大脑与节律-包爱民.ppt

Biological Rhythms Almost all land animals coordinate their behavior according to circadian rhythms - the daily cycles of daylight and darkness that result from the spin of the Earth. (The term is from the Latin circa, “approximately,” and dies,“day.”) In humans, there is an approximately inverse relationship between the propensity（倾向、习性） to sleep and body temperature When the cycles of daylight and darkness are removed - circadian rhythms continue on more or less the same schedule - the primary clocks for circadian rhythms are not astronomical (the sun and earth) but biological, in the brain. Brain clocks are imperfect and require occasional resetting External stimuli, such as light and dark, or daily temperature changes, help adjust the brain’s clocks to keep them synchronized with the coming and going of the sunlight. Brain clocks are an interesting example of the link between the activity of specific neurons and behavior. Biological clock The first evidence, a brainless organism - the mimosa plant that raises leaves during the day and lowers them at night: reacts to sunlight, in some kind of reflex movement? In 1729, French physicist de Mairan: mimosa plants continued to raise and lower their leaves in darkness, still sensing the sun’s movements? 100 yrs later, Swiss botanist de Candolle: a similar plant in the darkness moved its leaves up and down every 22, rather than 24, hrs, implying the plant was not responding to the sun and very likely had an internal biological clock. Biological clock Biological clock overrides （重写、无视）most environmental cues. To maintain clock-environment synchrony, zeitgebers induce changes in the concentrations of the molecular components of the clock to levels consistent with the appropriate stage in the 24-hr cycle, a process termed entrainment. In the presence of zeitgebers, animals become entrained to the day-night rhythm and maintain an activity cycle of exactly 24 hrs. Deprivation of zeitgebers: free-running E