Body rythms Flashcards
What are biological rythms?
They are cyclical changes in pshyiological systems, these occur due to us evoloving in an enviroment with cyclical changes such as the day/night cycle or the seasonal cycle.
The three types of biological are circadian, ultradian, and infradian.
circadian rythms
They are any cycle that lasts 24 hours, they are driven by the suprachiasmatic nucelei (SCN) which are in the hypothalamus. Nearly all organisms have a biologial representation of the 24 hour day and use the circadian rthyms to optimise their physiology and behaviour.
The rythms act as pacemakers for the body and must be reset to keep in synch with the outside world. Natural light is the input into this system, this sets the SCN to the right time through a process called photoentrainment. This allows the SCN to better cordinate the effects of circadian rythms through out the body .
Sleep wake cycle
The light intensity acts as a external signal which determines when we feel like we need to sleep and when we want to wake. This rythmn dips and peaks through at the day leading us to be the most sleepy at 2-4 AM and 1-3PM.
The Pineal gland releases the most melatonin during the hours of darkness. Melatonin supresses the neural mechanisms which promote wakefullness and the production of melatonin is in turn inhibited by light. The internal circadian rythmn will maintian a 24-25 hour cycle even without natural light.
Homostatic control
Sleeping and wakefullness are also under homeostatic control. When we have been awake for a long time homeostasis makes us more sleepy due to the amount of energy used during the time in which you are awake. This urge to sleep increases through out the day till it reaches its peak in the late evening.
While circadian rythms keep us awake when there is light homeostatic symptoms make us more sleepy wether or not is night or day the longer we have been awake.
Strengths of circadian rythms
-) It has practical aplications such as for medication through chronotheraputics which is when the time the medicine is taken is important for treatment success. An example is that a drug for preventing heart attacks can be taken before bed but activate in the morning at 6AM which is when people are most vulnerable to heart attacks.
weaknesses of circadian rythms
- ) There is individual differences in the length of circadain rythms with one study showed that the lengths can vary from 13-165 hours.
- ) Research on circadian rythms did not isolate participants from artificial lights as at the time they did not believe artificial lights affected circadian rythms but we now know this is not true. In one study they managed to get peoples circadian rythms down to 22 hours and up 28 hours only using artificial lights.
- ) There are also individual differencese in when the rythms peak with morning people who prefer to sleep and rise early and evening people who sleep and rise late.
- ) Buhr et al beleives tempreture not light controls the bodies internal clock not light and the SCN’s transform information about light levels into messages changing the tempreture in the rest of the body , these fluctations in tempreture set the timings for the rest of the body.
Ultradian rythms
These are rythms which span less then 24 hours , an example of this is the 5 sleep stages. Stages 1-4 are non rapid eye movement (NREM) sleep in whch the sleep gradually becomes deeper while rapid eye movement (REM) begins in stage 5.
This cycle repeats every 90 minutes. Each stage has their own EEG pattern with the 5th stage resembling the EEG pattern of an awake person and this is when dreaming ocurs.
Kleitman suggested that the 90 min sleep cycle also continues when we are awake however during the day we move from a state of alertness to a more mentally fatigued state instead of sleep cycles. Studies suport this by suggesting the average person can pay attention to something for about 90 minutes .
Ultradian rythms evaluation
+) a study looked at a group of elite violinists and found their practice sessions where limited to 90 minute. Ater this they often took naps to recover from practice, the best violinists also napped for longer, this supports ultradian rythms in real life.
-) It has been suggested that there are individual differences in ultradian rythmns whhich could be biologically and geneticly caused. Tucker had participants studied over 11 consecutive days in a lab and found that for time taken to porgress through each sleep stage, sleep duration and amount of time taken to fall asleep varied greatly betweeen people.
Infradian rythms
These span longer then 24 hours and may last weeks, months or even a year. An example of this is the menstrual cycle which lasts about a month but their are individual differences so it can range between lasting 23 days up to 36 days with a 28 day average.
Thw cycle is regualted by hormones such as oeastregon which increases till roughly half wway through the cycle which leads to ovulation after this the level of oestregon decreases while progesterone increases and then starts decreasing over time till the end of the cycle unless the egg gets fertilised.
Infradian rythms evaluation
+) Penton-Voak, found that women preferred feminised male faces when choosing a partner in a long term relationship but during ovulation showed preference for masculinised faces.
-) The menstrual cycle is not only governed by infradian rythms , when several women of childbearing age live together their menstrual cycles synchronise . In a study sweat samples where collected from one group of women and rubbed on the upper lip of other women , after this their menstrual cycles became synchronised. This suggests that the menstrual cycle is effected by pheromones and not just infradian rythms
