Biological rhythms - Circadian

Question 1

define circadian rhythm

Answer 1

having a periodicity of ~24 hours

Question 2

What is an example of the circadian rhythm

Answer 2

sleep-wake cycle

Question 3

How is the sleep-wake cycle controlled

Answer 3

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.

Question 4

State some research for the affect of endogenous pacemakers on the sleep-wake cycle

Answer 4

Ralph et al 1990

Question 5

Outline Ralph et al 1990

Answer 5

• 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.

Question 6

What were the results of Ralph et al 1990

Answer 6

eventually, the experimental group shifted to a 20-hour cycle.

Question 7

Give a conclusion for Ralph et al 1990

Answer 7

the hamsters’ circadian cycle was regulated by the SCN. When normal hamsters were given an abnormal SCN they developed an abnormal circadian cycle.

Question 8

How does the Supra-chiasmatic nucleus (SCN) regulate the sleep-wake cycle

Answer 8

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.

Question 9

State some research for the affect of Zeitgebers on the sleep-wake cycle

Answer 9

Kleitman 1967

Question 10

Outline Kleitman 1967

Answer 10

• 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.

Question 11

describe the findings of Kleitman 1967

Answer 11

Siffre’s circadian activity cycle lengthened, so he was working to a day of between 25 and 28 hours

Question 12

Give a conclusion for Kleitman 1967

Answer 12

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.