We all take advantage of sleep and think of it, at times, as a luxury more than a physiological and psychological necessity. Edwards, O’Dreiscoll, et al, in their paper over Aging and Sleep: Physiology and Pathophysiology, simply defined sleep as a natural state characterized by a reduction in voluntary motor activity (skeletal muscle movement) but not involuntary activity (heart, lungs, organs, etc.), and a decreased response to stimulation and stereotypic posture that is both reversible and self-regulating (makes the warning labels on sleep aids like Ambien make more sense). Although the exact concentrations of specific hormones or neurotransmitters needed for sleep is not known, some play a specific and important role in both sleep and
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We can divide sleep into two main categories: REM (rapid eye movement) and non-REM sleep. We can then divide non-REM further into 3 stages. Let us begin with non-REM. Sleep is considered a cycle because it cycles through REM and the non-REM stages. The first stage involves between 5-10% of each cycle. It is characterized by closed eyes with semiconsiousness (closer to unconsciousness). The EEG shows what is called theta waves measured to be 4-7 Hz. In contrast, subjects that are awake exhibit alpha waves characterized by 8-14 Hz waves. The second stage is characterized by light sleep and accounts for 45-55% of the cycle. The heart rate starts to slow and body temperature drops. The third, and last, stage of non-REM sleep is also known as deep sleep and accounts for 15-25% of the cycle. The body secretes bursts of growth hormone and prolactin in order to perform repairs in tissues, build bone and muscle, and strengthen the immune system. It is initiated in the preoptic area. Through the EEG it is characterized by delta waves measured to be 5-2 Hz. REM sleep typically starts 90 minutes after sleep initiation and typically lasts for 10 minutes through the first cycle then progressively lengthens as cycles pass. REM sleep is characterized by rapid eye movement and muscle paralysis. Heart rate, breathing, and temperature become unregulated. This stems the term paradoxical sleeping because vitals indicate the sleeper is awake and the brain uses more oxygen than it does when the sleeper is
We can divide sleep into two main categories: REM (rapid eye movement) and non-REM sleep. We can then divide non-REM further into 3 stages. Let us begin with non-REM. Sleep is considered a cycle because it cycles through REM and the non-REM stages. The first stage involves between 5-10% of each cycle. It is characterized by closed eyes with semiconsiousness (closer to unconsciousness). The EEG shows what is called theta waves measured to be 4-7 Hz. In contrast, subjects that are awake exhibit alpha waves characterized by 8-14 Hz waves. The second stage is characterized by light sleep and accounts for 45-55% of the cycle. The heart rate starts to slow and body temperature drops. The third, and last, stage of non-REM sleep is also known as deep sleep and accounts for 15-25% of the cycle. The body secretes bursts of growth hormone and prolactin in order to perform repairs in tissues, build bone and muscle, and strengthen the immune system. It is initiated in the preoptic area. Through the EEG it is characterized by delta waves measured to be 5-2 Hz. REM sleep typically starts 90 minutes after sleep initiation and typically lasts for 10 minutes through the first cycle then progressively lengthens as cycles pass. REM sleep is characterized by rapid eye movement and muscle paralysis. Heart rate, breathing, and temperature become unregulated. This stems the term paradoxical sleeping because vitals indicate the sleeper is awake and the brain uses more oxygen than it does when the sleeper is