Sleep spindles are seen in which stage of sleep ?

Ans is 'c' i.e., Stage 2 NREMStages of sleep Sleep is basically divided into two phases :?A) Non-REM (NREM) or slow-wave sleep :- It is called Non-REM sleep because no rapid eye movement (REM) is there on eletrooculogram, rather there is slow or quiscent eye movement. It is also referred as S-sleep (synchronized sleep) or quiet sleep or ohodox sleep because there is diminished physiological functions and a low level of overall activity. It is fuher 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 If-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 stas 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.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 stas with stage 1 of the NREM sleep which is followed by second, third and fouh stages. After this the sleep returns to stage 3 and 2. The first REM sleep occurs now, 7090 minutes after the the commencement of sleep (Note : - Stage 1 NREM sleep occurs only once at the sta of the sleep as this is only a transition phase between wakefulness and sleep. Once the sleep stas 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%).