Q.Write a brief note on REM sleep.

Sleep Physiology (REM Sleep)

Sleep is not a single "off" state — the brain cycles through distinct stages, and one of them is so active it almost resembles being awake. Understanding these stages, especially REM sleep, explains why sleep is far more than rest.

The two broad kinds of sleep

Sleep alternates between two main types that repeat in cycles through the night:

• Non-REM (NREM) sleep — the deeper, quieter phase, progressing from light sleep into deep slow-wave sleep. The body is restful, breathing and heartbeat slow and steady, and the brain's electrical activity slows into large, slow waves.
• REM sleep — the Rapid Eye Movement phase, named because the eyes dart quickly beneath closed lids.

What makes REM sleep special

REM sleep is sometimes called paradoxical sleep, and the paradox is the point: even though the person is deeply asleep, several features resemble wakefulness:

• The eyes move rapidly back and forth.
• Brain activity is high — the EEG looks almost like that of an awake person.
• Vivid dreaming mostly occurs during REM.
• Breathing and heart rate become faster and irregular.
• Yet the major skeletal muscles are temporarily paralysed (atonia) — which conveniently stops us from physically acting out our dreams.

Why the cycle matters …