Sleep is natural and reversible state of lowered responsiveness to outside stimuli, state of relative inactivity accompanied by loss of consciousness. During sleep no biological functions stop working.
Sleep phases
Sleep consists of two phases, non-REM phase and REM phase.
When falling asleep we enter non-REM phase at first, muscles relax, breathing calms down and blood pressure lowers. We can dream during non-REM phase but after waking up we don’t remember them.
REM phase is part of sleeping cycle characterized by quick eye movement, muscles are completely relaxed (we can call this condition atonia). Breathing is irregular and blood pressure is higher that during non-REM sleep. During REM phase we dream and after waking up we remember their content.
During this sleeping phase part of the brain, thalamus, sends images, sounds and other sensory stimuli which form dreams. Even amygdala (emotional center) sends signals to the brain therefor dreams can cause different emotions.
Non-REM sleep converts to REM sleep after approximately 90 minutes. This way non-REM and REM sleep cycle and before waking up REM sleep lengthen.
Sleep anatomy
Sleep anatomy is based on hypothalamus, concretely bundle of cells which make suprachiasmatic nucleus (SCN), adenosine and melatonin.
Suprachiasmatic nucleus (SCN)
SCN consists of cells which react to light from outside world. Lowered amount of light transfers signal to brain when to wake up and when to go to sleep. Other animals react to these stimuli as well.
Even blind people have perception of rotation of day and night which is evolutionary programmed in our brains.
Adenosine
Amount of adenosine depends on brain cells metabolism. It is created by break up of ATP (adenosine triphosphate- main molecule which gives brain energy) in brain when we are awake.
Therefor we can say that while we are awake, ATP disintegrates as brain uses it as source of energy. Adenosine is released and his high amount in brain causes we are tired.
In case we don’t provide body enough sleep adenosine cumulates and the result is way longer sleep and often unplanned naps during the day.
Melatonin
Melatonin is hormone secreted by pineal gland, which naturally creates sleepiness. Its levels increase during evening hours, the highest are at midnight and nearing the morning its levels decrease. Secretion of melatonin is naturally regulated based on the length of day. During the winter, when sun sets down sooner, melatonin is secreted for longer period of time. During the summer days it’s levels are regulated too and it is secreted for shorter period of time based on exposition to sun.
Amount of sleep we need
Different age groups need different amount of sleep. Newborns sleep 16-18 hours. Children need 10-12 hours of sleep while teenagers need 9-10 hours of sleep.
Adults need 7-9 hours of sleep. However, everybody needs different amount of sleep!
People sleep less than their body naturally needs and excessive sleep during weekend doesn’t mean you will catch up on sleep deprivation. Eventually it will catch up on you.
Sleep deprivation? How does it affect our body?
- Not getting enough sleep has negative effect on body. It can cause hypertension (high blood pressure), coronary diseases and heart attack
- Studies show connection between development of obesity, diabetes and sleep deprivation. When we don’t sleep enough, we have tendency to eat more during evenings and therefor negatively affect our metabolism.
- Not getting enough sleep has proinflammatory effect (development of diseases). It causes increased release of cytokines; cytokines are body chemicals that signal body that there is a virus or bacteria and body needs to start fighting it
- Sleep affects our mental health too, diseases like insomnia can higher the risk of occurrence of anxiety, depression, psychotic episodes and even suicide
- Sleep deprivation can result in slower reacting to various situations and outside stimuli. We are slower, we think slower and even our reactions are slower, that can be reason of many car accidents
- Sleep has beneficial effects on our memory. When we don’t provide our body enough sleep information which we required during day don’t get into long- term memory, it stays in our short- term memory, no new connects are created among neural cells
Sleep hygiene
