circadian rhythms

Question 1

what are biological rhythms?

Answer 1

cyclical patterns within biological systems.

Question 2

what are circadian rhythms?

Answer 2

rhythms that occur everyday, e.g. sleep wake cycle.

Question 3

what are infradian rhythms?

Answer 3

lasts longer than one day, e.g. menstrual cycle.

Question 4

what is an ultradian rhythm?

Answer 4

you have more than one per day.

Question 5

what are endogenous pacemakers?

Answer 5

internal mechanisms that govern biological rhythms, e.g. pineal gland.

Question 6

what are exogenous zeigebers?

Answer 6

external mechanisms that govern biological rhythms.

Question 7

what is the relationship between endogenous pacemakers and exogenous zeitgebers?

Answer 7

all living organisms are subject to biological rhythms

which are governed by endogenous pacemakers and entrained by exogenous zeitgebers.

Question 8

what is the biological basis for the sleep-wake cycle?

Answer 8

The suprachiasmatic nucleus (SCN) is a major endogenous pacemaker in mammals that controls the sleep wake cycle ‘master clock’.

It is in the hypothalamus where the optic nerves from the eye cross over.

It gets stimulated by light that penetrates our closed eye lids and the SCN (tiny bundle of nerve cells) then regulates our sleep wake cycle.

Question 9

what role does the pineal gland play in the sleep wake cycle?

Answer 9

SCN -> Sends messages to pineal gland -> dark – night increases melatonin -> induces sleep.

The SCN passes the information on day length and light that it receives - to the pineal gland.

Question 10

what is the role of homeostasis in the sleep wake cycle?

Answer 10

When an individual has been awake for a long time, homeostasis will tell the body that there is a need for sleep because of energy consumption.

• homeostatic drive for sleep increases throughout the day, reaching its maximum in the late evening, when most people fall asleep.

Question 11

what is another example of a circadian rhythm other than sleep?

Answer 11

• Body temperature
• at its lowest at 4:30am and at its highest at around 6pm.
• Sleep occurs when the core temperature begins to drop, and body temperature starts to rise during the last few hours of sleep, promoting a feeling of alertness in the morning

Question 12

what does Michel Siffre’s study imply?

Answer 12

• suggests that his 24 hour sleep wake cycle was increased by lack of external cues, making him believe one day was longer than it was, and leading to his thinking that fewer days had passed. Although he did still have a regular biological rhythm.
• implies that circadian rhythms are mainly controlled by EP’s rather than EZ’s – but that EZ’s do have a significant influence.

Question 13

describe Michel Siffre’s study.

Answer 13

• spent several extended periods of underground deprived of natural light and sound, but with food and water.
• wanted to investigate the effect of no environmental cues on his biological rhythms (known as free-running).
• found absence of external cues significantly altered his circadian rhythm. When he returned from an underground stay with no clocks or light, he believed the date to be a month earlier than it was.

Question 14

what is a criticism of Siffre’s study?

Answer 14

• researcher bias (he was the only researcher and participant)

Question 15

what other evidence is there for extended sleep-wake cycle in the absence of external light?

Answer 15

Aschoff and Wever (1976) convinced p’s to spend 4 weeks in WW2 bunker deprived of light.
All but one displayed a circadian rhythm of 24-25. The other extended to 29 hours.

Folkard conducted a study of circadian rhythms similar to Siffre, in a cave. This time, they had a clock to enforce strict bed and waking times. What participants didn’t know was researcher s[ed up the clock so their days were only 22 hours instead of 24.
Only 1 participant was able to comfortably adjust to the new regime.

Question 16

how can the sleep wake cycle become desynchronised?

Answer 16

Jetlag - is caused by traveling across several time zones within several hours. The internal clock is not synchronized with the daytime nighttime rhythm at the place of arrival. Jet lag can cause insomnia, fatigue, irritability, and poor concentration.

Shiftwork - causes desynchronisation in circadian rhythm which in turn leads to negative health effects.

Question 17

describe Ralph’s (1990) study on sleep-wake cycle in hamsters.

Answer 17

• Bred a group of hamsters to follow a (shortened) 20-hour circadian cycle.
• SCN cells were removed and transplanted into the brains of rat fetuses with normal rhythms.
• One born; these rats adopted a 20-hour cycle.
• Their brains were then transplanted with SCN cells from 24-hour cycle rats and within a week their cycles had adopted this new 24-hour cycle.

Question 18

what are findings and conclusions of Ralph’s study on the sleep wake cycle in hamsters?

Answer 18

• When cells from the SCN were removed from rats, the 24-hour cycle of neural activity persisted in the isolated cells.
• This suggests that circadian rhythms are primarily controlled by evolutionary-determined biological structures that exert a strong influence on us to maintain normal sleep-waking patterns.

Question 18

what experimental biological evidence is there for sleep-wake cycles existing outside the body?

Answer 18

Yamazaki (2001) found that isolated lungs and livers, and other tissues grown in a lab persist in showing circadian rhythms.

This suggests cells are capable of maintaining a circadian rhythm even when they are not under the control of any brain structures and that most bodily cells are tuned in to following a daily circadian rhythm.