The Sleep Cycle

All mammals do it. They sleep. Humans, horses, cats and dogs all need sleep to recharge the brain. It’s part of the biological and physiological function of being a mammal. A good night’s sleep often makes us feel:

  • Refreshed and alert.
  • Energized to face the day.
  • Happy, or at least in a good mood.

Without sleep, we cease to function. The consequences of not getting enough rest extends to both the psychological and physiological. But what actually happens when we sleep? Scientists and researchers have been asking that question for decades, and only recently are they beginning to unravel the mysteries of sleep.

Here’s what we know about the sleep cycle and its effects on the body:

Sleep often starts slowly. As night-time comes and the sun goes down, our body starts the sleep period of the circadian rhythm. It begins to release melatonin, which is an important hormone in the sleep cycle, and we eventually lay our heads down and shut our eyes. During this period, our journey into sleep can easily be interrupted. At this time, a person watching might see movements of the eyes, as the body has not yet settled into a deep sleep. Between 15 and 30 minutes into sleep, your brain begins to slow down. Cognitive function is less active. Your eyes are resting, and there is no noticeable eye movement.

Moderate sleep begins about 30 minutes after your head hits the pillow. During this time, your brain function has slowed down significantly. An EEG monitor of a person’s brain during this stage will show delta waves with occasional spikes of smaller faster waves in between. As we drift further into sleep, it becomes more difficult to be disturbed. A slight sound might not wake us as we drift deeper into our slumber.

Deep sleep (finally) begins. It can be hard to wake a person who is in this state. Your body’s muscles are extremely relaxed, and your hormones are changing rapidly. Snoring can begin in this period as we settle in for an extended time of sleep.  The EEG shows tall, slow waves known as delta wave

REM sleep begins after your body has settled into a nice, deep sleep. Actually, your body begins to wake up slightly, and rapid-eye-movement (REM) occurs. The eyes dance around, and your body is the most relaxed it will be during the night. During this stage, your body can actually be temporarily paralyzed. Some believe this is to keep you from acting out your dreams.

Dreaming occurs as we enter REM sleep. There is much debate about what happens when we dream and the reasons for it. Some posit that dreams help consolidate memories and aid in the learning process. Others have argued that dreams are a way of working through unresolved issues or problems. Our degree of control over our dreams varies from person to person. Some have the ability to manipulate and control dreams, while others hardly remember their dreams upon waking. Either way, dreaming takes place during REM sleep. But there are other things happening as well.

  • Hormones are released that improve the immune system, depress our appetite, and reduce the need to go to the bathroom, so we can have hours of uninterrupted sleep.
  • Insulin levels return to normal levels, which is important in the prevention of diabetes.
  • Cortisol – also known as the stress hormone – declines.

It is for these reasons that REM is the most important period of sleep, and your body fights to prevent waking during this time. One way our consciousness will prevent waking is through incorporating sounds in our physical environment into our dream. For example, when your alarm clock goes off, your mind will incorporate that sound into your dreams. The body wants to preserve and protect the REM period of sleep, so that regulation of itself can occur.

After REM, we begin waking up. As we get ready to wake, our body releases cortisol. This turns on our appetite and prepares the body to exert energy. Whether or not we wake with an alarm or naturally, the body will adjust and prepare us for the waking of the day. Eventually, we wake and the body is restored and rejuvenated. It’s a cycle we repeat over and over throughout our lifetime.

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