Among all the benefits of sleep, its physiological components are most significant. During sleep, skeletal muscles relax, and there is no goal-directed behavior. Sleep’s characteristic posture is horizontal repose, which is shared by humans and many animals. It suggests that the subject is passive toward their environment. Several questions remain, however, regarding the capacity of the brain. Sleepwalking and marine mammals have a similar brain activity pattern, with half of the brain active during sleep.

Although it is difficult to define the precise onset of sleep, there are several factors that can be considered to be essential for the proper onset of sleep. First, the eyelids are closed, which indicates decreased sensitivity to sensory stimuli. Secondly, sleep while eyes are open is often referred to as functional blindness. Thirdly, there are reversibility, spontaneity, and recurrence characteristics of sleep that differentiate it from other states of consciousness.

In the first stage of sleep, the heart rate and muscle activity slow down. While the pulse and muscles relax slowly during non-REM sleep, the heart and brain waves continue to slow. In addition, the total amount of energy expended by the body goes down. Finally, during the REM stage, most muscles in the body become paralyzed, so that they cannot flail in response to dream content. However, the muscles of the eyes and respiratory system remain active during this stage.

Sleep is essential to the brain. It helps regulate immune functions, protect the body from infectious agents, and even improve the functioning of the brain. It is also important for our overall health. Research has shown that sleep reduces activity in areas of the brain involved in decision making, emotion, and social interaction. Furthermore, studies show that poor sleep quality is linked to heart disease. In fact, scientists believe that getting less than seven hours of sleep per night could actually harm the heart.

Over the lifespan, humans develop two basic sleep patterns: polyphasic and monophasic. During childhood, slow-wave activity peaks, while adult sleep oscillations become weaker as we age. Consequently, the elderly tend to experience poor quality sleep. In addition, older people are more prone to sleep disorders. Moreover, the brain structures involved in sleep regulation are altered. Therefore, the sleep pattern of older people is characterized by longer 90-minute sleep cycles and decreased slow-wave activity.

Adolescents need eight to ten hours of sleep per night. Yet, according to a recent study, 60 percent of middle schoolers and 70 percent of high schoolers in Michigan do not receive this amount of sleep. Sleep deprivation can affect concentration, mood, following directions, and sports performance. Therefore, sleep deprivation must be prevented as much as possible. It is also important to keep in mind that adolescents’ brains are constantly changing and their bodies need eight to ten hours of sleep per night.

Inadequate sleep affects every system in the body, from the heart to the brain. Sleep deprivation causes elevated levels of the hormone ghrelin. The effect of these hormones is not only insufficient sleep, but it also affects the production of insulin and glucagon, two other hormones involved in regulating blood glucose levels. It is also necessary to have a healthy immune system, as inadequate sleep inhibits the immune response and leaves the body more susceptible to germs and viruses.