What Happens to the Brain When We are Sleeping?

Satchit Ghimire- An average human being spends one-third of their life sleeping. Sleeping is one of the most important things for our survival, such as eating and breathing. We feel energized and fresh after we woke up from sleep, but what happens to our brain and the body while we are sleeping?

Picture Credit: Freepik

Many of us think that our brain is inactive when we are sleeping, which is not true. Researchers have shown that the neurons in the sleeping brain fire nearly as they do during the waking state and consume almost the same energy. Many sleep scientists are spending a significant amount of their waking hours to understand the sleep as well as how sleep affects mental and physical health.

Sleeping is vital to brain and other bodily functions. According to scientists, sleep helps to reenergize the body cells, clear wastes/toxins from the brain that builds when we are awake, regulate mood, appetite, libido, and so on. Lack of chronic sleep affects every part of the body, including the brain. It increases the risk of high blood pressure, cardiovascular diseases, diabetes, depression, and so on.

Types of Sleep or Sleep Stages

The brain generates two types of sleep: REM (rapid-eye movement) sleep and non-REM (NREM) sleep. Both REM and non-REM sleep are linked to specific brain waves and neuronal activity. The NREM sleep cycle consists of three stages.

The first part of the cycle is non-REM sleep is the comes while changing from wakefulness to sleep. The second stage marks the light sleep when the heart rate and breathing slows, and body temperature drops. The third stage is the stage of deep sleep.

We cycle through all stages of NREM and REM sleep several times during a typical night. As we move into REM, our eyes rush behind the closed eyelids. Similarly, the frequency of the brain wave activity during REM are similar to those during wakefulness. The breath rate and blood pressure also increase during REM. Most of the dreaming occurs during REM sleep, while some of them even occur in non-REM sleep.

Sleep Mechanisms or How Our Body Controls Sleep?

Two biological mechanisms control our sleep – circadian rhythm and homeostasis.

Circadian rhythms are controlled by your body’s biological clock. They control the timing of the sleep that is why we are sleepy at night and wake in the morning without an alarm. They also respond to the environmental cues (light, temperature) and ramping up the production of the hormone, melatonin, which helps in the regulation of the sleep cycle. 

The homeostasis reminds the body to sleep after a particular time and also regulates sleep intensity. The body craves to sleep throughout the day, and when the desire reaches a certain point, we need to sleep.

Parts of Brain Involved With Sleep

1. The hypothalamus contains a group of nerve cells that acts as control centers for sleep and arousal. The suprachiasmatic nucleus (SCN) located at the hypothalamus receives information about the light exposure directly from the eyes and control the behavioral rhythm. 

2. The brain stem located between the brain and the spinal cord communicates with the hypothalamus to control the transitions between the wake and sleep. The hypothalamus and the brain stem produce an inhibitory neurotransmitter GABA (Gamma-Aminobutyric Acid) that enables the body and mind to relax and fall asleep.

3. The thalamus acts as a communication channel from the senses to the cerebral cortex. It becomes quiet during the most stages of sleep, helping you to ignore the external world except REM. During REM the thalamus is active, sending the cortex images, sounds, and other sensations

4. The pineal gland helps to receive signals from the hypothalamus and increases the production of the hormone melatonin, which assists in sleeping.

5. The basal forebrain, located to the front of and below the striatum also promotes sleep and wakefulness. It release an inhibitory neurotransmitter adenosine that supports the sleep drive.