Sleep is a complex biological process in which your body goes into reduced metabolic and motor activity. It is a reversible state of the brain unconsciousness. When the brain or body is tired and exhausted, they tend to go to a restful state known as sleep (US & Study, 2007). The brain has a dedicated small region that controls the sleep-wake cycle known as hypothalamic suprachiasmatic nucleus (SCN). SCN contains various kind of cells, proteins and neurotransmitters that help it interact with different parts of the brain to control the circadian rhythms (Ma & Morrison, 2019).
There are two phases of sleep - rapid eye movement (REM) sleep and non-REM (NREM) sleep. During the REM sleep, your eyes moves rapidly in random directions, but the brain does not receive any visual information. REM is about 20-25% of sleep in adults. During NERM sleep, blood flow to the brain, body temperature, and sympathetic nerve activity is decreased as compared to wakefulness. It is a dreamless state of the brain and corresponds to 75-80% of the NERM-REM sleep cycle. The whole NERM-REM cycle takes approximately 70-120min and then the cycle repeats itself (Colten et al., 2006).
Human circadian clock is a highly dynamic and complex mechanism on molecular level. Humans anticipate day and night because of the change in the expression level of hundreds of genes that control the rhythm thereby affecting their behavior, physiology and metabolic processes. Interestingly, the 24h sleep-wake cycle is switched from sleep to wakefulness or vice versa by only a single amino acid of the protein called BMLA1 (Kiyohara et al., 2006). This discovery by Paolo Sassone-Corsi, a professor at the University of California, gave a new hope to the treatment of the sleep disorders.
Now that you know, sleep can have a substantial impact on your quality of life, you’re probably thinking “I need to be sure to sleep properly.” But one question must be popping into your mind, “How much sleep is necessary for the proper functioning of the brain and body?” Well it depends.
According to National Sleep Foundation, young adults require 7-9 hours of deep sleep. However, the amount of sleep decreases as you get older. Infants (4-11 months) need 12-15h of sleep, young adults (18-25years) need 7-9h of sleep and older adults (65+ years) sleep only 7h or less (Hirshkowitz et al., 2015). Not only is the amount of sleep significant but also how you sleep can affect you. Recent research published by the Centre for Cognitive Neuroscience, Duke-NUS Medical School, Singapore showed that it is better to sleep in two cycles rather than one long sleep. People with split sleep had better memory, faster processing speeds, positive mood, and improved administrative functions even though the overall sleep hours were less than those with a continuous sleep. In other words, the optimum sleep hours depend upon your age but split sleep i.e., 6h at night and 2h nap at noon, is a great way to increase your mental and physical health and improve the overall quality of life (Lo et al., 2019).
Recent research in the field of neuroimmunology has revealed that there is a strong relationship between a healthy sleep and improved immunity. Studies have shown that, early nocturnal sleep increases the number of undifferentiated T cells and proinflammatory cytokines (Besedovsky et al., 2012). Increased number of undifferentiated Naïve T cells in the blood is a sign of a strong immunity. These naïve T cells proliferate and differentiate into cells that are capable of removing the antigen upon interacting with antigen. Similarly, cytokines help immune cells find the antigen and fight against it. Presence of more cytokines in the blood indicates a good immunity (Asif et al., 2017). That is why patients suffering from any infection tend to sleep more because it increases the production of cytokines leading to enhanced immune response.
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