Sleepy

Sleepy is a state of physiological rest characterized by reduced or absent consciousness, relatively suspended sensory activity, and inactivity of nearly all voluntary muscles. It is distinguished from wakefulness by a decreased ability to react to stimuli, and is more easily reversible than being in hibernation or a coma.

Physiology of Sleep

Sleep is a complex and dynamic process that affects how organisms function. The brain and other systems in the body play a key role in controlling sleep. The hypothalamus, a peanut-sized structure deep inside the brain, contains groups of nerve cells that act as control centers affecting sleep and arousal. Within the hypothalamus is the suprachiasmatic nucleus (SCN) — clusters of thousands of cells that receive information about light exposure directly from the eyes and control the behavioral rhythm.

Stages of Sleep

Sleep is divided into two basic types: REM sleep and non-REM sleep. Non-REM sleep consists of three stages: stage 1, stage 2, and stage 3, which is also known as deep sleep or slow-wave sleep. REM sleep, also known as dream sleep, is the stage of sleep associated with dreaming.

Sleep Disorders

There are many different sleep disorders, including insomnia, sleep apnea, narcolepsy, and restless legs syndrome. These disorders can significantly impact a person's health, quality of life, and overall well-being.

Sleep in Different Species

Sleep is observed in all mammals and birds, and in many reptiles, amphibians, and fish. However, the way that different species sleep varies greatly, both in terms of the amount and the distribution of sleep across the day and night.

See Also

• Circadian rhythm
• Dream
• Sleep deprivation
• Sleep hygiene
• Sleep medicine

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