Sleep

Sleep is more vital to health than most people realize.  Its a well known fact that infant sleep is conducive to brain development; however, there are many more health requirements associated with sleep that are often overlooked.  Although sleep is not yet fully understood, there is an immense amount of research which supports the vital impact that sleep (or sleep deprivation) has on health.  Because sleep is vital to human health, it is important to understand what sleep is and why it is important.

Sleep is defined as “the natural periodic suspension of consciousness during which the powers of the body are restored” (Sleep, n.d.).  Quality sleep consists of four stages: NREM1 (non-REM Stage 1), NREM2 (non-REM Stage 2), NREM3 (non-REM Stage 3), and REM (Random Eye Movement).  Humans cycle through these stages during sleep beginning with NREM1 and ending with REM.  One cycle through all four stages takes about 90 minutes and healthy adults  typically cycle through all four stages about five to six times per night.  Hence, the suggested amount of sleep is 8-9 hours per night.  In addition, REM sleep time increases throughout the night while other stages decrease (Siegel, 2005).  As humans progress through the four stages of sleep, brain waves become slower; however, remain interspersed by faster waves (Siegel, 2005).  REM sleep is characterized by high levels of brain activity which are comparable to that of wakefulness (Siegel, 2005).  In fact, researchers believe that REM sleep may play an important role in simulating wakefulness in order to provide opportunity for experience-based neuronal connections to be made, ascribing purpose to the mysterious experience of dreaming (Siegel, 2005).  This makes sense when considering the fact that infants spend more time in REM sleep than adults and are also deprived of many stimulating experiences simply due to their impending development (Siegel, 2005).  Adding to this enlightening concept is the fact that length of REM sleep has been found to reduce with age, signifying that the primary function of REM sleep also depreciates with age (Siegel, 2005).  This is evident in the apparent loss of memory and learning ability as age progresses and is also supported by evidence that memory and learning ability can be retained with continued cognitive use of learning and memory mechanisms.

It is not only the brain which experiences changes throughout the sleep cycle; however.  The body also experiences distinct changes.  Endocrine function, glucose regulation, immune function, monoamine regulation, blood pressure, body temperature, heart rate, breathing rate, muscle control, and eye movement are all affected.  Interestingly, it is during REM sleep in which the brain and body experience the most drastic changes.  During REM sleep the body becomes unable to regulate body temperature, causing body temperature to drift towards the temperature of the room; muscle atonia is experienced, causing muscles to paralyze; heart and breathing rates increase; blood pressure rises; and eye movement becomes rapid and erratic (Siegel, 2005).

Unsurprisingly, changes experienced during sleep are purposeful.  Researchers  have discovered that the changes experienced in relation to heart rate, breathing rate, and blood pressure are conducive to cardiovascular health (Siegel, 2005).  It has also been discovered that sleep has modulatory effects on endocrine function and glucose regulation (Besedovsky, Lange, & Born, 2011).  The endocrine system produces and secretes hormones which regulate cell and organ activity; metabolism, growth, as well as sexual development and function are all regulated by these hormones (Besedovsky et al, 2011).  In addition, the body intervenes during sleep to prevent glucose levels from dropping, indicating that sleep plays in important role in glucose regulation (Besedovsky et al, 2011).  Therefore, sleep has a tremendous impact on the body’s ability to regulate many of the body’s most essential functions.

Neurons located in the cerebral cortex and surrounding area fire individually during an awake state but seem to synchronize their firing during REM sleep (Siegel, 2005).  Researchers believe this is important  in the consolidation of both learning and memory (Siegal, 2005).  Walker & Stickgold (2004) report that animal studies have found an increase in REM sleep following learning tasks and new experiences as well as decrements in performance following disruptions of REM sleep.  Sleep also seems to play an important role in monoamine regulation (Leproult & Cauter, 2009).  During REM sleep monoamines such as norepinephrine, histamine, and serotonin are completely unavailable (Siegel, 2005).  Researchers believe this is due to the brain’s need to resensitize monoamine receptors, allowing them to regain full sensitivity during wakefulness (Siegel, 2005).  Sleep deprivation is therefore a contributor to mood disorders (Leproult et al, 2009).  Immune function has been discovered to be related to sleep and wakefulness rhythms (circadian rhythms) (Leproult et al, 2009).  In particular, pro inflammatory cytokines and T cells peak during NREM sleep while their counterparts peak during wakefulness (Besedovsky, Lange & Born, 2009).  Besedovsky et al (2012) suggest that sleep deprivation enhances risk for disease due to the consequence of chronic inflammation as well as increasing risk for immunodeficiency characterized by susceptibility to infection and a lowered immune response to immunization.

Because sleep is vital to human health, it is important to understand what sleep is and why it is important.  Humans experience four stages of sleep each night and cycle through these stages five to six times a night.  These cycles have been shown to be imperative in supporting vital body and brain functions.  Both quality and quantity of sleep are essential to the proper regulation of these functions.  REM sleep has been specifically shown to be immensely important in learning and memory consolidation as well as overall brain development in infants while numerous other functions are also regulated during sleep. It is for this reason that sleep is vital to overall health and well being.

References:

Besedovsky, L., Lange, T., & Born, J. (2011, November 10). Sleep and Immune Function. Retrieved January 21, 2017, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3256323/

Leproult, R., & Van Cauter, E. (2009, November 24). Role of Sleep and Sleep Loss in Hormonal Release and Metabolism. Retrieved January 21, 2017, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3065172/

Siegel, J. (2003, November). Why We Sleep. Retrieved January 19, 2017, from http://www.neurosciencegateway.ucla.edu/sites/all/files/sleep-research/sciam2003/sciamsleep.pdf

Sleep. (n.d.). Retrieved January 20, 2017, from https://en.wikipedia.org/wiki/Sleep

Sleep. (n.d.). Retrieved January 21, 2017, from https://www.merriam-webster.com/dictionary/sleep

Walker, M., & Stickgold, R. (2004, September). Sleep-Dependent Learning and Memory Consolidation. Retrieved January 21, 2017, from http://www.cell.com/neuron/fulltext/S0896-6273(04)00540-9