Sleep September 21, 2014

Sleep is a normally recurring state characterized by lessened consciousness, lesser awareness to the surroundings and lesser movement1. In humans, the main sleep episode usually occurs as one consolidated period of ~8 hours every night, and accounts for about one third of human life. Sleep is essential for mental and physical restoration: In studies of humans and other animals, scientists have discovered that sleep plays a critical role in immune function, metabolism, memory, learning, and other vital functions5.

Everyone knows that sleep is important for memory, but few people can explain why. The brain is very active during certain periods of sleep and scientists have discovered that sleep is essential to consolidate memories and reset the brain in preparation for a new day of learning and performing.

Physiology of sleep: how sleep works?

Our sleeping patterns are governed by two mechanisms4 6:

  • Homeostasis – the physiological tendency of various internal body systems to keep important functions, such as sleep and wake blood pressure, and body temperature in an optimal ‘steady state. Therefore, we intend to be more sleepy as we spend more time awake and less sleepy if we just woke up after a good restorative night’s sleep.

  • Circadian rhythm – describes the cyclical changes in the body over a 24-hour period. Most homeostatic functions show cyclical changes over the 24 hour day-night period and these changes are termed Circadian rhythms. In humans these rhythms are set to overlap the day-night period by the brain’s ‘clock’, a region known as the suprachiasmatic nucleus (SCN). This clock is very sensitive to the hormone melatonin that it identifies as a signal of darkness. The circadian clock governs the time period when we sleep, when we wake and feel naturally ready to do so. Disruption of the circadian rhythms affects the ability to get to sleep, sleep quality and ease of awakening and have deleterious effects on health.

Sleep and wakefulness are controlled by the brain, via a fine balance between the activity of nerve cells that promote arousal and sleep.

Quality and quantity of sleep

The optimal amount of sleep we should have each night varies from individual to individual but most people will feel fresh after 7-8 hours of sleep . The body’s natural method of regulating how much sleep we need and when such sleep can occur is set by the sleep homeostatic process and our natural circadian rhythms. When these rhythms become disrupted, the quantity and Quality of Sleep achieved can be affected, making an impact on our health and daytime functioning.
Accumulated evidence from large clinical studies suggests that sleep quality rather than quantity has a greater impact on Quality of Life and daytime functioning2, and sleep disruption may badly affect blood pressure control and cognition3.

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