Sleep is a natural process that is regulated by the cycle of day and night. The mechanism of sleep is not yet fully understood. The need for it, however, is related with physiological and psychological restorative. Humans evolved the need for sleep in synched with the cycle of daylight and night time darkness. Falling asleep involves a cascade of chemicals in the brain that begins as darkness falls and the temperature of the surrounding drops. This cycle typically decides the circadian.

Circadian beat

Most people have circadian rhythms that are synchronized with the local day and night cycle. This synchronization can be upset by self-imposed sleep deprival, drinking coffee or any caffeinated drinks, drinking alcoholic beverages, eating too much or by travelling to another time zone in an airplane. The latter is referred to as jet lag. It is a condition wherein the circadian rhythm of a person is still in synch with the time zone from where he or she started. Hence, the circadian rhythm conflicts with the actual night-day cycle of the locality.

When the sun begins to set, a series of neuro-electrical and chemical responses begins in the brain. It starts with the senses, especially involving the visual, tactile and thermo-regulatory views. All of these cues are centrally prepared in the hypothalamus.

Melatonin production

The suprachiasmatic nucleus receives signals from the hypothalamus gland which is then relayed to the pineal gland. In turn, the pineal gland gradually releases the sleep hormone, melatonin, into the blood stream.

Melatonin has the effect of slowing the heartbeat, relaxing the muscles and triggering sleepiness. Melatonin in the blood stream generally last for about twelve hours from around 9:00 p.m. to 9:00 a.m. Normal sleep patterns typically occur in two major parts, namely, the non-REM (rapid eye movement) sleep and the REM sleep.

NREM and REM components

The non-REM is consists of three stages that are recognizable based on the brainwave patterns as detected and measured by a hypnogram. The non-REM stages are as follow:

NREM stage 1: This is the twilight zone of sleep, the narrow gap between sleepiness and wakefulness. The muscles are still active but the eyes are rolling and the eyelids are moderately closing and opening. A sleeper may still be easily awaken and partially conscious.

NREM stage 2: This stage is marked by the theta wave brain pattern. A sleeper may already be hard to awaken during this stage. The alpha waves of the initial stage are suddenly interrupted. The unexpected disruption is known as sleep spindles and K-complexes.

NREM stage 3: It is during this stage that slow-wave sleep (SWS) begins. The SWS starts in the preoptic area and it is recognizable by delta wave activity, high amplitude waves at less than 3.5 Hertz. A sleeper will not anymore be delicate to non-intense environmental stimuli.

After the NREM stages, the REM component of sleep then follows. This is recognized by dreaming. The REM element sometimes happens at about 90-minute durations and it dominates about 50% of sleep.