regulation of sleep-wake patterns Flashcards
Circadian rhythm
-A circadian rhythm involves changes in bodily functions that occur as part of a cycle with a duration of about 24 hours.
-Hence, our sleep-wake cycle is a circadian rhythm.
-This cycle is aided or disrupted by zeitgebers which are environmental time cues that help maintain the biological clock to 24 hours.
-When an individual’s biological clock changes through the influence of a zeitgeber, it is said to be entrained.
-For the sleep-wake cycle, light is the main environmental cue.
ultradian rhythm
-An ultradian rhythm involves changes in bodily functions that occur as part of a cycle with a duration less than 24 hours.
-Therefore, a sleep cycle is an ultradian rhythm.
-Each sleep cycle, which consists of NREM and REM sleep, lasts approximately 90 minutes, and at least 5-6 sleep cycles occur in a sleep episode for a healthy adult.
The suprachiasmatic nucleus (SCN) and melatonin
-The suprachiasmatic nucleus (SCN) is an area of the hypothalamus in the brain and is considered the master biological clock that regulates the timing and activity of the sleep-wake cycle.
-Melatonin is a hormone produced by the brain that is produced in response to darkness.
-Higher levels of melatonin in the body is associated with greater levels of drowsiness (making an individual more sleepy), and vice versa.
-Accordingly, the presence of light can impede melatonin production.
The SCN and melatonin are essential in regulating the sleep-wake cycle via the following process:
- The SCN receives information about incoming light from the eyes, and works to adjust the sleep-wake cycle.
- The SCN sends neural messages to the pineal gland to either secret more, or less melatonin. The more light that is perceived, the less melatonin will be secreted, and vice versa.
- The levels of melatonin in the bloodstream will cause an individual to feel either more or less drowsy, hence affecting their sleep-wake cycle.
