This is the second post in my series on Sleep; and I will be discussing the mechanics of sleep. Basically explaining circadian rhythms, sleep cycles and sleep stages.
Circadian Rhythm is a natural recurring process that occurs on a 24-hour cycle. It is activated by lightness and darkness. The circadian system sends alerts in preparation for sleep. Less light at the end of the day sends a cue to produce melatonin which peaks at night and ebbs during the day. The greatest desire to sleep is between midnight and dawn with the lowest signal at about 4:30 am when people are generally hardest to awaken.
Circadian rhythm can be impacted by computer, phone and TV screens as well as fluorescent and LED lights. Certain photosensitive cells are sensitive to the short wave-length blue light which suppresses melatonin. This is why good sleep hygiene includes putting away screens at least one hour before bedtime and using incandescent light in the evening. Doing so will improve sleep onset, duration and quality.
Sleep Cycle is when we progress through the various stages of non-REM (NREM) and REM sleep. Each cycle is about 90-120 minutes which results in 4 – 5 cycles per full sleep time. A full night’s sleep allows you to go through the stages in order to reap all the benefits mentioned in the previous post.
Sleep Stages – The sleep cycles take us though stages labelled as NREM 1, 2, 3 & 4 and REM (stage 5).
- Stage 1 – (NREM1) This is the transition from wakefulness when we shift into drowsiness, sleep and eventually loss of awareness. During this stage, you may experience “micro-awakenings” (falling in and out of consciousness), muscle jerks, and falling sensations which may jolt you awake before shifting into Stage 2.
- Stage 2 – (NREM2) We spend about 50% of sleep time here and it is a lighter stage when the heart slows and body temperature decreases. Eye movement slows and eventually stops; and blood pressure lowers along with muscle tone. You can easily awaken without grogginess and be quickly alert and coherent. Dreaming doesn’t usually occur during this stage.
- Stage 3 & 4- (NREM3,4) These are the deepest stages and usually occur during the first two cycles (so approximately 4 hours in). This is a period of slow wave sleep meaning the brain slows to delta waves. Blood pressure continues to drop, breathing is regular but becomes deeper and more rhythmic. There is little to no eye movement, the body is immobile and you are difficult to arouse/awaken. If awakened, a person will usually be groggy, disoriented and confused. In these stages, disorders such as night terrors, sleep walking or talking and bruxism (teeth grinding) may occur. Dreams will occur but are not recalled. This deep sleep is essential for health as the mind rests and the body heals. If the sleep is restricted it is unrefreshing.
- Stage 5 (REM) – Adults spend about 20% of sleep time in this last cycle and the duration is about 90-110 minutes. Rapid eye movement (eyes dart in various directions) takes place and limbs and muscles are temporarily paralyzed (known as sleep/hypnogogic paralysis). Breathing is more shallow and the heart beat is irregular while the blood pressure rises. REM sleep suppression can cause moodiness and irritability. Some may experience more dreaming which is sometimes vivid and disturbing.
When you come in to see me for counseling, I will discuss your sleep patterns with you in order to get a sense of whether disturbed sleep patterns may be impacting your emotional and behavioral wellness. Give me a call today at 908-278-9073 to explore these patterns. My next post will discuss sleep disorders.