Sleep & Wakefullness
An article understanding the importance of good sleep
Sleep is the temporary state of unconsciousness indispensable for every human being after a long day of work. After a good night of sleep, one wakes up with a newly found vigour to start their day. Judging by our apparent state of inactiveness during sleep, most of us believe that sleep is that point of time when the brain takes rest after a whole day of hard work. But this is not at all the case! Electrophysiological trials have proved that sleep is specific brain wave criteria and comprise of a series of explicitly controlled brain states governed by a group of brain stem nuclei. Infants have a high requirement of 17 hours of sleep daily. This decline to 7-8 hours in case of adults and as one approaches old age, sleep becomes even lighter. A night of insufficient sleep leaves us restless for the entire day, creating a “sleep debt” and it should to be repaid in the following days for proper functioning of our mind and body.
Why is sleep important for us?
William Shakespeare had called sleep “nature’s soft nurse” owing to its ability to reinstate vitality within our body which in turn assists us to bring out the best performance every day. Sleep restocks the brain glycogen levels that had been exhausted during waking hours. It regulates our body temperature and preserves the energy which would have been otherwise expended by the body to keep warm during cold nights if we remained awake. Sleep assures superior immune response and is the best way to lead a healthy life.
If you crave beauty, then sleep well. This is because, the production of body cells is augmented and the breakdown of proteins is minimized during sleep. Sleep plays an important role in stabilising our mind. During the course of day we confront a great number of incidents which need to be learned and remembered. Sleep facilitates this learning process and ensures its long term preservation. While we remain dormant, the brain sorts out memories according to their emotional values in our life and stacks them likewise. Lack of sleep can lead to malfunctioning of the nervous system and our brain might go completely haywire. Impaired memory diminished noetic abilities, mood swings, delirium and hallucinations are only few of the disorders that arise due to scarce sleep.
How does sleep and wakefulness maintain a circadian rhythm?
A free running internal block within our body maintains pertinent episodes of sleep and wakefulness despite absence of cues regarding the time of day and variation of daylight and darkness in different seasons and places. This circadian rhythm of sleep-wake cycle is governed by specialised brain circuits. As darkness falls during night, the change in light intensity is detected by cells within the ganglionic cell layer of retina and depolarise melanopsin, the photopigment within them. The generated nerve impulse activates the suprachiasmatic nucleus (SCN) via retinohypothalamic neurons. SCN stir up neuronal response which in turn stimulate the pineal gland to synthesize and secrete melatonin into the blood and regulate the neural circuits of brain. As night ends and light appears, the level of melatonin in blood declines and one wakes up to witness the light of the day.
Stages of sleep:
As a person falls asleep they don’t go through a uniform deepness of sleep for the entire period of dormancy. The depth of the slumber increases exponentially and in a sequential manner. With the help of electroencephalographical recordings, Nathaniel Kleitman and Eugene Aserinksy (1953) became the first to prove this phenomenon. The phases of sleep is classified into 2 prime stages depending on the presence and absence of eye movement, namely, non rapid eye movement (non REM) sleep and rapid eye movement (REM) sleep. Non-REM sleep is further divided into four stages:
1st stage: As one goes to sleep one enters a phase of drowsiness from which he can be awakened easily. The person displays mild eye and muscle activities. There are lot of people to feel a plunging sensation followed by an abrupt jerk. This is due to sudden muscle contractions called hypnic myoclonia occurring during initial phase of sleep.
2nd stage: As a person ascends to this next phase, eye movement stops and the brain waves slow down, interrupted with high frequency waves called sleep spindles.
3rd stage: Occurrence of sleep spindles decline and the person goes into moderately deep sleep due to onset of extremely slow brain waves called delta waves.
4th stage: It is the deepest stage of sleep and is characterised by delta waves only.
Non-REM sleep exemplifies an inactive brain in an active body since it is followed by decrease in muscle tone, heart rate, metabolic rate, breathing and body temperature along with lack of body movement. After these consecutive stages, our mind enters a new state called REM sleep characterised as an active brain in an inactive body. Physiological conditions of the body are reversed along with pupillary constrictions, limbic paralysis, twitching of fingers, toes and the middle ear. Our mind keeps swinging between non-REM and REM stages of sleep till we wake up.
Why do we dream?
Dreams are elaborate, mostly bizarre interpretations of emotions like sadness, fear and anger, sometimes joy and excitement and sometimes sexual feelings. They mostly occur during REM sleep and seldom during non-REM ones. Our mind always remains engrossed with imaginations and fantasies. However, when we are conscious, they are suppressed by certain nerves. But when we sleep, these nerves become dormant and our imagination finds expression in our mind through dreams. The signals for dream are sent to brain through the same nerve path which coordinates our activities during wakefulness. Hence every episode we dream of seems realistic.
How the brain controls sleep-wake cycle?
During the sleep-wake cycle, a number of dedicated neural circuits are alternately switched on and off in a harmonized manner. Cholinergic neurons in brain stems or our reticular activating system produce neurotransmitters like serotonin and norepinephrine which activates certain hypothalamic neurons while we are conscious. As we go to sleep, these actions are inhibited while neurons at the base of the brain start evoking a response. As one enters REM sleep, the cholinergic neurons of pons-midbrain junction transmits signals to thalamocortical region of the brain as well as to the spinal cord leading to paralysis of limbs.
So, calm your body with sleep and stay healthy while you articulate your thoughts through dreams.
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