Sleep, Stages Of Sleep, Characteristics And Disorders(Problems)


Sleep is a state of unconsciousness in which the mind and brain apparently turn off the functions that create an experience. During sleep, we become less aware of our surroundings. Sleep also inhibited sensory activity and inhibition of nearly all voluntary muscles during REM ( rapid eye movement ) and reduced muscle activity.

The  stages  of  sleep  refer to  distinctive  changes  in  the electrical  activity  of  the  brain and  accompanying  physiological  responses  of  the  body  that occur  as  you  pass  through  different phases of sleep.

        Brain waves are described in terms of frequency  (speed) and amplitude  (height).  They are recorded by a  complex machine called an  EEG or electroencephalogram.  Each stage of sleep can be recognized by its distinctive pattern of EEGs.


What are the stages of sleep

Alpha Stage Before actually going into the first stage of sleep,  you briefly pass through a  relaxed and drowsy state,  marked by characteristic alpha waves. 


is marked by feelings of being relaxed and drowsy,  usually with the eyes closed.  Alpha waves have low amplitude and high frequency (8–12 cycles per second). after spending a  brief time relaxing in the alpha stage,  you enter stage  1  of non-REM sleep.


What is the meaning of Non- REM?

Non-REM sleep is where you spend approximately 80%  of your sleep time.  Non-REM is divided into sleep stages  1,  2,  3,  and  4;  each stage is identified by a  particular pattern of brain waves and physiological responses.  (REM  stands  for  rapid eye movement.)


STAGE  1  sleep is a transition from wakefulness to sleep and lasts 1–7  minutes.  In it,  you gradually lose responsiveness to stimuli and experience drifting thoughts and images.  Stage  1  is marked by the presence of theta waves,  which are lower in amplitude and lower in frequency  (4–7  cycles per second) than alpha waves.


STAGE  2  sleep marks the beginning of what we know as sleep,  since subjects who are awakened in stage  2  report having been asleep.  EEG  tracings show high-frequency bursts of brain activity called sleep spindles.

stage 2, your  muscle tension,  heart  rate, respiration,  and body  temperature gradually decrease,  and it becomes more difficult for you to be awakened.


STAGES 3 and 4: About  30–45  minutes after drifting off into sleep,  you pass through stage  3  and then enter into stage  4  sleep.

       Stage  4  sleep,  which is also called slow-wave or delta sleep,  is characterized by waves of very high amplitude and very low frequency  (less than  4  cycles per second)  called delta waves.  Stage  4  is often considered the deepest stage of sleep because it is the most difficult from which to be awakened.  During stage  4,  heart rate,  respiration,  temperature,  and blood flow to the brain are reduced,  and there is a  marked secretion of  GH  (growth hormone),  which controls levels of metabolism, physical growth, and brain development.

        After spending a  few minutes to an hour in stage  4,  you will backtrack through stages  3  and 2  and then pass into a  new stage, called  REM  sleep,  which is associated with dreaming.

Read more articles : Sleep: Sleep Stages, REM Sleep, Biological, and Circadian Rhythms

Biological Clock Sleep or Circadian Rhythm with examples


What is the meaning of REM SLEEP?

REM sleep makes up the remaining 20% of your sleep time. It is pronounced “rem” and stands for rapid eye movement sleep because your eyes move rapidly back and forth behind closed lids. REM brain waves have high frequency and low amplitude and look very similar to beta waves, which occur when you are wide awake and alert. During REM sleep, your body is physiologically very aroused, but all your voluntary muscles are paralyzed. REM sleep is highly associated with dreaming.

          You pass into REM sleep about five or six times throughout the night with about 30 to 90 minutes between periods. You remain in each period of REM sleep for 15 to 45 minutes and then pass back into non-REM sleep.


What are the characteristics of REM Sleep?

you are asleep during REM, your body and brain are in a general state of physiological arousal (Aserinsky & Kleitman, 1953). For example, during REM sleep, your heart rate and blood pressure are significantly higher than during non-REM sleep (L. Rosenthal, 2006). Because of this strange combination of being asleep yet physiologically aroused, REM sleep is often called paradoxical sleep. (A paradox is something with contradictory qualities.)


IN REM BEHAVIOUR DISORDER, which usually occurs in older people, voluntary muscles are not paralyzed, and sleepers can and do act out their dreams, such as fighting off attackers in dreams.


 What is the meaning of REM—DREAMING AND REMEMBERING? 

DREAMING: One of the biggest breakthroughs in dream research was the finding that about 80–90% of the times when subjects are awakened from a REM period, they report having vivid, complex, and relatively long dreams (Dement, 1999). 


What is the meaning of the REM REBOUND?

     REM REBOUND refers to individuals spending an increased percentage of time in REM sleep if they were deprived of REM sleep on the previous nights.


REMEMBERING: REM sleep helps us store or encode information in memory and advise students to get a good night’s sleep so that what they studied the previous day has a chance to be stored in the brain’s memory (Stickgold, 2000, 2005).


What  Causes  Sleep?

 Going to sleep involves a  very complicated process during which different areas of the brain are activated or deactivated.  The whole sleep process begins with something flipping the master switch for sleep.


MASTER SLEEP SWITCH: The master switch for sleep is in a  nucleus of the brain called the  VPN (Purves et al., 2008).

The  VPN—ventrolateral preoptic nucleus—is a  group of cells in the hypothalamus that act as a  master switch for sleep. When turned on,  the  VPN  secretes a  neurotransmitter  (GABA)  that turns off areas that keep the brain awake.  When the  VPN  is turned off,  certain brain areas become active and you wake up.


RETICULAR FORMATION: The reticular formation,  a  column of cells that stretches the length of the brain stem,  arouses and alerts the forebrain and prepares it to receive information from all the senses.

     The reticular  formation  is  important  in  keeping  the  forebrain  alert  and in  producing  a  state  of  wakefulness (Ropper,  2006).  If the reticular formation is stimulated in sleeping animals, they awaken;  if it is seriously damaged in animals or humans,  they lapse into permanent unconsciousness or coma.

What are the sleep disorders or sleep problems?

What is the meaning of insomnia?

 INSOMNIA  refers to difficulties in either going to sleep or staying asleep through the night.  Insomnia is associated with a  number of daytime complaints,  including fatigue, impairment of concentration,  memory difficulty, and lack of well-being.


What is the meaning of sleep apnea?

SLEEP  APNEA  refers to repeated periods during sleep when a  person stops breathing for  10  seconds or longer.  The person may repeatedly stop breathing,  momentarily wake up,  resume breathing,  and return to sleep.  Repeated awakenings during the night result in insomnia and leave the person exhausted during the day but not knowing the cause of the tiredness.


What is the meaning of narcolepsy?

NARCOLEPSY  (NAR-ko-lep-see)  is a chronic disorder that is marked by excessive sleepiness,  usually in the form of sleep attacks or short periods of sleep throughout the day.  The sleep attacks are accompanied by brief periods of  REM  sleep and loss of muscle control  (cataplexy),  which may be triggered by big emotional changes.



Meaning of Night Terrors

        NIGHT  TERRORS,  which occur during stage  3  or  4  (delta sleep),  are frightening experiences that often start with a  piercing scream,  followed by sudden waking in a  fearful state with rapid breathing and increased heart rate.  However,  the next morning the child has no memory of the frightening experience.  About  3–7%  of children have night terrors.


Meaning of the Nightmares

          NIGHTMARES,  which occur during REM sleep, are very frightening and anxiety-producing images that occur during dreaming. Nightmares usually involve great danger—being attacked,  injured, or pursued.  Upon awakening,  the person can usually describe the nightmare in great detail.


Meaning of the Sleepwalking

          SLEEPWALKING  usually occurs in stage  3  or  4  (delta sleep)  and consists of getting up and walking while literally sound asleep. Sleepwalkers  generally  have  poor  coordination,  are  clumsy  but can  avoid  objects,  can  engage  in  very  limited  conversation,  and have no memory of sleepwalking


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