Circadian Rhythmic Sleep Cycles

Biomechanisms of sleep

• Light detection

• Hormonal regulation

• Physiological adjustments

Light detection

• Retinal photoreceptors (Rods) detect light changes (Amplitude)

• Signals the suprachiasmatic nucleus, the body’s biological clock, that is time to wake up or go to sleep

Hormone regulations

• The suprachiasmatic nucleus controls the body’s circadian rhythm and signals the pineal gland to release melatonin when it gets dark, helping regulate sleep

• Norepinephrine

• Epinephrine

• Orexin

Norepinephrine

• Fight or flight

• Its levels rise during wakefulness, promoting alertness and focus

• As you approach sleep, norepinephrine levels drop to help facilitate the transition to rest

Epinephrine

• Boosts alertness during stress

• Released in response to stress or excitement to increase alertness and prepare the body for action

• It’s levels are higher during the day and lower at night to help regulate sleep

Orexin

• Stimulate wakefulness and recovery

• Keep you awake during the day by stimulating the brain’s arousal systems

• At night, it’s levels drop to allow sleep to occur

Physiological adjustments

• Pons activates to regulate respiration

• Triggers the yawn reflex

Circadian rhythmic cycles

• Circadian rhythms

• Sleep cycles

• Biorhythmic changes

Circadian rhythms

• Repeatable biological and behavioral patterns

• Synchronized to a 24 hour cycle

Sleep cycles

• Consist of 2 phases: REM and NREM

• Each stage has distinct biorhythmic changes

2 sleep cycles

• NREM: Stages 1 to 4 and 4 to 2

• REM: The complete last stage which is 1 which contains 4 to 5 cycles

Biorhythmic changes

• Neural electrical activity shifts between phases

• Respiratory system adapts to sleep depth

• Circulatory system adjusts heart rate and blood pressure

• Body temperature fluctuates throughout the cycle

Genetics of sleep

• 351 genetic factors influence circadian regulation and sleep cycles

• Human and neanderthal DNA mutations affect sleep patterns

• Sleep cycles evolve with age and environment

Key genes of genetics of sleep

• PER-3 gene

• CRY-1 gene

• DEC-2 gene

PER-3 gene

Early bird gene, linked to morning preference

CRY-1 gene

Night owl gene, associated with late sleep patterns

DEC-2 gene

Regulates the suprachiasmatic nucleus, maintaining an 8 hour cycle

NPSR1 mutation

• Linked to short sleepers

• Only about 5 hours of sleep

Stages of NREM sleep

• Hypnogogic Stage

• Stage 1

• Stage 2

• Stage 3

• Stage 4

Hypnogogic stage

Relaxed wakefulness before one starts to go to sleep

Stage 1

• Light sleep

• Easy to awaken

Stage 2

• Relaxed sleep

• Distinct decrease in blood circulation

Stage 3

• Delta sleep

• Slowed respiration

• Decreased body temperature

Stage 4

• Deep sleep

• Body unresponsive to stimuli

• Difficult to wake, even with alarm clocks

The 8 hour modle

• Complete sleep cycle

• Health needs

• Cycle completion

• Deep sleep timing

• REM sequences

• Adjustment period

• Wakefulness

Complete sleep cycle

NREM Stage 1 ➡ NREM Stage 2 ➡ NREM Stage 3 ➡ NREM Stage 4 ➡ NREM Stage 3 ➡ NREM Stage 2 ➡ REM Stage 1

Health needs

Both deep sleep and REM are essential for brain and body health

Cycle completion

• NREM and REM altogether happen 4 to 6 times in one night

• Each cycle lasts 90 minutes

• 8 hours of sleep is required

• The first 2 to 3 cycles are typically complete within 4 hours

Deep sleep timing

Allows deep sleep to be satisfied early in the night

REM sequences

Frequency and length of REM periods increase as morning approaches

Adjustment period

Sleep wake cycles can adjust to a new schedule within 3 to 5 days

Wakefulness

Waking up from stage 1 sleep is smoother because it’s a lighter and less deep sleep stage

Sleep deprivation

• 1/3 of all Americans suffer from sleep abnormalities

• Woman suffer more thane men

• Americans spend a lot of money to fall asleep and stay awake

• 31% or all drivers have fallen asleep behind the wheel