是周期大於一天的節律。月經周期就是一個次日節律的例子。由於季節性變化而發生的非晝夜節律，例如遷徙和冬眠，被稱為環年節律。
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.
月經周期的周期約為28天，儘管時間可以根據環境因素而變化。例如，如果婦女經常在一起，月經周期可能會變得同步，這可能是由於她們之間傳遞信息素的影響。
Circannual rhythms are under the control of body clocks. But, again, light makes them run on time by influencing melatonin levels.
周期性節律是在身體時鐘的控制下進行的。但是，同樣，光線通過影響褪黑激素水平使它們按時運行。
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.
是多少光照或日照時間（稱為光周期）提供了關於季節變化的有用信息；日照時間延長意味着春天和夏天的到來，日照時間縮短預示着秋天和冬天的到來。
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.
在人類中，秋季褪黑激素水平的增加似乎導致了一種被稱為SAD（季節性情感障礙）的抑鬱症。這可以通過每天暴露在明亮的光線下幾個小時來治療。
