Institute of Neurological Disorders and Stroke, “Nerve-signaling chemicals called neurotransmitters control whether we are asleep or awake by acting on different groups of nerve cells, or neurons, in the brain. Neurons in the brainstem, which connects the brain with the spinal cord, produce neurotransmitters such as serotonin and norepinephrine that keep some parts of the brain active while we are awake. Other neurons at the base of the brain begin signaling when we fall asleep. These neurons appear to "switch off" the signals that keep us awake” (National Institute of Neurological Disorders and Stroke). Researchers also suggest that a chemical called adenosine builds up in our blood while we are awake and causes drowsiness. This chemical slowly breaks down while we sleep. In order to be fully rested, we must follow all sleep stages. According to Sleep and Adolescents, Peg Dawson states, “Sleep is broadly classified into two types: rapid-eye-movement (REM) sleep and non-REM sleep (NREM). Cycling through all of the sleep stages for an adequate amount of time is essential to being fully rested”. NREM sleep consists of four stages that range from drowsiness to deep sleep. In the early stages (I and II), individuals awake easily and may not even realize that they have been sleeping. In the deeper stages (III and IV), waking is difficult. When awakened, individuals in stages III and IV may feel disoriented and confused. In NREM sleep their muscles are more relaxed than when awake. Although the sleeper in stages III and IV is able to move, this doesn’t happen because the brain is not sending signals to the muscles to move. REM sleep refers to active sleep, which is when dreaming occurs. During REM sleep, the breath and heart rate become irregular, the eyes move rapidly back and forth under the eyelids, and body temperature is
impaired so a sleeper does not sweat when hot or shiver when cold. Below the neck, however, the body is essentially paralyzed because the nerve impulses to the muscles are blocked.
Both REM and NREM sleep states develop before birth. Sleep cycle patterns and the amount of sleep needed changes from infancy to childhood, but at the age of four, most children sleep 10 hours a night and cycle through sleep patterns much like those of adults. The amount of sleep each person need depends on many factors, including age. According to National Sleep Foundation, “Infants generally require about 16 hours a day, while teenagers need about nine hours on average. For most adults,