During sleep, the body is in a recurrent state of inactivity. It is characterized by relatively inhibited muscle activity and sensory activity. It is believed that this state helps the body to repair itself and maintain an emotional state of stability.
During sleep, the brain’s glymphatic system clears waste from the central nervous system. This allows the brain to function well when awake. It also prevents sickness by producing antibodies and destroying harmful germs. The brain’s immune system also benefits from sleep. It produces cytokines, which help the immune system by promoting the growth of immune cells.
Sleep is an important part of the human physiology, which affects nearly every part of the body. It is essential for the body’s recovery, as well as for its memory function. It is also believed that it supports heart health. It also helps to improve learning.
There are four stages of sleep: drowsiness, deep sleep, wakefulness, and awakening. In humans, the body cycles through these four stages four to six times a night. Each stage is accompanied by complex changes in physiology. For example, breathing and eyelids tend to get heavier as people enter sleep. There are also changes in hormones and internally generated brain activity. These changes are a result of the brain’s activity and reorganization.
During sleep, the brain’s activity is heightened in areas of the brain that regulate emotions and memory. This is a reflection of the body’s need to replenish its energy stores. The brain’s glymphatic system also helps to remove toxic byproducts from the central nervous system.
The deepest stages of sleep, known as slow-wave sleep, are thought to help repair the body and strengthen the immune system. They may also help people maintain an optimal emotional state when awake. It is believed that the sleep patterning of animals is similar to that of humans. This is due to the fact that many animals exhibit recurring periods of inactivity. In some mammals, such as lizards, sleep is not widely accepted.
The deepest stage of sleep is the most difficult to wake from. It is also the phase of sleep where most dreaming occurs. It is believed that the REM phase is triggered by signals from the pons. These signals cause temporary paralysis of limb muscles. The thalamus then relays the signals to the cerebral cortex. This is where dreams are consolidated and encoded.
The typical posture of sleep is horizontal repose. This is the position that most mammals, birds, and insects adopt during sleep. It is suggested that this posture indicates a passive role toward the environment.
The stages of sleep are conventionally divided into three phases based on EEG criteria. The first phase is called the transition to sleep. This phase is generally deactivated. During the second phase, the brain is still a little active. The third phase is called slow-wave sleep. This phase is the deepest and most physically restorative.
In some species, such as kangaroos, dolphins, and elephants, half of the brain is reactive. This may reflect maturing or pressures from culture. In other mammals, such as rats, they appear to be responsive only during certain stages of sleep.