SLEEPING

Sleeping is a naturally recurring state of mind and body characterised by decreased ability to react to stimuli. It is in reality an attempt to reset the mind and body to a fresher state by going through a period of maintenance for removing metabolic waste compounds from the brain. 

During sleep, most systems are in an anabolic(building up) state, helping to restore the immune, nervous, skeletal, and muscular systems to their purer states.

Sleep is controlled by internal biological clock known as the “internal circadian clock” , also known as “circadian rhythm”, which promotes sleep daily at night controlled by strong lights via a light sensitive neurons in the suprachiasmatic nucleus which stimulates the pineal gland  to produce a hormone called “melatonin”. Also, the interaction of light with suprachiasmatic nucleus does stimulate the growth hormone, prolactin, and cortisol. It does control body temperature during sleep/awakening states as well.

There are two types of sleep: Rapid eye movement sleep(REM), and non-rapid eye movement sleep (NREM). REM & NREM do occur in consecutive cycles taking about 90 minutes each known as ” ultradian sleep cycle”, and any normal night sleep will contain 4 – 5 such cycles (6 to 7.5 hours). Most of the deep night sleep happens at the beginning of the night(the first 2 hours), then light sleep (about 4 hours), then deep sleep again for about one hour before natural waking time in the morning. Dreams and nightmares happen during REM sleep, and the deepest sleep happens in NREM sleep.