Humans sleep about eight hours daily, roughly one-third of their life.
Sleep is a reversible state of reduced responsiveness, motor activity, and metabolism.
The purpose of sleeping is yet, not well understood.
Experimental data support various potential functions, including
Energy conservation.
Restoration and clearance of metabolites.
Brain metabolism during sleep likely plays a restorative function via the
clearance of substances, such as adenosine,
which builds up during the day, and presumably helps to induce deep sleep.
Another potential benefit of sleep is Promotion of brain plasticity.
Sleep plays a role in brain plasticity
by promoting learning-dependent synapse formation and maintenance.
Humans clearly learn less well when not sleeping enough;
thus, sleep must have an impact on cognitive function and memory.
Growth hormone secretion peaks during sleep;
this may contribute to muscle growth and cell regeneration during the night.
We recognize TWO main stages of sleep, non-rapid eye movement, and Rapid Eye Movement stage.
A fully awake brain is associated with Behavioral cues, including open eyes,
movement, and conversation, demonstrating alertness.
However, as activities wind down, people recline and close their eyes.
This rhythm is the bridge between wake and sleep.
When this rhythm slows further, sleep has arrived.
Most people enter sleep from a drowsy state via NREM sleep.
Non-rapid eye movement sleep is divided into three sub-stages: stage N1, stage N2, and stage N3.
Stage N1 is the typical transition from wakefulness to sleep.
Eye movements are typically slow and rolling.
It is the lightest stage of sleep; patients awakened from it usually do
not perceive that they were asleep. This stage lasts for a few minutes.
Stage N2. represents roughly 50% of the night.
Generally, it comprises the largest percentage of total sleep time in an ordinary adult.
Stage N3 sleep is frequently referred to as "deep
sleep" or "slow-wave sleep. " This stage typically accounts
for 10 to 20 percent of the total sleep time in adults and decreases with age.
It is often more difficult to arouse sleepers during stage N3 than in the previous 2 stages.
And stage N3 is a typical time for sleepwalking and other sleep disorders.
REM sleep, also known as stage R. is characterized by
Rapid, irregular eye movements under the eyelids. sleep paralysis, which is the inactivity of all
voluntary muscles, except for the breathing and some eyes muscles.
REM sleep has typically been associated with vivid dreaming,
Although REM sleep accounts for less than a quarter of total sleep time,
REM sleep is associated with more irregularities in heart rate, respiratory rate, blood pressure,
and ventilation. Worsening preexisting obstructive sleep apnea or other sleep disorders.
REM sleep accounts for a minority of sleep time. It has an essential
role in physiological homeostasis and cognition.
Sleep stages shift in one of two ways. Alternatively, arousals will occur,
bringing the individual from deeper to lighter sleep or wakefulness.
Sleep is not a homogenous process and appears to go through multiple discrete cycles at night.
These cycles occur in fairly typical patterns of non-rapid eye movement
and rapid eye movement sleep, with each cycle lasting approximately 90 to 120 minutes.
Four to five cycles occur during a typical eight-hour night of sleep.
Young adults typically sleep approximately eight hours per night.
With a high percentage of stage N3 sleep, as humans transition to middle age and beyond,
the percentage of N3 decreases. And the percentage of wake and N1 increases.
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