Experts say sleep remodels our brains to enhance memory and balance our brain circuitry to promote happiness. No wonder a sleepy dog always seems happy! The definition of sleep is a condition of the mind and body such as that which typically recurs for several hours every night, in which the nervous system is inactive; the natural and periodic suspension of consciousness during which the powers of the body are restored. Normal sleep is characterized by a decrease in body temperature, blood pressure, breathing rate, and most other bodily functions. During this time, the human brain never decreases inactivity. The brain is as active during sleep as when awake.
Sleep is characterized by two distinct states, REM sleep, and non-REM sleep. They alternate in 90 to 110 minute cycles. A normal night’s sleep has 4-5 of these cycles. Non-REM sleep has four stages from deep sleep to mild dozing. About 75% of the sleep cycle is spent in non-REM sleep. Dreams cannot be recalled from non-REM sleep. *REM Sleep=rapid eye motion sleep
Stage 1 of non-REM is “dozing”, roughly only 5% of non-REM sleep. During this stage, a person can experience the sensation of falling or jerking (hypnic) into sudden wakefulness. The eyes do a slow roll.
Stage 2 is considered the onset of real sleep. This is roughly 45% of non-REM sleep. Eye movements stop, and brain waves become larger.
Stage 3 is more difficult to arouse. This is about 12% of non-REM sleep. Slow brain wave sleep begins. Sleep is progressively deeper.
Stage 4 is very deep sleep. Of roughly 75% of non-REM sleep, 13% is spent in Stage 4. If you awaken during deep sleep, you are groggy and disoriented for a period.
REM Sleep is where dreaming occurs, and periodic eye flutters, muscle paralysis, and irregular breathing occur. Body temperature, heart rate, and blood pressure are markedly different compared to non-REM sleep. Brain wave activity is similar to an awakened state. The brain blocks signals to the muscles so that dreams are not acted out. Adults spend about 20-25% of sleep in REM Sleep.
So why do we sleep? The major reason is our Circadian rhythms, also known as our biological clock. A cycle that lasts 24 hours is called Circadian. Included are physiological functions like body temperature, and hormone secretion. The suprachiasmatic nuclei (SCN) are small structures in the brain that are very sensitive to light, or dark. This may explain why nighttime sleep is more restful than daytime sleep.
For most of us, sleepy periods occur every 12 hours, at night and mid-afternoon. Daylight triggers periods of wakefulness. Research has proven that the absence of light does not alter our biological clock. The longer a person stays awake, the more sleep he or she requires. The need for sleep accumulates, to the point where it allows the body to reverse the effects of sleepiness by sleeping.
Two famous sleepers:
Normal peaks of wakefulness occur during the day. The mid afternoon drowsiness is called the postprandial dip, usually after lunch. The cause is a drop in body temperature. We tend to sleep more when our body temperature falls, than when it rises.
And the need for sleep? Can you believe the experts are not sure. But two reasonable explanations are restorative and adaptive. Restorative sleep enables the body and mind to rejuvenate, re-energize, and restore. The brain also does some mental housekeeping, like organizing long-term memory, integrating new information, repair and renew tissue nerve cells, and biochemicals. Sleep allows the body to rest, and sort out the past, present and future. So, when we say, “sleep on it”, I guess it has a firm scientific foundation!
Adaptive sleep most likely evolved as a protective mechanism, finding food in the daytime, and hiding at night. Logically, predators sleep more than their prey. For humans, the amount of sleep needed is directly proportional to the quality of the next day/s activities.
Why is sleep important? We need sleep for our emotional and physical well-being. It is a necessary bodily function. It makes us feel good. Without enough sleep, science has proven that even simple tasks become harder. Sleep deprivation can cause decreased performance, mood swings, erratic behavior, hallucinations, and even death. Perhaps most telling is that sleep deprivation causes a biological response similar to the body fighting off an infection.
Consequences of sleep deprivation? Nearly 50% of the American adult population is sleep deprived. Is it longer work hours or terribly long commutes? The rise in worker productivity comes at the cost of sleep. Many tragedies have been linked to sleep deprivation. These include the Exxon Valdez oil spill, NASA Challenger shuttle explosion, and the Chernobyl nuclear accident. Worse yet, one-third of all adult drivers have fallen asleep at least once at the wheel! The monetary cost is $30 billion annually.
Financial debt or sleep debt? Sleep debt is created when your personal sleep requirements are not met. You already know about financial debt, I hope. The bad news is that it accumulates quickly, builds, and does not decrease spontaneously. Repaying sleep debt is easier than financial debt. Most of the time it resolves itself naturally. The relationship between wakefulness and sleep prevents most of us from becoming too sleep deprived. Our bodies react to the lack of sleep by going to sleep early or sleeping in the next morning.
How much sleep do we need? Experts say between 6 to 8 hours for a normal, healthy adult, about one-third of your life! On average, we sleep one to one and a half hours less than the population of 100 years ago. Some people are short sleepers, like Jay Leno, Martha Stewart, Cosmo Kramer, and Thomas Edison. Long sleepers were Albert Einstein, and Calvin Coolidge. Ronald Reagan and Winston Churchill were known for their naps. Experts say your sleep requirement is met when you wake up naturally, not by an alarm clock. And the sleep requirement does NOT decrease with age!
Good night, Chet! Good night, David!