Sleep stages one through four are categorized as non-REM, or non-rapid eye movement, sleep. Stage one of sleep occurs as you begin to fall asleep. Muscles relax, breathing slows and pulse rate begins to lower. Internal organs continue to function as they do when you are awake. Brain activity during this stage is reduced, although you can easily be aroused.
Sleep is often viewed as a period of inactivity, however, the brain is active during sleep. There are five different stages of sleep, and each stage affects other body functions, such as pulse rate. Your body cycles through these stages four to five times each night, depending on how long you sleep. Your morning pulse rate correlates with the stage of sleep you are in.
Stage two of sleep begins when you fall asleep. Almost half of the non-REM sleep your body goes through occurs during stage two sleep. Brain activity begins to increase and your eyes stop moving. During this stage, your muscles are relaxed, blood pressure decreases, and breathing and pulse rate continue at the lowered rate.
Stages 3 & 4
Stages three and four of sleep are characterized by deeper sleep, and more input is required to arouse a person in these stages of sleep. You might wake up groggy and disoriented if you are woken up during stages three or four. Your body's physiological functions continue to be the same as the first two stages, and body temperature lowers as well.
Rapid Eye Movement
Rapid eye movement, or REM, sleep is when most dreams occur. This stage is characterized by increased eye movements, increased pulse rate, breathing and blood pressure. Stressful dreams can cause a greater increase in these functions. The amount of blood in the brain during REM sleep increases significantly, and brain wave activity is erratic.
- Talk About Sleep: An Intro to Sleep -- What is Sleep?
- PubMed Central; Inhibitory and Excitatory Intracortical Circuits Across the Human Sleep-Wake Cycle Using Paired-Pulse Transcranial Magnetic Stimulation; F. Salih, et al.; 2005
- National Institute of Health: Teacher's Guide -- Information About Sleep
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