Biological Rhythms and Sleep Notes

Biological Rhythms and Sleep Notes

Biological Rhythms

  • Definition: Repeating, predictable fluctuations of biological functions over time.
  • Types of Biological Rhythms:
    • Ultradian Rhythm: Biological processes that repeat more than once a day (e.g., activity levels, feeding, hormone release).
    • Infradian Rhythm: Biological processes that repeat less than once a day (e.g., menstrual cycles, seasonal behaviors).
    • Circadian Rhythm: Biological processes that cycle approximately every 24 hours (e.g., hormone levels, body temperature).

Circadian Rhythms

  • Endogenous Clock: Generated internally; humans are diurnal (active during the day).
  • Adaptation to Light/Dark Cycles: Environmental cues (zeitgebers) control circadian rhythms; mechanisms involve the suprachiasmatic nucleus (SCN) of the hypothalamus.
  • Free-Running Circadian Cycle: In absence of zeitgebers, rhythms persist; humans typically maintain a cycle lasting approximately 25 hours.
  • Phase Shift: Changes in activity due to stimuli (e.g., night shifts or jet lag); the process is called entrainment.

Sleep Measures

  • Electroencephalogram (EEG): Monitors brain activity, showing distinctive wave patterns.
  • Electrooculogram (EOG): Monitors eye movements; distinguishes REM (rapid eye movement) and NREM (non-REM) sleep.
  • Electromyogram (EMG): Monitors muscle activity, particularly in the neck region.

EEG Patterns During Sleep

  • Awake: Desynchronized EEG characterized by beta activity (high frequency, low amplitude).
  • Stage 1 Sleep: Transition to sleep with alpha waves and vertex spikes; slowing heart rate.
  • Stage 2 Sleep: Features sleep spindles and K-complexes.
  • Stage 3 Sleep (SWS): Recognized by delta waves, indicating deep sleep.
  • REM Sleep: High cerebral activity similar to wakefulness; marked by rapid eye movements and muscle atonia (loss of muscle tone).

Sleep Cycles

  • Sleep consists of several cycles; percentages of each sleep stage can change throughout the night.
    • Initial stages include NREM sleep followed by REM.

The Purpose of Sleep

  • Recuperation Theories: Propose that sleep helps to restore homeostasis disrupted during wakefulness.
  • Adaptation Theories: Suggest sleep patterns evolved to facilitate survival, minimizing danger from predators and conserving energy.
  • Physiological Function: Essential for virtually all mammals and birds, although quantity needed may vary.

Sleep Patterns Across the Lifespan

  • Infants exhibit high amounts of REM sleep necessary for brain development.
  • Adolescents require increased sleep; new research suggests later school start times improve health and academic performance.

Effects of Sleep Deprivation

  • Mild to Moderate Deprivation: Increases sleepiness, irritability, and difficulties in concentration.
  • Severe Deprivation: Can lead to hallucinations.
  • Recovery: Intense sleep following deprivation (REM rebound) but not all lost sleep can be fully recovered.

Functions of Sleep

  1. Energy Conservation: Metabolic functions decrease during sleep.
  2. Niche Adaptation: Sleep helps organisms function within their ecological niche.
  3. Body & Brain Restoration: Sleep deprivation negatively affects immune function and increases sensitivity to pain.
  4. Memory Consolidation: Slow wave sleep and REM play roles in memory processing and synaptic rearrangement.

Brain Regulation of Sleep

  • Forebrain System: Generates slow-wave sleep (SWS).
  • Brainstem System: Activates the forebrain for wakefulness (reticular activating system).
  • Pontine System: Triggers REM sleep; inhibits motor neuron activity to cause muscle atonia.
  • Hypothalamic System: Coordinates the functions of the above systems.

Sleep Disorders

  • Insomnia: Difficulty falling or staying asleep.
  • Sleep Apnea: Characterized by unreliable respiration during sleep.
  • Narcolepsy: Involves excessive daytime sleepiness and sudden sleep attacks.
  • REM Behaviors: Acting out dreams during REM sleep.
  • Sleep Paralysis: Inability to talk or move upon falling asleep or waking.

Drugs Affecting Sleep

  • Hypnotic Drugs (e.g., Benzodiazepines, Ambien): Used to induce sleep; chronic use may lead to dependency and distorted sleep patterns.
  • Melatonin: A hormone linked to sleep regulation, though its effectiveness is debated.
  • Anti-Hypnotic Drugs: Stimulants that can suppress REM sleep, with a high potential for addiction.