3.4 motive sleep

3.4 motive sleep

• Sleep is a state of 

• normal & recurring state of changed consciousness or partial unconsciousness from which one can be readily aroused.

SLEEP

• neurologically dynamic behavior with elevated arousal threshold

• a state of rapid reversibility

how is sleep regulated

• Circadian & homeostatic processes

two-process model

• determination of the state of alertness

 Normal circadian rhythmicity assures

• humans are awake in the daylight & ready for sleep in the night

Homeostatic regulation is reflected by

• rise in sleep propensity during waking & its dissipation during sleep.

• what determines the alertness/sleepiness.

• the interaction between circadian driven sleepiness-alertness cycles & homeostatic (sleep deprivation or excess of wakefulness)

Functions of sleep

• Increased waste clearance of the brain.

• Emotion regulation

• Memory & learning

Increased waste clearance of the brain (restorative function)

• may result from the enhanced removal of potentially neurotoxic waste products that accumulate in the awake central nervous system.

Cortical surface of brain - awake

• Reduced interstitial space

• restricted CSF flow

• Metabolites accumulate

Cortical surface of brain - asleep

• 60% increase in the interstitial space

• better CSF flow

  • effective clearance of metabolites

Conservation of energy accomplished via

• Decrease in body temperature of about 1-2 Celsius degrees in mammals.

• Decrease in muscle activity.

 Emotion regulation - sleep deprivation

• emotional disturbances → irritability or anxiety. 

• influences the effectiveness of different emotion regulation strategies

connectivity between the brain's

emotions, prefrontal cortex, & amygdala

• homeostatic sleep system

• connectivity between these brain networks →

1. higher when rested

2. lower when sleep deprived

Memory & learning

• slow-wave sleep (SWS) & rapid eye movement (REM) sleep = facilitates the stabilization & integration of new memories.

• Sleep recalibrates associative synaptic plasticity

SWS slow-wave-sleep linked to

reactivation & redistribution of hippocampus-dependent memories to the neocortex

REM sleep

• refine & stabilize memories

4 Sleep stages of NO REM

• Stage 1 (Light sleep – Alpha → Theta waves)

• Stage 2 → EEG

• Stage 3 → Deep sleep begins

• Stage 4 → Deepest sleep

Stage 1 (Light sleep – Alpha → Theta waves)

• Transition stage between wakefulness & sleep.

• Alpha waves fade, theta waves begin.

• Easy to wake up.

• May experience hypnic jerks (sudden muscle twitches).

Stage 2 EEG

• Lower frequency, higher amplitude waves (sleep spindles + K-complexes).

• Heart rate & temperature drop.

• Body relaxes more.

• Still light sleep but deeper than stage 1.

Stage 3 Deep sleep begins

• EEG: Slow-wave sleep (delta waves appear).

• Muscle relaxation increases, body temperature and blood pressure decrease.

• Very hard to wake someone.

Stage 4 Deepest sleep

• Dominated by delta waves.

• Maximum muscle relaxation.

• Growth hormone released → important for tissue repair and development.

• Sleepwalking or night terrors may occur here

REM Sleep (Rapid Eye Movement)

• EEG becomes desynchronized (similar to wakefulness).

• Dreams are vivid & frequent.

• Body is paralyzed (muscle atonia) except for eye and respiratory muscles.

• Heart rate, breathing, & brain activity increase.