PSYB64H3 Chapter 11: Chapter 11
20 Dec 2011
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In the absence of natural light, human free-running circadian rhythms last approximately 24. 2 hours to. In addition to light, other zeitgebers include physical activity, feeding, body temperature, and sleep-related hormones. In the phase-advance shift in spring, cohen observed a comparable 7 percent increase in traffic accidents. Internal clocks y the body s internal master clock in the suprachiasmatic nucleus (scn) in the hypothalamus. Isolated scn tissue cultures continued to show rhythmic fluctuations in activity consistent with the source animal s previous day-night cycle: transplants of scn tissue also support its role as a master internal clock. when scn tissue from a short-period hamster is transplanted into a normal hamster, the normal hamster shoes the short free-running cycle. when scn tissue from a normal hamster is transplanted into a short-period hamster, the hamster shows normal 24-hour cycles: the scn acts as a master clock that coordinates the activities of other internal, peripheral clocks that exist.
