Sleep is one of the single most important things our bodies need to survive. Without it, the brain starts to shut down and the ability to process information is significantly hindered. Sleep allows the body to rest and recover from the day, with the brain performing a number of vital processes only possible during sleep.
There are 4 general stages of sleep, three non-REM stages and REM sleep. A complete cycle through all 4 stages can take over a couple of hours. The shortest stage is normally the first stage where you are falling asleep. Your body begins to relax and your brain activity slows a small amount. Stage 2 brings a more noticeable drop in brain activity, as the body begins to shift into a more passive state. The muscles relax and body temperature drops while breathing and heart rate slow. This stage starts out being about 10 to 25 minutes long but can lengthen over the course of the night. You might spend half the night in this stage of sleep altogether. Stage 3 is critical to memory and the restoration of the mind and body. In this stage, one’s breathing and heart rate drop even further with an accompanying drop in muscle tone. A lot of the body’s immune system support and damage reparations are bolstered most heavily during this stage. In contrast to Stage 2, Stage 3 gets progressively shorter as the night goes on and is initially anywhere from 20 to 40 minutes long. Then comes the type of sleep you’ve likely heard the most about, REM sleep! In this final stage of sleep, the body is completely locked down while your brain lights up as if you were still awake. It is during REM sleep that you are thought to have most of your narrative style dreams with structure and vivid realism. This stage is crucial to processing and consolidating your very real memories and is thought to be a big part of the learning and long-term memory mechanism. These four stages of sleep repeat through the night with REM sleep starting roughly 90 minutes after you fall asleep.
The body’s sleep/wake cycle is governed in part by the circadian rhythms. We may discuss the circadian rhythms in more detail in a later article but it is enough to say that the circadian rhythms are often described as the body’s internal clock, telling us when it is time to rest and time to wake. There are numerous environmental factors that might impact the proper functioning of our rhythms, but humans seem to generally run on an innate 24-hour cycle. Interrupting this cycle with, say, shift work or redeye travel results in issues ranging from minor issues like jetlag to major problems in mental and physical functioning.
So how much sleep does the average person actually need? Well, that depends on a combination of genetics, age and one’s overall unique biochemical makeup but, generally speaking, the needs vary most noticeably with age. Infants need the most sleep, clocking about 16 - 18 hours a day. Children follow with the youngest still needing around 10 -13 hours while under the age of 5. Older kids under the age of 12 need a little less with averages ranging from 9 - 12 hours. Teenagers take a significant cut needing 8 - 10 and once you are old enough to vote, you are thought to need a vague 7+ hours to be rested. Next time we will talk more about sleep quality but for now, here are a few articles for additional sleep themed reading.
From the National Institute of Neurological Disorders and Stroke