What are rhythm and its uses



Fig. 11.1 Rest-activity rhythm of a test person who was continuously recorded for more than a year. Each horizontal line corresponds to a day (from 3 p.m. to 3 p.m. the next day). Lines correspond to periods of activity, white spaces to periods of rest. The time to go to bed and get up varies little. Two trips to the USA cause significant rhythm shifts due to the time zone change. In the summer vacation, the sleeping time is a little longer. The later getting up on the weekends can be seen from the periodic, white cuts in the morning. Longer downtimes in daily activity are due to defects in the recorder. (28k JPG file)











Fig. 11.2: The »internal clock« controls the sleep-wake cycle. Schematic representation of an insulation test in the bunker. During the first 3 days with a clock, the test person sleeps from 11 p.m. to 7 a.m. For the next 12 days without a watch, the time to go to bed is shifted by one hour each day. The human "internal clock" runs with a period of about 25 hours. (35k JPG file)











Fig. 11.3: Title page of the reports of the Royal Academy of Sciences from 1729. Here De Mairan described the diurnal cycle of a plant for the first time. (39k JPG file)
Fig. 11.4: The "internal clock" determines the resting-activity rhythm of a rat that lives under permanent dark conditions. Horizontal lines correspond to periods of activity, white spaces to periods of rest. To clarify the rhythm shift, 2 days are shown next to each other on a line (i.e. day 1 and 2 at the top, days 2 and 3 below, etc.). In the first 2 weeks the animal lives under the usual "12 hours light -12 hours dark" conditions. Periods of activity are largely limited to the dark period (11 p.m. to 11 a.m.). In the following 3 weeks it is permanently dark. The rest-activity rhythm is maintained, but the end of the activity period is delayed by about 25 minutes each day. The circadian rhythm controlled by the "internal clock" is thus longer than the 24-hour rhythm. (23k JPG file)

Fig. 11.5: The daily rhythm disappears when certain groups of nerve cells in the diencephalon are switched off. Left: the normal daily rhythm of a rat. The animal is particularly active during the dark. Right: After switching off the suprachiasmatic nerve cell nuclei in the diencephalon, the circadian rhythm is completely lost. Activity and rest are now randomly distributed throughout the day. (40k JPG file)