Stages Of Sleep

STAGES OF SLEEP

Divided into two phases:

• Non-REM (N-REM)/Slow-wave sleep.
• Rapid Eye Movement (REM)/Paradoxical sleep.

1. NON-REM (N-REM)/SLOW-WAVE/S-SLEEP/SYNCHRONIZED/QUIET/ORTHODOX SLEEP:

• No rapid eye movement (REM) recorded on electrooculogram.
• Rather slow/quick eye movement.
• Diminished physiological functions & lowered overall activity – 
• Hence, referred  “Quiet/Orthodox sleep” 

STAGES OF N-REM SLEEP:

Stage 1:

• Transition from wakefulness to sleep.
• Characterized by disappearance of alpha activity & appearance of theta activity.
• Positive for slow eye movements.

Stage 2:

• Characterized by typical EEG activity.
• Ie., Sleep spindles & “K” complexes.
• No eye movement.

Stage 3 & 4:

• Stages of deep sleep.
• Also referred “Slow-wave sleep”
• Due to slow delta waves.
• Delta wave appears in stage 3 & dominates in stage 4.

REM/PARADOXICAL SLEEP:

• Due to “presence of rapid eye movement” recorded on electrooculogram.
• Has paradoxical elevation of brain activity, metabolism & physiological activity.
• “High-amplitude slow waves” replaced by “rapid, low voltage activity & beta wave” – 
• During stage 3 & 4 REM sleep.

FEATURES OF REM SLEEP:

1. In EEG RECORDING:

• Beta-wave.
• Reappearance of alpha wave.
• Saw-tooth wave (low voltage fast activity).
• Ponto- genital-occipital spikes.

2. Dreaming.

3. Other features –

• Generalized muscular atony.
• Penile Erection.
• Autonomic hyperactivity (Increased pulse rate & BP).
• Intermittent movement of small muscle groups.

DURATIONS OF N-REM & REM SLEEP:

• NREM (all four stages) & REM sleep – 
• Repeat several times a night in a cyclic manner.
• 4-6 times depending on sleeping length.
• Typical cycle starts with stage I NREM followed by 2nd, 3rd & 4th stages.
• Sleep returns to stage 3 & 2.
• 1st REM sleep- 70-90 minutes after sleep commencement.
• Note- Stage I NREM sleep occurs only once at starting of sleep.
• Since it is only transition phase between wakefulness & sleep.
• Once sleep starts cycle rotates between stage 2,3, 4 N-REM & REM sleep.
• REM sleep – 20-30% of total sleep.
• N-REM Sleep – 60-70% of total sleep.
• Stage 1-5: 10%.
• Stage 2: 40-50%.
• Stage 3 & 4 – 15-20%

IMPORTANT EVENTS DURING N-REM SLEEP:

• Deep/Slow wave sleep disorder –
• Occur during stage 3 & 4 of N-REM.

Important disorders:

• Somnambulism – Night walking during sleep.
• Sleep terror/Night terrors – Pavor nocturnus.
• Sleep-related enuresis/Nocturnal enuresis – Bed wetting.
• Bruxism – Teeth grinding.
• Sleep-talking – Somniloquy.

IMPORTANT EVENTS DURING REM SLEEP:

1. Nocturnal Penile Tumescence:

• Spontaneous occurrence of penis erection during sleep.
• Normal phenomenon.

2. Nightmares/Dream anxiety disorder:

• Characterized by fearful dreams.
• Occurring in last 1/3rd of night sleep.
• Wakes up frightened & remembers dream vividly (contrast to night terror).

3. Narcolepsy:

• Characterized by excessive daytime sleep.
• Often disturbed nighttime sleep & REM sleep disturbances.

• Associated with one or more accessory symptoms : –

3a. Cataplexy –

• Most common accessory symptom.
• Characterized by sudden decrease in muscle tone either, local or generalized.

3b. Hypnagogic hallucination – 

• Hallucination occurring just before falling asleep.

3c. Sleep paralysis – 

• Least common.

Note: Hallucination occurring just before awakening – “Hypnopompic” hallucinations.

Exam Question

STAGES OF SLEEP

• Non-REM sleep also referred as “N-REM/Slow sleep/S-sleep/Synchronized sleep/Orthodox sleep.
• Stage 1 N-REM sleep – There is disappearance of alpha activity & appearance of beat activity. 
• Stage 2 –  Sleep spindles & “K” complexes.
• Stage 3 & 4 – Deep sleep stages – Characterized by slow delta waves.
• REM – Presence of “Rapid Eye Movements”.
• REM also referred as “Paradoxical sleep” – Because of paradoxical elevation of brain activity, metabolism & physiological activity.
• High-amplitude slow waves seen in stage 3,4 of REM sleep is replaced by rapid low voltage activity (beta wave).
• Features of REM sleep in EEG recording – Beta-wave, reappearance of alpha wave & ponto- genital-occipital spike, dreaming, generalized muscular atony & increased pulse rate & BP.
• REM sleep – 20-30% of total sleep.

  N-REM Sleep – 60-70% of total sleep.

  Stage 2 – 40-50%.

  Events during NREM sleep include, 

  • Deep sleep/Slow wave sleep disorder – Occur during stage 3 & 4 of N-REM.
  • Somnambulism – Night walking.
  • Sleep terror/Night terrors – Pavor nocturnus.
  • Bruxism – Teeth grinding.

  Events during REM sleep include, 

  • Nocturnal Penile Tumescence – Normal phenomenon.
  • Nightmares/Dream anxiety disorder.
  • Narcolepsy presents,
  • Cataplexy.
  • Hypnagogic hallucination – Hallucination just before falling asleep.