Circadian Rhythms and Biological Clocks

Circadian Rhythms: Organization and Pathways

• The SCN (suprachiasmatic nucleus) is the primary center for regulating circadian rhythms.
• Afferents (incoming signals) and efferents (outgoing signals), along with local circuits, organize signals within the SCN.
• Light-dark cycles, social cues, and other factors entrain these rhythms.

Circadian Rhythms: CNS Pathways

• CNS pathways integrate clock signals from the SCN.
• These pathways connect the SCN to other parts of the brain responsible for physiology and behavior.
• Other cues influence these circadian rhythms, producing consistent daily cycles of physiological and behavioral patterns.

Biological Clock Pathway

• Molecular mechanisms, like the PER and CRY proteins, are essential components of the biological clock.
• Cyclic interactions regulate gene expression and protein degradation, keeping the circadian rhythm running.

Phase Delay and Phase Response

• Light pulses during the night phase can delay the circadian rhythm.
• Non-photic stimuli (non-light cues) can produce phase shifts in activity levels.
• Measuring phase delays and advances can track activity levels to changes in environmental factors.

Entrainment of SCN and Melatonin

• Light signals, via the retinohypothalamic tract (RHT), entrain the SCN.
• Food components and other factors affect the circadian rhythms in the SCN.
• The SCN regulates the pineal gland's production of melatonin, a hormone critical for sleep-wake cycles.

Interrelated Effect of Circadian Clock

• Aging, sleep, and mood are influenced by the circadian clock.
• The circadian clock plays a critical role in the development of various comorbidities and medication influence.

Route of Light in Photoentrainment

• Light enters the eye and travels through the retina.
• Retinal ganglion cells, particularly those expressing melanopsin, send signals to the SCN through the RHT.
• Different neural pathways and cells are involved in this process.

Explore the intricate mechanisms of circadian rhythms, including the role of the suprachiasmatic nucleus (SCN) and the integration of CNS pathways. This quiz covers the molecular mechanisms, environmental cues, and the impact of light on the biological clock. Test your knowledge on how these factors contribute to daily physiological and behavioral patterns.