Stages of sleep
Stage | Description | EEG |
Awake | - Cycling (~90 minutes) of gastric motility, hunger, and alertness during the day is likely a persistence of circadian rhythms. - Active 5-HT, NE, and ACh | |
Awake (eyes open) | - Alert, active mental concentration | β (highest frequency, Lowest amplitude) |
Awake (eyes closed) | α waves (10 Hz) | |
Non REM sleep | - Decreased temperature, blood pressure, respiratory rate, CBF, and cerebral metabolism - Decreased stage 4 and REM sleep are associated with hypothyroidism, Down’s syndrome, dementia, and phenylketonuria. - All neurotransmitters are decreased | |
N1 (5%) | - Light sleep | θ wave Decreased voltage loss of α waves |
N2 (45%) | - Deeper sleep - When bruxism (tooth grinding occurs) | Sleep spindles (0.5- to 2-second bursts of 13 Hz) K complexes (sharp slow waves of high amplitude |
N3 (25%) | - Deepest non REM sleep (slow-wave sleep), sleepwalking, night terrors, bed wetting (wee and flee in N3) | Highest-amplitude δ waves (1–2 Hz), deepest sleep stage |
N4 | - Visual dreaming - Somnambulism | δ waves. |
REM Sleep | - Increased ACh and decreased 5-HT and NE | |
REM sleep (25%) | - Loss of motor tone (α and γ motor neuron inhibition, decreased H response, and decreased reflexes) - Increased blood pressure, pulse, respiratory rate, and CBF. - Inc. ACh. - Dreaming, nightmares, and penile/clitoral tumescence occur; - May serve memory processing function. - Extraocular movements due to activity of PPRF (paramedian pontine reticular formation/ conjugate gaze center). - Pupillary dilation and constriction. - Occurs every 90 minutes, and duration inc. through the night. | β desynchronized EEG with increased frequency and decreased amplitude. Changes in older adults: • Dec. REM • Dec. N3, • Inc. sleep latency, • Inc. early awakenings. Changes in depression: • Inc. REM sleep time • Dec. REM latency • Dec. N3 • Repeated night time awakenings • Early morning awakening (terminal insomnia). Change in narcolepsy: • Dec. REM latency. At night, BATS Drink Blood. |
REM sleep
- The first REM cycle is at 1.5 hours, and then it repeats every 4 to 6 hours.
- Later cycles have
- Decreased stage 4
- Increased REM components (mainly stage 2 and REM).
- Organization of the sleep cycle.
- Awake → Nonrapid eye movement (NREM stage 1, 2, 3, 4) → REM → Awake
- 1st third of night → NREM > REM
- 2nd third of night → NREM ~ REM
- Last third of night → REM > NREM
- Newborns have
- 50% REM
- 60-minute cycles.
- Young adults
- 25% REM,
- 5% stage 1,
- 50% stage 2,
- 20% stages 3 and 4 sleep.
- Older people
- Have decreased stages 3 and 4 sleep (5%).
The REM and non-REM cycles are controlled by pons (pedunculopontine nucleus)
- 5-HT
- NE
- ACh
Hormonal changes
- Cortisol and thyroid stimulating hormone (TSH) decrease with sleep onset
- Cortisol increases with awakening.
- LH and prolactin levels increase with sleep.
- GH levels surge in the first 2 hours of sleep.
- Melatonin is only made at night.
K complexes
- Begin to appear at 6 months of age
- Appear at N2
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