Types of sleep

Sleep

Sleep is defined as a state of unconsciousness from which a person can be aroused by appropriate sensory or other stimuli.

Types of sleep :-

During each night a person goes thorugh two stages of sleep that alternate with each other. They are (1) Slow wave sleep and (2) REM sleep.

Slow wave sleep :- In this type of sleep the brain waves are very slow. Though this sleep is frequently called 'dreamless sleep', dreams actually occur very often and even nightmares occur during this sleep. During this sleep the process of consolidation of the dreams in memory does not occur. This sleep is highly useful in decreasing blood pressure, respiratory rate and basal metabolic rate.

REM sleep or Rapid eye movement sleep :- In a normal night sleep, REM sleep lasting 5-30 minutes usually appear on an average every 90 minutes. It is usually associated with active dreaming. The muscle tone throughout the body is exceedingly depressed during this sleep indicating strong inhibition of the spinal projections from the reticular formation of the brain stem.

The heart rate and respiration usually become irregular, which is characteristic of the dream state. During REM sleep, the brain is quite active. But, the brain activity is not channeled in the proper direction for persons to be aware of their surroundings and therefore to be awake.

Physiological effects of sleep :- Sleep restores both normal sensitivities of nervous system and 'balance' among the different parts of the central nervous system. Due to good sleep arterial blood pressure falls, pulse rate decreases, skin vessels dilate, muscles fall into relaxed state and overall metabolic rate of the body falls by 10-30 percent.