Circadian Rhythms and Sleep Regulation

Master Clock

  • Located in the anterior hypothalamus known as the Suprachiasmatic Nucleus (SCN).
  • SCN sends nerve fibers to multiple parts of the body: pineal gland, eyes, blood vessels, and sweat glands in the head.
  • At night, the SCN "allows" the Superior Cervical Ganglion (SCG) to stimulate the pineal gland to release melatonin, which promotes sleep.

Peripheral Clocks

  • Influenced by the Autonomic Nervous System (ANS) and systemic cells.
  • Key markers of Circadian Rhythm:
    • Melatonin secretion
    • Plasma level secretion

Hypothalamic Control of Circadian Rhythm

  • The SCN generates signals to synchronize organ function.
  • Major hypothalamic nuclei involved:
    • VLPO (Ventrolateral Preoptic Area)
    • PVH (Paraventricular Nucleus)
    • POA (Preoptic Area)
    • PH (Posterior Hypothalamus)
  • Hypothalamic nuclei regulate sleep, wakefulness, temperature, and endocrine processes.

Sleep Regulation Mechanisms

  • The SCN communicates with hypothalamic nuclei, causing arousal to the cerebral cortex.
  • SCG modulates melatonin release, prompting physiological changes for sleep preparation.

Physiological Variables in Sleep

  • Indicators that follow a circadian pattern include:
    • Systolic pressure
    • Core temperature
    • Urine volume

Impact of Sleep Deprivation

  • Lack of sleep increases appetite by disrupting hormone balance that regulates hunger.

Effect of Artificial Light on Melatonin

  • Artificial light, particularly blue light from screens, inhibits melatonin production.
  • The brain signals the SCN and SCG to block melatonin release, mistaking day for night.

Sleep Regulation Processes

  • Sleep regulation involves two processes: homeostatic and circadian processes.

Acute Sleep Deprivation

  • Can elevate overall sleep pressure.
  • Staying up late contributes to circadian buildup, leading to Sleep Rebound, wherein the body compensates with longer and deeper sleep afterward.

Sleep Characteristics

  • Relative Mobility: minimal muscular activity.
  • Perceptual Disengagement: reduced responsiveness to external stimuli.
  • Subdued Consciousness: lower levels of awareness.

Assessing Sleep Patterns

  • MEQ (Morningness-Eveningness Questionnaire): self-report tool assessing chronotype.
  • The Pineal Gland plays a critical role in circadian rhythm regulation through the production of melatonin:
    • Peak secretion at night, lowest during the day.

Sleep Analysis Measurement Tools

  • Green-light PPG Measurements:
    • Detects decreases in heart rate during deep sleep.
    • Identifies spikes in heart rate linked to awakenings.
    • Assesses parasympathetic and sympathetic control.
  • Actigraphy: objective measurement method involving a device tracking movement during sleep.

Wakefulness-promoting Neuromodulators

  • Key substances related to wakefulness include:
    • Serotonin
    • Orexin
    • Histamine

EEG Wave Categories

  • Beta Waves: Fast, high-frequency brain waves (active thinking).
  • Theta Waves: Observed during light sleep (N2).
  • Delta Waves: Dominant in deep sleep (N3), characterized by low frequency and high amplitude.
  • Alpha Waves: Observed while relaxing but still awake.

Chronotype and Social Jet Lag

  • Chronotype: Individual's natural preference for being a morning or evening person.
  • Social Jet Lag: Misalignment of internal rhythms with social schedules, often due to weekend sleep habits.

Benzodiazepines

  • Act by binding to GABA-A receptors, enhancing GABA's inhibitory effects to create a calming effect.

Advanced Sleep Phase Disorder (ASPD)

  • A condition characterized by an earlier sleep onset and wake time than usual due to shifted circadian rhythms.

Sleep Hygiene

  • Practices and behaviors that promote consistent, quality sleep.
  • Essential for improving sleep quality and regulating sleep-wake cycles.

Sleep Measurement Tests

  • Objective Tests: Utilize measurable data with standardized scoring criteria.
  • Subjective Tests: Rely on self-reported data and personal experiences.