tidal rhythms (periods ~ 12.4 hours) fiddler crab foraging
TRANSCRIPT
• Tidal rhythms (periods ~ 12.4 hours)• fiddler crab foraging
Free running vs Entrained
• In constant conditions (DD), the period is slightly less than 24 hours, so each day it starts earlier
• In a predictable light cycle (LD), wheel running becomes entrained to a 24 hour period
• Light is the zeitgeber = “time giver”
Actogram showing free-running & entrained rhythms in cricket singing
LL schedule
LD schedule
The animal’s behavior free-runswithout a zeitgeber
With a zeitgeberthe animal’s internalclock is reset each day by exogenouscues (the light-darkcycle)
SCN Lesions in hamsters
Environmental cues reset the internal circadian clock daily
Synchronization of internalclock with external cues via entrainment pathways
The pacemaker sends out signals to coordinate physiology & behavior
Endogenous rhythms
The rhythms persist even when animals are kept under constant conditions
Infradian rhythms within the annual hibernation period: