The Physiology of Sleep
During the night, your body passes through four to six cycles of sleep. Each cycle is comprised of four stages. Each cycle lasts approximately 90 minutes.
Passing through the cycles without disruption is important to cellular rejuvenation, memory consolidation, and restoration of physical and emotional reserves.
There are four individual stages of sleep, three are referred to collectively as ‘non-REM sleep’ and the fourth is called ‘REM Sleep’.
Occurs just as you are falling asleep.
It’s short in duration and is considered light sleep. Physiologically, your heartbeat, breathing, and eye movements slow, and your muscles relax and may twitch. Your brain waves begin to slow down and your mind disengages from the activities of the day.
A transition stage between light sleep and deeper sleep.
During this time, your heartbeat and breathing slow, and muscles relax. Your body temperature drops and eye movements stop. Brain wave activity slows even further and you begin to phase into deep sleep.
The period of deep sleep.
This stage of sleep is vital to feeling rested in the morning and it’s most important to phase for our regenerative processes, allowing for our bodies to recover and grow. It also plays a role in bolstering our immunity system. During this phase, brain activity slows down and it is thought Stage 3 sleep aids in the development of insightful thinking, creativity, and memory. Heartbeat and breathing rates reach their lowest level in this stage. Your muscles are at maximal relaxation and sleep is so deep, it may be difficult to wakeup if disturbed.
REM sleep— first occurs about 90 minutes after falling asleep.
It’s called REM because of the rapid eye movements you experience during this stage. During REM sleep, your brain wave activity increases and you dream. Your breathing and heart rates also increase to near awake levels. Although your brain and physiologic functions are similar to those seen in wakefulness, your muscles become temporarily paralyzed, which prevents you from acting out your dreams. REM sleep plays an important part of memory consolidation and as we age, we sleep less time in REM sleep.
Ref: By Dr. Zach Bush & Dr. Peter Cummings