/Users/chloewong/Library/Containers/2B1BE8A8-4026-4D1A-92B6-913985F3D052/Data/tmp/usfca.instructure.com-6261817/75748802/Spring+2025_Chap+5+Body+Rhythms.pdf

Introduction to Biological Rhythms and Zeitgebers (00:00 - 03:15)

  • Historical views of sleep as a passive state versus modern understanding of active brain states.

  • Definition of biological rhythms, endogenous pacemakers, and free-running periods (τ≈24.2 hours\tau \approx 24.2\text{ hours}).

  • Role of environmental cues (zeitgebers), particularly blue-wavelength light (460 to 480 nm460\text{ to }480\text{ nm}), in circadian entrainment.

The Suprachiasmatic Nucleus and Peripheral Clocks (03:15 - 06:45)

  • Structural and functional role of the suprachiasmatic nucleus (SCN) as the master circadian pacemaker in the anterior hypothalamus.

  • Molecular transcription-translation feedback loops involving Period and Cryptochrome genes.

  • Non-image-forming photoreception via melanopsin-containing intrinsically photosensitive retinal ganglion cells (ipRGCs).

  • Regulation of pineal melatonin secretion and synchronization of peripheral oscillators in the liver, heart, and kidneys.

Polysomnography and Sleep Architecture (06:45 - 11:30)

  • Measurement techniques: Electroencephalography (EEG), Electrooculography (EOG), and Electromyography (EMG).

  • Electrophysiological characteristics across stages: Beta and Alpha in wakefulness; Theta in N1; Sleep Spindles (12 to 14 Hz12\text{ to }14\text{ Hz}) and K-complexes in N2.

  • Slow-Wave Sleep (N3): Delta waves (0.5 to 2 Hz0.5\text{ to }2\text{ Hz}), growth hormone secretion, and glymphatic clearance of metabolic toxins (amyloid-beta).

  • Paradoxical REM sleep: Cortical desynchronization, limb muscle atonia mediated by brainstem glycine/GABA pathways, limbic activation, and prefrontal deactivation.

The Two-Process Model: Homeostatic and Circadian Drivers (11:30 - 15:00)

  • Alexander Borbély's Two-Process Model.

  • Process S: Homeostatic sleep pressure, accumulation of adenosine, and its antagonism by caffeine.

  • Process C: Circadian alerting signal from the SCN and the wake maintenance zone.

  • Circadian misalignment: Mechanisms of jet lag, phase delay versus phase advance, and health implications of shift work.

Sleep Disorders and Pathophysiology (15:00 - 17:45)

  • Insomnia disorder: Psychophysiological hyperarousal and cognitive behavioral therapy for insomnia (CBT-I).

  • Narcolepsy Type 1: Loss of lateral hypothalamic orexin/hypocretin neurons destabilizing the sleep-wake flip-flop switch; cataplexy and REM intrusion.

  • Obstructive Sleep Apnea (OSA): Pathophysiology of upper airway collapse, sleep fragmentation, and autonomic consequences.

Ultradian/Infradian Rhythms and Functions of Dreaming (17:45 - 20:00)

  • Distinction between ultradian (<24 hours<24\text{ hours}) and infradian (>24 hours>24\text{ hours}) cycles, including Seasonal Affective Disorder.

  • Theories of dreaming: Activation-Synthesis hypothesis versus modern emotional consolidation models (REM as overnight emotional therapy).

  • Summary of sleep's critical role in systemic health and cognitive functioning.