Do you ever think about why we sleep? Our bodies are highly efficient machines that utilize a lot of energy over the course of a day. In particular, our brain utilizes a lot of oxygen and energy. Sleep is meant to be a process organized by the brain and responsive to our body’s needs. Sometimes those needs are immediate, and sometimes those needs are scheduled. Contrary to what is often thought, we’re not designed to just black out when we’re tired. Sleep is actually a process orchestrated by the brain.
How and when we sleep is governed by a number of factors. These include factors under our control, such as whether or not we are sleep deprived, and factors beyond our conscious control. Chief among the latter consideration is the fact that we actually do have an internal “clock” that regulates our biologic rhythm (also called a circadian rhythm) over a 24-hour period. The circadian rhythm maintains our sleep-wake cycle and prompts us to want to sleep during similar times of the day and/or night. Sometimes that internal rhythm and the body’s routine call for sleep can be disrupted, making sleep a response to abnormal functioning within the brain (such as occurs in narcolepsy).
Sleep also has an internal organization—the sleep cycle—regulated by different areas of the brain. Sleep occurs in two stages, which recur through the night: rapid eye movement (REM) sleep and non-rapid eye movement (non-REM) sleep. Non-REM sleep is further divided into four stages (1 through 4), with stages 3 and 4 often referred to as “deep sleep.” In adults, non-REM sleep occupies around 80 percent of the night, and REM sleep 20 percent. REM sleep occurs every 90-110 minutes. These cycles recur until we awaken due to a schedule or decision to arise. You will feel most refreshed after sleeping and waking up at the completion of the final stage in a sleep cycle.
The body replenishes and restores itself during non-REM sleep, releasing hormones to repair damage done during the day. During REM sleep, you process memories and thoughts from the day and you dream. As best as we understand dreams, they also represent a form of processing mental information that you received during the day. During REM sleep, we normally lose the use of our limb muscles. Yes, it’s true that while we’re sleeping (at least in REM sleep), we have an active mind in an inactive body. This is actually a good thing. This normal loss of muscle activity during REM sleep helps prevent us from acting out our dreams. Thus, it stands to reason that sleepwalking and night terrors usually occur in non-REM sleep. When disorders of REM sleep occur and patients lose that protective phase of muscle inactivity, patients may act out violent dreams and harm themselves or others.
How much sleep you need is best defined by how well you function on different amounts of sleep, and as such, there is quite a bit of variation on what is considered normal and needed. For many adults, the average normal amount of sleep is around 7.5 hours per night. Many of you know people that can function on much less, and others that require as much as 9 hours per night. In general, your body feels most rested if you awaken at the end of a sleep cycle. Given that each cycle takes about 90 minutes, many people find that they’re more refreshed if they sleep some increment of 1.5 hours (e.g., 6, 7.5 or 9 hours).
If you are getting what you consider to be an adequate amount of sleep but are still unrefreshed and sleepy, then you might have an organic sleep disorder and should consider seeking professional consultation.
Additional Straight, No Chaser Blogs have addressed several of the sleep disorders.
- Click here and click here for discussions about insomnia.
- Click here for a discussion of night terrors.
- Click here for a discussion of hypersomnia (excessive sleepiness).
- Click here for a discussion of narcolepsy (sleep attacks).
- Check back for a discussion of sleep apnea.
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