endogenous pacemakers and exogenous zeitgbers

Question 1

what is endogenous pacemakers?

Answer 1

internal BODY CLOCKS that regulate our biological rhythms such as the influence of suprachiasmatic nucleus (scn) on the sleep wake cycle

Question 2

What is superchiasmatic nucleus?

Answer 2

role is establishing and maintaining the circadian sleep wake cycle.

Nerve cells located in the hypothalamus
It is one of the primary endogenous pacemakers in mammalian species ( including humans)

It receives information about light directly from this structure. This continues even when our eyes are closed allowing the biological clock to adjust the changing pattern of daylight whilst we are asleep.

Question 3

animal studies scn

Answer 3

Patricia de courtesy et al 2000 destroyed scn connections in the brain of 30 chipmunks who were then returned to their natural habitat and observed for 80 days.

The sleep wake cycle of chipmunks disappeared and by the end of the research a significant proportion of them had been killed by predators ( presumably awake and vulnerable to attack when they should have been asleep)

Question 4

Pineal gland and melatonin

Answer 4

Pineal gland increases production of melatonin - a chemical that induces sleep and is inhibited during periods of wakefulness.
Melatonin has also been suggested as a causal factor in sad.

Question 5

Exogenous zeitgeber and the sleep wake cycle

what is exogenous zeitgeber?

what two things does light do?

what are social cues?

Answer 5

Exogenous zeitgeber = external cues that may affect or entrain our biological rhythms such as influence of light on sleep wake cycle.

Light is a key zeitgeber. It resets the body’s main endogenous pacemaker , (scn) and thus plays a role in maintaining sleep wake cycle.

Light also has indirect influence on key processes in the body such as hormone secretion and blood circulation.

Social cues = infants sleep wake cycle is random and their circadian rhythm begins around 16 weeks where most babies are entrained. The schedules parents impose are more likely to be a key influence such as meal time and bed times.

Question 6

evaluation

Answer 6

beyond the master clock
Francesca Damilola et al 2000 demonstrated how changing feeding patterns in mice could alter circadian rhythms of cells in the liver by up to 12 hrs whilst leaving the rhythm of scn unaffected. This suggest that there may be other complex influences on sleep wake cycle aside from master clock (scn)

Ethics in animal studies
De courtesy study the animals were exposed to considerable harm and subsequent risk when returned to their natural habitat. This breaks the ethical guidelines also there may problems in generalising findings of sleep wake cycle from animal studies to humans.

Laughton Miles et al (1997) recounted the story of a young man blind from birth with circadian rhythm of 24.9hrs. Despite exposure to social cues his sleep wake cycle could not be adjusted and consequently had to take sedatives at night and stimulants in morning to keep pace with 24hr world. This example suggests that there are occasions when exogenous zeitgeber may have little bearing on our internal rhythm.