Biological Rhythms

Circadian
1. Decoursey and krulas: Found that chipmunks that had their endogenous clocks surgically damaged so that they lost their normal rest-activity cycles were more prone to predation in the wild.
  1. Animals which lose the ability to adjust to these 24 hour cycles do not survive for as long as those that can adjust.
2. Observation has made it apparent that the rhythms are controlled endogenously. The cycles continue in absence of exogenous cues. Studies has isolated humans from from all exogenous cues that may indicate time such as light and temperature.
  1. Micheal Siffre: Spent long periods of time isolated under ground in caves. His longest study lasted 205 days. He had no way of knowing what the time was. Researchers found that his sleeping pattern was erratic but soon settled into a regular free-running rhythm. his day shifted to 25 hours in length.
Ultradian
1. Sleep has it's own identifiable Ultradian Rhythm. REM and NREM.
  1. When we go to sleep we enter our first 4 stages of NREM sleep. Stages 3+4 are known as SWS (slow wave). After 20 mins of SWS we enter REM sleep. For the rest of the night sleep shifts from SWS to REM aprox every 90 mins. A typical nights sleep of 8 hrs may have contained 5 cycles of NREM and REM sleep.
    1. The regularity of the cycle suggests that there is a brain mechanism causing sleep to alternate between NREM and REM sleep. Research has suggested that this mechanism in in the brain stem. JOUVET found that destruction of an area called the Locus Coeruleus in the brain cell of cats would permenantly destroy their REM sleep.
  2. Klietman: Rest-activity cycle - It is a human biological cycle of approximately 90 minutes, that is characterized by different level of excitement and rest. The cycle is controlled by the human biological clock. It is best observed in stages of sleep, for example, REM and the delta activity cycle. When awake, your brainwaves are faster during the first half of your BRAC, when you feel alert and focused, and then your brainwaves slow during the second half, till you reach the last 20 minutes when you feel dreamy and perhaps a little tired, while your body's being readied for the alert part of the following BRAC; when asleep, your brainwaves first slow and then rise, and the BRAC occurs as stages of sleep — first falling into deep sleep, then rising into the REM (Rapid Eye-Movement) stage, when dreams occur.
    1. Ultradian Rhythm in Neurochemical Activity: Salomon et al- investigated neurochemical ultradian rhythms in people with depression. they took Cerebrospinal fluid from 15 depressed patients at 10 minute intervals for 24 hours before and after anti-depressants. there was a change in ultradian rhythms suggesting that abnormal ultradian rhythms are part of the general pathophysiology of depression.
    2. Ultradian Rhythms in Urine flow. Mandell et al: found evidence of ultradian rhythms in urine flow. They catherterised 7 men and measured urine flow over 11 nights. Periods of urine flow were associated with REM sleep. Within 2 minutes of REM sleep urine flow decreased. At the end of REM sleep urine flow increased again.
Infradian
1. Adjusted cycles which are greater than 24 hours. EG: as seasons change, the day length changes so organisms learn to adapt accordingly. The monthly cycle, tidal rhythms, seasonal change and anuual change are examples of infradian rhythms.
  1. Hibernation: Endogenous mechanisms allow organisms to make serious changes of hormones, which in turn influence the hibernation process of preparation, initiation, maintanece and final arousal. Dawe and Spurrier: transfused blood from hibernating squirrels into awake active ones and noted that within 48 hours they began hibernating too, even though it was spring ( a time they would not usually hibernate). The hibernation induction trigger is said to be released when triggered by zeitgebers (days becoming shorter and cooler)
  2. Seasonal Affective Disorder- some people experience annual episodes of depression which occur on a seasonal basis. Sufferers from SAD have a number of Circadian abnormalities, including sleep disturbances, increase in core body temperature and disturbances in melatonin and cortisol secretion. Many researchers have pointed out the role of melatonin in the seasonal behaviour of many animals. This hormone is only released during hours of darkness and excess of secretion of melatonin in the winter were thought to explain the symptoms of SAD. Eastman Et Al treated patients with bright light or a placebo. They found that those treated with bright light were most likely to respond with partial or full remission of symptoms.
  3. The Menstrual Cycle: Arden et al- reported that 80% of women believed that when extended time spent with women resulted in synchrony. McClintock suggested that women who spent extensive amounts of time together tend to synch. Weller and Weller suggested that sychrony depends on the closeness of the women eg. mother and daughter, women who work togetyher, basketball players and lesbian couples. McClintock suggested that synchrony was caused by Pheremones
    1. Russel et al: collected odor from women's armpits, then rubbed it on the upper lip of another woman, this happened three times a week for six months, they found that the menstural cycles dramatically shifted resembeling the donors cycle.

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Biological Rhythms

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	Created by Lauren Bass over 9 years ago