HMSC1000_Wk_3_Lecture_2_Homeostatic___Circadian_Regulation

Homeostatic and Circadian Regulation & Dysregulation of Sleep

• Overview of the significance of studying sleep regulation through homeostatic and circadian mechanisms.

• Importance of sleep science at the University of Western Australia.

Introduction to the Centre for Sleep Science

• Dr. Kath Maddison, PhD, serves as the Director of the Centre for Sleep Science and is associated with West Australian Sleep Disorders Research Institute.

Learning Outcomes

• Summarize the two primary drivers influencing sleep: homeostatic drive and circadian regulation.

• Describe the anatomical features of the circadian system and their roles in regulation.

• Identify adaptive factors that influence sleep.

Mechanisms of Sleep/Wakefulness

• Homeostatic Drive: Increases with time awake; regulates sleep pressure.

• Circadian Drive: Regulates wakefulness tied to circadian rhythms.

• Two Process Model of Sleep Regulation: Integrates homeostatic and circadian influences.

• Adaptive Drives: Behavioral and environmental factors impacting sleep.

Two-Process Model of Sleep Regulation

• Proposed by Borbely et al. in 1982.

• Homeostatic drive escalates with wake duration and diminishes during sleep.

• Circadian drive fluctuates due to circadian variations in sleep/wake promoting substances.

• Pattern demonstrates sleep onset when homeostatic drive is high and circadian drive for wakefulness is low.

Homeostatic (Intrinsic) Drive

• Sleep pressure escalates the longer one remains awake.

• Adenosine plays a vital role in sleep regulation, accumulating during wakefulness and decreasing during sleep.

• Caffeine functions as an adenosine antagonist, heightening alertness.

• Homeostatic drive predominantly influences NREM sleep over REM sleep.

Circadian Drive/Regulation

• Involves the interaction of key anatomical structures:

  • Pineal Gland: Secretes melatonin, modulating sleep cycles.

  • Suprachiasmatic Nucleus (SCN): Central clock regulating circadian rhythms.

  • Retina and Optic Nerve: Relay light information crucial for circadian entrainment.

Circadian Entrainment

• The endogenous sleep-wake cycle averages ~24.2 hours absent light/dark cues.

• External environmental factors can modify this cycle.

Circadian Rhythm Changes Across the Lifespan

• Infancy: Sleep patterns are irregular, with fluctuating amplitudes.

• Childhood and Adolescence: Increasing regularity in sleep/wake patterns; various hormonal changes influence sleep timing.

• Adulthood to Later Life: Shift in sleep patterns, impacting melatonin and cortisol levels.

Adaptive Drives Influencing Sleep

• Psychological Factors:

  • Motivation for sleep, attention to environment, mental stimulation, and anxieties.

• Bed Comfort and Social Activity: Influences sleep routines.

• Light: Major synchronizing factor affecting circadian cycles; influenced by intensity and duration.

• Other Factors: Noise, temperature, exercise, and food consumption.

Circadian Dysregulation

• Causes of dysregulation include:

  • Shift work, social jet lag, light exposure, and medical conditions.

• Circadian rhythm assessment can involve monitoring cortisol, melatonin, and activity using actigraphy.

Chronotypes and Their Importance

• Defined as a natural preference for sleep timing; assessed via questionnaires and actigraphy.

• Categorized into morning types, evening types, and intermediates.

• Evening types report more sleep complaints and are more affected by sleep quality on workdays.

Conclusions and Summary

1. Sleep regulation involves both homeostatic and circadian drives.

2. Several behavioral and reflexive adaptive factors influence sleep beyond biological rhythms.

3. Light serves as the primary factor synchronizing the circadian system.

4. Understanding the circadian system is critical in the regulation and occurrence of sleep.

Further Reading

• Recommended chapters from "Principles and Practice of Sleep Medicine, 7th edition"; significant for deepening understanding of sleep medicine and related neuroscience.