What is Sleep?
Sleep is a period of inactivity which results in decreased responsiveness to external stimuli. Scientists define sleep based on brain wave activity patterns and other physiological changes. Many physiological levels remain constant through the day at levels that are optimal for the body’s functions, but at night demand decreases and our temperature and blood pressure drops.
We know from extensive sleep science that not every physiological duty of the body decreases during sleep. For example, an increase in the release of growth hormones is induced by sleep. Certain physiological activities associated with digestion, cell repair, and growth are often at their peak during sleep, suggesting that cell repair and growth may be an important function of sleep. Although scientists remain unsure precisely why we sleep, there are many clues about the functions that sleep serves and how getting more and higher quality sleep can improve our health and well-being.
How Do We Sleep?
Transitions between wakefulness and sleep are controlled and regulated by the brain, which also plays a key role in directing quantity and depth of sleep. However, sleep is also strongly influenced by external factors, such as light and caffeine. When the areas of the brain that promote sleep are most active, they inhibit activity in areas of the brain responsible for promoting wakefulness. This inhibition of wakefulness results in stable sleep and is a key component of sleep science.
Under normal conditions, two systems inside the body interact to allow us to sleep and remain alert when we want to: Our drive for sleep and our body’s internal clock. Our internal clock, or circadian rhythm, uses light to determine the function of the body. It tells us when it’s time to sleep and when it’s time to awaken.
Non-REM (Non-Rapid Eye Movement)
During non-rapid eye movement (Non-REM) sleep, we go through stages of light and deep sleep. During the first stage, we’re easily awoken. Our eye movement is slow, and our muscles may be active. During the second stage, heavier sleep begins to set in. We become disengaged from our surroundings, our heartbeat and breathing becomes steady, our body temperature drops, and our brain waves slow down. We sleep the deepest during the last two stages of Non-REM sleep. We’re hard to awaken as the blood supply increases to our muscles. Our blood pressure drops and our breathing slows as our muscles relax. During these stages, our body creates new tissue, repairs cells, and releases growth hormones.
REM (Rapid Eye Movement)
Although the average person is not fluent is all the specifics of sleep science, most have heard the term REM. During rapid eye movement (REM) sleep, our breathing becomes more rapid and irregular. Our heart rate and blood pressure increase, and our arms and legs become paralyzed. This is the stage of sleep where our most vivid dreams occur. We typically remember dreams best when we’re awoken from REM sleep.