<prompt> Which of the following is not true about sleep -REM sleep comes earlier than NREM sleepREM sleep is also called paradoxical sleepSleep walking comes in NREM sleepDreams come in REM sleep  <response>: Ans. is a i.e. REM sleep comes earlier than NREM sleep Stages of SleepA Non-REM NREM or slow-wave sleep :- It is called Non-REM sleep because no rapid eye movement REM is there on eletro-oculogram, rather there is slow or quiscent eye movement. It is also referred as S-sleep synchronized sleep or quiet sleep or orthodox sleep because there diminished physiological functions and a low level of overall activity. It is further divided into:-1 Stage 1:- It is a transition from wakefulness to sleep and is characterized by disappearance of alpha activity and appearance of theta activity. There is slow eye movements.2 Stage 2:- It is characterized by typical EEG activity i.e., Sleep spindles and K-complex. No eye movement occurs.3 Stage 3 4:- Stage 3 4 are stages of deep sleep. These are also called slow wave sleep as these stages are characterized by slow delta waves. Delta wave appearance starts in stage 3 and dominated in stage 4.B REM sleep:- The REM sleep is so named as there is rapid roving movements of eye, i.e., rapid eye movement REM on electro-oculogram. It is also called paradoxical sleep because there is a paradoxical elevation of brain activity metabolism and physiological activity. The high-amplitude slow waves seen in stage 3,4 of REM sleep is replaced by rapid low voltage activity beta wave. Features of REM sleep are:-i EEG - Beta wave, Reappearance of alpha wave, Saw-tooth wave low voltage fast activity, Ponto-genital- occipital spikes.ii Dreamingiii Other features: - Generalized muscular atony, Penile erection, autonomic hyperactivity Increased pulse rate BP and intermittent movement of small muscle groups.o The NREM with its four stages and REM sleep repeat several times a night in cyclic manner, 4-6 times depending on the length of sleep. A typical cycle starts with stage 1 of the NREM sleep which is followed by second, third and fourth stages. After this the sleep returns to stage 3 and 2. The first REM sleep occurs now, 70-90 minutes after the commencement of sleep Note : - Stage 1 NREM sleep occurs only once at the start of the sleep as this is only a transition phase between wakefulness and sleep. Once the sleep starts the cycle rotates between stage 2, 3, 4 NREM and REM sleep. REM sleep occupies 20-30 of total sleep and NREM sleep occupies 60-70 Stage- 1 - 5-10; Stage 2 - 40-50; Stage 3 4 - 15-20. Slow wave sleep stage 3 4 of NREM sleep disorders:- Sleep walking somnambulism, night terror sleep terror or pavomoctumus, Nocturnal enuresis, Bruxism teeth grinding, and sleep talking somniloquy. REM sleep eventsdisorder:- Nightmares, nocturnal penile tumescence, Narcolepsy. 