Biological rhythms - Circadian Flashcards
define circadian rhythm
having a periodicity of ~24 hours
What is an example of the circadian rhythm
sleep-wake cycle
How is the sleep-wake cycle controlled
It is controlled by the supra-chiasmatic nucleus (SCN), a small structure situated in the hypothalamus. The SCN is the body’s main circadian body clock. It generated a circadian rhythm independently of other brain structures.
State some research for the affect of endogenous pacemakers on the sleep-wake cycle
Ralph et al 1990
Outline Ralph et al 1990
- Aim - to show that the SCN generates the circadian rhythm in mammals
- sample - hamsters, some with the genetic abnormality affecting their circadian cycle.
- method - a group of hamsters was identified with a genetic abnormality that resulted in a 20-hour circadian cycle, rather than a 24-hour one. Their SCNs were removed and placed in the brains of an experimental group of hamsters with a normal 24-hour cycle.
What were the results of Ralph et al 1990
eventually, the experimental group shifted to a 20-hour cycle.
Give a conclusion for Ralph et al 1990
the hamsters’ circadian cycle was regulated by the SCN. When normal hamsters were given an abnormal SCN they developed an abnormal circadian cycle.
How does the Supra-chiasmatic nucleus (SCN) regulate the sleep-wake cycle
The SCN (Supra-chiasmatic nucleus regulates the activity of the pineal gland, which produces melatonin. It is the level of melatonin in the brain which affects whether a person feels sleepy.
State some research for the affect of Zeitgebers on the sleep-wake cycle
Kleitman 1967
Outline Kleitman 1967
- aim - to find out what happens to the sleep-wake cycle when people are isolated from information about the time of day.
- sample - single human male
- method - A cave explorer, Siffre, spent six months underground. He had no clocks, radios and was cut off from daylight. He was allowed to regulate his own activity as he wished. He was monitored remotely by researchers on the surface.
describe the findings of Kleitman 1967
Siffre’s circadian activity cycle lengthened, so he was working to a day of between 25 and 28 hours
Give a conclusion for Kleitman 1967
without any external influences, the SCN’s endogenous rhythm gets out of synch with the 24 hour day. Therefore, zeitgebers must play a role in regulating the sleep-wake cycle.