When is the body most susceptible to sleep

The first such episode usually lasts for only a few minutes, but REM time increases progressively over the course of the night. The final period of REM sleep may last a half-hour. During the night, a normal sleeper moves between different sleep stages in a fairly predictable pattern, alternating between REM and non-REM sleep. When these stages are charted on a diagram, called a hypnogram see Figure 2 , the different levels resemble a drawing of a city skyline.

Sleep experts call this pattern sleep architecture. Most deep sleep occurs in the first half of the night. As the night progresses, periods of REM sleep get longer and alternate with stage N2 sleep. Later in life, the sleep skyline will change, with less stage N3 sleep, more stage N1 sleep, and more awakenings.

Control of many of the features of sleep architecture resides in the brainstem, the area that also controls breathing, blood pressure, and heartbeat. Fluctuating activity in the nerve cells and the chemical messengers they produce seem to coordinate the timing of wakefulness, arousal, and the minute changeover that occurs between REM and non-REM sleep.

A generous donor will match all contributions made before December 31 — doubling your gift and your impact! Cookie Policy. Your internal clock circadian rhythms Certain brain structures and chemicals produce the states of sleeping and waking. Exposure to light at the right time helps keep the circadian clock on the correct time schedule. However, exposure at the wrong time can shift sleep and wakefulness to undesired times.

As a person reads clocks, follows work and train schedules, and demands that the body remain alert for certain tasks and social events, there is cognitive pressure to stay on schedule. Levels of melatonin begin climbing after dark and ebb after dawn.

In the result, immune system of human body is altered by releasing immunomodulators in the response of infections as reported by various researchers. Basic reasons and mechanisms of most of the poor sleep networks and release of proinflammatory modulators are still uncertain.

Written by Eric Suni. Medically Reviewed by Dr. Anis Rehman. Sign up below for your free gift. Your privacy is important to us. Was this article helpful? Yes No. Anis Rehman Endocrinologist MD. Borbely, A. Concepts and models of sleep regulation: An overview. Journal of Sleep Research, 1 2 , 63— In Merriam-Webster. Duffy, J. Effect of light on human circadian physiology. Sleep Medicine Clinics, 4 2 , — Valdez, P. Circadian Rhythms in Attention. Yale Journal of Biology and Medicine, 92 1 , 81— Fisk, A.

Light and cognition: Roles for circadian rhythms, sleep, and arousal. Frontiers in Neurology, 9, Green, A. Evening light exposure to computer screens disrupts human sleep, biological rhythms, and attention abilities. Chronobiology International, 34 7 , — Wielek, T.

On the development of sleep states in the first weeks of life. PloS One, 14 10 , e Other systems also follow a daily rhythm, many of which are controlled by hormones and other compounds that receive cues from the biological clock.

For example, the hormones responsible for hunger and metabolism rise and fall over the course of the day. The chemicals involved in immune system function also vary.

Compounds that encourage the inflammatory response rise at night, which is why fevers tend to spike then , and those that inhibit it rise during the day. This is likely because the body is better at fighting infection while it is at rest, and energy can be poured into the effort, rather than into other functions.

And activity of the stress response system -- particularly in secretion of the stress hormone, cortisol -- is reduced during the nighttime hours, and heightened in the early morning. Although there are certain areas of the body, like the heart, that are able to govern their own function to some degree, there is strong evidence that the body clock plays a major role in controlling many of these fluctuations such as in blood sugar over the hour period.

Some of the best knowledge we have about the roles the biological clock plays in our health come from instances in which the cycle gets out of sync. This can happen for different reasons, and we're just starting to understand them in greater detail.

Sometimes we do things ourselves that disrupt our normal rhythms, like flying to a distant time zone. Sometimes it's other factors, like genes or biology that play a role. When jet lag sets in, we feel disoriented, foggy, and sleepy at the wrong times of day because, after changing time zones, our body clock tells us it's one time and the outside environment tells us it's another.

In fact, jet lag can be considered one type of circadian rhythm disorder. It can be treated simply be allowing the body to adjust to the new time, although it may take several days for external cues light to help the internal clock catch up or fall back with its new cycle. Shift work is another example of how we can get ourselves off-cycle, and this too can develop into a circadian rhythm disorder over the long term.

People who work the night shift not only have a hard time with their sleep patterns feeling sleepy at work or experiencing insomnia during the day , but other systems in their bodies can also feel the effects -- and they can be chronic. It's not been clear exactly why this connection exists, but weight gain or metabolic changes may be involved. These phenomena underline how particular behaviors or lifestyles can affect the body's clock, but there are other factors at play, like genetics and body chemistry.

The interactions of the clock are complex, and their effects on different body systems are intricate, but we're starting to understand more about how the nuts and bolts of the clock work, and affect each system of the body, from our hearts to our moods.

Since the biological clock is, in fact, a biological entity, things can go wrong with it that may have less to do with lifestyle or the environment, and more to do with the mechanisms of the clock itself.

For example, there's more to the clock-diabetes link than just turning our sleep cycle around, though sleep can make a difference. The same genes that control the receptors for the sleep hormone melatonin are involved in insulin release, which could also play a role in diabetes risk. When melatonin receptor genes have mutations that damage the connection between the biological clock and insulin release people have a significantly higher risk of developing diabetes.

The heart is one organ that, although it can keep time by itself to some degree, relies on the brain's biological clock for cues. For years doctors and researchers have noticed that heart problems like fatal arrhythmias are more likely to occur at certain times of the day, both in the early morning and to a lesser degree, in the evening hours.