As the night wears on, we enter into a blissful sleep and wake up the next day energized. The phenomenon of sleep is shrouded in mystery just waiting to be unearthed. Before you read further ask yourself -What exactly is sleep?
Sleep is defined as unconsciousness from which a person can be aroused by sensory or other stimuli.
Sleep is an essential component of our functionality. Limited sleep deteriorates our productivity as well as health. The exact reason behind this important physiological phenomenon is yet to be established. Sleep is believed to assist in cognition, brain waste clearance, neural maturation, facilitation of learning, conservation of energy.
Sleep is classified into two types - REM Sleep and Slow Wave Sleep (non-REM).
Each sleep cycle has the two types of sleep alternating with each other and REM sleep occurs on an average every 90 minutes and lasts about 5-30 minutes.
The depth of sleep decreases with each cycle whereas the duration of REM sleep increases with each successive cycle.
Slow Wave Sleep
It is called so as in this state, the EEG records brain waves which are strong and of low frequency.
The non-REM sleep aids in restfulness and is characterized by a decrease in peripheral vascular tone, blood pressure, respiratory rate, and basal metabolic rate.
Contrary to common expectation, even in slow-wave sleep, we dream. These dreams are often not consolidated into memory. They differ from REM sleep as in the latter dreams are associated with more body muscle activity.
REM Sleep
REM stands for rapid eye movement. Here, although the person is asleep his eyes undergo rapid movements.
Also known as Desynchronized Sleep because it's EEG (Electroencephalography) shows desynchronized nervous activity as found in the awake state.
Interestingly, it's also been referred to as the Paradoxical Sleep. REM sleep is characterized by high activity in the brain yet still the person is truly asleep as he isn't completely aware of his surroundings.
It is marked by vivid dreams. Here, heart rate and breathing become irregular which is characteristic of the dream state. REM sleep is thought to be important for refreshing cognitive processes and deprivation of which causes tiredness, irritability, and impaired judgment.
REM Sleep Behavior Disorder (RBD)
It is a rare sleeping disorder where people tend to act out their dreams during REM sleep ( where muscle tone is depressed).
It is characterized by sudden and potentially dangerous limb movements with vocalizations. This condition often precedes the development of Dementia with Lewy bodies or other neurodegenerative disorders.
Sleep and Hormonal Release
Hormone release is influenced by multiple factors such as seasonal changes, diurnal variation, sleep, and the different stages of development and aging, in addition to their negative and positive feedback control.
The secretion of growth hormone is increased significantly during the early period of sleep ( first 2 hours of deep sleep) but is decreased during the later stages.
Circadian Rhythms and the Sleep-Wake Cycle
Circadian Rhythms are daily cycles that repeat every 24 hours. They are endogenously generated,i.e., natural factors in the body produce them. Circadian rhythms are influenced by certain environmental factors such as light; the best example of such is the sleep-wake cycle.
Biological clocks produce circadian rhythms and regulate their timing. A living organism contains these biological clocks in every tissue and organ. The controller of these clocks is the master clock - Suprachiasmatic Nucleus (SCN) located in the hypothalamus. The input for SCN is the light rays.
SCN regulates the secretion of melatonin, a hormone that makes us drowsy. Light suppresses melatonin secretion.
Blue light does have an impact on sleep. With the increased usage of electrical gadgets as well as artificial lighting, there is increased exposure to blue night, which strongly suppresses melatonin secretion. Therefore, it is best to avoid your phone before going to bed!
DISCLAIMER: All the articles on this website are intended for educational purposes only. It is not a substitute for a doctor's medical advice.
REFERENCES -
1)Taber's Cyclopedic Medical Dictionary. Edition 21.
2) Guyton and Hall Textbook of Medical Physiology. Second South Asia Edition.
3) Davidson's Principles and Practice of Medicine. 23rd Edition.
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