Which of the following is not true about sleep -

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 events/disorder:- Nightmares, nocturnal penile tumescence, Narcolepsy.