Biological rhythms Flashcards
Circadian rhythms
Biological rhythms that occur approximately every 24 hours, such as the sleep/wake cycle.
Infradian rhythms
Biological rhythms that occur less frequently than once every 24 hours, such as the menstrual cycle.
Ultradian rhythms
Biological rhythms that occur more frequently than once every 24 hours, such as the stages of sleep.
Endogenous pacemakers
Internal body clocks that regulate biological rhythms, such as the suprachiasmatic nucleus (SCN) for the sleep/wake cycle.
Exogenous zeitgebers
External environmental cues that influence biological rhythms, such as light and social cues in the sleep/wake cycle.
Sleep/wake cycle
A circadian rhythm regulated by the interaction of endogenous pacemakers (like the SCN) and exogenous zeitgebers (like light).
Suprachiasmatic nucleus (SCN)
A cluster of nerve cells in the hypothalamus that acts as the main endogenous pacemaker, regulating the sleep/wake cycle.
Melatonin
A hormone released by the pineal gland that promotes sleep, influenced by the SCN and light exposure.
Phase delay
A disruption to the circadian rhythm where the sleep/wake cycle is pushed later, common in jet lag when traveling west.
Phase advance
A disruption to the circadian rhythm where the sleep/wake cycle is pushed earlier, common in jet lag when traveling east.
Light as a zeitgeber
The most important exogenous zeitgeber for regulating the sleep/wake cycle, affecting the SCN and melatonin release.
Social cues
Exogenous zeitgebers such as meal times and social interactions that help regulate biological rhythms.
Menaker et al (1978)
Found that lesions to the SCN in hamsters resulted in disrupted circadian rhythms, highlighting the role of the SCN as an endogenous pacemaker.
Aschoff and Wever (1976)
Placed participants in a WWII bunker without natural light and found that circadian rhythms extended slightly beyond 24 hours, indicating the role of endogenous pacemakers in the absence of exogenous zeitgebers.
Pengelly and Fisher (1957)
Demonstrated hibernation-like behavior in squirrels even in constant environmental conditions, showing that endogenous rhythms can persist without external cues.
Schwartz et al (1995)
Found that baseball teams traveling westward performed better than those traveling eastward, likely due to the effects of phase delay being easier to adjust to than phase advance.
Wegman et al (1986)
Reported that circadian rhythms adapt more quickly when traveling westward compared to eastward, supporting the idea of easier adjustment to phase delays.
Czeisler et al (1982)
Showed that exposure to bright light could reset circadian rhythms, demonstrating the significant role of light as an exogenous zeitgeber.
Evaluation of research: practical applications
Research on biological rhythms has practical applications, such as improving shift work schedules to reduce health risks (e.g., night shifts disrupting circadian rhythms).
Evaluation of research: artificial environments
Many studies, such as those by Aschoff and Wever, involve artificial environments, reducing ecological validity.
Evaluation of research: animal studies
Animal studies, such as Menaker et al., provide insights into the role of endogenous pacemakers but may lack generalizability to humans.
Evaluation of research: individual differences
Individual differences in circadian rhythms, such as ‘morning larks’ and ‘night owls,’ are often overlooked in research.
Evaluation of research: managing jet lag
Studies like Czeisler et al. have shown how exogenous zeitgebers like light can be used to manage jet lag and improve sleep hygiene.