the biological approach

• Biological rhythms are cyclical changes in the way biological systems behave
• Biological rhythms can vary in duration from short periods to monthly cycles.
• Why do humans have biological rhythms?

  To optimize behavior
• The most important biological rhythm for humans is the circadian rhythm.
• What is the duration of a circadian rhythm?

  24 hours
• Nearly all organisms possess a biological representation of a 24-hour day.
• What does the circadian rhythm optimize in humans?

  Physiology and behavior
• Circadian rhythms are driven by body clocks
• Where is the master circadian pacemaker located?

  Hypothalamus
• Match the term with its definition:

  SCN ↔️ Suprachiasmatic nuclei

  Photoentrainment ↔️ Alignment with light-dark cycle
• What is the primary input that resets the master circadian pacemaker?

  Light
• Light-sensitive cells in the eye act as brightness detectors
• The sleep/wake cycle is regulated by circadian rhythms.
• When does the strongest sleep drive occur in humans?

  2:00-4:00 AM
• The post-lunch dip commonly occurs between 1:00 and 3:00 PM
• Insufficient sleep makes the post-lunch dip more intense.
• What does homeostatic control contribute to sleep regulation?

  The need for sleep
• The drive for sleep increases throughout the day and peaks in the late evening
• The circadian system maintains wakefulness as long as daylight is present.
• What does it mean when a circadian clock is described as freerunning?

  It maintains a 24-25 hour cycle
• Major alterations in sleep schedules can disrupt the circadian system
• What is the lowest core body temperature in a normal circadian rhythm?

  36 degrees
• Order the changes in core body temperature during a normal circadian rhythm:

  1️⃣ Lowest at 4:30 AM

  2️⃣ Rises during sleep

  3️⃣ Highest at 6:00 PM

  4️⃣ Small drop between 2:00-4:00 PM
• Which hormone encourages feelings of sleep?

  Melatonin
• Melatonin production peaks during daylight hours.

  False
• The production of melatonin decreases when it is light
• What is chrono therapeutics the study of?

  Drug timing and treatment
• The risk of heart attacks is greatest during the early morning hours.
• Medications for heart attacks can be administered before sleep but released during the vulnerable period
• Who studied freerunning circadian rhythms in cave environments?

  Michel Siffre
• Case studies of circadian rhythms may have limited generalizability