SLEEP

                                                                 Sleep

                                                PKGhatak, MD

Sleep is a state of the body during which most of the bodily functions are suspended, consciousness and voluntary actions are absent but readily reversible to external stimuli.

Sleep is a compulsory phase of daily occurrence for all animals - even whales sleep in water; and sharks who must move in order to force water through the gills to meet oxygen requirements, undertake a kind of restfulness, a phase equivalent to sleep. Young dolphins are seen sleeping while swimming but remaining in bodily contact with others within the pods. Plant physiologists have observed sleep like state in plants. Developing human fetuses also sleep in the mother's womb. Newborns sleep most of the time with short periods of wakefulness, which gradually increases as the child advances in age. Adults sleep 6 to 8 hrs. a day, the elderly require less sleep and octogenarians experience short periods of awakening during nocturnal sleep.

People who work shift duty jobs have difficulties in falling asleep after switching over and most of them develop hypertension, diabetes, obesity, metabolic syndrome, ulcers, increased irritability and behavioral changes. Night duty workers have a 10 % reduction in longevity compared with the workers doing the same job during the daytime.

Sleep deprivation causes increased Cortisol release, increased Ghrelin secretion, decreased Leptin and increased hunger and appetite.

The circadian rhythm controls hormone release; at the start of darkness, Melatonin is released from the pineal gland, which prepares the body to fall asleep. During sleep, cortisol level falls, and the antidiuretic hormone release is stopped. Pituitary Growth hormone is released. Cytokines - tissue necrosis factor (TNF), and interleukin 1(IL-1) are released and help tissue repair at night; also, TNF and IL-6 levels increase, which activates the liver cell regeneration.

Long term memory development takes place during sleep, and growth in children accelerates during sleep. The BP, heart rate, and respiration rate decrease. The voluntary muscles cease to function temporarily but the cardiac and smooth muscles continue to work. As we begin to wake up, all the above changes are reversed. Increased cortisol secretion and elevation of BP may trigger a heart attack in patients with coronary artery disease.

Dreams during sleep are a natural occurrence, many remember the dream on waking up, but most others fail to recall. Scientists believe rewiring neurons in the Neocortex and Hippocampus during sleep generates dreams. Many believe octopuses dream during sleep as evidenced by the color changes.

Young children develop nightmares during their dreams, which experts think is a benign phase of brain development. Sleepwalking at a young age is also a benign condition but in adults, it is not normal.

Sleep apnea in an obese person is a risk factor for hypertension, cardiac arrhythmia, and heart attacks. This condition is due to the decreased tone of muscles of the glottis and tongue falling backward, obstructing the entry of air into the laryngopharynx. Snoring during sleep is a similar condition but airways still remain partially open and breathing does not stop.

In any discussion on sleep, REM (rapid eye movement) and Non-REM (NREM) are discussed. In adults, NREM sleep takes place about 70% of sleep time. Scientists have divided NREM into 3 phases based on the frequency of the brain waves. Phase 3 of NREM is deep sleep, and most of the bodily functions are lowest during this period but at the same time, tissue repairs, healing and rejuvenation of the body and mind take place here. The changeover from one stage to the next does not necessarily follow any particular order. In babies, REM happens 50% of sleep time. In younger adults, NREM takes place at the beginning of sleep, followed by REM about 90 minutes later. Initial REM sleep lasts only 10 minutes and increases progressively and at the end may last 60 minutes. Heart rate, BP and respiration increase during this phase and dreams, that can be recalled, happen during REM sleep, though scientists believe humans dream in each phase of sleep. Reinforcement of memory happens in REM sleep. The brain switches REM and NREM in some order initially but in older individuals, no particular pattern is recognizable. In old age, REM and NREM switch back and forth in short order and even at the onset of sleep and no order is observed.

Narcolepsy and Restless Leg Syndrome are neurological disorders and are not discussed here.

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