"Until the 1950s, most people thought of sleep as a passive, dormant part of our daily lives. We now know that our brains are very active during sleep. Moreover, sleep affects our daily functioning and our physical and mental health in many ways that we are just beginning to understand.
Nerve-signaling chemicals called neurotransmitters control whether we are asleep or awake by acting on different groups of nerve cells, or neurons, in the brain. Neurons in the brainstem, which connects the brain with the spinal cord, produce neurotransmitters such as serotonin and norepinephrine that keep some parts of the brain active while we are awake. Other neurons at the base of the brain begin signaling when we fall asleep. These neurons appear to "switch off" the signals that keep us awake. Research also suggests that a chemical called adenosine builds up in our blood while we are awake and causes drowsiness. This chemical gradually breaks down while we sleep.
During sleep, we usually pass through five phases of sleep: stages 1, 2, 3, 4, and REM (rapid eye movement) sleep. These stages progress in a cycle from stage 1 to REM sleep, then the cycle starts over again with stage 1. We spend almost 50 percent of our total sleep time in stage 2 sleep, about 20 percent in REM sleep, and the remaining 30 percent in the other stages. Infants, by contrast, spend about half of their sleep time in REM sleep.
During stage 1, which is light sleep, we drift in and out of sleep and can be awakened easily. Our eyes move very slowly and muscle activity slows. People awakened from stage 1 sleep often remember fragmented visual images. Many also experience sudden muscle contractions called hypnic myoclonia, often preceded by a sensation of starting to fall. These sudden movements are similar to the "jump" we make when startled. When we enter stage 2 sleep, our eye movements stop and our brain waves (fluctuations of electrical activity that can be measured by electrodes) become slower, with occasional bursts of rapid waves called sleep spindles. In stage 3, extremely slow brain waves called delta waves begin to appear, interspersed with smaller, faster waves. By stage 4, the brain produces delta waves almost exclusively. It is very difficult to wake someone during stages 3 and 4, which together are called deep sleep. There is no eye movement or muscle activity. People awakened during deep sleep do not adjust immediately and often feel groggy and disoriented for several minutes after they wake up. Some children experience bedwetting, night terrors, or sleepwalking during deep sleep.
When we switch into REM sleep, our breathing becomes more rapid, irregular, and shallow, our eyes jerk rapidly in various directions, and our limb muscles become temporarily paralyzed. Our heart rate increases, our blood pressure rises, and males develop penile erections. When people awaken during REM sleep, they often describe bizarre and illogical tales – dreams.
The first REM sleep period usually occurs about 70 to 90 minutes after we fall asleep. A complete sleep cycle takes 90 to 110 minutes on average. The first sleep cycles each night contain relatively short REM periods and long periods of deep sleep. As the night progresses, REM sleep periods increase in length while deep sleep decreases. By morning, people spend nearly all their sleep time in stages 1, 2, and REM" - (http://www.ninds.nih.gov/disorders/brain_basics/understanding_sleep.htm)
This is probably one of the only things that I miss from my school days. Sleep. For most of us, sleep is that state we go into after patiently waiting for it in our beds. We preoccupy our minds with the things we experienced during our days, plans for the future and so on and so forth; but for (most, not all) Rhodes students, this is something only heard about in myth and legend. Many of us have very little time for sleep due to assignments and tests which is why many of us prefer to sit in the back of the lecture theater to catch up on those long lost Z's. Sometimes it's not the workload that gets to us, but the lack of work. When some students have nothing better to do, they will gather some of their friends together and head down to a local water hole to have a drink and be merry (as is tradition here).
I speak from experience when I say that quite a few of us only go to bed at about 02:00 AM (where's that curfew now mom?), which is why many of us choose to miss lectures in the mornings and preferably get the lecture slides later. Personally I have never missed a lecture, but it does take its toll on me from time to time which is why I absolutely love weekends (sleep until 13:00). When I decide to sleep in on weekends, I make it perfectly clear that I do not wish to be disturbed (and silently vow to take anyone's eye out should they even dare to try and get me out of bed before 10:00 AM).
I'll leave you with this small message: Sleep may not seem to be that important to us, but a merchant never realizes just how much the simplest of his wares are in value until he has already sold them.
Good night and sleep tight everyone.
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