AP PSYCHOLOGY

Detailed explanation-1: -The first sleep cycle is often the shortest, ranging from 70 to 100 minutes, while later cycles tend to fall between 90 and 120 minutes. In addition, the composition of each cycle – how much time is spent in each sleep stage – changes as the night goes along.

Detailed explanation-2: -Sleep cycles across the night are only approximately 90 minutes in length. There are lots of individual differences in cycle length and the variation may be from around 60 to 110 minutes.

Detailed explanation-3: -An average sleep cycle lasts about 90 minutes. Ideally, you need four to six cycles of sleep every 24 hours to feel fresh and rested. Each cycle contains four individual stages: three that form non-rapid eye movement (NREM) sleep and one rapid eye movement (REM) sleep.

Detailed explanation-4: -You pass through the other stages of non-REM sleep, followed by a short period of REM sleep. Then the cycle begins again at stage 1. A full sleep cycle takes about 90 to 110 minutes. Your first REM period is short.

Detailed explanation-5: -For our purposes, it suffices to say that one sleep cycle lasts an average of 90 minutes: 65 minutes of normal, or non-REM (rapid eye movement), sleep; 20 minutes of REM sleep (in which we dream); and a final 5 minutes of non-REM sleep.