Why do We Sleep?

Article provided by Dr. John Collins, MD, Fort Wayne

We all spend about a third of our lives sleeping, yet the reason why we sleep remains a mystery. Sleep is a complex neurologically driven behavior that is required for everyone.

The amount of required sleep reduces overtime from infancy to adulthood. Newborns sleep about 16-18 hours per day, while with toddlers and adolescent children that number gradual reduces to about 10 hours per night. For teenagers, the amount is about 8-9 hours and about 7-8 hours as adults. The sleep pattern changes with maturity going from primarily REM and deep sleep in infancy and childhood, to insomnia and then fragmented sleep in adulthood and old age.

We do know that contrary to popular opinion, the brain does not shut down during sleep. There are several theories on why we need sleep based on this knowledge: sleep as rest and energy conservation; cognitive processing and memory consolidation; and restorative sleep.

The widespread belief is sleep allows the body to rest and conserve energy. This was based on the assumption that the body shuts down like a laptop computer to preserve battery life. However, the brain and body remain active during sleep. What we know is our metabolism slows down during sleep. In addition, blood pressure, respirations, heart rate and body temperature decrease allowing lower calorie requirements. Muscles relax and at times (during REM sleep), we become paralyzed so as to avoid acting out our dreams.

Sleep is considered an active brain state. The neuronal activity serves to consolidate memory and process information. This is facilitated by the lack of external input from the sensory system, since it’s suppressed during sleep, and the lack of interaction with the environment. Deep sleep is associated with ordered slowing of brain processes while REM sleep is described as a waking brain activity during sleep. Both are important for cognitive processing.

john collins md, Fort Wayne Headache SpecialistSleep allows the body to restore itself. Growth hormone secretion increases in deep sleep, which is important for growth and cell repair in the body. Physiologic studies have shown that decreased blood pressure, heart rate, body temperature and caloric demand is more supportive evidence of the restorative attributes of sleep. Animal studies show that sleep deprivation leads to collapse of the immune system and eventually death. In infants, sleep is integral to proper brain development. It has been widely believed that it plays a role in proper brain cellular metabolism. This was recently supported by research suggesting that sleep serves to actively clean up waste by-products of normal awake neuronal cellular activity.

Sleep is essential and the reason is most likely a combination of all the above. This may be why we feel rejuvenated, more alert, and able to function better after sleep. Sleep is also individualized from person to person based on their circadian rhythms or sleep patterns. Inability to sleep or insomnia is the most common type of sleep disorder and tends to disproportionately affect women. Understanding sleep is an important first step.

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