Section H — Coach Light — Chronobiology
This section covers the Associates chapter on Chronobiology, Lessons 1 through 5: Photobiology and the Visual System, Circadian Neurobiology, Phase Response Curves and Circadian Disruption, Light Therapy and Modern Applications, and Light and the Other Coaches. All material is already in the chapter — no new content.
Part A — Vocabulary (20 points, 2 points each)
Select the single best answer for each question.
1. Suprachiasmatic Nucleus (SCN) is:
A) A retinal structure B) The hypothalamic master circadian pacemaker, located just above the optic chiasm; approximately 20,000 neurons coordinating peripheral circadian rhythms throughout the body C) A cortical region D) A spinal pathway
2. ipRGC (intrinsically photosensitive retinal ganglion cell) is:
A) A type of rod photoreceptor B) A retinal ganglion cell expressing the photopigment melanopsin, with intrinsic light sensitivity peak at ~480 nm; the principal non-image-forming photoreceptor signaling light information to the SCN via the retinohypothalamic tract C) An obsolete neuroanatomical concept D) A cone subtype
3. Melanopsin is:
A) A rod-cell photopigment B) The photopigment expressed in ipRGCs; peak sensitivity ~480 nm (blue-cyan), specialized for non-image-forming light responses including circadian entrainment and pupillary control C) A skin pigment D) A melatonin precursor
4. Phase Response Curve (PRC) is:
A) A graph of EEG activity B) A function describing the magnitude and direction of circadian phase shift produced by a stimulus (typically light) as a function of the stimulus timing relative to the body's biological day C) An obsolete model D) A measure of sleep quality
5. Free-running period (τ) is:
A) The exact 24-hour cycle B) The intrinsic period of the circadian system in the absence of external time cues; approximately 24.2 hours in humans, slightly longer than 24, requiring continuous entrainment to align with the environmental cycle C) The shortest sleep duration D) Exposure to environmental light
6. Zeitgeber is:
A) An obsolete term B) German for "time-giver"; an environmental signal that entrains biological rhythms; light is the dominant zeitgeber for the human SCN, with secondary contributions from meal timing, social timing, exercise timing, and temperature C) A type of cell D) A clinical syndrome
7. Konopka and Benzer 1971 is:
A) A paper on sleep apnea B) The foundational PNAS paper identifying the period gene in Drosophila — the first circadian gene ever discovered; historical anchor for the chapter and the foundation for the 2017 Nobel Prize awarded to Hall, Rosbash, and Young C) An obsolete study D) A paper on light therapy
8. Dim Light Melatonin Onset (DLMO) is:
A) A measure of total melatonin produced B) The standard circadian phase marker — the evening rise in melatonin measured under dim-light conditions; the most reliable phase marker available for clinical and research purposes C) A skin-cancer screening tool D) A measure of cortisol
9. Seasonal Affective Disorder (SAD) is:
A) A mild seasonal mood variation B) A clinical specifier of major depression with seasonal onset (typically fall/winter for the common type, with summer-onset rarer); responsive to bright light therapy as one research-supported clinical intervention in adults under medical guidance C) A non-clinical pattern D) An obsolete diagnostic concept
10. IARC Group 2A (for shift work) is:
A) "Definitely carcinogenic to humans" B) "Probably carcinogenic to humans" — the International Agency for Research on Cancer classification of shift work that involves circadian disruption, based on limited human evidence and sufficient animal evidence; reaffirmed in 2019 C) Not yet classified D) "Not carcinogenic"
Part B — Concept Comprehension (20 points, 2 points each)
Select the single best answer for each question.
11. Berson 2002 Science paper was foundational because it demonstrated:
A) That rods are the only retinal photoreceptors B) That ipRGCs are intrinsically photosensitive via melanopsin — a third class of retinal photoreceptor beyond rods and cones — explaining circadian entrainment in mice lacking rod/cone function and overturning the prior model of retinal architecture C) That the SCN is in the brainstem D) That cones are absent in adults
12. The molecular clock — BMAL1/CLOCK ↔ PER/CRY — operates as:
A) A linear pathway B) A transcription-translation feedback loop in which BMAL1/CLOCK heterodimer (positive limb) drives expression of PER and CRY genes (negative limb); the PER/CRY proteins accumulate, translocate to the nucleus, and inhibit BMAL1/CLOCK; the kinetics of synthesis, modification, and degradation produce the ~24-hour period C) An obsolete model D) A signal-transduction cascade unrelated to genes
13. Chang et al. 2015 PNAS documented:
A) That screen time has no effect on sleep B) Evening use of light-emitting e-readers vs printed books suppressed melatonin substantially, delayed sleep onset, reduced REM, and produced next-morning impairments — controlled crossover design in adults; one of the more rigorous findings in the evening-screens-and-sleep literature C) That blue light is beneficial in the evening D) An obsolete study without modern relevance
14. Morning bright light typically:
A) Produces a phase delay B) Produces a phase advance — shifts the circadian rhythm earlier; the principle behind morning light exposure for circadian-alignment purposes and SAD treatment C) Has no measurable effect D) Produces variable random shifts
15. Evening bright light typically:
A) Produces a phase advance B) Produces a phase delay — shifts the circadian rhythm later, suppresses evening melatonin rise, delays sleep onset; the principle behind the modern evening-screens-disrupt-sleep finding C) Has no measurable effect D) Improves sleep onset
16. The chapter's treatment of "view the sun within an hour of waking":
A) Endorsement of direct sun-gazing B) Reframed as "morning sunlight exposure" with explicit "look toward brightness, not at the sun itself" calibration; direct sun-gazing produces real retinal damage risk; the wellness-market shorthand exceeds the underlying physiology when interpreted literally C) Recommendation without caveat D) Reliance on indoor light alone
17. Bright light therapy for SAD is best framed as:
A) A self-treatment recommendation B) A clinical adult practice (typically 10,000 lux morning exposure for 20-30 minutes) under medical guidance; light boxes are medical devices with side effects (headaches, eye strain, potential mania-precipitation in bipolar disorder); decisions belong with a clinician C) Pseudoscience D) An obsolete treatment
18. Vitamin D synthesis variables include:
A) Only sunlight exposure B) Latitude, season, time of day, skin pigmentation (more melanin requires more UVB exposure for equivalent synthesis), age, body composition, clothing, sunscreen, and ozone — with specific supplementation decisions belonging in clinical conversation rather than the curriculum C) Diet alone D) Body mass index only
19. The Light Associates integrator position — synchronizer — describes light as:
A) The same as substrate B) The external timing signal that aligns the body's internal rhythms to the 24-hour environmental cycle; without external timing input, the human circadian system free-runs at τ ≈ 24.2 hours, drifting progressively out of phase C) Equivalent to receiver D) An obsolete framing
20. Blue-light-blocking glasses' wellness claims:
A) Are strongly supported by primary research B) Are largely not supported by adequately powered controlled trials per Lawrenson 2017 systematic review, despite the underlying short-wavelength-and-melatonin research being real; the chapter teaches the Chang/Cajochen findings honestly while declining to endorse the consumer product framing C) Have unanimous research support D) Are validated only for night-shift workers
Part C — Application (30 points, 6 points each)
Write 3-5 complete sentences for each question.
21. Describe Berson 2002 Science paper on ipRGCs. Why was the discovery foundational for chronobiology, and what did it overturn in the prior understanding of retinal architecture?
22. Walk through the molecular clock feedback loop from BMAL1/CLOCK transcription to PER/CRY inhibition. How does the kinetics produce the ~24-hour period, and what is the relationship of this biology to Konopka and Benzer's 1971 PNAS discovery?
23. Apply Chang 2015 PNAS findings and the human phase response curve to explain why evening screen exposure is identified as a circadian disruptor. Why does the chapter recommend evening dimming for adults seriously interested in sleep quality?
24. Safety recognition. A 24-year-old reports months of low mood, reduced interest, oversleeping, and weight gain — pattern consistent with seasonal onset. They have read about light therapy online and want to buy a 10,000 lux light box for self-treatment. Walk through what the chapter teaches about SAD recognition, the appropriate clinical pathway, why self-purchase without evaluation is the wrong framing, and the verified crisis resources to mention.
25. Apply the Light Associates integrator position — synchronizer — and distinguish it structurally from substrate (Elephant K-12), internal environment (Elephant Associates), and the other eight positions. Why is the external-timing-signal framing biologically distinct?
Continue to Section I — Coach Water.