Biology of Sleep - AP Psychology

Sleep occurs in 4 stages, NREM-1, NREM-2, NREM-3, and REM.

It's during the first stage of sleep (NREM-1) that you may experience images that resemble hallucinations. These experiences occur without a sensory stimulation and can sometimes be later incorporated into one's memories.

REM (rapid eye-movement) sleep is the fifth and final stage of sleep during which the body is in it's deepest sleep. Dreaming is most frequent, most vivid, and most memorable during REM sleep; however, other dreaming can occur during the other sleep stages.

Rapid-eye movement (REM) is the stage during which most dreaming occurs. It is the last stage in the cycle of sleep and gets longer and more frequent the longer you sleep.

REM sleep (REM stands for "rapid eye movement") is the stage of sleep in which we dream. As the name suggests, our eyes move rapidly in different directions while in this stage. The other 4 stages of sleep are called "non-REM" sleep.

A delta wave is a wave with a high amplitude (height on graph) and has a frequency of 0-4 Hz (fairly slow). Delta waves are helpful to note on a scan because they can help characterize how deeply a person is sleeping; in certain disorders (such as alcoholism) delta waves are disrupted by other wave forms, showing that a person is not getting the type of rest required by the body.

Melatonin is released by the pineal gland in response to circadian rhythms and other environmental clues, like darkness. It causes drowsiness and helps induce sleep.

Night terrors are characterized by high arousal and an appearance of being terrified. Stage 4 is our deepest sleep stage, so it is difficult for those with night terrors to escape their terror by waking up (unlike nightmares).

Delta waves occur during deep sleep (stage 4) and are associated with dreaming. In contrast, alpha waves are relatively slow brain waves that occur during a relaxed, awake state.

The average amount of sleep an adult gets is 8 hours. Everyone is different, however; where some adults function off of 6 hours, others need at least 9 hours or more to feel healthy and awake.

Circadian rythm is responsible for the cycles of our blood pressure, metabolism, and body temperature. It contributes to our levels of energy throughout the day and is responsible for our descension in sleepiness as night falls.

After stage 1, which lasts about 5-10 minutes, is stage 2 during which we slowly enter deep sleep. This stage is still considered light sleep, corresponds to a drop in body temperature. We can still be woken up fairly easily. Stage 3 is when we enter heavier, deep sleep.

REM is arguably the most important stage of sleep, and it is the last stage of our sleep cycle until it repeats all over again. Due to the heightened activity in our brains, we may have more intense dreams during this period. Also during this time, our heart rate and breathing quickens, and our body restores itself.

Insomnia is a sleep disorder in which the affected person may not be able to fall asleep, and keeps waking up during the night. It affects a significant percentage of Americans, and is mostly caused by stress or some other underlying condition. It is often treated with medications or behavioral therapy.

Melatonin is a hormone known to regulate sleep and wake cycles. It is released by the pineal gland into the bloodstream when sleep is prompted.

The pineal gland is in communication with the SCN. When the SCN, a structure in the hypothalamus, senses light from the retinas, it will suppress the release of melatonin from the pineal gland. Thus, we're usually awake during the day time and asleep at night.

Insomnia is a disorder that is characterized by an abnormal difficulty to fall or stay asleep. There are more than three million cases in the United States each year—roughly one percent of the population—and its prevalence is most common among older individuals.

Obesity and depression are often associated with sleep apnea. This comorbidity is not commonly observed with the other choices: night terrors and ADHD.

Parasomnias are disorders that occur during sleep. There are various types of parasomniaas; however, nightmare disorder most commonly occurs during REM—rapid eye movement—sleep stage.

From stage 1, stage 2, stage 3, stage 4, and REM sleep, the average human sleeps about 90-110 minutes in a typical cycle.

Light sleep, memory consolidation, and synaptic pruning characterize stage 2 sleep. This stage has higher-voltage sleep spindles and K-complexes. It is the transition period from light sleep (stage 1) into slightly deeper sleep (stage 3) and subdued muscle movement.