endogenous pacemakers and exogenous zeitgebers

Question 1

endogenous pacemakers

Answer 1

Internal body clocks that regulate our biological rhythms.

Question 2

Suprachiasmatic nucleus (SCN)

Answer 2

Tiny bundle of nerve cells located in hypothalamus in each hemisphere of the brain. It is one of the primary endogenous pacemakers in humans and is important in maintaining circadian rhythms such as sleep wake cycle. It receives info about light even when our eyes are closed enabling biological clocks to adjust to changing patterns of daylight while we are asleep.

Question 3

Animal studies and the SCN

Answer 3

Decoursey et al destroyed SCN in brains of 30 chipmunks who were then returned to their natural habitat and observed for 80 days.
Findings: their sleep/wake cycles disappeared and a significant amount were killed by predators ( vulnerable to attack when they should have slept.

Question 4

Ralph et al

Answer 4

bred mutant hamsters with a 20 hour sleep/wake cycle. SCN from these hamsters these were then transplanted into normal hamsters and their cycles defaulted to 20 hours

Question 5

SCN and its link to pineal gland

Answer 5

SCN passes information on day light and length to pineal gland. During night it increases melatonin production.

Melatonin- chemical that induces sleep and is inhibited when we are awake.

Question 6

Exogenous Zeitgebers

Answer 6

External cues that may affect or entrain our biological rhythms such as the influence of light on the sleep/wake cycle.

Question 7

How is light an zeitgeber

Answer 7

resets the body’s main endogenous pacemakers and maintains the sleep/wake cycle. It also influences the release of hormones such as melatonin.

Question 8

Campbell and Murphy

Answer 8

Demonstrated that light is detected by skin receptors when when our eyes are not open. 15 ppts were woken up at various times and light pad was shone on the back of their knees. researchers managed to deviate ppts sleep/wake up to 3 hours. Suggests that light is a powerful exo zeitgeber.

Question 9

Social cues

Answer 9

In humans at about 6 weeks of age, circadian rhythm begins and by 16 weeks most babies are entrained. These can be used to determine meal times and bedtimes. Research into social cues have shown that adapting to eating and sleeping time of locals is effective in entraining circadian rhythm and beating jet lag.

Question 10

Apply it: how can endogenous pacemakers or exogenous zeitgebers be used to explain Siffre’s cave study

Answer 10

supported the presence of endogenous pacemakers in the sleep/wake cycle as his circadian rhythm maintained a regular rhythm without the aid of any external cues in the form of light (zeitgebers).

Question 11

Apply it: how can endogenous pacemakers or exogenous zeitgebers be used to explain Aschoff and Wever’s study

Answer 11

found that a free-running cycle persisted with a sleep/wake cycle of 25 hours, therefore showing that light has an effect on controlling circadian rhythms(because they were not 24 hours when there was no light). The findings also show that there is an endogenous pacemaker because the participants had regular rhythms.

Question 12

Apply it: how can endogenous pacemakers or exogenous zeitgebers be used to explain McClintock’s study

Answer 12

evidence suggests that external factors (zeitgebers) can play a role in ovulation and menstruation. It is thought that women at different stages of the menstrual cycle give off different pheromones. McClintock’s and Stern’s findings show that the menstrual cycle is influenced by these zeitgebers, and explain to an extent how women’s menstrual cycles can come to synchronise.