Your internal body clock has a powerful influence over your sleep patterns and dictates your body’s internal activities throughout the day.
Your sleeping and waking cycle is set by your internal body clock, like a pace maker at the center of your brain. This internal rhythm controls all the biological events in your body, including your body temperature, blood pressure and hormone production. These events, in turn, influence your sleeping and waking cycle, controlling when you feel tired and when you are alert.
Sleep is not a passive part of your day, as a lot of activity occurs in your brain while you are asleep. Even when you are in deepest sleep, your brain activity is only slightly lower than when you are awake. Since sleep has a restorative and regenerative effect on your body, your body requires more sleep after physical exertion or illness. However, you can’t alter your sleeping rhythms as you please, as your body has specific needs, but sleeping patterns do naturally change throughout life and vary from person to person.
Your sleeping and waking cycle is controlled by specific hormones. As you wake up, stress or activity’ hormones like corticosteroids and adrenaline surge quickly into your bloodstream. They make you feel alert and active and block the manufacture of growth hormone so that your body uses its energy for daytime activities rather than the growth and repair of cells and tissues. During the day, sleep hormones like melatonin are in short supply, but as daylight reduces and darkness increases, you produce greater amounts melatonin, inducing drowsiness and sleep. Your stress hormones decrease and growth hormones stimulate your body to regenerate itself.
The two basic components of sleep non-REM (non-rapid eye movement) and REM sleep recur four to five times during an average eight-hour sleep, in a particular sequence.
Stage 1 lasts only about ten minutes. Your eyes are closed, you feel relaxed as your brain activity slows down, and you are only half-aware. Twitching movements from sudden muscle contractions may occur. You can be easily arounsed and may not realize you were asleep.
Stage 2 is also a period of reasonably light sleep. However, during this stage your brain activity becomes increasingly irregular, though still strong. Arousal becomes much more difficult as your body prepares to enter the first stage of deep sleep.
Stage 3 and 4 are stages of deep sleep, also call slow wave’ sleep. In stage 3, you are difficult to wake up, your body temperature falls, your muscles relax and your breathing and heart rate slow down. You need to pass to stage 4, the deepest sleep, to feel rested when you wake.
Stage 5, REM sleep, occurs around one-and-a-half hours after you first fall asleep. Your brain is almost as active as when awake, and your blood pressure, heart rate, body temperature and breathing rate increase. Your eyes move rapidly behind your eyelids and you are likely to dream.
A number of factors have large effects on your sleep cycle. Many of these are unavoidable, but awareness of them can help you make the most of your sleep time.
Age affects the sleep cycle. Babies need the most sleep, especially REM sleep. Their total sleep time reduces during childhood, but then increases again in adolescence. As adults get older, they need less sleep and the amount of REM sleep reduces.
High levels of progesterone during ovulation help induce sleep. Low levels of the hormone at the beginning and end of the menstrual cycle make it harder to fall asleep.
Pregnant women may find that daytime sleepiness occurs in the first trimester. Increased energy during the second trimester can make some women wakeful at night. During the final trimester, most women feel tired, but may not be comfortable in bed.