Sleep spindles are seen in which stage of sleep -

Ans is 'c' i.e., Stage 2 NREM Stages of sleepo Sleep is basically divided into two phases :-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 orthodox sleep because there is diminished physiological functions and a low level of overall activity. It is further divided into : -Stage I 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.Stage 2 It is characterized by typical EEG activity i.e., Sleep spindles and 'K-complex' .No eye movement occurs.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 wrave appearance starts in stage 3 and dominated in stage 4.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 lowr voltage activity (Beta wave). Features of REM sleep are:-EEG - Beta-wave, Reappearance of alpha wave. Saw-tooth wave (low voltage fast activity), Ponto-genital-occipital spikes.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 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%).