There are two different kinds of sleep, and they alternate with each other throughout the night. During REM sleep dreams are experienced, and during NREM sleep there are few or no dreams at all. When we fall asleep we go through NREM sleep, then REM sleep; these two combine to form one sleep cycle and we have a few sleep cycles throughout the night In this chapter we are going to study NREM sleep in detail.
In NREM or non-REM sleep there is an absence of rapid eye movement as recorded by the electro-oculogram or EOG. The brain waves are also calmer, in contrast to those of REM sleep. During REM sleep, the brain waves are not much different from those of the awake state. However, during NREM sleep the brain waves are slow and big and are divided into four stages according to their frequency.
During NREM sleep the mind is in complete rest, and is passive, peaceful, and calm. In REM sleep, in contrast, the mind is active and explosive, and the whole brain is working to capacity. Some experts report a 40 per cent increase in the blood flow to the brain during REM sleep.
During NREM sleep, the breathing is slow and regular. The blood pressure is lower than when we are awake, and the heart rate is also slower as if we are in complete rest On the other hand, during REM sleep the breathing is very heavy, and irregular. The blood pressure can be sky-high and the heart rate can be as fast as if we had just finished a 100 m race. It has been observed that if a heart attack or stroke takes place during sleep at night, it occurs during the REM stage. However, the peak incidence of heart attacks is between 7 a.m. and 11 a.m. in the morning and not during sleep. So you can sleep easy.
What about the muscular system during sleep? During NREM sleep, the muscles are active and the muscular system is fully engaged with the brain. There are spontaneous movements in the body during NREM sleep. We turn over many times during the night. This movement is important. People who cannot move because of illness such as quadriplegia suffer from bedsores. They need to be turned by nursing staff continuously throughout the 24 hours. The reason is that if the body is not moving during sleep, the skin which is under pressure from the weight of the body will be blanched and the blood supply to that part of the skin will be insufficient. That area of skin will break down and slough off to form a bedsore. So it is important that the body turns automatically during sleep. Also, this turning and moving of the limbs prevents the stiff neck and joint pain that most people experience the morning after they have been drunk the night before.
During REM sleep the muscular system is disengaged, as if a jamming mechanism is preventing the body from moving. This prevents the physical acting out of dreams. REM sleep is also called ‘paradoxical sleep’; the brain is so active and yet, paradoxically, the body is completely paralyzed.
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