Biological Rhythms and Sleep

We all have a biological clock that keeps us on a 24 hour sleep/wake cycle (well, technically about 11 minutes longer than this but exposure to light each morning helps keep us on a 24 hour routine). This is called our circadian rhythm and affects all of our physiological systems like hunger, body temperature and hormone levels. If we try to sleep at a time that is not in sync with our circadian rhythm we will have more difficulty
falling asleep and staying asleep and we will generally not feel as good throughout the day. The same goes for if we try to stay awake when we should normally be sleeping. This is why sleeping around the same time each day is so important. Not doing so can literally make us feel ill and sleepy all the time and often results in bad behaviors in children.

We reset our circadian rhythm each day when we are exposed to light in the morning. This light exposure is also what helps us slowly (over several days) adjust our biological clock to where it should be when we change time zones. "Light affects the clock differently depending upon what 'time' it is inside your body when the exposure occurs: light at noontime has very little effect, but light after sunset or toward morning makes your body think the day ends later or starts earlier, and so the clock adjusts in the corresponding manner." (Ferber) Light, or lack of it, at noontime can still be useful as a sleeping cue and is often useful to help block out distractions.

When we eat, sleep and have daily activities at inconsistent times from day to day our physiological rhythms can become very unorganized giving us the feeling of a constant, uncomfortable "jet lag". If you've ever been a shift worker or traveled through time zones a lot you know this doesn't feel good. Why put our kids through this? How can we expect them to act appropriately when they feel like this? I personally don't think it's very fair to expect much from them in this condition.

During the middle of the day (or a little later than this if you normally go to bed really late) we have a dip in alertness which makes this the best time to take a nap for children that are on one nap. If a child needs a nap and doesn't take it at this time he will often become cranky. Sometimes even adults will become a little cranky if they don't get a nap or at least a rest period at this time too :)

Ferber describes a period of time a few hours before we go to sleep called the "forbidden zone of sleep" or "second wind". During this time he says that sleep is nearly impossible and children become more awake and alert. This "zone" is much stronger in "night owls" and weaker in "larks", or those who feel alert in the morning. This explains why the longest period of wakefulness for a child is usually at the end of the day and why a child may appear sleepy during dinner but suddenly appear wide awake after.

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