Non- and Rapid Eye Movement Sleep Essay

Introduction

In Greek Mythology, night has two sons, death and sleep. Dement in 1994 noted the association between death and sleep in the medical literature as early as 1834 when Robert MacNish inferred that death is an intermediate state between wakefulness and death. Recent understanding of sleep infers that sleep and wakefulness are two phases of brain activity that are separate physiologically and physiologically. However, both conditions are reflected on each other; further, sleep is a physical need and is an active physiological process and is a dynamic behavior not just the absence of wakening. Sleep is a state of altered consciousness that differs from coma in that an individual can be aroused. Further, during sleep the human brain is responsive to internal than to external stimuli (Kamal, p. 156).

Discussion

Animal laboratory studies show that rats deprived from sleep has an average life span of 3 weeks (instead of 2-3 years) with decreasing weight and sores on their tails possibly because of impaired immune mechanisms. From this, we know that sleep is needed for normal immune system functioning. The human brain shows significantly lowered metabolic activity after 24 hours of sleep deprivation. With sleep deprivation, body temperature becomes lowers and the white blood cells count (needed for body defenses against bacteria and various allergens) decreases. In addition, chronic sleep deficiency results in various arrhythmias. About the central nervous system, sleep deprivation results in impaired memory with altered ability to do simple mathematical calculations and lack of concentration. If sleep deprivation continues, mood changes and even hallucinations occur. For children and young adult, sleep is essential for growth, human cells show increased protein production and less breakdown during sleep. Besides, growth hormone release shows nocturnal increase during sleep. Thus, in brief, sleep is essential for physical, emotional, and social well-being of humans (Staud and Adamec, Pp. 189-193).

Sleep is not a uniform state of being; rather it is a complex, and a cyclical process of human physiology. It occurs in cycles of rapid eye movement (REM) sleep alternating with non-rapid eye movement sleep. Non REM sleep represents 75% of sleep duration and occurs in four stages (1 to 4) and REM sleep represents stage 5 (25%) of sleep. REM and Non REM sleep have different control mechanisms and serve different functions (Le Bon and others, 2002).

Animal transaction studies and lesion studies identified a small region in the lateral pontine tegmentum (corresponding to the lateral parts of the nucleus reticularis pontis oralis) and the part ventral to the locus ceruleus to be responsible for REM sleep. The question is whether these parts are enough for generation of REM sleep and the associated phenomena (muscle atonia, cortical desynchrony, rapid eye movements and altered sensory threshold) remains incompletely answered. Evidence suggests a role played by non-brainstem systems in shaping REM sleep. Non REM sleep generation involves interactions among many brainstem, diencephalic and forebrain cell groups. In the intact animal, this network is involved; however, in experimental animals, it is possible to observe various signs of Non REM sleep after transactions of the neural axis. This lead to the conclusion there may be multiple Non REM sleep generators (Kamal, Pp. 156-164).

Fragmentation of cognitive brain activity is a characteristic of Non REM sleep. The first Non REM sleep stage (1-7 minutes) serves as a transitional stage when the individual is easily awakened (law arousal threshold). If awakened, the individual does not recall being asleep, and the EEG shows decreased alpha activity. In stage 2 (10-25 minutes), the EEG characteristically shows bursts of distinctive 12-14 Hz sinusoidal waves against a background of low voltage mixed frequency activity (sleep spindles). In addition, characteristic high voltage waves (K complexes) appear especially after auditory stimulation. The EMG is low to moderate with no or rare eye movements. The characteristic of the third sleep stage is the high amplitude (>75 UV), slow delta waves. The EMG is low to moderate with no or rare eye movements. Occasionally, the EOG trace shows large voltages because of contamination from the EEG trace. In stage four (20-40 minutes), there is increase in delta waves which dominate the EEG trace (>50%). The EMG and EOG are the same as stage three. The REM stage (when individuals dream) is characterized by fast EEG waves similar to those in stage 1 (Non REM) sleep. Body muscles are almost paralyzed so as not to act our dreams, and there are bursts of rapid eye movements. REM sleep is not divided into stages, but there are two major periods; phasic (short clusters of rapid eye movements) and tonic (relative eye movement inactivity) periods (Roth, Pp. 8-11).

Conclusion

Sleep is an active physiological process that is essential to health, yet, at present, there are still many unresolved questions. Like what is the functional importance of REM and Non REM sleep alternation, and whether these two stages share the same general environment and compete for expression, or they are inter related with definite interactions.

Works Cited

1. Kamal, I. “What we know about sleep. Part 1: An introduction to sleep medicine.” Postgraduate Doctor vol 20 (5) 2004. p. 156-164.
2. Le Bon, O., Staner, L.,Rivelli, S. K., Hofmann, G. et al. “Correlations using the NREM-REM sleep cycle frequency support distinctive regulation mechanisms for REM and NREM sleep.” J Appl Physiol vol 93 2002. p. 141-146.
3. Roth, T. “Characteristics and Determinants of Normal Sleep.” J Clin Psychiatry vol 65 [suppl 16] 2004. p. 8-11.
4. Staud, R., and Adamec, C. A. Fibromyalgia For Dummies (chapter 14). New York: For Dummies, 2007.