Final answer:
The human sleep cycle repeats approximately every 90 minutes, and is part of the broader 24-hour circadian rhythm governed by the biological clock in the brain.
Step-by-step explanation:
The human sleep cycle repeats itself about every 90 minutes. This cycle typically involves different stages, including light sleep, deep sleep, and Rapid Eye Movement (REM) sleep. The duration and sequence of these stages can vary slightly across different sleep cycles throughout the night, but the entire cycle recurs on average every 90 minutes.
Circadian rhythms, which dictate several biological processes within the body, follow a roughly 24-hour cycle that is driven by the biological clock located in the brain. These rhythms align with the environment's light-dark cycle and induce daily patterns in behavior, such as sleep and wakefulness. Although the circadian rhythm spans a 24-hour period, the individual sleep cycle within this framework is much shorter.