Ever wondered what’s going on in your brain while you are catching your dreams each night?? Read on to know about how your sleep cycle works.
The word ‘Sleep’ can be defined as a condition of body and mind which typically recurs for several hours every night, in which the nervous system is inactive, the eyes closed, the postural muscles relaxed, and consciousness practically suspended. Sleep affects our daily functioning and our physical and mental health in many ways that we are just beginning to understand.
Beliefs of the ancient times
Prior to the era of modern sleep research in the early 1920s, scientists regarded sleep as an inactive brain state. It was generally accepted that as night fell and sensory inputs from the environment diminished, so too did brain function. In essence, scientists thought that the brain simply shut down during sleep, only to restart again when morning came. Until the 1950s, most people thought of sleep as a passive, dormant part of our daily lives. Sleep was then considered an inactive, or passive, state in which both the body and the brain “turned off” to rest and recuperate from the day’s waking activities.
A Biological clock is an inherent timing mechanism in a living system that is inferred to exist in order to explain the timing or periodicity of various behaviors and physiological states and processes. In other words, it is a system in the body that controls the occurrence of natural processes (such as waking, sleeping, and aging), which change on a daily, seasonal, yearly, or other regular cycle.
Our bodies require sleep in order to maintain proper function and health. In fact, we are programmed to sleep each night as a means of restoring our bodies and minds. Researchers observed that sleep was a dynamic behavior, one in which the brain was highly active at times, and not turned off at all. Two interacting systems — the internal biological clock and the sleep-wake homeostat — largely determine the timing of our transitions from wakefulness to sleep and vice versa. These two factors also explain why, under normal conditions, we typically stay awake during the day and sleep at night. But what exactly happens when we drift off to sleep?
Nerve-signalling chemicals called neurotransmitters control whether we are asleep or awake by acting on different groups of nerve cells, or neurons, in the brain. Neurons in the brainstem, which connects the brain with the spinal cord, produce neurotransmitters such as serotonin and norepinephrine that keep some parts of the brain active while we are awake. Other neurons at the base of the brain begin signaling when we fall asleep. These neurons appear to “switch off” the signals that keep us awake. Research also suggests that a chemical called adenosine builds up in our blood while we are awake and causes drowsiness. This chemical gradually breaks down while we sleep.
The stages of Sleep
During sleep, we usually pass through five phases: stages 1, 2, 3, 4, & REM (Rapid Eye Movement) sleep sometimes referred to as Ultradian Rhythms (“ultradian” meaning within a day). These stages progress in a cycle from stage 1 to REM sleep, then the cycle starts over again with stage 1. We spend almost 50 percent of our total sleep time in stage 2 sleep, about 20 percent in REM sleep, and the remaining 30 percent in the other stages. Infants, by contrast, spend about half of their sleep time in REM sleep.
It has been known, since as early as 1937, that sleep goes in cycles, and the distinction between REM and non-REM sleep was established in 1953. Since then, the various sleep stages have been defined and redefined until we have the breakdown of types and stages we know today.
- Stage One
During stage 1, which is light sleep, we drift in and out of sleep and can be awakened easily. Our eyes move very slowly and muscle activity slows. People awakened from stage 1 sleep often remember fragmented visual images. Many also experience sudden muscle contractions called hypnic myoclonia or hypnic jerks, often preceded by a sensation of starting to fall. These sudden movements are similar to the “jump” we make when startled.
- Stage Two
When we enter stage 2 sleep, our eye movements stop and our brain waves become slower, with occasional bursts of rapid waves called sleep spindles.
- Stage Three & Four
In stage 3, extremely slow brain waves called delta waves begin to appear, interspersed with smaller, faster waves. By stage 4, the brain produces delta waves almost exclusively. It is very difficult to wake someone during stages 3 and 4, which together are called deep sleep. There is no eye movement or muscle activity. People awakened during deep sleep do not adjust immediately and often feel groggy and disoriented for several minutes after they wake up. Some children experience bedwetting, night terrors, or sleepwalking during deep sleep.
- REM Sleep
When we switch into REM sleep, our breathing becomes more rapid, irregular, and shallow, our eyes jerk rapidly in various directions. Interestingly, during REM sleep, muscles in the limb, arms and legs are temporarily paralyzed. This is thought to be a neurological barrier that prevents us from “acting out” our dreams. Our heart rate increases, our blood pressure rises, and males develop penile erections. When people awaken during REM sleep, they often describe bizarre and illogical tales – dreams.
In many cultures, particularly those with roots in tropical regions, afternoon napping is commonplace and is built into daily routines. Afternoon nap time typically coincides with a brief lag in the body’s internal alerting signal. This signal, which increases throughout the day to offset the body’s increasing drive to sleep, wanes slightly in mid-afternoon, giving the sleep deprived a slight edge. Napping also typically happens during the warmest period of the day and generally follows a large mid-day meal, which explains why afternoon sleepiness is so often associated with warm afternoon sun and heavy lunches.
Afternoon naps for most people typically last between 30 to 60 minutes. According to sleep experts, napping can be a good way for people who do not sleep well at night to catch up. They do caution, however, that people with insomnia may make their night time sleep problem worse by sleeping during the day. Otherwise, they generally recommend naps for people who feel they benefit from them.
Each sleep stage in any particular sleep cycle fulfills a distinct physiological and neurological function, each of which appears to be necessary for the health of the body and mind, to the extent that, if sleep is interrupted or if certain stages are missing for any reason, their physiological functions are not fully executed, and the person may feel tired or groggy even after an apparently sufficient sleep period, a phenomenon known as “sleep inertia”. In recent years, special alarm clocks have become available which purport to monitor a person’s sleep stages and cycles and only wake them during periods of light sleep, when the deleterious effects of this sleep inertia are least acute.
Sleep Cycle Alarm Clock
Waking up easy is all about timing. Sleep Cycle alarm clock tracks your sleep patterns and wakes you up during light sleep. Waking up during light sleep feels like waking up naturally rested without an alarm clock. While you sleep, you go through cycles of sleep states. The first state in a sleep cycle is light sleep, followed by deep sleep and a dream state referred to as REM-sleep. A full sleep cycle lasts about 90 minutes and is normally repeated several times each night.
Your movements vary with each sleep phase. Sleep Cycle uses sound analysis to identify sleep states by tracking movements in bed. Sleep Cycle uses a wake-up phase (30 minutes by default) that ends at your desired alarm time. During this phase, Sleep Cycle will monitor signals from your body to wake you softly when you are in the lightest possible sleep state.
The first sleep cycle is typically around 90 minutes in length, with the succeeding cycles averaging around 100-120 minutes, although some individuals may have longer or shorter average cycles and they are usually shorter in children.
The amount of sleep each person needs depends on many factors, including age. Infants generally require about 16 hours a day, while teenagers need about 9 hours on average. For most adults, 7 to 8 hours a night appears to be the best amount of sleep, although some people may need as few as 5 hours or as many as 10 hours of sleep each day. Women in the first 3 months of pregnancy often need several more hours of sleep than usual. The amount of sleep a person needs also increases if he or she has been deprived of sleep in previous days.
Now that we all know the major role that sleep plays in our lives, understanding these patterns and the factors that affect them, may help in making choices that will lead to better quality sleep. Take care of your sleep, because only a relaxed mind has the tendency to perform better. Happy Sleeping!!