Circadian Rhythms and Biological Clocks

This collection of flashcards covers key concepts and findings from lectures on circadian rhythms, highlighting biological clocks' importance in organisms' behavior and physiology.

What are the main factors that influence circadian rhythms in organisms?

Circadian rhythms are influenced by light, environmental cycles like day-night and seasonal changes, which organisms use to anticipate recurring events.

Define circadian rhythm.

A circadian rhythm is a biological cycle that repeats approximately every 24 hours, significantly influenced by the light-dark cycle.

What is the significance of a biological clock for organisms?

A biological clock allows organisms to predict changes in their environment and adjust their behavior and physiology accordingly.

What is photoperiodism?

Photoperiodism is the ability of an organism to respond to changes in day length, influencing processes such as flowering in plants and reproductive cycles in animals.

What are ultradian and infradian rhythms?

Ultradian rhythms are biological cycles that occur more frequently than once in a 24-hour period, while infradian rhythms are cycles that take longer than 24 hours.

Name one key experiment related to the biological clock in plants conducted by Jean Jacques d’Ortois de Mairan.

He observed that the Mimosa plant displayed rhythmic movements that continued even in the absence of light, indicating an endogenous rhythm.

What role does the SCN (suprachiasmatic nucleus) play in mammals?

The SCN is considered the master clock, regulating circadian rhythms and synchronizing peripheral clocks in response to light and other cues.

What is the function of melatonin in relation to circadian rhythms?

Melatonin production is rhythmically timed, with levels rising at night; it helps signal the onset of night and influences various biological processes.

Explain the significance of the phase angle of entrainment.

The phase angle of entrainment reflects the timing difference between an organism's internal rhythm and the external environmental cues, such as the light-dark cycle.

How do external cues like light affect the circadian clock?

Light serves as a major zeitgeber that can phase shift circadian rhythms, promoting either phase advances or delays depending on the time of light exposure.

What is the concept of a free-running rhythm?

A free-running rhythm is a biological cycle that persists without external cues, showing a natural period longer or shorter than 24 hours.

Describe the role of cryptochromes in circadian rhythms.

Cryptochromes are light-sensitive proteins that can affect circadian rhythms by responding to blue light, influencing the transcription of clock genes.

What is the difference between the internal coincidence model and the external coincidence model of photoperiodism?

The internal coincidence model suggests that an organism's internal circadian clock generates a photosensitive phase, while the external coincidence model states that photoperiodic response occurs only if light coincides with this phase.

What are some potential effects of circadian misalignment in humans?

Circadian misalignment can lead to increased risk of cardiovascular disease, mood disorders, and impaired metabolic function.

Identify the role of dopamine in MELT and circadian influences.

Dopamine may play a role in regulating circadian rhythms and is linked to the timing of behaviors and mood regulation in relation to the circadian clock.

What is 'Zugunruhe' and why is it significant?

Zugunruhe is the restlessness observed in migratory birds prior to migration, indicative of an internal circannual clock that governs migratory behavior.

Explain how the circadian clock affects sleep patterns.

The circadian clock regulates sleep patterns by signaling when to sleep and wake based on environmental light cues, leading to distinct sleep phases and cycles.