Sleep is regulated by two main systems: the circadian rhythm, which aligns with the 24-hour light-dark cycle, and the homeostatic sleep drive, which increases with time spent awake. These systems ensure that sleep occurs at the right time and duration.

 There are two main types of sleep: non-REM (NREM) sleep and rapid eye movement (REM) sleep, which alternate in cycles of about 90 minutes.

1.Non-REM Sleep has three stages:

 Stage 1: Light sleep where the body begins to relax.

 Stage 2: Heart rate slows, and body temperature drops as sleep deepens.

 Stage 3: Deep sleep, essential for physical recovery, immune function, and memory consolidation.

 

2. REM Sleep: The brain becomes highly active, similar to wakefulness, and vivid dreaming occurs. This phase supports learning, memory processing, and emotional regulation.

 Throughout the night, 4-6 sleep cycles occur, with varying proportions of REM and NREM sleep. Deep sleep dominates early cycles, while REM sleep becomes more prominent later.

 During sleep, the body repairs tissues, strengthens the immune system, and clears brain waste, such as amyloid-beta, linked to Alzheimer’s. Sleep also regulates hormones that affect appetite, stress, and metabolism.

 Inadequate sleep impairs cognitive function, weakens immunity, and increases the risk of chronic conditions like heart disease and diabetes. Prioritizing consistent, quality sleep is vital for overall well-being, comparable to nutrition and exercise.