Endogenous Pacemakers And Exogenous Zeitegebers Flashcards
How do we regulate our biological rhythms
Through endogenous pacemakers and exogenous zeitgebers. Endogenous pacemakers are our internal biological clocks, but exogenous zeitgebers are external cues that include things like light to help regulate and reset our internal biological clocks every day
What are endogenous pacemakers
Endogenous pacemakers are internal mechanisms that govern biological rhythms, in particular, the circadian sleep-wake cycle. Although endogenous pacemakers are internal biological clocks, they can be altered and affected by the environment. For example, although the circadian sleep-wave cycle will continue to function without natural cues from light, research suggests that light is required to reset the cycle every 24 hours.
What is the most important endogenous pacemaker
The most important endogenous pacemaker is the suprachiasmatic nucleus, which is closely linked to the pineal gland, both of which are influential in maintaining the circadian sleep/wake cycle.
How does the SCN work?
The suprachiasmatic nucleus (SCN), which lies in the hypothalamus, is the main endogenous pacemaker (or master clock). It controls other biological rhythms, as it links to other areas of the brain responsible for sleep and arousal. The SCN also receives information about light levels (an exogenous zeitgeber) from the optic nerve, which sets the circadian rhythm so that it is in synchronisation with the outside world, e.g. day and night.
The SCN sends signals to the pineal gland, which leads to an increase in the production of melatonin at night, helping to induce sleep. The SCN and pineal glands work together as endogenous pacemakers
Strengths of endogenous pacemakers
Folkard studied a university student called Kate aldcroft, who spent 25 days in a laboratory. She had no access to exogenous zeitgebers of light to reset the SCN. However at the end Of day 25, her core temperature rhythm was still at 24hrs suggesting that we don’t need exogenous zeitgebers of light to maintain internal biological rhythms
Morgan bred a strain of hamsters that had abnormal circadian rhythms of 20hrs and these SCN neurons were transported to normal hamsters. These normal ones started to display abnormal 20 hr circadian rhythms, demonstrating the vital importance of endogenous zeitgebers for maintaining constant and regular biological rhythms
Weaknesses endogenous pacemakers
Many studies on the SCN have been carried out on animals, whereby unethical procedures are carried out to meet the requirements of the study. In addition to being unethical (breeding to have abnormal circadian rhythms), it is not ecologically valid as in the real world, people don’t have their circadian rhythms tampered with.
Folkard also found that Kate’s sleep wake cycle had extended to 30hrs, with periods of sleep lasting as long as 16 hours. This suggests that exogenous zeitgebers may also be important in controlling the sleep wake cycle. This study shows that exogenous zeitgebers may have more of an effect on the sleep wake cycle than endogenous s
What are exogenous xeitgebers
these can be described as environmental events that are responsible for resetting the biological clock of an organism. They can include social cues such as meal times and social activities, but the most important zeitgeber is light, which is responsible for resetting the body clock each day, keeping it on a 24-hour cycle.
How does light act as an exogenous zeitgeber
A protein in the retina called melanopsin, which is sensitive to natural light is critical in this system as it sends information regarding the levels of light to the scn which synchronises the activity of the body’s organs and glands. Light resets the internal biological clock every day keeping it on a 24 hour cycle.
Why people tired after flying time zones?
When people move or night shift of travel to country with a different time some, their endogenous pscemakers try to impose their inbuilt rhythm of sleep, but this is out of synchrony with the exogenous zeitgebers of light. Out of sync biological rhythms lead to disrupted sleep patterns, increased anxiety and decreased alertness and vigilance
Strengths exogenous
Vast majority of blind people who still have light perception have normal circadian rhythms. Blind people without light perception show abnormal circadian rhythms. This shows the vital role of exogenous zeitgeber of light in mainting internal biological rhythms
Burgess et al found that exposer to bright light prior to east west flight decreased the time needed to adjust circadian rhythms to local time
Weakness exogenous
Studies of individuals who live in arctic regions where the sun does not set in the summer months, show normal sleeping patterns despite the prolonged exposeure to light. This suggests that there are occasions where exogenous zeitgeber may have little affect on internal biooogical rhythms.
